Size effects on the mechanical properties of nanocrystalline NbMoTaW refractory high entropy alloy thin films

被引:142
作者
Feng, X. B. [1 ]
Zhang, J. Y. [1 ]
Wang, Y. Q. [1 ]
Hou, Z. Q. [1 ]
Wu, K. [1 ]
Liu, G. [1 ]
Sun, J. [1 ]
机构
[1] Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Peoples R China
基金
中国国家自然科学基金; 中国博士后科学基金;
关键词
High entropy alloys; NbMoTaW thin films; Strain rate sensitivity; Deformation mechanism; Size effects; STRAIN-RATE SENSITIVITY; DEPENDENT DEFORMATION MECHANISMS; STACKING-FAULT ENERGY; TEM IN-SITU; GRAIN-SIZE; TENSILE PROPERTIES; SINGLE-PHASE; STRENGTHENING MECHANISMS; THERMAL-ACTIVATION; FATIGUE BEHAVIOR;
D O I
10.1016/j.ijplas.2017.04.013
中图分类号
TH [机械、仪表工业];
学科分类号
0802 ;
摘要
The newly-surged high-entropy alloys (HEAs), in particular the refractory HEAs, manifest excellent properties for practice applications. In this work, we systematically investigated the plastic deformation characteristics (including the hardness, strain rate sensitivity (SRS), and activation volume) of nanocrystalline (NC) equiatomic NbMoTaW body-centered cubic (BCC) high-entropy alloy films (HEAFs) with thicknesses spanning from 100 to 2000 nm at room temperature. The BCC NbMoTaW HEAFs exhibited the strongest grain size similar to 10 nm with the hardness of similar to 16.0 GPa, above which the hardness decreases with increasing the grain size or film thickness, while below this critical size the material softening occurs. Given the friction stress and the source activation stress cannot be additive because they don't appear under the same circumstances, the size-dependent ultra-high strength in BCC HEAFs was discussed in terms of the solid solution hardening, the boundary dislocation density and the source strength. It was unveiled that above a critical grain size of similar to 40 nm, the solid solution hardening becomes the predominant strengthening mechanism, while below this critical size the source strengthening becomes the predominant one in BCC NbMoTaWHEAs. Also, the strong size-dependence of SRS is emerged, which monotonically increased with decreasing thicknesses (just opposite to the activation volume). A thermally activated model based on the depinning process of bowed-out dislocations was employed to quantitatively account for the size-dependent SRS of the NbMoTaW HEAFs. Our findings not only provide deep insight into understanding the mechanical behavior of the NC BCC NbMoTaW HEAFs, at least in the studied size-range, also offer some clues for the metastability engineering strategy to design high performance HEAFs at small-scales. (C) 2017 Elsevier Ltd. All rights reserved.
引用
收藏
页码:264 / 277
页数:14
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