New insights into ductility improvement of a nickel-based superalloy through grain boundary engineering

doi:10.1016/j.msea.2024.146786

Materials Science and Engineering: A
材料科学与工程：A

Volume 908, August 2024, 146786
卷 908，2024 年 8 月，146786

https://doi.org/10.1016/j.msea.2024.146786 Get rights and content 获取权利和内容

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Abstract 摘要

Grain boundary engineering (GBE) provides an effective approach for tailoring the properties of metallic materials by optimizing the grain boundary character distribution (GBCD). Using electron backscatter diffraction analysis and uniaxial tensile testing at room temperature, this study systematically investigated the impact of GBE-type thermomechanical processing (TMP) on the ductility of an Incoloy 925 nickel-based superalloy (Alloy 925). The results showed that at 5 % strain, increasing the annealing temperature results in larger twin-related domains through strain-induced boundary migration. The GBE-type TMP can significantly enhance the ductility of Alloy 925, namely, the elongation increases from 64.22 % to 95.86 % as the annealing temperature increases from 1050 °C to 1100 °C. The evolved GBCD introduces more coherent twin boundaries with lower average residual Burgers vectors, enabling efficient dislocation transmission. In addition, extensive twinning can widely generate some soft orientations and simultaneously reduce the average Taylor factor within the twin clusters, leading to easy dislocation activation during plastic deformation. The synergistic effect of the optimized grain boundary network and twin cluster anisotropy promotes uniform plastic flow and effective strain accommodation, thereby enhancing the ductility of Alloy 925. Overall, this work provides novel and valuable insights into ductility optimization through GBE in a nickel-based superalloy.
晶界工程（GBE）通过优化晶界特征分布（GBCD）为调整金属材料性能提供了一种有效方法。本研究采用电子背散射衍射分析和室温单轴拉伸试验，系统研究了 GBE 型热机械加工（TMP）对 Incoloy 925 镍基高温合金（Alloy 925）延展性的影响。结果表明，在 5%应变下，提高退火温度会导致应变诱导边界迁移形成更大的孪晶相关区域。GBE 型 TMP 能显著提高 Alloy 925 的延展性，即随着退火温度从 1050°C 升高到 1100°C，延伸率从 64.22%增加到 95.86%。形成的 GBCD 引入了更多具有较低平均残余伯格斯矢量的位相孪晶边界，从而实现高效的位错传输。此外，广泛的孪晶能广泛产生一些软取向，同时降低孪晶团簇内的平均泰勒因子，导致在塑性变形过程中位错易于激活。优化晶界网络和孪晶簇各向异性的协同效应促进了均匀塑性变形和有效应变 accommodation，从而提高了 Alloy 925 的延展性。总体而言，这项工作为镍基高温合金通过晶界工程优化延展性提供了新颖且宝贵的见解。

Keywords 关键词

Incoloy 925

Grain boundary engineering

Ductility

Residual burgers vectors

Strain hardening

Incoloy 925 晶界工程延展性剩余伯格斯矢量应变硬化

1. Introduction 1. 引言

Grain boundary engineering (GBE) was proposed as an effective approach for controlling the properties of polycrystalline metals by tailoring the grain boundary character distribution (GBCD) to obtain a high fraction of ‘special’ boundaries that can steadily interrupt the connectivity of random boundaries. These ‘special’ boundaries, usually referred to as low-Σ coincidence site lattice (CSL) grain boundaries, demonstrate low boundary energy, lower susceptibility to impurity or solute segregation, and greater resistance to grain boundary sliding and intergranular degradation, and thus can strongly affect grain boundary segregation, precipitation, corrosion, sliding and migration. Kobayashi et al. [1] investigated the connectivity of high-energy random grain boundaries on the basis of fractal analysis in SUS316L stainless steel to demonstrate the benefits of a refined approach to GBE for more precise prediction and control of intergranular corrosion in polycrystalline materials. Guan et al. [2] examined the fatigue behavior of non-GBE and GBE samples at relatively high stress amplitudes and found that the fracture type can change from intergranular to transgranular when cracking extends to Σ3ⁿ (n = 1, 2, and 3) grain boundaries, which significantly enhances the fracture toughness of polycrystalline Cu-Al alloys. Arguably, these characteristics tend to make “grain boundary engineered (GBEed)” metallic materials more advantageous and competitive.
晶界工程（GBE）被提出作为一种有效方法，通过调整晶界特征分布（GBCD）来控制多晶金属的性能，以获得高比例的“特殊”晶界，这些晶界能够稳定地中断随机晶界的连接性。这些“特殊”晶界通常被称为低Σ coincidence site lattice（CSL）晶界，它们表现出低晶界能、较低对杂质或溶质偏析的敏感性，以及更强的抗晶界滑移和晶间腐蚀能力，因此能够显著影响晶界偏析、析出、腐蚀、滑移和迁移。Kobayashi 等人[1]基于分形分析研究了 SUS316L 不锈钢中高能随机晶界的连接性，以证明精细 GBE 方法在更精确预测和控制多晶材料晶间腐蚀方面的优势。Guan 等人 [2] 研究了非晶界工程（non-GBE）和晶界工程（GBE）样品在相对较高的应力幅值下的疲劳行为，发现当裂纹扩展至Σ3 ⁿ (n = 1, 2, 和 3)晶界时，断裂类型会从沿晶界断裂转变为穿晶断裂，这显著提高了多晶 Cu-Al 合金的断裂韧性。可以说，这些特性使得“晶界工程（GBEed）”的金属材料更具优势与竞争力。

In addition to the abovementioned particular applications, GBCD optimization has a unique effect on the tensile properties of metallic materials. According to conventional studies, grain boundaries, which are prevalent defects in crystalline materials, lead to dislocation accumulation and stress concentration [3]. However, the special CSL grain boundaries introduced by the GBE-type process, which feature Miller indices, minimal disorder, and low interface energy, enable certain dislocations to slip across interfaces [4,5]. Thus, with a constant grain size, the mechanical properties of single-phase FCC metals, such as austenitic stainless steels [6] and copper alloys [7], can be affected by GBCD optimization to some extent. Previous studies have shown that the effect of GBCD optimization on the yield strength and tensile strength can be negligible [8,9], but its impact on ductility is related to the roles of the different types of GBs in dislocation slip behavior [10]. Wu [11] suggested that special GBs can improve the deformation uniformity and resistance to intergranular cracking, thereby enhancing ductility. Another study attributed this improvement in plasticity to the impact of Σ3ⁿ boundaries on multisystem slip during plastic deformation [12]. Theoretically, for FCC materials with a high stacking fault energy, the dislocations are generally perfect dislocations or extended dislocations with a low width, which may increase the average free path within a special GB network. Therefore, the deformation mode for this type of alloy is still dominated by the planar slip of dislocations [13], and GBCD optimization effectively increases the average free path of dislocations. Additionally, owing to variations in the stacking fault energy, short-range ordering, and frictional stresses, the dislocation slip mode varies across different materials [14]. Predictably, the effect of GBE-type structures on physical properties is complex and multidimensional. Two critical issues must still be addressed for a better understanding of the mechanism of the effect of the GBCD on ductility: i) Whether the relationship between GBEed microstructure and ductility in polycrystalline materials can be better constructed on account of twinning-related structure by considering comprehensive impact factors? ii) If so, what are the specific GBE optimization mechanisms?
除上述特定应用外，晶界工程化对金属材料抗拉性能具有独特作用。根据传统研究，晶界是晶体材料中常见的缺陷，会导致位错累积和应力集中[3]。然而，GBE 型工艺引入的特殊 CSSL 晶界，具有密勒指数、低无序度和低界面能的特点，使某些位错能够跨过界面滑移[4,5]。因此，在晶粒尺寸不变的情况下，单相 FCC 金属（如奥氏体不锈钢[6]和铜合金[7]）的力学性能在一定程度上会受到晶界工程化优化的影响。先前研究表明，晶界工程化优化对屈服强度和抗拉强度的影响可能可以忽略不计[8,9]，但其对延展性的影响与不同类型晶界在位错滑移行为中的作用有关[10]。Wu[11]提出，特殊晶界可以改善变形均匀性和抗晶间开裂能力，从而提高延展性。另一项研究将塑性提高归因于Σ3 ⁿ 边界对塑性变形过程中多体系滑移的影响[12]。理论上，对于具有高堆垛层错能的 FCC 材料，位错通常是完美位错或宽度较低的扩展位错，这可能增加特殊晶界网络内的平均自由程。因此，这种合金的变形模式仍然由位错的平面滑移主导[13]，而 GBCD 优化有效增加了位错的平均自由程。此外，由于堆垛层错能、短程有序和摩擦应力的变化，不同材料的位错滑移模式有所不同[14]。可以预见，GBE 型结构对物理性质的影响是复杂且多维度的。为了更好地理解 GBCD 对延展性影响的机制，仍需解决两个关键问题：i) 是否可以通过考虑综合影响因素，包括孪晶相关结构，来更好地构建多晶材料中 GBEed 微观结构与延展性之间的关系？ ii) 如果是这样，具体的 GBE 优化机制是什么？

To address the aforementioned inquiries, the concept of twinning-related domains [15,16] was employed to elucidate the influence of different grain boundaries in special GB networks on the mean free path of dislocations. Furthermore, twin polysynthetism and twin anisotropy [17] were incorporated to quantify the effects of twinning clusters on the microstructural orientation and multisystem slip mechanisms. In this study, GBE was applied to a typical nickel-based alloy, namely, an Incoloy 925 superalloy (referred to as Alloy 925). First, the microstructure evolution during thermomechanical processing (TMP) was studied to understand the formation mechanism of GBCD. Second, the influence of twinning-related domains (TRDs) on the strain hardening behavior of Alloy 925 was systematically investigated through tensile tests at room temperature. In detail, two new quantitative indices based on the theory of twinning clusters, namely, the average residual Burgers vector and the average Taylor factor, have been proposed to evaluate the impact mechanism of GBCD on mechanical properties. Finally, the detailed fracture microstructure characteristics were determined using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Analysis of the combined results will help us to critically evaluate the effects of TRDs on the ductility of Alloy 925.
为了解决上述问题，采用了孪晶相关域[15,16]的概念，阐明特殊 GB 网络中不同晶界对位错平均自由程的影响。此外，还引入了孪晶多合成和孪晶各向异性[17]，以量化孪晶团簇对微观结构取向和多系统滑移机制的影响。在本研究中，GBE 应用于一种典型的镍基合金，即 Incoloy 925 高温合金（简称 Alloy 925）。首先，研究了热机械加工（TMP）过程中的微观结构演变，以理解 GBCD 的形成机制。其次，通过室温拉伸试验系统地研究了孪晶相关域（TRD）对 Alloy 925 应变硬化行为的影响。具体而言，基于孪晶团簇理论提出了两个新的定量指标，即平均残余伯格斯矢量和平均泰勒因子，以评估 GBCD 对力学性能的影响机制。最后，采用扫描电子显微镜（SEM）和电子背散射衍射（EBSD）测定了详细的断裂微观结构特征。综合分析结果将有助于我们批判性地评估 TRDs 对合金 925 延展性的影响。

2. Materials and procedures
2. 材料与程序

A commercial Alloy 925 rod (42.4Ni-28.08Fe-21.42Cr-2.8Mo-2.24Cu-2.16Ti-0.5Al-0.34Si-0.05P-0.01C, wt. %) was used as the experimental material in this work. The rod was subjected to an initial solution annealing (SA) process at 1100 °C for 2 h, resulting in a uniform single-phase microstructure with a substantial grain size. After the SA process, the rod was sectioned into several small rectangular strips with the dimensions of 50 mm×16 mm × 4 mm. Subsequently, the strips underwent cold rolling with a 5 % reduction ratio. The cold-rolled plates were then subjected to annealing at different temperatures (1050, 1075, and 1100 °C) for 10 min, followed by water quenching.
本研究采用商业合金 925 棒材（42.4Ni-28.08Fe-21.42Cr-2.8Mo-2.24Cu-2.16Ti-0.5Al-0.34Si-0.05P-0.01C，质量分数）作为实验材料。该棒材在 1100 °C 下进行 2 小时的初始固溶退火（SA）处理，形成均匀的单相微观结构，晶粒尺寸较大。固溶退火后，将棒材切割成多个 50 mm×16 mm × 4 mm 的小矩形条带。随后，条带进行 5%的冷轧。冷轧板然后在不同温度（1050、1075 和 1100 °C）下退火 10 分钟，并水淬。

For the mechanical measurements, tensile samples with a gauge width of 4 mm and length of 40 mm (see Fig. 1) were cut along the RD of the TMPed strips. Then, the samples were ground parallel to the orientation of the primary load to eliminate the influence of stress concentration and the heterogeneous thickness distribution. Tensile tests were then conducted using a Shimadzu AG-X plus universal testing machine at a crosshead speed of 1 mm/min. Three tensile samples were cut from each joint to ensure the reliability of the tensile data. Notably, the fracture was preserved for subsequent EBSD observations, as shown in Fig. 1.
在力学测试中，沿 RD 方向从 TMPed 条带中切割了标距宽度为 4 毫米、长度为 40 毫米的拉伸样品（见图 1）。然后，将样品平行于主载荷方向磨削，以消除应力集中和厚度分布不均匀的影响。随后，使用 Shimadzu AG-X plus 万能试验机以 1 毫米/分钟的横梁速度进行拉伸试验。从每个接头切割了三个拉伸样品，以确保拉伸数据的可靠性。值得注意的是，断裂部分被保留以供后续的 EBSD 观察，如图 1 所示。

For microstructural characterization, the TMPed samples were cut to obtain a cross-section parallel to the RD-ND surface for EBSD mapping. Considering the slight difference in the strain between the surface and the mid-plane due to the synergetic effect of shear strain and additional friction on the rolling surface, the representative microstructure should be selected without the layer approximately 0.5 mm away from the rolling surface when performing EBSD analysis. The EBSD samples were first mechanically ground with sandpaper and polished with a diamond slurry. Then, all of the samples were electrolytically polished in a solution containing HClO₄ (20 ml) and CH₃COOH (80 ml) at a voltage of 20 V for 40 s to obtain a smooth surface with less residual stress. The EBSD experiments were finally performed using a TESCAN MIRA3 scanning electron microscope equipped with an HKL-EBSD system with an accelerating voltage of 20 kV and a working distance of 12 mm. Multiple EBSD scans with a step size of 1.5 μm were carried out for each sample to obtain statistically significant results.
为了进行微观结构表征，将 TMPed 样品切割以获得平行于 RD-ND 表面的横截面进行 EBSD 映射。由于剪切应变和轧制表面附加摩擦的协同作用导致表面和中平面之间的应变略有差异，在进行 EBSD 分析时，应选择去除距离轧制表面约 0.5 毫米的层作为代表性微观结构。EBSD 样品首先用砂纸进行机械研磨，然后用金刚石悬浮液抛光。然后，所有样品在含有 HClO ₄ （20 毫升）和 CH ₃ COOH（80 毫升）的电解液中以 20 伏电压电解抛光 40 秒，以获得残余应力较小的平滑表面。最后，使用配备 HKL-EBSD 系统的 TESCAN MIRA3 扫描电子显微镜进行 EBSD 实验，加速电压为 20 千伏，工作距离为 12 毫米。对每个样品进行多次步长为 1.5 微米的 EBSD 扫描，以获得具有统计意义的实验结果。

The twin microstructure from EBSD was processed using the ARPGE [18] and MATLAB software with the related MTEX toolkit. In the present work, Σ3ⁿ boundaries were identified by the Palumbo-Aust criterion (Δθ_max = 15°Σ^−5/6) [19], which is stricter than the Brandon criterion because it reduces the chances of misidentifying boundaries, leading to a more reliable analysis. The rest of the grain boundaries were considered to be random high-angle grain boundaries (RHAGBs). Additionally, to elucidate the impact of the TMP parameters on the grain boundary networks (GBNs), TRDs were introduced to describe large grain clusters. Based on the hierarchical twinning sequence of the Σ3ⁿ boundaries, Cayron [17] reconstructed the TRDs distribution map, and realized automation and subsequent data analysis in ARPGE. Furthermore, to quantify the topological connectivity of RHAGBs, the characteristics of TRDs, such as the length of the longest chain (LLC), were evaluated.
EBSD 获得的孪晶微观结构通过 ARPGE [18]和 MATLAB 软件及相关 MTEX 工具包进行处理。在本工作中，通过 Palumbo-Aust 标准（Δθ _max = 15°Σ ^−5/6 ）[19]识别了Σ3 ⁿ 边界，该标准比 Brandon 标准更严格，因为它减少了边界误识别的可能性，从而实现更可靠的分析。其余晶界被认为是无序高角晶界（RHAGBs）。此外，为了阐明 TMP 参数对晶界网络（GBNs）的影响，引入了 TRDs 来描述大晶粒簇。基于Σ3 ⁿ 边界的分级孪晶序列，Cayron [17]重建了 TRDs 分布图，并在 ARPGE 中实现了自动化及后续数据分析。此外，为了量化 RHAGBs 的拓扑连通性，评估了 TRDs 的特征，如最长链长度（LLC）。

3. Results 3. 结果

3.1. Microstructural characterization
3.1. 微观结构表征

Fig. 2 displays the evolution of the RHAGBs and CSL boundaries superimposed on the kernel average misorientation (KAM) maps under different processing conditions. The Σ3, Σ9, Σ27 boundary, and RHAGBs are indicated by the red, purple, yellow, and black lines, respectively. A significant number of straight Σ3 twin boundaries, known for their low mobility, are preserved in the SA sample, as shown in Fig. 2(a). However, we can rarely observe any high-order twin boundaries (e.g., Σ9, Σ27). Furthermore, the residual strain is substantially eliminated after the solution treatment, as indicated by the quantified proportion based on the KAM maps.
图 2 显示了在不同处理条件下，核平均取向（KAM）图上叠加的 RHAGBs 和 CSL 边界的变化。Σ3、Σ9、Σ27 边界和 RHAGBs 分别用红色、紫色、黄色和黑色线条表示。如图 2(a)所示，SA 样品中保留了大量的直Σ3 孪晶边界，这些孪晶边界以其低迁移率而闻名。然而，我们很少观察到任何高阶孪晶边界（例如，Σ9、Σ27）。此外，在固溶处理后，残余应变已大幅消除，如图所示的 KAM 图量化比例所示。

The TMPed samples subjected to 5 % strain show more local strain preserved within the matrix. As depicted in Fig. 2(b), for the sample annealed at 1050 °C, the proportion of the areas with a KAM exceeding 0.8° reaches 1.1 %, and these areas are predominantly located around the grain boundaries. Notably, Fig. 3 illustrates the significant reduction in Σ27, likely due to the more stringent CSL grain boundary criterion conditions. We can infer that the CSL boundaries deviate slightly from the standard orientation due to dislocation absorption during the local grain boundary migration. However, the average grain size (∼98.29 μm) and GBCD remained consistent between the SA and 5%-1050 °C samples, indicating that the applied thermal conditions and strain level were not sufficient to induce extensive grain boundary migration. This consistency suggests that while some local boundary migration may occur, the overall driving forces, primarily the stored energy from dislocations and the thermally activated movement at 1050 °C, are not sufficient to cause significant changes across the broader microstructure [20]. Strain-induced boundary migration (SIBM), influenced by both temperature and strain, can eliminate the strain-concentration regions near the grain boundaries, thus tailoring the residual strain distribution.
经过 5%应变处理的 TMPed 样品在基体中保留了更多的局部应变。如图 2(b)所示，对于在 1050 °C 退火的样品，KAM 超过 0.8°的面积比例达到 1.1%，这些面积主要位于晶界附近。值得注意的是，图 3 显示了Σ27 的显著减少，这可能是由于更严格的 CSL 晶界标准条件所致。我们可以推断，CSL 晶界由于位错吸收而在局部晶界迁移过程中略微偏离了标准取向。然而，SA 和 5%-1050 °C 样品的平均晶粒尺寸（~98.29 μm）和 GBCD 保持一致，表明所施加的热条件和应变水平不足以引起广泛的晶界迁移。这种一致性表明，尽管可能发生一些局部边界迁移，但整体驱动力，主要是位错储存的能量和 1050 °C 时的热激活运动，不足以在整个更广泛的微观结构中引起显著变化[20]。应变诱导的晶界迁移（SIBM），受温度和应变共同影响，可以消除晶界附近的应变浓度区域，从而调整残余应变分布。

The sample annealed at 1075 °C has a smaller grain size of approximately 93.63 μm and exhibits an increased proportion of Σ9 and Σ27 grain boundaries of approximately 1.14 %, as depicted in Fig. 2, Fig. 3. This observation suggests that an increase in the grain boundary migration rate, in line with the “growth accident model”, may prompt the formation of special grain boundaries, concurrently increasing the ratio of high-order twin boundaries. Intriguingly, a lower proportion of Σ3 grain boundaries indicated more active grain boundary reactions and dislocation absorption compared to the 1050 °C annealed sample. Therefore, an annealing temperature of 1075 °C can distinctly stimulate the migration and interaction between grain boundaries and dislocations, confirming that the annealing temperature can facilitate grain boundary reactions.
在 1075 °C 退火的样品具有约 93.63 μm 的更小晶粒尺寸，并表现出约 1.14%的Σ9 和Σ27 晶界的增加比例，如图 2 和图 3 所示。这一观察表明，晶界迁移率的增加（与“生长事故模型”一致）可能会促使特殊晶界的形成，同时增加高阶孪晶界的比例。有趣的是，与 1050 °C 退火样品相比，Σ3 晶界的比例较低，表明晶界反应和位错吸收更为活跃。因此，1075 °C 的退火温度可以明显刺激晶界与位错之间的迁移和相互作用，证实退火温度可以促进晶界反应。

For the TMPed sample annealed at 1100 °C, the elevated temperature can further accelerate the migration of mobile grain boundaries, leading to the formation of larger twinned clusters surrounded by RHAGBs, which can internally encapsulate abundant CSL grain boundaries. The increase in the number of grain boundaries also causes a further decrease in the average grain size to approximately 89.58 μm. The measured KAM levels indicate that more strain is eradicated during the annealing process, with only 0.3 % of the residual strain retained in the form of substructures within the grains. Moreover, the proportions of high-order twin boundaries increase markedly with increasing annealing temperature. Furthermore, we calculate the value of Σ3/(Σ9+Σ27), which reflects well the extent of the grain boundary reaction. It is observed that this proportion in the 5%-strain samples decreases with increasing annealing temperature, indicating that strain-induced boundary migration mainly accounts for the formation of GBNs.
对于在 1100 °C 退火的 TMPed 样品，高温可以进一步加速可移动晶界的迁移，导致形成更大的孪晶团簇，这些团簇被 RHAGBs 包围，可以内部包裹丰富的 CSL 晶界。晶界数量的增加也导致平均晶粒尺寸进一步减小至约 89.58 μm。测量的 KAM 水平表明，在退火过程中更多的应变被消除，晶粒内部仅保留了 0.3 %的残余应变，以亚结构的形式存在。此外，随着退火温度的升高，高阶孪晶界的比例显著增加。此外，我们计算了Σ3/(Σ9+Σ27)的值，该值很好地反映了晶界反应的程度。观察到在 5%应变样品中，该比例随着退火温度的升高而降低，表明应变诱导的边界迁移主要导致了 GBNs 的形成。

3.2. Tensile properties 3.2. 拉伸性能

Fig. 4(a) presents the stress‒strain curves under different TMP conditions. The corresponding tensile property values, including yield strength (

σ_{0.2}

), ultimate tensile strength (

σ_{UTS}

), elongation-to-failure (

ε_{f}

), and the product of strength and elongation, are summarized in Table 1. An examination of the results clearly shows that the SA and 5%-1050 °C samples have a similar product of strength and elongation. Compared with that of the SA sample, the tensile strength of the 5%-1050 °C sample increased from 563.86 MPa to 599.38 MPa, but the elongation rate decreased from 66.94 % to 64.22 %, primarily because the lower annealing temperature (1050 °C) was not adequate to facilitate GBCD, as demonstrated in Fig. 3. Therefore, work hardening, which hardly breaks the balance between strength and plasticity, mainly contributes to the performance change of Alloy 925.
图 4(a)展示了在不同 TMP 条件下应力-应变曲线。相应的拉伸性能值，包括屈服强度（

σ_{0.2}

）、抗拉强度（

σ_{UTS}

）、断裂延伸率（

ε_{f}

）以及强度与延伸率的乘积，汇总于表 1。结果分析表明，SA 和 5%-1050 °C 样品的强度与延伸率乘积相似。与 SA 样品相比，5%-1050 °C 样品的抗拉强度从 563.86 MPa 增加到 599.38 MPa，但延伸率从 66.94 %降至 64.22 %，主要因为较低退火温度（1050 °C）不足以促进 GBCD，如图 3 所示。因此，加工硬化主要导致合金 925 性能变化，它几乎不会破坏强度与塑性的平衡。

Table 1. Yield strength ( $σ_{0.2}$ ), ultimate tensile strength ( $σ_{UTS}$ ), elongation-to-failure ( $ε_{f}$ ), and the product of strength and elongation obtained from the stress‒strain curves.
表 1. 屈服强度（ $σ_{0.2}$ ），抗拉强度（ $σ_{UTS}$ ），断裂延伸率（ $ε_{f}$ ），以及从应力-应变曲线得到的强度与延伸率的乘积。

Sample 样品	$σ_{0.2}$ /MPa	$σ_{UTS}$ /MPa	$ε_{f}$ /%	The product of strength and elongation/MPa·% 强度与延伸率的乘积/MPa·%
SA	194.04 ± 8.56	563.86 ± 13.12	66.94 ± 7.12	377.45
5 %/1050 °C	207.67 ± 7.88	590.22 ± 18.26	64.22 ± 6.56	379.03
5 %/1075 °C	228.73 ± 7.23	595.65 ± 17.26	85.23 ± 7.25	507.67
5 %/1100 °C	206.56 ± 7.11	599.38 ± 15.28	95.86 ± 7.85	574.57

For the GBE-type samples, as the temperature increases from 1050 °C to 1100 °C, the tensile strength of the TMPed sample increases from 590.22 MPa to 599.38 MPa, which is consistent with the trend of the average grain size. It can be inferred that the evolved GBN significantly contributes to the strength enhancement. Additionally, it is generally believed that the enhanced tensile strength is associated with the strain hardening; thus, the modest growth rate in tensile strength can imply that the obstruction of Σ3ⁿ boundaries to dislocation movement is not significant. Interestingly, the elongation increases significantly from 64.22 % to 95.86 %, leading to a notable increase in the product of strength and elongation. Comparison with other superalloys [[21], [22], [23], [24], [25], [26], [27], [28]] that have undergone annealing or solution treatment, as shown in Fig. 4(b), clearly shows that Alloy 925 exhibited superior comprehensive mechanical performance after treatment at 5 % and 1100 °C. However, as shown in Fig. 3, the samples annealed at 1100 °C and 1050 °C exhibited similar proportions of Σ3ⁿ boundaries. It can be conjectured that the CSL grain boundary proportion alone may not be the sole determinant of the ductility enhancement. Furthermore, elongation is closely related to the twin cluster structure, which will be discussed in detail below.
对于 GBE 型样品，随着温度从 1050 °C 升高到 1100 °C，TMPed 样品的拉伸强度从 590.22 MPa 增加到 599.38 MPa，这与平均晶粒尺寸的变化趋势一致。可以推断，形成的 GBN 对强度提升有显著贡献。此外，通常认为增强的拉伸强度与应变硬化有关；因此，拉伸强度的适度增长率可以表明Σ3 ⁿ 边界对位错运动的阻碍并不显著。有趣的是，延伸率从 64.22 %显著增加到 95.86 %，导致强度与延伸率的乘积显著增加。与其他经过退火或固溶处理的超合金[[21], [22], [23], [24], [25], [26], [27], [28]]（如图 4(b)所示）相比，925 合金在 5 %和 1100 °C 处理后的综合力学性能表现出优越性。然而，如图 3 所示，在 1100 °C 和 1050 °C 退火的样品中，Σ3 ⁿ 边界的比例相似。可以推测，CSL 晶界比例本身可能并非延展性提高的唯一决定因素。此外，延伸量与孪晶簇结构密切相关，将在下文中详细讨论。

3.3. Fracture analysis 3.3. 断裂分析

The fracture morphology at different annealing temperatures, as shown in Fig. 5, was characterized for samples with 5 % strain to illustrate the fracture mechanism. Fig. 5 (a) and 5(d) show that the fracture surface of the 1050 °C sample exhibits a mix of numerous dimples separated by some torn edges. Furthermore, we can observe smooth cleavage facets in some localized regions (highlighted by the yellow dashed box), which is typically a specific low-index crystal plane that is highly coherent with the matrix orientation. The variation in the dislocation migration rate on different crystal planes is prone to induce a series of cleavage steps. In addition, river patterns can be generated with the gradual accumulation of cleavage planes. The cracks favor brittle fracture along the cleavage planes during propagation; thus, the usual course of the river aligns with the crack propagation direction. The sample exhibits mixed ductile‒brittle fracture characteristics.
不同退火温度下的断裂形貌如图 5 所示，对 5%应变的样品进行了表征以说明断裂机制。图 5(a)和 5(d)显示，1050°C 样品的断裂表面呈现出许多凹坑和撕裂边缘的混合。此外，我们可以在一些局部区域观察到平滑的解理面（黄色虚线框突出显示），这通常是高度与基体取向一致的特定低指数晶面。不同晶面上的位错迁移率差异容易导致一系列解理台阶的产生。此外，随着解理面的逐渐积累，可以形成河流纹。裂纹在扩展过程中沿解理面发生脆性断裂；因此，河流纹通常与裂纹扩展方向一致。该样品表现出混合的延性-脆性断裂特征。

As shown in Fig. 5(b) and (c), with increasing annealing temperature, the fractures of the 5%-1075 °C and 5%-1100 °C samples consisted of many circular and elliptical dimples of different sizes, demonstrating the transition of the fracture mechanism from mixed fracture to ductile fracture. By magnifying the images of the local regions, as illustrated in Fig. 5(e) and (f), it can be observed that the fracture of the 5%-1075 °C sample exhibits numerous shallower and smaller equiaxed dimples that are evenly distributed across the entire fracture surface. Meanwhile, for the 5%-1100 °C sample, the equiaxed dimples on the fracture surface have different depths, with some smaller dimples scattered around the larger dimples. This clearly implies that significant plastic deformation occurred prior to fracture in the experimental alloy. Moreover, within some dimples, a few fragmental particles can be observed, as indicated by the yellow dashed frame in Fig. 5(f), which can lead to crack initiation. However, fewer secondary phase carbide particles can be observed in the SA sample, indicating that the size and depth of the dimples can directly represent the plastic deformation capability. The fracture morphology characteristics of the different TMP states are consistent with the elongation results, as shown in Table 1.
如图 5(b)和(c)所示，随着退火温度的升高，5%-1075 °C 和 5%-1100 °C 样品的断裂面由许多不同大小的圆形和椭圆形凹坑组成，表明断裂机制从混合断裂向延性断裂转变。通过放大局部区域的图像，如图 5(e)和(f)所示，可以观察到 5%-1075 °C 样品的断裂面呈现出大量较浅、较小的等轴凹坑，这些凹坑均匀分布在整个断裂面上。而 5%-1100 °C 样品的断裂面上，等轴凹坑的深度不同，一些较小的凹坑散布在较大的凹坑周围。这清楚地表明，在实验合金中断裂前发生了显著的塑性变形。此外，在一些凹坑中可以观察到一些碎片颗粒，如图 5(f)中黄色虚线框所示，这可能导致裂纹萌生。然而，在 SA 样品中观察到的次生相碳化物颗粒较少，表明凹坑的大小和深度可以直接代表塑性变形能力。不同 TMP 状态的断裂形貌特征与延伸结果一致，如表 1 所示。

To elucidate the plasticity mechanism introduced by the GBE-type microstructure, the fracture morphology was further characterized using EBSD, which can show distinct interfaces for both the microstructure and substructure via orientation mapping. As depicted in Fig. 6(a), the inverse pole figure (IPF) map of tensile fracture in the 5%-1075 °C sample is shown in Fig. 6(a). A distinct 45° tensile fracture can be observed through the macroscopic features, mostly according to the direction of maximum shear stress during the unidirectional tensile process. It is well-known that a higher symmetry of FCC metals can activate more slip systems, which always initiate a directional slip at a 45° angle with respect to the tensile direction.
为阐明 GBE 型微观结构引入的塑性机制，进一步采用 EBSD 对断裂形貌进行表征，该技术可通过取向图显示微观结构和亚结构的明显界面。如图 6(a)所示，5%-1075 °C 样品的拉伸断裂的逆极图(IPF)地图显示在图 6(a)中。通过宏观特征可以观察到明显的 45°拉伸断裂，这主要与单向拉伸过程中最大剪应力方向一致。众所周知，FCC 金属具有更高的对称性，可以激活更多的滑移系统，这些系统通常在拉伸方向 45°角处开始定向滑移。

Moreover, some localized EBSD images of different fracture sections (highlighted by the yellow dotted frames) were collected with a smaller step size of 0.1 μm, enabling a more accurate capture of local orientation features, as shown in Fig. 6(b)-6(d). Numerous parallel deformation shear bands are generated to accommodate larger strains, which is a consequence of directional dislocation movement and uneven deformation. These shear bands exhibit a distinct 60° {111} orientation relationship, as depicted in Fig. 6(d1). Within the twin clusters near the fracture, more deformation twins can be observed, which are generally distributed along the trace direction of the {111} crystal plane. Moreover, high strain is prone to cause significant lattice distortion, concurrently inducing rapid increases in the dislocation density. In this case, dislocation slip may be inefficient at accommodating the strain, inducing the formation of deformation twins, which are newly generated within the deformation grains and reduce the local stress concentration under large strain. However, due to the limited twin width, accurately capturing the corresponding microstructure with EBSD is challenging in the other two regions, as demonstrated in Fig. 4 (b1) and 4 (c1). Nevertheless, we can still observe many slip traces along the {111} crystal plane, which largely correlate with the local strain distribution. The stress concentration around the crack tip can influence the deformation twins in the proximity of the crack propagation direction, characterizing them as longer, thinner, and somewhat angled.
此外，使用 0.1 μm 的小步长采集了不同断裂截面的一些局部 EBSD 图像（黄色虚线框突出显示），如图 6(b)-6(d)所示，能够更精确地捕捉局部取向特征。为了适应更大的应变，产生了许多平行变形剪切带，这是由定向位错运动和变形不均匀性引起的。这些剪切带表现出明显的 60° {111}取向关系，如图 6(d1)所示。在断裂附近的孪晶簇中，可以观察到更多的变形孪晶，它们通常沿着{111}晶面的迹线方向分布。此外，高应变容易导致显著的晶格畸变，同时引起位错密度的快速增加。在这种情况下，位错滑移可能无法有效适应应变，从而诱导变形孪晶的形成，这些孪晶在变形晶粒中新生成，并在大应变下降低局部应力集中。然而，由于孪晶宽度有限，在另外两个区域中用 EBSD 准确捕捉相应的微观结构具有挑战性，如图 4 (b1) 和 4 (c1) 所示。尽管如此，我们仍然可以看到许多沿着{111}晶面的滑移迹线，这些滑移迹线与局部应变分布密切相关。裂纹尖端的应力集中会影响裂纹扩展方向附近的变形孪晶，使其呈现为更长、更薄且略微倾斜的特征。

Furthermore, the twin clusters were reconstructed through the deformed fracture microstructure (corresponding to the yellow dashed box), as shown in Fig. 6(b2), 6 (c2), and 6 (d2). Notably, some deformation twins (marked by black arrows) exist across different TRDs. However, the significant discontinuity of high-angle grain boundaries (HAGBs) can create an energy barrier for the propagation of deformation twins [29]. Therefore, it can be speculated that the interfaces crossed by deformation twins are annealing twin boundaries. However, the initial twin boundaries continuously absorb dislocations, leading to an accumulation of dislocations and subsequently exceeding the threshold of the Palumbo-Aust criterion. Previous research [30] indicates that movable dislocations can traverse low-energy CSL grain boundaries with greater symmetry. The formation and propagation of deformation twins are connected to the slip system, which involves the systematic movement of atoms within the crystal. As shown in Fig. 6(e), when deformation twins encounter CSL grain boundaries, the alignment and matching of atomic positions at the grain boundaries allow the twins to continue to extend along the existing slip system under some specific conditions. With increasing deformation, this will eventually lead to the formation of complex twin networks, as reported in Ref. [31]. Overall, due to the differences in the coherency between the CSL grain boundaries and RHAGBs, the GBCD has a significant impact on the plastic deformation mechanism of Alloy 925.
此外，孪晶簇通过变形的断裂微观结构（对应黄色虚线框）进行重构，如图 6(b2)、6(c2)和 6(d2)所示。值得注意的是，一些变形孪晶（用黑箭头标记）存在于不同的 TRD 之间。然而，高角度晶界（HAGB）的显著不连续性可以为变形孪晶的传播创建一个能量势垒[29]。因此，可以推测变形孪晶穿过的界面是退火孪晶界。然而，初始孪晶界持续吸收位错，导致位错积累并随后超过 Palumbo-Aust 标准的阈值。先前研究[30]表明，可移动的位错可以跨越具有更高对称性的低能 CSL 晶界。变形孪晶的形成和传播与滑移系统有关，该系统涉及晶体中原子系统的运动。如图所示。 6(e)，当变形孪晶遇到 CSS 晶界时，晶界处原子位置的排列和匹配使得孪晶在特定条件下能够沿着现有的滑移系统继续扩展。随着变形的增加，这最终会导致复杂孪晶网络的形成，正如参考文献[31]所报道的那样。总体而言，由于 CSS 晶界和 RHAGB 之间共格性的差异，晶界共格度差异（GBCD）对合金 925 的塑性变形机制有显著影响。

4. Discussions 4. 讨论

4.1. Effect of the grain boundary characteristics distribution
4.1. 晶界特征分布的影响

Generally, the plastic deformation mechanism is intimately associated with the migration behavior of dislocations. During the uniaxial tension process, in addition to the interaction and entanglement of moving dislocations, the strain hardening behavior is also influenced by the GBCD. The dislocations inside the grains can slip along the close-packed planes relatively freely or climb under the influence of temperature. By contrast, the grain boundary, as a localized area of concentrated energy, can absorb or hinder movable dislocations, which markedly affects the strain transmission between multiple grains. The mechanical properties of the TRDs in the GBEed sample can be tailored by optimizing the GBCD. Fig. 7(a) shows that the hardening curves of the different TMPed samples exhibit similar tendencies. Due to the short elastoplastic transition stage, the TMPed alloy shows a sharp hardening drop at the beginning of the curve.

θ_{0}^{Ⅲ}

is a hardening limit extrapolated to (σ - σ_0.2) = 0 to represent the strain hardening value of stage III. As the annealing temperature increases from 1050 °C to 1100 °C,

θ_{0}^{Ⅲ}

decreases from 1162 MPa to 589 MPa. Interestingly, the 5%-1100 °C curve shows a clear peak-valley stage at (σ - σ_0.2) = 100 MPa. This is primarily because the relatively elevated annealing temperature can promote the comprehensive development of TRDs through SIBM, leading to the formation of more strain-free regions within the matrix that can effectively accommodate the proliferation of dislocations. During the subsequent deformation process, the weak hindrance of the dislocations by twin boundaries leads to a slight increase in the hardening rate.
通常情况下，塑性变形机制与位错的迁移行为密切相关。在单轴拉伸过程中，除了运动位错的相互作用和缠结外，应变硬化行为也受晶界位错偏聚（GBCD）的影响。晶粒内的位错可以沿着密排面相对自由地滑移，或在温度影响下攀移。相比之下，晶界作为集中能量的局部区域，可以吸收或阻碍运动位错，这显著影响多晶粒间的应变传递。通过优化 GBCD，可以调整 GBEed 样品中 TRDs 的力学性能。图 7(a)显示不同 TMPed 样品的硬化曲线表现出相似趋势。由于弹性塑性转变阶段较短，TMPed 合金在曲线开始处显示出急剧的硬化下降。

θ_{0}^{Ⅲ}

是延伸至(σ - σ _0.2 ) = 0 的硬化极限，用以表示 III 阶段的应变硬化值。随着退火温度从 1050°C 升高到 1100°C，

θ_{0}^{Ⅲ}

从 1162 MPa 降至 589 MPa。有趣的是，5%-1100 °C 曲线在(σ - σ _0.2 ) = 100 MPa 处显示出明显的峰谷阶段。这主要是因为相对较高的退火温度可以通过 SIBM 促进 TRDs 的全面发展，从而在基体中形成更多的无应变区域，这些区域可以有效地容纳位错的增殖。在随后的变形过程中，位错被孪晶边界弱阻碍，导致硬化速率略有增加。

Furthermore, the strain hardening behavior is closely correlated with dislocation accumulation that is manifested by the evolution of the dislocation density. Some previous works [32,33] have shown that a well-matched structure on a small scale can be considered smooth and can be simply analogized to that of the next larger scale. Based on the Kock strain hardening model, an analytical relationship between the curve of (σ - σ_0.2)θ vs. (σ - σ_0.2) and the curve of

ρ^{'}

vs.

ρ^{\frac{1}{2}}

was constructed [34]. Therefore, the relationship between the rate of dislocation storage

ρ^{'}

and the dislocation density

ρ^{\frac{1}{2}}

throughout the whole strain hardening stage can be obtained from Fig. 7(b). The initial segment of the curve can be approximated by a straight line passing through the coordinate origin point. In this section, the dislocation density approaches zero, and the GBCD is the most significant factor influencing the dislocation storage rate, showing different slope values of θ₀ for the three fitted straight lines. Some related research [35] shows that twins can also impede dislocation movement; therefore, a decrease in twinning tends to weaken the strain hardening effect. However, in the present work, the opposite conclusion can be drawn: the TMPed samples unexpectedly possess a lower θ₀ value, mostly owing to the different abilities of the grain boundaries to impede the motion of dislocations. Hence, the TMPed samples demonstrated a reduced work-hardening capability due to the relatively lower proportion of RHAGBs. Moreover, the 5%-1075 °C sample undergoes an early elastoplastic transition when (σ - σ_0.2) ≈ 40 MPa; that is, stage III of strain hardening occurs. Dislocation absorption by grain boundaries during annealing can lead to a deviation in the standard orientation, particularly for Σ3ⁿ boundaries, significantly hindering the movement of dislocations and accelerates the buildup of strain. These results showed that GBCD can be strongly related to the rate of dislocation storage during the strain hardening stage.
此外，应变硬化行为与位错累积密切相关，这通过位错密度的演变来体现。一些先前的研究[32,33]表明，在小尺度上具有良好匹配的结构可以被认为是光滑的，并且可以简单地类比为下一个更大尺度的结构。基于 Kock 应变硬化模型，构建了(σ - σ₀)θ与(σ - σ₁)的曲线和

ρ^{'}

与

ρ^{\frac{1}{2}}

的曲线之间的解析关系[34]。因此，从图 7(b)中可以获得位错存储速率

ρ^{'}

和整个应变硬化阶段中的位错密度

ρ^{\frac{1}{2}}

之间的关系。曲线的初始段可以近似为通过坐标原点的直线。在本节中，位错密度接近于零，GBCD 是影响位错存储率的最显著因素，显示出三条拟合直线的不同θ ₀ 斜率值。一些相关研究[35]表明，孪晶也可以阻碍位错运动；因此，孪晶的减少往往会削弱应变硬化效果。然而，在本工作中，可以得出相反的结论：经过 TMP 处理的样品意外地具有较低的θ值，这主要归因于晶界阻碍位错运动能力的不同。因此，经过 TMP 处理的样品由于相对较少的 RHAGBs 而表现出降低的加工硬化能力。此外，5%-1075 °C 样品在(σ - σ) ≈ 40 MPa 时发生早期的弹塑性转变；也就是说，发生应变硬化第三阶段。退火过程中晶界对位错的吸收会导致标准取向的偏差，特别是对于Σ3 晶界，这会显著阻碍位错的运动并加速应变的积累。这些结果表明，GBCD 与应变硬化阶段的位错存储速率密切相关。

To better illustrate the impact of grain boundary type on dislocation movement in twin clusters, we introduced the residual Burgers vector (RBV), which is necessary to ensure continuity of the Burgers vector upon transmission from the slip system of adjacent grains. Several previous studies [36,37] have shown that a lower RBV at grain boundaries can increase the ease of strain transfer. Therefore, typical slip transmission criteria based on the minimization of the RBV were proposed, which have been investigated experimentally and computationally for FCC materials [38], body-centered cubic (BCC) materials [39], and interphase boundaries in alloys [40] to control the activation of slip systems. However, the minimization of the RBV is usually applied to predict the specific slip coefficients during the deformation process, which is not applicable to the macroscopic evaluation of the plastic deformation capacity. In this work, the average residual Burgers vector (ARBV,

\overline{b}

) was employed to evaluate the resistance of grain boundaries to dislocation penetration as follows [41]:
为了更好地说明晶界类型对孪晶团中位错运动的影响，我们引入了残余伯格斯矢量（RBV），这是确保伯格斯矢量在相邻晶粒的滑移系中传递时保持连续性所必需的。已有几项先前研究[36,37]表明，晶界处的较低 RBV 可以提高应变传递的容易程度。因此，基于 RBV 最小化的典型滑移传递标准被提出，这些标准已被用于实验和计算研究面心立方（FCC）材料[38]、体心立方（BCC）材料[39]以及合金中的相界[40]，以控制滑移系的激活。然而，RBV 的最小化通常用于预测变形过程中的特定滑移系数，这并不适用于宏观评价塑性变形能力。在本工作中，采用平均残余伯格斯矢量（ARBV，

\overline{b}

）来评估晶界对位错穿透的阻力，具体如下[41]：(1)

\overline{b} = \frac{1}{N} \sum_{1}^{N} | {\vec{b}}_{i} |

(2)

{\vec{b}}_{i} = {\vec{g}}_{i n} \cdot {\vec{b}}_{i n} - {\vec{g}}_{o u t} \cdot {\vec{b}}_{o u t}

where N indicates the possible slip transmission interactions. The number of possible interactions is obtained by considering the slip systems within the incident grain and the transmitted grain. For FCC alloys with 12 slip systems, 144 possible interactions exist for slip transmission at each grain boundary. In addition,

{\vec{b}}_{i n}

and

{\vec{b}}_{o u t}

are Burgers vectors of the incident slip dislocation and transmitted slip dislocation, respectively, while

{\vec{g}}_{i n}

and

{\vec{g}}_{o u t}

are the rotation matrices used to describe the orientation change of the crystal associated with the incident and transmitted slip dislocations, respectively. Thus, the ARBV reflects the ability of grain boundaries to impede dislocation motion during plastic deformation. As dislocations are generated and move to grain boundaries, some dislocations can be blocked and then accumulate around grain boundaries, resulting in a local strain concentration. However, local strain may also be directly transferred through grain boundaries to adjacent grains. The high local strain concentration around grain boundaries can be relaxed by either crack formation or activation of the slip system within adjacent grains. It can be inferred that a lower ARBV provides less resistance to dislocations, which may increase the plastic deformation capacity.
其中 N 表示可能的滑移传递相互作用。通过考虑入射晶粒和传递晶粒内的滑移系统，可以得到可能的相互作用数量。对于具有 12 个滑移系统的 FCC 合金，每个晶界处存在 144 种可能的滑移传递相互作用。此外，

{\vec{b}}_{i n}

和

{\vec{b}}_{o u t}

分别是入射滑移位错和传递滑移位错的柏格斯矢量，而

{\vec{g}}_{i n}

和

{\vec{g}}_{o u t}

分别是用于描述与入射和传递滑移位错相关的晶体取向变化的旋转矩阵。因此，ARBV 反映了晶界在塑性变形过程中阻碍位错运动的能力。当位错产生并移动到晶界时，一些位错会被阻挡并在晶界周围积累，导致局部应变集中。然而，局部应变也可能直接通过晶界传递到相邻晶粒。晶界周围的局部高应变集中可以通过裂纹形成或激活相邻晶粒内的滑移系统来缓解。可以推断出，较低的 ARBV 提供了对位错的较小阻力，这可能增加塑性变形能力。

As depicted in Fig. 8, the ARBV values for each selected grain boundary under various TMP conditions were calculated. It can be clearly seen that the RHAGBs and high-order twin boundaries (e.g., Σ9 and Σ27) show higher ARBV values, commonly ranging from 0.525 to 0.55. It is difficult for dislocations to pass through grain boundaries when the RBV exceeds 0.5 for RHAGBs [42]. However, because of its reduced energy and improved geometric compatibility, the Σ3 twin boundary displays a lower ARBV value of ∼0.508. The transmission of dislocation slip is more efficiently facilitated at twin boundaries when the residual Burgers vector is less than 0.6 [42]. Interestingly, our experimental findings indicate that this transmission also applies to deformation twins, as depicted in Fig. 6. Some related studies [43,44] have also shown that screw dislocations can directly pass through Σ3 twin boundaries and hardly decompose into dislocations with other Burgers vectors on the twin boundary. Moreover, edge dislocations can facilitate slip transmission more readily, leading to only a minimal RBV value. Thus, it can be inferred that dislocation pile-up is less likely to occur in the vicinity of Σ3 twin boundaries. Concurrently, the twin boundaries are capable of storing dislocations, facilitating dislocation slip at the twin interface, which can therefore accommodate significant plastic deformation and enhance the plasticity of the crystal. In summary, for the twin cluster structure, which internally comprises the Σ3ⁿ grain boundary network and is externally enclosed by RHAGBs, although these special boundaries can affect the dislocation propagation within this twin cluster, the reduced ARBV indicates a diminished obstruction. Furthermore, Σ3 grain boundaries can absorb decomposed dislocations and allow them to slip on the twin interface [45], promoting a uniform strain distribution in the matrix and thereby accommodating substantial plastic deformation.
如图 8 所示，在多种 TMP 条件下计算了每个选定晶界的 ARBV 值。可以明显看出，高角度晶界（RHAGBs）和高阶孪晶界（如Σ9 和Σ27）显示出更高的 ARBV 值，通常在 0.525 至 0.55 之间。当 RHAGBs 的 RBV 超过 0.5 时，位错难以通过晶界[42]。然而，由于其能量降低和几何相容性改善，Σ3 孪晶界显示出约 0.508 的较低 ARBV 值。当残余伯格斯矢量小于 0.6 时，孪晶界更有效地促进位错滑移的传递[42]。有趣的是，我们的实验发现这种传递也适用于变形孪晶，如图 6 所示。一些相关研究[43,44]也表明，螺位错可以直接通过Σ3 孪晶界，并且在孪晶界上几乎不会分解成其他伯格斯矢量的位错。此外，刃位错更容易促进滑移传递，导致 RBV 值极小。因此可以推断，位错堆积在Σ3 孪晶边界附近不太可能发生。同时，孪晶边界能够存储位错，促进孪晶界面处的位错滑移，从而能够容纳显著的塑性变形并提高晶体的塑性。总之，对于由Σ3 ⁿ 晶界网络内部构成并外面包裹着 RHAGBs 的孪晶簇结构，虽然这些特殊边界会影响孪晶簇内的位错传播，但减少的 ARBV 表明阻碍作用减弱。此外，Σ3 晶界可以吸收分解的位错，并允许它们在孪晶界面上滑移[45]，促进基质中的均匀应变分布，从而能够容纳大量的塑性变形。

4.2. Effect of TRD anisotropy
4.2. TRD 各向异性影响

As mentioned above, the size of twin clusters is a crucial factor affecting elongation. However, the dislocation transfer is influenced by both GBCD and the grain orientation, which can determine the critical shear stress required to activate the slip system [46]. Dislocations move along specific crystallographic planes under applied shear stress, causing shear deformation of the lattice. Thus, the soft and hard orientations can directly influence the plastic deformation capability. Additionally, GBE-type samples can introduce more different sets of orientations through multiple twinning, which is bound to affect the plastic deformation mechanism. To better evaluate the impact of TRD anisotropy on plastic deformation, an average Taylor factor value [47] was applied to assess the plastic deformation ability of the twin clusters as follows:
如前所述，孪晶团簇的尺寸是影响延伸率的关键因素。然而，位错转移受晶界倾角差异（GBCD）和晶粒取向的共同影响，这些因素决定了激活滑移系统所需的临界剪切应力[46]。在施加的剪切应力下，位错沿特定的晶体学平面运动，导致晶格剪切变形。因此，软取向和硬取向可以直接影响塑性变形能力。此外，GBE 型样品通过多次孪晶可以引入更多不同的取向组，这必然会影响塑性变形机制。为了更好地评估 TRD 各向异性对塑性变形的影响，采用了平均泰勒因子值[47]来评估孪晶团簇的塑性变形能力，具体如下：(3)

{\overline{M}}_{k}^{T R D} = \frac{1}{n} \sum_{i = 1}^{n} m_{i} \cdot f_{i}

where

{\overline{M}}_{k}^{T R D}

denotes the average Taylor factor of the twin cluster k. Here, n specifies the number of daughter grains within the twin cluster k and

m_{i}

and

f_{i}

represent the Taylor factor value and the area of daughter grain i, respectively. Typically, a higher average Taylor factor indicates greater shear stress to initiate the macro deformation. As shown in Table 2, the

{\overline{M}}^{T R D}

values were calculated for the TMPed samples under different annealing temperatures. The

{\overline{M}}^{T R D}

value of the non-GBE samples is the highest, peaking at 4.0526. For the GBE-type samples, the

{\overline{M}}^{T R D}

values decrease with increasing annealing temperature, which can significantly promote the ability of SIBM to tailor GBCD under these TMP conditions. The enlargement of the twin clusters leads to a lower

{\overline{M}}^{T R D}

value, indicating a reduction in the slip shear strain necessary to activate dislocation movement. It can be concluded that triggering multiple twinning events can efficiently stimulate the formation of soft orientations in the matrix by regulating grain orientation, making it easier to activate slip systems during uniform plastic deformation in GBE samples.
其中

{\overline{M}}_{k}^{T R D}

表示孪晶簇 k 的平均泰勒因子。这里，n 指定孪晶簇 k 内子晶粒的数量，

m_{i}

和

f_{i}

分别代表子晶粒 i 的泰勒因子值和面积。通常，较高的平均泰勒因子意味着更大的剪切应力才能启动宏观变形。如表 2 所示，

{\overline{M}}^{T R D}

值是在不同退火温度下对 TMPed 样品计算的。非 GBE 样品的

{\overline{M}}^{T R D}

值最高，达到 4.0526。对于 GBE 型样品，

{\overline{M}}^{T R D}

值随着退火温度的升高而降低，这可以显著促进 SIBM 在这些 TMP 条件下调整 GBCD 的能力。孪晶簇的扩大导致

{\overline{M}}^{T R D}

值降低，表明激活位错运动所需的滑移剪切应变减少。可以得出结论，通过调节晶粒取向触发多次孪晶事件可以有效地刺激基体中软取向的形成，使 GBE 样品在均匀塑性变形期间更容易激活滑移系统。

Table 2. Average Taylor factor values of non-GBE- and GBE-type samples.
表 2. 非 GBE 型和 GBE 型样品的平均泰勒因子值。

Samples 样品		${\overline{M}}^{T R D}$
Non-GBE 非 GBE	SA	4.0526
GBE	1050 °C	4.0105
	1075 °C	3.8583
	1100 °C	3.8160

As depicted in Fig. 9, we further analyzed two TRDs that have similar sizes but differ in their multiple twinning characteristics. For the non-GBE parent grain (TRD A), the grain boundary network predominantly comprises straight and coherent Σ3 grain boundaries that generally possess limited mobility. However, higher-order Σ3ⁿ grain boundaries can rarely be found. By contrast, the GBE-type parent grain (TRD B) displays a complicated GBCD. In addition, all pairs of grains in this cluster retain a strict Σ3ⁿ orientation relationship, as was also reported in our previous work [48]. To analyze the mutual misorientation relationships within the clusters, two corresponding twin tree structures were established, as shown in Fig. 9(c) and (d). The twin tree features 7 unique orientations for TRD B, while TRD A contains only 3 unique orientations. The emergence of a heavily twinned microstructure, with the largest LLC value of 5 can also be found through the twin tree. In addition, Fig. 9(e) and (f) illustrate the distributions of the Taylor factor values within TRD A and TRD B, respectively. The minimum average Taylor factor of the child grains within TRD A is approximately 3.9 (marked in dark blue), which is clearly greater than that within GRD B. For the non-GBE-type sample, because the multiple twinning mechanism is not fully activated, a higher frequency of large Taylor factor values (M > 3.9) can be obtained due to the relatively singular orientation. Conversely, in the GBE-type sample, multiple twinning enhances the anisotropy of the twinned cluster structures, leading to a greater proportion of low Taylor factor values (M < 3.9). To some extent, GBE generates a moderate soft-hard composite structure in the matrix. During plastic deformation, soft-oriented areas are favorable for the initiation of mobile dislocations. The obstruction of the dislocations propagation within the twin clusters by Σ3 is limited. Hence, it can be inferred that the soft or hard nature of the twinned clusters is primarily determined by the soft orientation. The synergistic effect of hard-oriented and soft-oriented structures promotes effective absorption and dispersion of stress during plastic deformation, thereby preventing fracture and enhancing the overall plasticity.
如图 9 所示，我们进一步分析了两个尺寸相似但孪晶特征不同的 TRD。对于非 GBE 母晶粒（TRD A），晶界网络主要由直且连续的Σ3 晶界构成，这些晶界通常具有有限的迁移能力。然而，很少能找到高阶Σ3 ⁿ 晶界。相比之下，GBE 型母晶粒（TRD B）显示出复杂的 GBCD。此外，该团簇中所有晶粒对都保持严格的Σ3 ⁿ 取向关系，这与我们之前的工作[48]中的报道一致。为了分析团簇内的相互取向关系，建立了两个相应的孪晶树结构，如图 9(c)和(d)所示。TRD B 的孪晶树具有 7 种独特的取向，而 TRD A 仅包含 3 种独特的取向。通过孪晶树还可以发现，出现重孪晶微观结构，其最大的 LLC 值为 5。此外，图 9(e)和(f)分别展示了 TRD A 和 TRD B 内的 Taylor 因子值分布。 TRD A 中子晶的平均泰勒因子最小值约为 3.9（以深蓝色标记），这明显大于 GRD B 中的值。对于非 GBE 型样品，由于多重孪晶机制未完全激活，由于相对独特的取向，可以获得更高频率的大泰勒因子值（M > 3.9）。相反，在 GBE 型样品中，多重孪晶增强了孪晶团结构的各向异性，导致低泰勒因子值（M < 3.9）的比例更高。在一定程度上，GBE 在基体中产生了一种中等软硬复合结构。在塑性变形过程中，软取向区域有利于移动位错的启动。Σ3 对孪晶团中位错传播的阻碍有限。因此，可以推断孪晶团的软硬性质主要由软取向决定。硬取向和软取向结构的协同效应促进了塑性变形过程中应力的有效吸收和分散，从而防止断裂并提高整体塑性。

5. Conclusion 5. 结论

In this work, the evolution of the microstructure and mechanical properties of Alloy 925 subjected to different TMP routes was systematically investigated. A more accurate relationship between the GBE-type microstructure and ductility property was constructed based on the twinning-related structure to provide novel insights into ductility optimization. The key findings are as follows:
在本工作中，系统地研究了不同退火工艺下合金 925 的微观结构和力学性能的演变。基于孪晶相关结构，构建了更精确的 GBE 型微观结构与延展性之间的关系，为延展性优化提供了新的见解。主要发现如下：

(1)
Specific TMP methods were proposed to tailor GBCD through the SIBM mechanism. Increasing the annealing temperature from 1050 °C to 1100 °C can lead to a greater fraction of Σ3ⁿ twin boundaries and the formation of larger TRDs, which is associated with an increase in the elongation from 64.22 % to 95.86 %.
提出了特定的退火方法，通过 SIBM 机制来定制 GBCD。将退火温度从 1050 °C 提高到 1100 °C，可以导致更多的Σ3 孪晶边界和更大 TRD 的形成，这与延伸率从 64.22 %增加到 95.86 %相关。
(2)
The GBE-type microstructure can introduce more Σ3 grain boundaries and soft orientations through extensive generation of TRDs. The Σ3 boundaries are prone to lower ARBV values, indicating their reduced resistance to dislocation transmission, which can facilitate uniform plastic deformation within the twin clusters. In addition, the soft-oriented areas corresponding to lower average Taylor factor values are favorable for the initiation of mobile dislocations.
GBE 型微观结构可以通过大量产生 TRD 来引入更多Σ3 晶界和软取向。Σ3 晶界倾向于具有较低的 ARBV 值，表明它们对位错传输的阻力较低，这可以促进孪晶团簇内的均匀塑性变形。此外，对应于较低平均 Taylor 因子值的软取向区域有利于可动位错的启动。
(3)
The synergistic effect of the grain boundary network and twin cluster anisotropy can promote dislocation storage, stress dispersion, and retardation of crack propagation, thus strongly enhancing the overall plasticity of Alloy 925.
晶界网络和孪晶团簇各向异性的协同效应可以促进位错存储、应力分散和裂纹扩展的延缓，从而显著增强合金 925 的整体塑性。

CRediT authorship contribution statement
CRediT 作者贡献声明

Yulong Zhu: Writing – original draft, Investigation. Yu Cao: Writing – review & editing. Wei Tian: Investigation. Li Tan: Investigation. Qubo He: Visualization, Software. Rui Luo: Data curation. Xuhong Jia: Writing – review & editing. Quanyi Liu: Writing – review & editing.
余永录：撰写——原始草稿，研究。曹宇：撰写——审阅与编辑。田伟：研究。谭丽：研究。何曲博：可视化，软件。罗瑞：数据管理。贾旭红：撰写——审阅与编辑。刘全毅：撰写——审阅与编辑。

Declaration of competing interest
利益冲突声明

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
作者声明他们没有已知的利益冲突或个人关系可能影响本论文中报告的工作。

Acknowledgments 致谢

The authors are greatly appreciating the funding support of National Natural Science Foundation of China (No. 2033206), State Key Laboratory of Compressor Technology (Anhui Laboratory of Compressor Technology) (No. SKL-YSJ202004), Sichuan Natural Science Foundation (No. 2022NSFSC0302), Sichuan Civil Aircraft Fire Science and Safety Engineering Key Laboratory Project (No. MZ2023JB01), and Doctoral Program of CAAC Flight Academy (No. PHD2023-063).
作者对以下资助机构的大力支持表示衷心感谢：国家自然科学基金（项目编号：2033206）、压缩机技术国家重点实验室（安徽压缩机技术实验室）（项目编号：SKL-YSJ202004）、四川省自然科学基金（项目编号：2022NSFSC0302）、四川省民航飞机消防科学与安全工程重点实验室项目（项目编号：MZ2023JB01）以及中国民航飞行学院博士研究生项目（项目编号：PHD2023-063）。

Appendix A. Supplementary data
附录 A. 补充数据

The following is the Supplementary data to this article:
以下是本文的补充数据：Download: Download Acrobat PDF file (79KB)

Multimedia component 1.

Data availability 数据可用性

Data will be made available on request.
数据将根据要求提供。

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D. Kirch, E. Jannot, L. Barrales-Mora, D. Molodov, G. Gottstein
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Acta Mater., 56 (2008), pp. 4998-5011
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[31]
B. Ellyson, K. Fezzaa, T. Sun, N. Parab, A. Saville, C. Finfrock, C. Rietema, D. Smith, J. Copley, C. Johnson
Transformation and twinning induced plasticity in metastable Ti-Mo alloys under high strain rate deformation
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[32]
Y. Wang, H. Choo
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Acta Mater., 81 (2014), pp. 83-97
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[33]
W. Yuan, S.K. Panigrahi, J.-Q. Su, R. Mishra
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Scripta Mater., 65 (2011), pp. 994-997
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[34]
U. Kocks, H. Mecking
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Prog. Mater. Sci., 48 (2003), pp. 171-273
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[35]
C. Zhao, X. Chen, F. Pan, S. Gao, D. Zhao, X. Liu
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[36]
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J. Mater. Sci. Technol., 162 (2023), pp. 234-246
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[38]
F. Shuang, K.E. Aifantis
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[39]
L. Patriarca, W. Abuzaid, H. Sehitoglu, H.J. Maier
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[40]
E. Bayerschen, A. McBride, B. Reddy, T. Böhlke
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J. Mater. Sci., 51 (2016), pp. 2243-2258
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[41]
W.Z. Abuzaid, M.D. Sangid, J.D. Carroll, H. Sehitoglu, J. Lambros
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[42]
J. Chen, J. Lu, W. Cai, Y. Zhang, Y. Wang, W. Jiang, M. Rizwan, Z. Zhang
In-situ study of adjacent grains slip transfer of Inconel 718 during tensile process at high temperature
Int. J. Plast., 163 (2023), Article 103554
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[43]
L. Lim, R. Raj
Interaction between lattice and grain boundary dislocations and their role in mechanical properties of interfaces
J. Phys. Colloq., 46 (1985)
C4-581-C4-595
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[44]
S. Xu, L. Xiong, Y. Chen, D.L. McDowell
Sequential slip transfer of mixed-character dislocations across Σ3 coherent twin boundary in FCC metals: a concurrent atomistic-continuum study
npj Comput. Mater., 2 (2016), pp. 1-9
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[45]
K. Lu, L. Lu, S. Suresh
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[46]
F. Javaid, H. Pouriayevali, K. Durst
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J. Mater. Res., 36 (2021), pp. 1-13
Google Scholar
[47]
C.-G. Oertel, I. Huensche, W. Skrotzki, W. Knabl, A. Lorich, J. Resch
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[48]
Y. Zhu, Y. Cao, Q. He, R. Luo, H. Di, G. Huang, Q. Liu, J. Xiao
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Cited by (9)

The influence of heat treatment process on electroplated metallized through glass vias (TGV) substrates
热处理工艺对玻璃通孔 (TGV) 基板电镀金属化的影响
2025, Journal of Alloys and Compounds
2025, 合金与化合物杂志
Ensuring low warpage for electroplated metallized through glass vias (TGV) substrates constitutes a pivotal technical bottleneck in engineering applications. The regulation of residual stress in the electroplated layer to improve substrate warpage has been proven to be an effective strategy recently. In this study, we successfully improved the warping phenomenon of TGV substrates after metallization by employing an appropriate heat treatment process. Molecular dynamics simulation analysis indicates that the presence of titanium atoms can effectively promote the segregation behavior of copper on the SiO₂-Ti-Cu structure, enhancing interface stability. The applied heat treatment process promotes atomic diffusion, which can further improve the interface bonding strength between copper and SiO₂. During heat treatment, the warpage curvature radius of copper-overburden TGV substrates initially increases then decreases, peaking at 979 m at 100 ℃, which minimizes wafer warpage. However, the Vickers hardness (HU) of the interconnect copper pillars is the lowest at this temperature, with a value of 3.64 × 10⁻² GPa. After heat treatment, electron backscatter diffraction (EBSD) reveals that electroplated copper pillars within glass vias exhibit grain refinement, with the 200 ℃ treated sample showing a high proportion of grain boundary misorientation angles (greater than 50°) up to 51.63 % and a minimum grain orientation spread (GOS) of 0.5, aiding crack resistance and reducing lattice distortion. When the temperature increases to 300 ℃, combined constrained thermal stress-induced twinning phenomena along the via axis direction occur, with the proportion of ∑3 and ∑9 type twin boundaries increasing to 45.46 %. The resistivity of the copper pillars increases gradually from 15.83 × 10⁻⁶ Ω·m at room temperature to 18.11 × 10⁻⁶ Ω·m after heat treatment at 300 ℃. X-ray photoelectron spectroscopy (XPS) analysis suggests that residual organic polymer additives are likely the main cause of the significant difference in resistivity between the electroplated copper pillars and oxygen-free copper. Overall, this study offers novel insights into fabricating low warpage electroplated metallized TGV substrates, balancing mechanical and electrical performance of vertical interconnect copper pillars.
An optimal grain boundary engineering approach to improving the mechanical properties of FeCoCrNi high-entropy alloys at different temperatures
一种优化晶界工程方法，用于改善 FeCoCrNi 高熵合金在不同温度下的力学性能
2025, Materials Science and Engineering A
2025, 材料科学与工程 A
The influence of grain boundary engineering (GBE) on the mechanical properties of FeCoCrNi high-entropy alloy (HEA) at different temperatures was systematically examined. An optimal GBE process, namely cold rolling (with 5 % reduction) followed by annealing (at 900 °C for 4 h), was ascertained to markedly modify the grain boundary character distribution (GBCD) in the alloy, and significantly increase the fraction of special boundaries (Σ3-Σ29) to as high as 82.4 %, and meanwhile, the connectivity of random high-angle grain boundaries (RHAGBs) has been effectively disrupted. Such a modified GBCD leads to an improvement in room-temperature tensile ductility without loss of strength, but to a simultaneous enhancement in strength and ductility at high temperatures (600 °C–800 °C). The improved properties result mainly from the inducement of abundant Σ3 boundaries that effectively inhibit intergranular crack initiation and propagation during plastic deformation. Also, the GBE process optimizes deformation uniformity, mitigates dynamic recovery and recrystallization and suppresses dynamic strain aging at high temperatures, further facilitating more stable and homogeneous plastic deformation. This study has offered a detailed perspective on how GBE affects the plastic deformation and damage behavior of FeCoCrNi HEA at different temperatures, thus providing a novel pathway to improve the mechanical properties of HEA especially at high temperatures.
Enhancing oxidation resistance via grain boundary engineering in L12-strengthened medium entropy alloys
通过晶界工程增强 L12 强化中熵合金的抗氧化性能
2025, Journal of Materials Science and Technology
2025, 材料科学与技术杂志
The concept of grain boundary engineering (GBE) has been successfully applied to L1₂-strengthened (CoCrNi)₉₄Al₃Ti₃ medium entropy alloy, with the aim of improving the oxidation resistance by increasing the ratio of special boundaries and suppressing discontinuous precipitation. Surprisingly, our results reveal that GBE treatment not only slows down the oxidation kinetics and but also alters the oxide scale from TiO₂ and multi-defect Cr₂O₃ to continuous and protective Cr₂O₃ and Al₂O₃, thereby contributing to an enhanced oxidation and anti-spalling resistance. The GBE treatment reduces the oxidation weight gain of the current alloy from 1.950 mg cm^–2 to 1.211 mg cm^–2 after 100 h of cyclic oxidation at 800 °C. The findings show that the extensive outward diffusion of Ti accelerates ion transport and promotes microporosity, thus leading to more defects being formed in the oxide film. The GBE treatment suppresses the discontinuous precipitation of the Ti-bearing L1₂ phase and breaks the random large angular grain boundaries network, inhibiting the diffusion of Ti and ultimately enhancing the oxidation properties of the alloy. The current work provides an idea of oxidation resistance enhancement for Ti-bearing L1₂-strengthened alloys without changing the alloy composition.
Recrystallization behavior and grain boundary character evolution in an additively manufactured Ni-based GH4099 alloy during heat treatment
再结晶行为和晶界特征演变在热处理过程中对增材制造镍基 GH4099 合金的影响
2025, Journal of Alloys and Compounds
Grain boundary engineering (GBE) is a thermomechanical strategy employed to enhance material properties by optimizing the grain boundary character distribution (GBCD). Traditionally, deformation processing is necessary to obtain GBE materials with high-density ‘special’ grain boundaries. In this study, GBE in the GH4099 alloy fabricated by selective laser melting (SLM) is achieved through a simple heat treatment without pre-deformation treatment. The results indicate that the optimal GBE-1200 GH4099 alloy exhibits a high fraction of low-Σ coincident site lattice (CSL, Σ ≤ 29) boundaries (over 70 %), including 63.4 % Σ3 grain boundaries (twin boundaries, TBs). The existing high density of cellular structures with tangled dislocations in the as-built alloy provides the driving force for recrystallization. After heat treatment, the tensile strength of the GH4099 alloy improves significantly without sacrificing plasticity, while the anisotropy in mechanical properties is nearly eliminated through complete recrystallization. The tensile strength and elongation of the GBE-1200 alloy are 1168.8 MPa and 38.3 % in the XOY plane, respectively, demonstrating a favorable strength-ductility synergy. This enhancement is attributed to the coupled effects of multiple strengthening mechanisms, including frequent dislocation-TB interactions, the shear effect of nano γ′ precipitation, multiple stacking faults (SFs), and Lomer–Cottrell (L-C) locks.
Low plastic deformation: Its impact on the microstructural evolution during heat treatment of nickel-based wrought superalloy GH4698
低塑性变形：其对镍基变形高温合金 GH4698 热处理过程中微观结构演变的影响
2025, Intermetallics
A comprehensive investigation into the effects of low plastic deformation (LPD) at ambient temperature on the microstructural evolution of the nickel-based wrought superalloy GH4698 during solution heat treatment (SHT) was conducted. Applying 2%–10 % LPD to cylindrical specimens did not markedly alter the grain morphology. However, a portion of the initial annealing twin boundaries (TBs) would transform into other types of grain boundaries under the application of the stress field. Deformation microstructures with effective strains ranging from 0.025 to 0.042 (corresponding to the entire region of the 4 % deformed sample and the near-end region of the 6 % deformed sample) exhibited a pronounced increase in twin fraction during SHT, accompanied by the formation of multiple large twin-related domains (TRDs) and several abnormally large grains (ALGs). The occurrence of TRDs and their internal ALGs stems from the constrained nucleation of recrystallization and extensive twinning. The residual strain energy not alleviated through recrystallization, driven by thermal stress, initiates twin nucleation and promotes grain boundary migration. The emergence and disappearance of island-like twins, as well as twins terminating within grains, suggest that the introduced TBs include not only coherent TBs but also potentially highly mobile incoherent TBs during the evolution of TRDs.
Effect of annealing treatment on the phase transformation and mechanical properties of TA15 alloy fabricated by WAAM
热处理对 WAAM 制备的 TA15 合金的相变和力学性能的影响
2025, Intermetallics 2025, 金属间化合物
Wire arc additive manufacturing (WAAM) is a promising additive manufacturing technique with growing acceptance in aerospace applications. In this study, the effects of annealing treatment on the microstructure, texture and tensile properties of Ti-6.5Al-2Zr-1Mo-1V alloy fabricated by WAAM were investigated. The results indicated that the microstructure of the as-built specimens is composed of fine basketweave structure within the columnar prior-β grains. With the increase of annealing temperature, the microstructure of the specimen was transformed from fine basketweave structure to lamellar structure and then to bi-lamellar structure. Compared with the as-built specimen (0.48 μm), the average primary α phase thickness of the specimens annealed at 900 °C, 940 °C and 980 °C increased by 0.67 μm, 0.88 μm and 2.66 μm, respectively. Secondary α phases with width of 200 nm were also precipitated for the annealed specimen at 980 °C. In addition, compared with the as-built specimen (1014.8 ± 28.4 MPa, 5.87 %), the tensile strength of the annealed specimens at 900 °C (970.3 ± 9.5 MPa), 940 °C (929.1 ± 4.9 MPa) and 980 °C (922.4 ± 2.1 MPa) decreased slightly. The elongation of the specimens annealed at 900 °C, 940 °C and 980 °C increased by 63.5 %, 82.3 % and 125.4 %, respectively.

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Acta Mater., 56 (2008), pp. 4998-5011
View PDF View article View in Scopus Google Scholar

[31] [31]
B. Ellyson, K. Fezzaa, T. Sun, N. Parab, A. Saville, C. Finfrock, C. Rietema, D. Smith, J. Copley, C. Johnson
Transformation and twinning induced plasticity in metastable Ti-Mo alloys under high strain rate deformation
Mater. Sci. Eng., A, 857 (2022), Article 143716
View PDF View article View in Scopus Google Scholar

[32] [32]
Y. Wang, H. Choo
Influence of texture on Hall–Petch relationships in an Mg alloy
Acta Mater., 81 (2014), pp. 83-97
View PDF View article View in Scopus Google Scholar

[33] [33]
W. Yuan, S.K. Panigrahi, J.-Q. Su, R. Mishra
Influence of grain size and texture on Hall–Petch relationship for a magnesium alloy
Scripta Mater., 65 (2011), pp. 994-997
View PDF View article View in Scopus Google Scholar

[34] [34]
U. Kocks, H. Mecking
Physics and phenomenology of strain hardening: the FCC case
Prog. Mater. Sci., 48 (2003), pp. 171-273
View PDF View article View in Scopus Google Scholar

[35] [35]
C. Zhao, X. Chen, F. Pan, S. Gao, D. Zhao, X. Liu
Effect of Sn content on strain hardening behavior of as-extruded Mg-Sn alloys
Mater. Sci. Eng., A, 713 (2018), pp. 244-252
View PDF View article View in Scopus Google Scholar

[36] [36]
R. Alizadeh, M. Peña-Ortega, T. Bieler, J. Llorca
A criterion for slip transfer at grain boundaries in Al
Scripta Mater., 178 (2020), pp. 408-412
View PDF View article View in Scopus Google Scholar

[37] [37]
X. Zeng, C. Zhang, W. Zhu, M. Zhu, T. Zhai, C. Ma, T. Shu, K. Song
Strain transfer behavior and crystallographic mechanism of crack initiation during cyclic deformation in zirconium
J. Mater. Sci. Technol., 162 (2023), pp. 234-246
View PDF View article View in Scopus Google Scholar

[38] [38]
F. Shuang, K.E. Aifantis
Using molecular dynamics to determine mechanical grain boundary energies and capture their dependence on residual Burgers vector, segregation and grain size
Acta Mater., 195 (2020), pp. 358-370
View PDF View article View in Scopus Google Scholar

[39] [39]
L. Patriarca, W. Abuzaid, H. Sehitoglu, H.J. Maier
Slip transmission in bcc FeCr polycrystal
Mater. Sci. Eng., A, 588 (2013), pp. 308-317
View PDF View article View in Scopus Google Scholar

[40] [40]
E. Bayerschen, A. McBride, B. Reddy, T. Böhlke
Review on slip transmission criteria in experiments and crystal plasticity models
J. Mater. Sci., 51 (2016), pp. 2243-2258
Crossref View in Scopus Google Scholar

[41] [41]
W.Z. Abuzaid, M.D. Sangid, J.D. Carroll, H. Sehitoglu, J. Lambros
Slip transfer and plastic strain accumulation across grain boundaries in Hastelloy X
J. Mech. Phys. Solid., 60 (2012), pp. 1201-1220
View PDF View article View in Scopus Google Scholar

[42] [42]
J. Chen, J. Lu, W. Cai, Y. Zhang, Y. Wang, W. Jiang, M. Rizwan, Z. Zhang
In-situ study of adjacent grains slip transfer of Inconel 718 during tensile process at high temperature
Int. J. Plast., 163 (2023), Article 103554
View PDF View article Google Scholar

[43] [43]
L. Lim, R. Raj
Interaction between lattice and grain boundary dislocations and their role in mechanical properties of interfaces
J. Phys. Colloq., 46 (1985)
C4-581-C4-595
Google Scholar

[44] [44]
S. Xu, L. Xiong, Y. Chen, D.L. McDowell
Sequential slip transfer of mixed-character dislocations across Σ3 coherent twin boundary in FCC metals: a concurrent atomistic-continuum study
npj Comput. Mater., 2 (2016), pp. 1-9
Google Scholar

[45] [45]
K. Lu, L. Lu, S. Suresh
Strengthening materials by engineering coherent internal boundaries at the nanoscale
Science, 324 (2009), pp. 349-352
Crossref View in Scopus Google Scholar

[46] [46]
F. Javaid, H. Pouriayevali, K. Durst
Dislocation–grain boundary interactions: recent advances on the underlying mechanisms studied via nanoindentation testing
J. Mater. Res., 36 (2021), pp. 1-13
Google Scholar

[47] [47]
C.-G. Oertel, I. Huensche, W. Skrotzki, W. Knabl, A. Lorich, J. Resch
Plastic anisotropy of straight and cross rolled molybdenum sheets
Mater. Sci. Eng., A, 483 (2008), pp. 79-83
View PDF View article View in Scopus Google Scholar

[48] [48]
Y. Zhu, Y. Cao, Q. He, R. Luo, H. Di, G. Huang, Q. Liu, J. Xiao
On the critical strain of thermal-mechanical processing to tailor grain boundary character distribution in Incoloy 925 alloy
Intermetallics, 148 (2022), Article 107635
View PDF View article View in Scopus Google Scholar

Outline 概要

Cited by (9) 被引文献 (9)

Figures (9) 图 9 幅

Tables (2) 表格 (2)

Extras (1) 附加材料 (1)

Materials Science and Engineering: A
材料科学与工程：A

Abstract 摘要

Keywords 关键词

1. Introduction 1. 引言

2. Materials and procedures
2. 材料与程序

3. Results 3. 结果

3.1. Microstructural characterization
3.1. 微观结构表征

3.2. Tensile properties 3.2. 拉伸性能

3.3. Fracture analysis 3.3. 断裂分析

4. Discussions 4. 讨论

4.1. Effect of the grain boundary characteristics distribution
4.1. 晶界特征分布的影响

4.2. Effect of TRD anisotropy
4.2. TRD 各向异性影响

5. Conclusion 5. 结论

CRediT authorship contribution statement
CRediT 作者贡献声明

Declaration of competing interest
利益冲突声明

Acknowledgments 致谢

Appendix A. Supplementary data
附录 A. 补充数据

Data availability 数据可用性

References

Cited by (9)

The influence of heat treatment process on electroplated metallized through glass vias (TGV) substrates
热处理工艺对玻璃通孔 (TGV) 基板电镀金属化的影响

An optimal grain boundary engineering approach to improving the mechanical properties of FeCoCrNi high-entropy alloys at different temperatures
一种优化晶界工程方法，用于改善 FeCoCrNi 高熵合金在不同温度下的力学性能

Enhancing oxidation resistance via grain boundary engineering in L12-strengthened medium entropy alloys
通过晶界工程增强 L12 强化中熵合金的抗氧化性能

Recrystallization behavior and grain boundary character evolution in an additively manufactured Ni-based GH4099 alloy during heat treatment
再结晶行为和晶界特征演变在热处理过程中对增材制造镍基 GH4099 合金的影响

Low plastic deformation: Its impact on the microstructural evolution during heat treatment of nickel-based wrought superalloy GH4698
低塑性变形：其对镍基变形高温合金 GH4698 热处理过程中微观结构演变的影响

Effect of annealing treatment on the phase transformation and mechanical properties of TA15 alloy fabricated by WAAM
热处理对 WAAM 制备的 TA15 合金的相变和力学性能的影响

New insights into ductility improvement of a nickel-based superalloy through grain boundary engineering通过晶界工程改善镍基高温合金延性的新见解

Abstract 摘要

Keywords 关键词

1. Introduction 1. 引言

2. Materials and procedures2. 材料与程序

3. Results 3. 结果

3.1. Microstructural characterization3.1. 微观结构表征

3.2. Tensile properties 3.2. 拉伸性能

3.3. Fracture analysis 3.3. 断裂分析

4. Discussions 4. 讨论

4.1. Effect of the grain boundary characteristics distribution4.1. 晶界特征分布的影响

4.2. Effect of TRD anisotropy4.2. TRD 各向异性影响

5. Conclusion 5. 结论

CRediT authorship contribution statementCRediT 作者贡献声明

Declaration of competing interest利益冲突声明

Acknowledgments 致谢

Appendix A. Supplementary data附录 A. 补充数据

Data availability 数据可用性

References

New insights into ductility improvement of a nickel-based superalloy through grain boundary engineering
通过晶界工程改善镍基高温合金延性的新见解

2. Materials and procedures
2. 材料与程序

3.1. Microstructural characterization
3.1. 微观结构表征

4.1. Effect of the grain boundary characteristics distribution
4.1. 晶界特征分布的影响

4.2. Effect of TRD anisotropy
4.2. TRD 各向异性影响

CRediT authorship contribution statement
CRediT 作者贡献声明

Declaration of competing interest
利益冲突声明

Appendix A. Supplementary data
附录 A. 补充数据