Strain rate sensitivity of a novel refractory high entropy alloy: Intrinsic versus extrinsic effects
Strain rate sensitivity of a novel refractory high entropy alloy: Intrinsic versus extrinsic effects
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DOI：
10.1016/j.msea.2019.138326
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发表时间：
2019-10
期刊：
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通讯作者：
Maryam Sadeghilaridjani;Saideep Muskeri;V. Hasannaeimi;M. Pole;S. Mukherjee
中科院分区：
文献类型：
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作者：
Maryam Sadeghilaridjani;Saideep Muskeri;V. Hasannaeimi;M. Pole;S. Mukherjee
近年来，人们对开发用于下一代核应用的“低活性”耐火合金产生了浓厚的兴趣，以实现安全高效的服役后回收。在这里，研究了由所有还原活化元素组成的难熔高熵合金（即 HfTaTiVZr）的应变率敏感性。评估了速率敏感性的内在与外在影响，以便从根本上了解负载条件的差异。在各种应变率下进行单轴体积和微柱压缩测试以及多轴纳米压痕测试。微柱压缩和体压缩获得的外在应变率灵敏度高于纳米压痕确定的内在特性。纳米压痕获得的应变率灵敏度较低是由于压头下方有限体积内位错缠结程度较高。另一方面，微柱压缩测试中应变率敏感性的高值归因于较大表面与体积比的外在效应，这有助于通过自由表面消除位错。还观察到应变率敏感性的显着压痕尺寸效应。与较大压痕深度相比，在较小深度处，自由表面附近位错的较高迁移率和扩散导致较高的应变率敏感性。
In recent years, there is great interest in development of “reduced activity” refractory alloys for next generation nuclear applications for safe and efficient post-service recycling. Here, the strain rate sensitivity of a refractory high entropy alloy, namely HfTaTiVZr, was investigated consisting of all reduced activation elements. The intrinsic versus extrinsic effects in rate sensitivity were evaluated for fundamental understanding of the differences in loading condition. Uniaxial bulk and micro-pillar compression tests were performed along with multi-axial nano-indentation in a wide range of strain rates. The extrinsic strain rate sensitivity obtained from micro-pillar compression and bulk compression was higher than its intrinsic characteristic determined from nano-indentation. The low value of strain rate sensitivity obtained from nano-indentation was attributed to greater degree of dislocation entanglement in confined volume beneath the indenter. On the other hand, the high value of strain rate sensitivity in case of micro-pillar compression tests was attributed to the extrinsic effect of larger surface to volume ratio which helped in annihilation of dislocations through the free surface. A pronounced indentation size effect of strain rate sensitivity was also observed. At smaller depth, higher mobility and diffusion of dislocations near the free surface resulted in higher strain rate sensitivity compared to that at larger indentation depth.