Ordering effects on deformation substructures and strain hardening behavior of a CrCoNi based medium entropy alloy
Ordering effects on deformation substructures and strain hardening behavior of a CrCoNi based medium entropy alloy
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DOI：
10.1016/j.actamat.2021.116829
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发表时间：
2021-04-01
期刊：
影响因子：
9.4
通讯作者：
Mills, Michael J.
中科院分区：
文献类型：
--
作者：
Miao, Jiashi;Slone, Connor;Mills, Michael J.
在淬火状态下，加入少量Ti、Al和Nb（表示为（CrCoNi）（93）Al4Ti2Nb）的CrCoNi基中熵合金在室温下具有与等原子CrCoNi合金相当的拉伸性能。暗场透射电镜（TEM）、原子分辨率高角环形暗场扫描透射电镜（HAADF-STEM）和原子探针层析成像（APT）表明，该合金中存在空间定域的LRO L1(2)畴。利用电子背散射衍射（EBSD）、电子通道对比成像（ECCI）和基于STEM的技术（包括最近开发的弱束暗场STEM成像）表征了该合金变形子结构随塑性变形的演变。塑性变形是由a/2位错滑移引起的，这些位错在{111}滑移面上被狭窄地分解成肖克利部分位错。它们在（CrCoNi）（93）Al4Ti2Nb合金中的解离距离远小于等原子CrCoNi合金中相应部分的宽度，这是由于一种或多种次要合金元素（Al, Ti, Nb）的作用。这种合金的位错滑移具有明显的平面特征。由于LRO畴的存在，滑移带中的前导位错成对滑动。多极是由相邻{111}滑移面上符号相反的位错滑移形成的。这些多极子是形成由细滑动带组成的亚晶粒结构的基石。滑移带之间的距离在塑性变形过程中不断细化，滑移带的动态细化在应变硬化过程中起着至关重要的作用。讨论了LRO畴对该合金的平面位错滑移、变形孪晶失活和应变硬化的影响。(C) 2021材料学报Elsevier Ltd.出版。版权所有。
A CrCoNi based medium entropy alloy with small additions of Ti, Al and Nb (denoted as (CrCoNi)(93)Al4Ti2Nb) in the as-quenched condition, exhibits tensile properties comparable to those of the equiatomic CrCoNi alloy at room temperature. Dark field transmission electron microscopy (TEM), atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) together with atom probe tomography (APT) show that spatially-localized long range ordering (LRO) L1(2) domains exist in this alloy. The evolution of deformation substructure with plastic deformation in this alloy was characterized using electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and STEM based techniques including the recently developed weak beam dark field STEM imaging. Plastic deformation occurs by the slip of a/2 dislocations, which are narrowly dissociated into Shockley partial dislocations on {111} slip planes. Their dissociation distances in the (CrCoNi)(93)Al4Ti2Nb alloy are much smaller than the widths of the corresponding partials in the equiatomic CrCoNi alloy due to one or more of the minor alloying elements (Al, Ti, Nb). Dislocation slip in this alloy has a pronounced planar character. The leading dislocations in slip bands glide as pairs due to the existence of LRO domains. Multipoles were formed through the slip of dislocations with opposite signs on adjacent {111} slip planes. Those multipoles serve as building blocks for the formation of subgrain structures consisting of fine slip bands. The distances between slip bands were continuously refined during plastic deformation and dynamic refinement of slip bands plays a crucial role in strain hardening. The effects of LRO domains on planar dislocation slip, the deactivation of deformation twinning and strain hardening of this alloy are discussed. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.