Temperature dependence of strain rate sensitivity, indentation size effects and pile-up in polycrystalline tungsten from 25 to 950 °C
Temperature dependence of strain rate sensitivity, indentation size effects and pile-up in polycrystalline tungsten from 25 to 950 °C
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DOI：
10.1016/j.matdes.2018.06.063
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发表时间：
2018-10
影响因子：
8.4
通讯作者：
B. Beake;A. Harris;J. Moghal;D. Armstrong
中科院分区：
文献类型：
--
作者：
B. Beake;A. Harris;J. Moghal;D. Armstrong
高温纳米压痕测量是在高真空条件下对多晶钨进行的，温度高达950 °C，热漂移非常低。研究了硬度、弹性模量、应变速率敏感性、激活体积和硬度的压痕尺寸效应与温度的关系。从850 °C开始观察到更显著的时间依赖性变形。压痕蠕变数据分析确定的应变速率敏感性随温度的增加。活化体积在750-800 °C达到约50 b3的峰值。>800 °C的活化体积降低是应变速率敏感性增加的结果。对于体心立方金属晶格电阻取决于T/Tc（其中Tc，临界温度，在该温度下，流动应力变得对温度不敏感，对于W为527 °C）;尺寸效应将预期与该相对温度成比例。在高温下，硬度的压痕尺寸效应更强。卸载数据上的时间依赖性变形的影响被占的粘弹性顺应性校正。校正后，在750-800 °C下的弹性模量在文献值的约1%内，在950 °C下在6%内。这些小的剩余差异与AFM测量结果一致，AFM测量结果表明在这些高温压痕中堆积是显著的。
Elevated temperature nanoindentation measurements were performed on polycrystalline tungsten to 950 °C under high vacuum conditions with very low thermal drift. The temperature dependence of the hardness, elastic modulus, strain rate sensitivity, activation volume and the indentation size effect in hardness were studied. More significant time-dependent deformation was observed from 850 °C. Strain rate sensitivity determined by analysis of indentation creep data increased with temperature. Activation volume reached a peak of ~50b3at 750–800 °C. Decreasing activation volume >800 °C was a consequence of the increased strain rate sensitivity. For a bcc metal lattice resistance depends onT/Tc(whereTc, the critical temperature, at which flow stress becomes insensitive to temperature, is 527 °C for W); size effects would be expected scale with this relative temperature. Stronger indentation size effects in hardness were found at elevated temperatures. The influence of the time-dependent deformation on the unloading data was accounted for by a viscoelastic compliance correction. After correction the elastic moduli were to within ~1% of literature values at 750–800 °C and to within 6% at 950 °C. These small remaining differences are consistent with AFM measurements which show that pile-up is significant in these high temperature indentations.