结构迟豫对Zr基大块非晶敏感因子的影响

Effect of Relaxation on Pressure Sensitivity Index in a Zr-Based Metallic Glass

采用Rockwell压痕测试和SEM、DSC技术研究了铸态和退火Zr41.2Ti13.8Cu12.5Ni10Be22.5大块非晶的剪切带和焓变特征。样品在玻璃转变温度以下等温退火,DSC放热峰随着退火温度的增加不断减少,这表明自由体积不断减少。对压痕周围剪切带形态的观察表明,退火样品中被激活的剪切带减少,剪切带之间的夹角2θ不断变化,铸态大约为88o,经过633K保温1h减小为79o。由Mohr–Coulomb准则可知,通过测量2θ可以确定压力敏感因子,随着退火温度的升高,原子间相互摩擦的作用加剧,导致压力敏感因子增加。

Shear-banding features of as-cast and annealed Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass were investigated through the Rockwell indentation tests. Isothermal annealing of the as-cast samples was conducted at temperatures below its glass transition temperature, Tg. The exothermal enthalpy during continuous heating below Tg decreases with increasing annealing temperature, indicating the gradual reduction of free-volume upon annealing. The observation on the morphology of shear-banding pattern around the indents implies a reduced shear bands activity in the annealed samples. The included angles （2θ） between two families of shear bands emanating from the edge of Rockwell indent decrease from 88° for the as-cast sample to 79° for the sample annealed at 633 K for 1h, indicating a pressure sensitive plasticity. The pressure sensitive index can be obtained by measuring2θaccording to the Mohr-Coulomb criterion. It is found that the pressure sensitive index increases with increasing the annealing temperature, indicating an increase of ＂atomistic friction＂ due to the reduction of free volume during annealing.