Martensitic twinning transformation mechanism in a metastable IVB element-based body-centered cubic high-entropy alloy with high strength and high work hardening rate
Martensitic twinning transformation mechanism in a metastable IVB element-based body-centered cubic high-entropy alloy with high strength and high work hardening rate
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DOI：
10.1016/j.jmst.2022.03.005
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发表时间：
2022-04
期刊：
影响因子：
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通讯作者：
Yuhe Huang;Junheng Gao;V. Vorontsov;Dikai Guan;R. Goodall;D. Dye;Shuize Wang;Q. Zhu;W. Rainforth;I. Todd
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文献类型：
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作者：
Yuhe Huang;Junheng Gao;V. Vorontsov;Dikai Guan;R. Goodall;D. Dye;Shuize Wang;Q. Zhu;W. Rainforth;I. Todd
实现高加工硬化，从而提高强度-塑性协同是体心立方高熵合金（BCC-HEAs）实际应用的先决条件。在这项研究中，我们报道了一种新的动态强化机制，即基于亚稳耐火元素的BCC-HEA (TiZrHf) 87 Ta 13 （at.%）的马氏体孪晶转变机制，该机制可以显著提高加工硬化能力，同时实现大均匀延展性和高强度。与传统的相变诱发塑性（TRIP）和孪生诱发塑性（TWIP）强化机制不同，马氏体相变强化机制结合了TRIP和TWIP强化机制的最佳特点，极大地缓解了BCC组织合金中普遍存在的强度-延性权衡问题。利用x射线衍射（XRD）和电子背散射衍射（EBSD）对其微观结构进行了表征，结果表明，拉伸后，α”（正交）马氏体转变、自调节(SA) α”孪晶和机械α”孪晶依次被激活。透射电镜（TEM）分析表明，连续孪晶激活是由{351}α”孪晶面上SA”{351}”< 2¯11> α”α”II型孪晶α”变体的形核机械{351}α”型孪晶通过简单剪切转变继承而来的，从而通过孪晶剪切调节了过量的塑性应变，同时细化了晶粒结构。因此，在整个塑性变形过程中，获得了2-12.5 GPa的高加工硬化速率，从而获得了1.3 GPa的高抗拉强度和24%的均匀伸长率。提出了激活这种马氏体孪晶转变强化机制的合金开发指南，对开发具有最佳力学性能的新型BCC-HEAs具有重要意义。
Realizing high work hardening and thus elevated strength–ductility synergy are prerequisites for the practical usage of body-centered-cubic high entropy alloys (BCC-HEAs). In this study, we report a novel dynamic strengthening mechanism, martensitic twinning transformation mechanism in a metastable refractory element-based BCC-HEA (TiZrHf) 87 Ta 13 (at.%) that can profoundly enhance the work hardening capability, leading to a large uniform ductility and high strength simultaneously. Different from conventional transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) strengthening mechanisms, the martensitic twinning transformation strengthening mechanism combines the best characteristics of both TRIP and TWIP strengthening mechanisms, which greatly alleviates the strength-ductility trade-off that ubiquitously observed in BCC structural alloys. Microstructure characterization, carried out using X-ray diffraction (XRD) and electron back-scatter diffraction (EBSD) shows that, upon straining, α”(orthorhombic) martensite transformation, self-accommodation (SA) α” twinning and mechanical α” twinning were activated sequentially. Transmission electron microscopy (TEM) analyses reveal that continuous twinning activation is inherited from nucleating mechanical {351} α” type I twins within SA ‘‘{351}’’< 2¯ 11> α” type II twinned α” variants on {351} α” twinning plane by twinning transformation through simple shear, thereby accommodating the excessive plastic strain through the twinning shear while concurrently refining the grain structure. Consequently, consistent high work hardening rates of 2–12.5 GPa were achieved during the entire plastic deformation, leading to a high tensile strength of 1.3 GPa and uniform elongation of 24%. Alloy development guidelines for activating such martensitic twinning transformation strengthening mechanism were proposed, which could be important in developing new BCC-HEAs with optimal mechanical performance.