Thermodynamic instability of a nanocrystalline, single-phase TiZrNbHfTa alloy and its impact on the mechanical properties

被引:259
作者
Schuh, B. [1 ]
Voelker, B. [1 ]
Todt, J. [2 ]
Schell, N. [3 ]
Perriere, L. [4 ]
Li, J. [5 ]
Couzinie, J. P. [4 ]
Hohenwarter, A. [1 ]
机构
[1] Univ Leoben, Dept Mat Phys, Jahnstr 12, A-8700 Leoben, Austria
[2] Austrian Acad Sci, Erich Schmid Inst Mat Sci, Jahnstr 12, A-8700 Leoben, Austria
[3] Helmholtz Zentrum Geesthacht, Inst Mat Res, Geesthacht, Germany
[4] Univ Paris Est, ICMPE UMR 7182, CNRS, UPEC, 2-8 Rue H Dunant, F-94320 Thiais, France
[5] Univ Leoben, Chair Casting Res, Franz Josef Str 18, A-8700 Leoben, Austria
基金
奥地利科学基金会;
关键词
Severe plastic deformation; High-entropy alloy; Decomposition; Mechanical properties; Microstructure; HIGH-ENTROPY ALLOY; NANOSTRUCTURED METALS; TENSILE DUCTILITY; MICROSTRUCTURE; STRENGTH; DEFORMATION; CRMNFECONI; STABILITY;
D O I
10.1016/j.actamat.2017.09.035
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
An equiatomic, single-phase TiZrNbHfTa high-entropy alloy was subjected to high-pressure torsion, leading to a grain size below 100 nm. Introducing a nanocrystalline microstructure to the material should help to accelerate a possible phase decomposition of the material by having a high amount of fast diffusion pathways and possible nucleation sites in the form of grain boundaries. In order to test the materials thermodynamic stability the nanocrystalline high-entropy alloy. was subjected to various heat treatments for temperatures between 300 degrees C and 1100 degrees C. Isochronal heat treatments (1 h) resulted in a hardness increase from 420 HV1 for the as-processed state to 530 HV1 for an annealing temperature of 500 degrees C, while for temperatures of 700 degrees C and higher a softening compared to the as-processed state occurred. In order to clarify this unexpected annealing response, analysis of selected microstructural states was performed utilizing electron microscopy, x-ray diffraction as well as mechanical testing to gain further information on microstructure-property relationships. Complementary, thermodynamic simulations were performed via the Calphad approach and compared to the experimental results. A phase decomposition of the originally equimolar single-phase high-entropy alloy into a NbTa-rich body-centered cubic phase and ZrHf-rich phases, which occurred in two different crystal structures depending on the annealing temperature, was the main reason for the property changes. The obtained results not only give valuable new insights into the phase stability of the TiZrNbHfTa alloy, but also demonstrate the impact of the newly forming phases in regards to mechanical properties and its implication for a possible practical application of this alloy. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.
引用
收藏
页码:201 / 212
页数:12
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