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金属学报, 2025, 61(4): 526-540 DOI: 10.11900/0412.1961.2024.00042

综述

钨材料中缺陷的形成及演化规律

罗来马,1,2,3, 魏国庆1,2,3, 刘祯1, 朱晓勇1,3, 吴玉程1,2,3

1 合肥工业大学 材料科学与工程学院 合肥 230009

2 合肥工业大学 材料科学与工程学院 高性能铜合金材料及成形加工教育部工程研究中心 合肥 230009

3 合肥工业大学 材料科学与工程学院 有色金属与加工技术国家地方联合工程研究中心 　合肥 230009

Formation and Evolution of Defects in Tungsten Materials

LUO Laima,1,2,3, WEI Guoqing1,2,3, LIU Zhen1, ZHU Xiaoyong1,3, WU Yucheng1,2,3

1 School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China

2 Engineering Research Center for High-Performance Copper Alloys and Forming Processing of the Ministry of Education, School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China

3 National-Local Joint Engineering Research Centre of Nonferrous Metals and Processing Technology, School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China

通讯作者: 罗来马，luolaima@126.com，主要从事钨基复合材料制备及辐照损伤方面的研究

责任编辑: 肖素红

收稿日期: 2024-02-04   修回日期: 2024-05-29  

基金资助: 国家重点研发计划项目(2019YFE03120002, 2022YFE03140000)
安徽省重大基础研究项目(2023z04020006)

Corresponding authors: LUO Laima, professor, Tel: 13685512719, E-mail:luolaima@126.com

Received: 2024-02-04   Revised: 2024-05-29  

Fund supported: National Key Research and Development Program of China(2019YFE03120002, 2022YFE03140000)
Major Basic Research Project of Anhui Province(2023z04020006)

作者简介 About authors

罗来马，男，1980年生，教授，博士

摘要

钨材料作为一种重要的工业材料，以其高密度、高熔点和卓越的硬度及耐磨性能而闻名。晶体缺陷在钨材料的晶体结构中是常见的，调控钨材料中的缺陷是改善其性能的重要手段，深入理解钨材料中缺陷的形成与演化是实现其调控的理论基础。本文从烧结过程引入缺陷、应力效应引入缺陷2个关键方面，综述了钨材料缺陷的形成机制及其研究进展，对应地从制备、加工等角度来理解钨材料中的缺陷，并对相关领域近年来的研究进展进行了评述和展望，旨在为钨材料的研究提供参考。

关键词： 钨材料; 缺陷; 烧结; 塑性变形; 晶体缺陷

Abstract

Tungsten material is an industrially important material owing to its high density, high melting point, excellent hardness, and wear resistance. Crystal defects (e.g., dislocations and vacancies) are common in its structure, thereby influencing the performance of tungsten materials. Therefore, controlling these defects is crucial for enhancing their performance. A deep understanding of how defects form and evolve serves as a theoretical basis for controlling them. This article reviews the mechanisms of defect formation and research advancements in tungsten materials from two key perspectives: defect introduction during the sintering process and through stress effects. Accordingly, this study explores defects in tungsten materials from the viewpoint of preparation and processing, summarizing recent advancements and prospects in related fields, aiming to provide a valuable reference for future research on tungsten materials.

Keywords： tungsten material; defect; sintering; plastic deformation; crystal defect

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本文引用格式

罗来马, 魏国庆, 刘祯, 朱晓勇, 吴玉程. 钨材料中缺陷的形成及演化规律[J]. 金属学报, 2025, 61(4): 526-540 DOI:10.11900/0412.1961.2024.00042

LUO Laima, WEI Guoqing, LIU Zhen, ZHU Xiaoyong, WU Yucheng. Formation and Evolution of Defects in Tungsten Materials[J]. Acta Metallurgica Sinica, 2025, 61(4): 526-540 DOI:10.11900/0412.1961.2024.00042

理论上金属晶体内部的原子呈现规则排列，这是理想的晶体结构。在实际晶体中，或多或少存在偏离理想结构的区域，称为晶体缺陷[1,2]。在人类文明几千年的发展过程中，金属及其合金的进步并非源自对完美无缺的合金的追求，而是基于对晶体缺陷行为的理解与控制，这在某种程度上推动了该领域的发展。这一历史可以追溯到青铜器和铁器时代，那时我们的祖先虽然不完全理解背后的机理，却已经掌握了利用溶质以及其他晶体缺陷来固定位错，制造出更坚固的农具或更锋利的刀剑。现代物理冶金学揭示了晶体缺陷在确定合金性能中的核心作用[3,4]：如何通过晶体缺陷行为(例如位错运动、孪晶形成、晶界(GB)滑移)来改善金属及其合金的强度和韧性[5~8]；如何通过研究晶体缺陷与活性原子、分子及离子的相互作用来提升合金的抗氧化和耐腐蚀性能[9,10]；以及如何通过了解点缺陷的迁移来增强材料的耐辐射性能[11]等。此领域的研究在持续积极进行中，新兴的概念、理论、模型和技术层出不穷，这些都在不断更新人们对现有合金的理解，并加速新合金的设计与开发。

钨合金作为一种重要的工业材料，以其高密度、高熔点和卓越的硬度及耐磨性能而闻名[12]。然而，晶体缺陷(如位错、空位等)在钨合金的晶体结构中是常见的，在实际W晶体中，原子(或离子、分子)的热运动、晶体形成条件和冷热加工过程，以及其他因素(如辐射或异质元素)的影响，使得W原子排列无法像理想结构那样规则完整，这些缺陷显著影响钨合金的性能[13]。例如，它们可能改变钨合金的屈服强度和断裂韧性，这对于那些需要承受极端条件的应用(例如航空航天领域)尤为关键[14~17]。晶体缺陷还会影响钨合金的塑性、电阻率、磁导率、热处理和机械加工过程，进而影响最终产品的品质和性能[18]。在钨合金中，常见的缺陷类型包括空洞、异质界面、裂纹和位错等。这些缺陷可以在合金的生产和使用过程中形成，例如粉末冶金、热处理、塑性变形及辐照应用等[19,20]。

因此，研究钨合金中的晶体缺陷不仅具有理论意义，也对改善和优化钨合金的性能与应用具有实际价值。通过对这些缺陷的深入理解和精确控制，可以开发出性能更优的钨合金，以满足特定应用的需求。本文从烧结、应力等方面，综述了钨材料缺陷的形成机制和演化规律，对应地从制备、加工的角度来理解钨材料中的缺陷，为研究者提供一个成熟的理论框架与参考素材，以理解钨材料缺陷形成的基础科学，并进一步解释了如何通过调控这些缺陷来优化钨材料的综合性能，在此基础上为研究者设计和开发出具有优良性能的钨材料提供理论基础和指导。

1 烧结过程引入缺陷

1.1 粉体烧结本征缺陷

对于W这种具有代表性的难熔金属而言，烧结所产生的缺陷是无法逾越的难题。W及其合金的制备以合成粉末为起点，涉及成形和烧结的固结过程。其中有2个主要的烧结问题相互交织：致密化(孔隙率降低)和晶粒生长[21]。目前，将W及其合金烧结到全密度是具有挑战性的，烧结过程中会产生难以去除的缺陷和粗大的晶粒，根本原因在于致密化和晶粒生长都是由毛细力驱动的，它们的热激活动力学通常具有相似的激活能，因此难以分别控制[22,23]。烧结钨通常需要非常高的温度，这很容易导致全局(正常晶粒生长)或局部(异常晶粒生长)微观结构的快速粗化[24,25]，从而形成空洞、裂纹等缺陷，这显著恶化了材料的性能。

目前围绕着钨粉体研究的重点是将粉体细化从而降低烧结温度，合成高质量的细粉是制造高性能钨材料的前提条件[26]。细粉由于尺寸更细、比表面积更高和烧结驱动力更大，因此烧结起始温度更低，已有研究[27]表明其具有优异的烧结能力。但是细粉的装填密度通常低于粗粉末，这对烧结不利，需要使用特殊的成型技术来解决。此外，细钨粉容易团聚，易于在压实过程中形成塞积而使生坯具有较低的装填密度[28]。这些特性对烧结性能有害，并可能导致粉末压坯中的不均匀性，最终导致烧结部件中的局部烧结和微观结构分叉，在烧结过程中形成缺陷并最终产生层状裂纹。同时，细钨粉容易生长，它们的尺寸优势在加热时很快耗尽[29]。首先，高温烧结会导致W晶粒生长，晶界迁移速率加快，从而使晶粒边界明显移动。这种迁移是由于晶界处的原子比晶粒内部原子更易于移动，温度的升高使得这种迁移现象加剧，如图1a1~a3[30]所示。同时，晶界迁移会伴随着原子的扩散，即原子在晶体内部的长距离移动。在高温烧结过程中，晶界附近的孔隙可能会由于晶界的快速移动而与原来的晶界位置分离，这时，孔隙就不能跟随晶界移动而被消除，如图1b所示，这种现象称为孔隙-晶界分离。孔隙-晶界分离的结果就是在材料内部形成空洞缺陷，如图1c[31]所示。这些空洞不利于材料的致密化，并且会显著降低材料的力学性能，如强度和韧性[32]。此外，持续的高温烧结还可能导致晶内孔隙的生成，如图1d[32]所示。这些孔隙是因为晶界迁移过快，周围的原子来不及填补其后所留下的空间而形成的。晶内孔隙位于晶粒内部，与表面孔洞相比，它们更难以通过后续的烧结处理来消除，因为内部的原子迁移速率比表面慢，最终产生难以移除的晶内孔隙和具有不均匀及局部烧结的微观结构分叉[32]。由于局部热激活和快速晶界迁移，细钨粉的不利影响被放大，更容易产生难以控制的缺陷，从而大幅度影响钨材料的性能。

图1

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图1   钨材料烧结过程中产生的缺陷[30~32]

Fig.1   Defects generated during sintering process in tungsten materials


(a1-a3) initial particle configuration (a1), diffusion mechanisms leading to microstructural changes (a2), and neck growth and grain boundary formation during sintering (a3) showing the interface evolution during sintering[30] (GB—grain boundary, c—conserved variable)

(b) schematic of voids formed during sintering

(c) overall morphology of intragranular pores[31]

(d) typical morphology of pore-triple junction separation and residual intragranular pores[32]

为了避免这些问题，需要精心调控钨的烧结工艺，包括烧结温度、保温时间、升/降温速率、气氛等，以确保获得高密度、均匀微结构的钨材料。同时，一些先进的烧结技术，例如无压两步烧结法(TSS)是实现上述目标的一种有效方法[33,34]，最近它被引入到金属系统中，成功地生产出具有高烧结密度、细晶粒尺寸且均匀微观结构的钨材料[35]。通过优化烧结工艺，可以有效控制晶粒生长和孔隙的形成，从而生产出具有优异物理和力学性能的钨制品。

1.2 异质原子诱发点缺陷

在钨材料的烧结过程中，异质原子容易在晶体内部形成点缺陷或在晶界处偏析，从而显著影响材料的品质。异质元素可能来源于原始的合成粉末或是烧结过程中的污染，在高温下可能不均匀地分布在W的晶体结构中，如图2a和b所示，形成微观尺度的点缺陷。这些点缺陷通常表现为原子尺度的错位或空位，它们会影响W晶格的完整性和稳定性，进而降低材料的强度和导电性。异质原子的尺寸可能与W原子不同，当它们取代W原子位置时，会引起局部晶格畸变，导致应力集中，这些应力有可能在烧结过程中或后续应用中诱发裂纹的形成。为了评估异质元素对W晶界结合的强化或弱化效应，主流的方法是计算强化/脆化能量(ΔESE)[36,37]，这是由Rice和Wang[37]所建模型计算出的晶界与无断裂表面之间的偏聚能量(Eseg)的差来确定的，这种方法从能量的角度描述了异质原子对晶间脆化的影响。为了清晰地显示ΔESE与异质原子半径之间的关系，图2c[38]展示了不同W晶界的ΔESE与异质原子半径的关系。通常，随着异质原子半径的增加，ΔESE也随之增加，这表明较小的异质原子似乎对W晶界起到了增强作用，而较大的原子倾向于起到弱化作用。图2d[38]展示了包含3d、4d、5d过渡金属原子的Σ3(111)晶界的Eseg和强化能量ΔESE的典型例子。每个溶质原子占据的晶界原子位置显示在横坐标上。对于半径过小的溶质，所有偏聚位置的Eseg都是负值，表明这些原子在晶界中是稳定的。对于半径过大的溶质和那些与W原子半径相同的溶质，不同位置的Eseg显示正值或负值，这意味着这些原子有稳定和不稳定的位置，这与图2c[38]所得结果相对应。同时，异质原子可能阻碍晶界移动，从而影响致密化过程，限制了材料致密度的提高。并且人们普遍认为是W晶界杂质的存在导致晶界容易断裂，这是由于晶界处的高度晶体无序结构和杂质偏析降低了晶界的内聚力[39~41]，影响元素包括但不限于C、O、K和P等[42~44]。H、O、Si、P和S等元素削弱了W的晶界强度，但少数杂质如B和C则起到了增强效果[45,46]，对钨材料来说最令人担忧的杂质之一是O，它很难被完全移除，并可能在致密化、加工过程及最终性能表现(例如脆化问题)中产生负面影响[47~50]。现有的解释是当杂质原子分布在W的位错核周围时，可以减缓位错移动或增加位错移动的激活能，从而降低延展性或提高韧脆转变温度(DBTT)[46]。在确定杂质的限量标准时，不应仅考虑某些最大杂质含量，而应综合考虑晶粒尺寸、晶界面积以及杂质在晶界上的分布情况。杂质对材料延展性的影响可以通过晶界分离的难易程度以及位错运动的影响来定量描述。无论是削弱晶界还是降低位错的迁移能力，都可能导致钨材料基体的延展性降低。在这一认识的基础上，众多研究已致力于探究商业纯度钨材料的脆性问题，其中大部分研究将脆性归咎于杂质偏聚引起的晶界弱化，因此，改变杂质分布和增强晶界的方法将有效地提高晶界的强度和延性。比如通过真空和区域熔炼减少杂质，可以将DBTT降低到约200 ℃[51]，此外，还有研究[52]表明，Ti和Zr等微合金元素可以吸收O2，减少O2在晶界处的偏析，从而显著提高晶界的强度[53]。

图2

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图2   杂质原子形成点缺陷、不同W晶界的强化/脆化能量(ΔESE)与异质原子半径关系示意图[38]及过渡金属原子晶界的偏聚能量和强化能量的典型例子[38]

Fig.2   Schematic of the relationship between the formation of point defects by impurity atoms, strengthening/embrittling energies (ΔESE) at different W grain boundaries, and the radius of heteroatoms, as well as typical examples of the segregation energy (Eseg) and strengthening energy at transition metal atomic grain boundaries

(a) three-dimensional schematic of impurity atoms embedded in the matrix lattice

(b) point defects formed by impurity atoms

(c) dependence of ΔESE on the metallic radii of solutes at their most favorable positions for Σ3(112), Σ5(310), Σ3(111), Σ5(210), and Σ11(323) GBs[38] (γ—GB energy)

(d) Eseg and the strengthening energies ΔESE for 3d, 4d, and 5d transition metals (TM) atoms in different positions of a typical Σ3(111) GB[38]


1.3 掺杂第二相粒子引入面缺陷

目前掺杂第二相弥散强化是提高钨基复合材料力学性能的主要方式之一[54]，并且其形成缺陷的方式也与杂质原子不同，第二相与钨材料基体之间会产生大量的共格/半共格界面[55]，在钨材料基体内部形成面缺陷。这些界面在原子层面的特殊排列能够优化载荷传递和分散裂纹或位错的传播路径，增强材料的塑性变形能力。第二相与基体的界面具有双重作用。一方面，良好的界面黏结能提高材料的力学性能，如提升硬度、抗拉强度和抗冲击韧性，并且能确保应力加载时载荷能够均匀分布于基体与第二相之间，在钨基复合材料中有效地传递和分散；弥散分布的异相界面被认为具有更优异的抗辐照损伤能力，因为高密度的界面可以汇集缺陷[56,57]。另一方面，如果界面不稳定或存在严重的化学、热膨胀或结构不匹配，可能会导致界面解键、裂纹形成和应力集中，这些都会恶化材料的力学性能，并可能导致早期失效。界面的性质，包括结构、化学组成、能量状态以及与周围材料的相容性，都是影响钨基复合材料力学性能的关键[58]。在钨基复合材料中，异相界面的结构和能量是确定复合材料整体性能的决定性因素，它们在钨基复合材料设计和性能优化过程中扮演着至关重要的角色。因此，为了提高钨基复合材料的性能，必须研究界面的微观特性和宏观效应，优化界面。

依据异相界面结构的差异性，可将掺杂的第二相粒子归为氧化物和碳化物2种主要类型，相对应的合金分别为氧化物弥散强化钨合金(ODS-W)与碳化物弥散强化钨合金(CDS-W)。在氧化物掺杂物中，常见的成分包括Y2O3、La2O3、HfO以及ZrO2等[59~66]。这些氧化物在界面处与基体的相互作用和黏结机理对整体性能有着显著的影响[67,68]，由于O与W原子半径差异较大，2者在界面区域的结构和性质显著不同，这种差异体现在原子结构(晶格参数)、力学性能(Young's模量)和功能性能(热膨胀系数)上[69]，如图3a[70]所示。金属原子间的键合主要是由金属离子和自由电子的交互作用决定的，这种键合通常具有较大的配位数和更为简单、规则的晶体结构[71~74]。相比之下，氧化物原子键的形成则主要依赖于正、负离子的相互作用，其结构较为复杂。这些不同导致金属与氧化物界面出现明显的面缺陷[75~81]。在ODS-W中，以W-Y2O3复合材料为例，由于其在高温强度、再结晶温度、抗蠕变能力以及热震抵抗性能等方面的显著提升而备受关注。Y2O3具有立方晶体结构，晶格常数为1.061 nm，与W晶体(晶格常数为0.316 nm)存在较大的晶格不匹配，依据错配度的计算，Y2O3与钨材料基体界面结构通常表现为半共格界面[82,83]。在烧结过程中，Y2O3颗粒倾向于在W晶界处偏聚[84]，相应的W/Y2O3界面容易成为应力集中区域，进而加剧面缺陷和裂纹的形成[85]。为了克服这一挑战，Hu等[86,87]采用特殊的粉末制备技术，例如冷冻干燥和水热合成，再加上后续的低温烧结工艺，制得性能卓越的W-Y2O3复合材料。这确保了纳米级Y2O3粒子在W晶粒内部及晶界上的均匀分散，除了W/Y2O3界面，钨材料基体中还观察到大量Y2WO6颗粒，在Y2O3与钨材料基体之间形成了Y-W-O扩散层，如图3b[87]所示，有效缓解了界面缺陷并大幅度增强了钨材料基体的性能。

图3

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图3   第二相与钨基体材料界面关系及实例[70,87,92]

Fig.3   Interface relationship between secondary phase and tungsten matrix and examples

(a) schematic of differences between metal and oxide[70] (F represents force)

(b) HRTEM images of small particles within Y2O3 grains (b1, b2), W and Y2O3 interface (b3, b4), and small particles within W grains (b5, b6)[87]

(c) HRTEM image of the TiC/W interface (c1), the fast Fourier transformation (FFT) patterns of areas marked by blue and red dash-line in Fig.3c1, respectively (c2, c3), the parallelism between (1¯11¯)TiC and (1¯10)W (c4, c5), and the constructed TiC/W interface supercell (c6)[92]


在碳化物掺杂物中，具有高熔点特性的碳化物，例如ZrC、TiC、TaC和HfC[88~91]等，被广泛应用于CDS-W复合材料。与氧化物不同，某些碳化物可以与钨材料基体形成较为匹配的界面，如图3c[92]所示，TiC与钨材料基体的界面呈现共格状态，从而具备了出色的力学性能。Kurishita等[39,40,93]制备了细晶W-TiC复合材料，晶粒尺寸为0.9 µm，在室温下显示出高达1.6~2.0 GPa的三点弯曲断裂强度，且表现出对中子和氦离子优异的抗辐照性能。W-TiC复合材料所具备的优异的抗辐照能力，被认为是由于碳化物与钨材料基体优异的界面结合而产生的晶界强化效应[94~96]。Xie等[97]通过火花等离子烧结制备了W-(0.2, 0.5, 1.0)%ZrC (质量分数)复合材料，其DBTT为500~600 ℃，ZrC的熔点高达3540 ℃，这比Y2O3的熔点(2425 ℃)要高得多。W和ZrC之间良好的相容性可以引入共格界面，导致界面强度增加。此外，ZrC可以捕获杂质O，在晶界形成稳定的Zr-C-O或ZrO2颗粒，这有利于提高晶界的强度。共格的碳化物与钨材料基体之间的异质界面能够在受力状态下钉扎晶粒内的位错，有效提高材料的强度并同时改善其延展性。共格界面还有可能消除界面上的应力集中点，增加钨材料基体的延展性，因此在提升钨基复合材料的延展性和强度方面，共格界面扮演了至关重要的角色。

2 应力效应引入缺陷

2.1 塑性变形调控位错

由于钨合金的高DBTT，单纯的烧结制备工艺已无法满足工业需求，目前通过塑性变形工艺引入高比例的位错、亚晶界(小角度晶界)等线缺陷来降低W及其合金的DBTT已经成为制备工业级钨基复合材料的重要手段。位错是金属加工硬化的关键因素，塑性变形过程中产生的高密度位错阻碍了位错的进一步移动，这导致金属强度增加和延展性降低，这是加工硬化的基本原理。然而，与此不同，已经有大量工作[98,99]证实W在塑性加工后的延展性得到明显改善。塑性变形过程中引入的线缺陷对于W和其他具有类似结构的bcc金属至关重要。

钨合金的高DBTT是由其晶体结构决定的，W是bcc结构，在低温下位错的运动受到限制，导致塑性差。虽然目前的烧结制备工艺能够生产出纯度高、致密度高的钨材料，但是这种方法不引入额外的位错和晶界，因此无法显著降低钨材料的DBTT。针对此问题，工业界和科研机构寻求通过塑性变形工艺(如锻造、轧制等方法)改善W及其合金的延展性，如图4a~c所示。塑性变形过程中的高应力和高应变能够在材料中引入大量的位错。位错的引入不仅能够增加材料的强度(通过位错强化机制)，还能够提高材料的塑性，尤其是在低温下的塑性，因此有助于降低DBTT。此外，通过适当的变形处理，可以在材料中形成亚晶界，也称为小角度晶界(LAGB)，它们是由于相邻晶粒间微小的取向差异所形成的。亚晶界可以作为位错的源头，并且有助于位错的移动，从而改善材料的低温塑性。通过这些塑性变形过程，不仅可以增加材料内部的位错密度，还可以优化位错结构，提升晶粒的细化程度，减小晶粒间的取向差异，这些都有助于降低材料的DBTT，增强材料在低温下的性能。如图4d[100]和e[101]所示，经过多道次的轧制或锻造处理，W的晶粒尺寸可以被有效减小，位错网络也更加复杂，晶界数量增加，这些微观结构的优化共同提高了材料的室温延展性及低温韧性。

图4

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图4   W的塑性变形工艺实例及微观结构[100,101]

Fig.4   Examples of plastic deformation process and microstructure of W

(a-c) examples of plastic deformation processes for W (HERF—high-energy-rate forging)

(d) schematic summarizing the microstructure evolution of HERF-W during the HERF process[100]

(e) schematic of W after plastic deformation[101]


如图5a[64,88,91,97,100,102~106]所示，经过塑性变形的W及钨合金[64,88,91,100,102~104]相比于烧结态[91,97,105,106]其DBTT均大幅度下降，并且随着目前塑性变形工艺的改进，已经可以在不损失强度的情况下将钨材料的DBTT降到室温。如图5b[61,64,88,91,92,100,102~104]所示，在各种工艺对比中，高能锻造(HERF)表现出了令人惊讶的增强效果，比如Xie等[100]制备的HERF-W的室温拉伸强度高达1.35 GPa，并且在100 ℃时极限抗拉强度(UTS) > 1.0 GPa，延伸率> 4%，Dong等[107]制备的HERF-W-Y2O3也具备室温韧性，且延伸率> 4%。与烧结或再结晶的钨材料相比，HERF-W的晶界密度更高，LAGB的相对数量也增加。高比例的LAGB可以提高W晶粒之间的应变相容性。基于模拟工作，Cheng等[108]研究表明，W晶粒间的LAGB能够在基体没有断裂的情况下更好地传递应变，因为它可以有效地减少独立滑移系统的要求。对多晶W进行的三点弯曲测试也表明，LAGB的抗断裂能力高于高角度晶界(HAGB)[109]。因此，这些结果表明，在HERF-W中观察到的高比例的LAGB可以显著增强晶粒间的应变相容性，从而提高钨材料的延展性。

图5

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图5   W及钨合金拉伸性能汇总[61,64,88,91,92,97,100,102~106]

Fig.5   Summaries of tensile properties of W and tungsten alloys

(a) Nil ductility temperature (NDT)-ultimate tensile strength (UTS) summary (SPS—spark plasma sintering)[64,88,91,97,100,102-106]

(b) total elongation (TE)-UTS at 100 oC[61,64,88,91,92,100,102-104]


HAGB的晶格差异显著增加了位错迁移的壁垒，并导致位错堆积和缠结。位错缠结引入晶格中的局部应变，这可能导致裂纹的形成。由于裂纹尖端的位错启动和迁移是影响钨材料DBTT的2个主要因素[110]，没有移动性的位错缠结将导致钨材料的DBTT增加。与HAGB相比，LAGB具有更一致的晶格，相当于晶界处的一系列位错。对于轧制/锻造的钨材料，高比例的LAGB实现了位错跨晶界迁移，这种位错迁移减少了位错堆积[111]。因此，与HAGB相比，LAGB可以大幅降低钨材料的DBTT。在LAGB中，位错网格充当Frank-Read或Bardeen-Herring位错源，为位错成核提供位点并增强钨材料基体的延展性[112]。Rice等[113]和Khantha等[114]系统描述了脆韧性转变与位错成核和迁移率的关系，揭示了影响材料延展性的关键因素是位错源的数量和位错运动。对于bcc结构金属，韧脆转变由螺位错与刃位错迁移速率之比控制[115]，足够高的相对迁移率是螺位错和刃位错协调运动以维持位错增殖的先决条件，螺位错和刃位错的运动激活能差异很大，螺位错具有固有的紧凑和三维性质，从而具有相对较高的Peierls势垒[116]，这对螺位错的移动性至关重要。因此，在合理的应力作用下，需要相对较高的温度来实现螺位错的迁移[117]。相比之下，刃位错的激活能明显较低。因此，刃位错在接近室温的温度下就能活跃起来[118]。如图6a1~a3[100]所示，Xie等[100]使用消光法确定了HERF-W中刃位错与混合位错的占比高达58.2%，这也是HERF-W具有优异低温性能的原因之一；如图6b1~b9[119]所示，Ren等[119]在冷轧W中也发现了大量的刃位错与混合位错。由于裂纹前沿的位错移动性是描述钨材料DBTT最重要的因素，可以预期，确定螺旋位错和刃位错迁移率之间的差异对于解释塑性变形后钨材料优异的低温延展性至关重要，如图6c[119]所示，计算所得W中刃位错的变形速率比具有相同密度的螺位错的样品快7个数量级。Gumbsch[120]的研究还强调了位错源对延展性的重要性。LAGB的增加为位错的增殖提供了2个主要的积极影响：位错的成核与位错滑移。经历过塑性变形的W晶粒在轧制/锻造方向上伸长，产生大量的刃位错和LAGB。

图6

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图6   W中的位错类型及迁移特性[100,119]

Fig.6   Types and migration characteristics of dislocations in W

(a) characteristics of dislocations in a W grain under the same zone axis of z = [1¯11] but different g vectors conditions[100] (a1-a3) left: different two-beam bright-field TEM images of dislocation structures (a1-a3) right: the Burgers vectors of dislocations are highlighted using different colors. Black arrows indicate the edge or mixed-type dislocation based on the criterion of geometrical orientation relationship between a dislocation line and its Burgers vector (b) TEM images of cold-rolled tungsten in the as-rolled, 1200 oC annealed, and 1400 oC annealed conditions[119] (b1-b3) overview (b4-b6) dislocation structure (b7-b9) grain boundaries (c1) deformation velocity of W with screw or edge dislocations as a function of dislocation density[119] (c2) deformation velocity of W with screw dislocations as a function of temperature[119] (c3) deformation velocity of W with edge dislocations as a function of temperature[119]


总体来说，轧制/锻造后的钨材料具有较高的位错密度，且部分表现为刃型位错特性。这些高移动性的刃位错可能通过适应塑性来钝化裂纹尖端。轧制/锻造后的钨材料还包含相当一部分LAGB。大量的LAGB为位错穿过晶界提供了接近理想的条件，这限制了位错钉扎效应和在这些晶界处裂纹的形核。与刃位错相比，螺位错的移动性要低得多。晶界特征、位错源和位错移动性都是控制钨材料延展性的重要因素。高密度的位错源有利于钝化裂纹尖端和适应应变。位错的优异移动性可以更好地适应变形过程并控制裂纹生长。因此，为了获得具有良好延展性和低DBTT的多晶W，具有大量LAGB和高密度刃位错/混合位错的微观结构是必不可少的。

综上，塑性变形工艺在制备工业化钨基复合材料时起着至关重要的作用。通过适当控制变形参数和后续的热处理过程，可以得到具有较低DBTT和良好力学性能的钨合金，以满足严苛工况下的应用需求。未来的研究也许会专注于如何更精确地控制这些微观线缺陷的形成与演化，以及如何利用新型塑性变形工艺进一步提高材料性能。

2.2 应力-尺寸效应诱导孪晶

孪晶是晶体内部一种特殊类型的面缺陷[121]，是重要的塑性变形机制之一，尤其在那些晶格滑移系统受限的材料中，孪晶能提供另一种变形路径，有助于材料在外力作用下产生变形而不是断裂[122~124]。在一些具有fcc和hcp结构的金属和合金中，孪生变形在塑性变形过程中起着关键作用。然而，对于W这种具有bcc晶体结构的材料来说，室温下孪生变形并不常见。W的高熔点和强的共价键结合导致其在室温表现为脆性，而孪生变形通常需要较高的应变能来激活[125,126]。bcc晶体结构的特点是，当温度较低或应变速率较高时，其主导的塑性变形机制是位错滑移，而不是孪生。

随着实验方法的创新与表征技术的进步，Wang等[127]利用原位透射电镜(TEM)技术观察到了W中孪晶的形成与演化，并且发现W中孪晶的形成具有非常明确的取向性，如图7a1~a4[127]所示，在室温和低应变速率下，当沿着<100>、<110>和<111>方向加载时，变形孪生是bcc结构W纳米晶体中的主导变形模式。在循环负载下，变形孪生是伪弹性的。而在<112>方向加载下，位错迁移是主要的变形模式，导致塑性屈服。加载方向效应归因于小尺度bcc结构晶体中缺陷的竞争成核机制，相关的模拟工作也证实了这一现象，如图7a5~a8[127]所示。之后，Wang等[128]又捕获了W原子尺度的自发去孪生过程，如图7b1~b12[128]所示，揭示了bcc结构W纳米晶体中不稳定的孪晶状态。此外，还提出W中孪晶的固有不稳定性与具有高界面能的倾斜孪晶界面有关，这提供了自发去孪晶的驱动力。与fcc结构金属中孪晶部分位错的高滑移速率[129]相比，W中位错滑移的晶格阻碍非常大，特别是对于螺位错而言[130~132]。如图7c1~c3[128]所示，孪晶部分被认为是由螺位错的解离形成，这些发现为理解bcc结构金属中的变形孪生提供了新的见解。在钨材料中，反孪生变形[133,134]曾被认为是不可能的，因为反孪生本质上具有很高的阻力，通常在bcc结构晶体中位错滑移占主导地位，Wang等[135]发现了直径小于约20 nm的bcc结构W纳米线中的反孪生现象，如图7d1~d7[135]所示。随着纳米线直径的减小，观察到从位错滑移到反孪生的转变，这一转变归因于纳米尺度bcc结构晶体中有限的塑性变形载体，由此产生的超高应力触发了反孪生的形成和生长。这项工作为小体积bcc结构晶体中的尺寸依赖变形提供了新的见解，并对用非传统变形机制实现纳米材料的高机械预成型具有广泛的影响。

图7

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图7   W中孪晶的形成与机理[127,128,135]

Fig.7   Formation and mechanism of twinning in W


(a1-a4) sequential TEM images showing deformation twinning in a W bicrystal nanowire (15 nm in diameter) at room temperature under a strain rate of 10-3 s-1 [127] (σ—stress)

(a5-a8) molecular dynamics (MD) snapshot and zoomed-in image showing the nucleation of a deformation twin embryo in a W single-crystal nanowire[127]

(b1-b12) the formation of the deformation twin under tension[128] (MF—Moiré fringes)

(c1) the three-dimension twin structure with the inclined twin boundary in the nanocrystal. The curved dislocation lines are marked by the orange line on the twinning plane (112) and the inclined twin boundary is marked by the gray hook surface[128]

(c2) the front view of MF along [11¯0][128] (MF region—the projection of the inclined twin boundary region and the fully grown twin are marked by the blue and red polygons, respectively)

(c3) one selected twinning plane in the twin. One individual curved twinning partial on the twinning plane (112), mainly suffering four forces, the restoring force (Frestore), the stacking-fault force (FSF), the positive force (Fimage+), and negative image forces (Fimage-), respectively, and the friction force under unloading (Ffriction). The detwinning direction is indicated by the bold green arrow[128]

(d1-d7) twinning versus anti-twinning in [1¯10] oriented W nanowires[135]

在W中，孪生变形的发现是一个值得关注的里程碑。通常情况下，纳米尺度材料的塑性变形机制与其大块材料的行为有显著差异。这主要归因于尺寸效应，即材料的尺寸对其力学性能有着决定性的影响。对于纳米尺度的W而言，由于尺寸的限制，材料内部的位错活动可能受到很大限制，而其他变形机制(如孪生)可能变得更加容易。在纳米结构W中，孪生变形的存在表明位错滑移可能不再是唯一的变形机制。这对科研工作者们研究这类材料的变形行为意义重大，因为它意味着现有的塑性变形理论框架可能需要更新，以便更好地描述和预测材料在纳米尺度下的性能。由于孪生变形能提供额外的塑性变形路径，纳米W的塑性和韧性可能会比预期要高。此外，孪生变形的发现还标志着尺寸依赖性可能在纳米W中起到了关键作用。在纳米尺度上，材料的表面效应、晶界效应和尺寸效应都可能导致材料表现出异常的变形行为。例如，随着晶粒尺寸的减小，晶界与总体材料体积的比例增加，这可能有助于孪生变形的激活。晶界既可以作为非晶滑动的路径，也可能成为孪生核心的源。纳米晶粒内部由于体积小，所以位错的积累和储存能力有限，这可能促使孪生成为更为重要的变形机制。因此，孪生变形在纳米尺度W中的发现不仅刷新了人们对这些材料变形机制的认识，还可能打开新的研究方向，推动先进材料设计和应用的发展。通过深入了解尺寸依赖性和孪生变形在纳米材料中的作用，可以更好地控制和优化这些材料的性能，以满足特定工业应用的需求。

3 总结与展望

钨材料中缺陷的调控不仅是改善其材料性能的关键而且也是科研工作者进行钨材料改性的一个重要手段。由于钨材料在航空航天、军工及核能等领域的广泛应用，其内部缺陷对使用性能有着决定性的影响。因此，深刻认知并理解钨材料中缺陷的形成机制、影响因素及其对材料性能的具体影响，对于开发高性能钨材料具有重要意义。本文针对钨材料的缺陷进行了全面的分析和探讨，从烧结、应力等关键方面，深入综述钨材料缺陷的形成机制和演化规律，对应地从制备、加工的角度来理解钨材料中的缺陷，为研究人员设计和开发出具有优良性能的钨材料提供理论基础和指导。通过这种多角度的分析，科研工作者可以更好地掌握缺陷控制的策略，进而优化钨材料的性能，满足工业和科研上对高性能钨材料的需求。

(1) 对于钨材料在烧结过程中引入的缺陷，主要为自身形成的孔隙与异质原子诱发点缺陷，2种缺陷问题的产生最终都可以追溯到烧结工艺和粉体制备这2个环节。烧结工艺的优化旨在准确控制加热速率、烧结温度、保温时间和冷却过程等参数，以实现粉末颗粒间的充分结合并尽量减少孔隙的生成。此外，气氛控制也非常重要，以避免不必要的氧化和杂质的引入。而在制粉工艺方面，粉末的粒度分布、形貌和纯度对于最终烧结体的密实度和微观结构有着直接影响。粉末尺寸的均匀性可以确保在烧结过程中均一的收缩和致密化，而较高纯度的粉末可以减少点缺陷的引入。因此，为了获得高性能的钨材料，必须采用优异的烧结与制粉工艺，这不仅要求对烧结过程的每一个环节进行精细化管理，还需要不断优化粉末的制备技术，从而提高材料的一致性和可靠性。通过对这些工艺环节的深入研究和改进，科研人员和工程师能够设计和制造出具有更好性能的钨基材料，满足现代工业和技术发展的严苛要求。而掺杂第二相作为一种人为引入可靠面缺陷的方式，为确保第二相的有效性和功能性，需要对第二相的种类、含量、尺寸、第二相与钨材料基体界面关系等方面进行精细调控，从而制备出性能优异的钨基复合材料，以满足工业上对高性能材料的需求。

(2) 科研工作者们在钨合金材料的研发中，采用塑性变形等技术手段，以应力效应为主导，恰当地在W的微观结构中引入位错、孪晶等缺陷。这些缺陷不仅能够调控材料的晶体结构，而且还能够显著影响材料的力学性能。通过控制变形参数，例如变形温度、应变速率、变形程度，科研人员能够在钨合金中产生大量的位错与亚晶，这些缺陷在适当的条件下可以促进材料内部的位错滑移和位错攀移，增加材料的塑性和延展性。随后，通过后续热处理过程，可以进一步优化这些缺陷的分布和含量，从而实现材料性能的调节和完善。热处理过程包括退火温度、保温时间、冷却速率等，可消除或减少加工硬化效应，降低钨合金内部的残余应力，以及调整缺陷结构，如通过位错回复和再结晶过程来精细调控材料的晶粒尺寸和晶界分布。这种变形加工与热处理相结合的方法，能够有效地降低钨合金的DBTT，使其在较低的温度下仍然保持良好的塑性和韧性。此外，通过这些方法，还能改善钨合金的硬度、抗拉强度和抗疲劳性能等。这种通过应力效应引入和控制缺陷的策略，综合了材料科学、固体力学和热处理学等多个领域的先进知识和技术，通过这些技术的应用，可以设计和生产出适应极端环境要求的高性能钨合金材料，为现代工业的发展提供更多可能性。

目前钨材料具有优异的发展前景，但其缺点也非常明显，如需要非常高的烧结温度，较高的韧脆转变温度导致其极难加工等等。理解和人为地控制钨材料中缺陷将有效的改善其宏观性能，正如本文所综述的，缺陷对钨材料的使用起到决定性作用。但想要人为改善钨材料中的缺陷具备一定难度，如高纯度低O含量钨粉的制备与塑性变形工艺的局限性，所得的高性能钨基材料样品往往还停留在实验室阶段 (具有较小的尺寸)。想要实现批量化制备缺陷可控的高性能钨基材料还需要科研工作者改进粉体制备、烧结、塑性变形等工艺。总之，从W的本征结构特征出发，深入研究钨材料中缺陷的形成及演化机制，对实现钨材料的结构调控、性能优化和损伤控制具有重要意义。

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为探究近服役温度时效行为对ODS钢微观组织和力学性能的影响，通过SEM、TEM和拉伸性能测试等方法，研究了9Cr ODS钢在700℃时效不同时间后的碳化物(M<sub>23</sub>C<sub>6</sub>)、纳米氧化物演变和力学性能变化。结果表明：在时效初期(≤ 200 h)，M<sub>23</sub>C<sub>6</sub>在晶界处呈条带状快速析出并聚集长大，纳米氧化物无明显变化；在时效中期(200和1000 h)，M<sub>23</sub>C<sub>6</sub>和纳米氧化物稳定长大；在时效后期(2000和3000 h)，M<sub>23</sub>C<sub>6</sub>达到亚微米级，纳米氧化物的平均尺寸和数密度趋于稳定，与初始态相比，其平均尺寸的增长率为19.7%，数密度的下降率为27.1%。因纳米氧化物对不断增殖位错的钉扎，在部分晶粒内出现了位错胞和回复亚晶。9Cr ODS钢的拉伸强度在时效初期快速下降。在时效中后期，虽然纳米氧化物平均尺寸增加、数密度降低，但其钉扎作用仍然显著，以及基体中不断增殖的位错使得材料的拉伸强度维持稳定，延伸率在时效1000和2000 h期间处于低谷。

Xiao F N, Xu L J, Zhou Y C, et al.

Preparation, microstructure, and properties of tungsten alloys reinforced by ZrO2 particles

[J]. Int. J. Refract. Met. Hard Mater., 2017, 64: 40

Rui X, Li Y F, Zhang J R, et al.

Microstructure and mechanical properties of a novel designed 9Cr-ODS steel synergically strengthened by nano precipitates

[J]. Acta Metall. Sin., 2023, 59: 1590

DOI      [本文引用: 3]

Oxide dispersion-strengthened (ODS) steels with nano-scale Y2O3 or Y-Ti-O oxides have been considered as potential structural materials used in advanced nuclear systems. In this work, a novel 9Cr-ODS steel, namely, MX-ODS steel, was designed by decreasing carbon content to eliminate conventional M23C6-type carbides and by increasing the content of nitrogen and vanadium to form MX-type precipitates. In addition, the MX-ODS steel was synergistically strengthened by nano-scale MX precipitates and oxides. After fabrication by powder metallurgy, microstructural observation, and mechanical property tests were conducted after different heat treatments. The density of the prepared materials using hot forging instead of hot isostatic pressing was about 98%. Results of the microstructure observation of the MX-ODS steel indicated that after normalizing and tempering, the tempered martensitic structure dominated, and the mean effective grain size was approximately 1 μm. Moreover, the preferential orientation of coarse-grained and fine-grained mixed grains was not detected. By diminishing carbon content, M23C6-type carbides precipitated at the grain and sub-grain boundaries were eliminated. By contrast, MX-type precipitates with a diameter of approximately 30-200 nm were formed in the matrix. Furthermore, nano-scale Y-rich oxides with an average size of approximately 3.0 nm were dispersed in the matrix, and a number density can reach to approximately 1.9 × 1023 m-3. Furthermore, “core-shell” structure precipitates were found, which were spherical in shape with a diameter ranging from 10 to 20 nm. Such precipitates also contained Y, Ta, and O as the core and V as the shell. The mechanical properties indicate that microhardness decreased from 372 to 320 HV with the increase of normalizing temperature from 980oC to 1200oC. In addition, microhardness decreased significantly after tempering but initially increased and then decreased with the increase of tempering temperature from 700oC to 800oC, with a peak microhardness at approximately 750oC. Excellent strength and ductility were obtained after normalizing at 1100oC for 1 h and then tempering at 750oC for 1 h. Yield strength, ultimate tensile strength, and total elongation were 1039 MPa, 1103 MPa, and 20.5% when tested at room temperature and 291 MPa, 333 MPa, and 16% at 700oC, respectively.

芮 祥, 李艳芬, 张家榕 等.

新型纳米复合强化9Cr-ODS钢的设计、组织与力学性能

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DOI     

FeAl coatings with yttrium (Y) doping were prepared at 600 degrees C on pure iron. The anti-flaking properties of Al2O3-oxide films at 1000 degrees C oxidation was improved significantly by Y doping in FeAl coatings. The spallation was 0.47 mg/cm(2) for 200 h of oxidation and only similar to 1/6 of that without Y. The first principle calculation results demonstrate that the interfacial bond strength were enhanced with Y doping, that is because Y substituted primarily in the Al-1 and Al-2 position at the Al2O3/FeAl interfacial zone as the most negative interfacial cohesive energy of -13.94 eV and -12.72 eV. Remarkably, it is found that the maximum tensile strength of Y-FeAl/Al2O3 reaches to 20.48 GPa on uniaxial tensile strain, which is 1.33 times than that of FeAl/Al2O3 interface (15.36 GPa). Meanwhile, compared with a pure interface, Y doping would change ductile fracture on the Al2O3/FeAl interface as the strain was enhanced significantly by 49.12%. The bond length of the Al-1-Y showed little change under external stress, which resulted in an increase in bonding strength of the Al2O3/FeAl interface and the inhibition of the generation and propagation of micro-cracks. The formation of a YAlO3 layer induced a release of thermal stress at the Al2O3/FeAl interface. Due to the improvement of interfacial strength, the enhancement of interfacial toughness and the formation of a YAlO3 stress-release layer between the Al2O3 film and FeAl coating, therefore, Y doping can significantly improve the anti-flaking performance of the Al2O3-oxide films in high temperature oxidation.

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With excellent creep resistance, good high-temperature microstructural stability and good irradiation resistance, oxide dispersion strengthened (ODS) alloys are a class of important alloys that are promising for high-temperature applications. However, plagued by a nerve-wracking fact that the oxide particles tend to aggregate at grain boundary of metal matrix, their improvement effect on the mechanical properties of metal matrix tends to be limited. In this work, we employ a unique in-house synthesized oxide@W core-shell nanopowder as precursor to prepare W-based ODS alloy. After low-temperature sintering and high-energy-rate forging, high-density oxide nanoparticles are dispersed homogeneously within W grains in the prepared alloy, accompanying with the intergranular oxide particles completely disappearing. As a result, our prepared alloy achieves a great enhancement of strength and ductility at room temperature. Our strategy using core-shell powder as precursor to prepare high-performance ODS alloy has potential to be applied to other dispersion-strengthened alloy systems.© 2021. The Author(s).

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