Chen Heng, Zhang Taihua, Ma Yi
Institution of Micro/Nano-Mechanical Testing Technology & Application, College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, China.
Materials (Basel). 2017 Jun 27;10(7):711. doi: 10.3390/ma10070711.
In order to investigate the effect of applied stress on mechanical properties in metallic glasses, nanoindentation tests were conducted on elastically bent Zr-Cu-Ag-Al metallic glasses with two different structure states. From spherical curves, elastic modulus was found to be independent on applied stress. Hardness decreased by ~8% and ~14% with the application of 1.5% tensile strain for as-cast and 650 K annealed specimens, while it was slightly increased at the compressive side. Yield stress could be obtained from the contact pressure at first pop-in position with a conversion coefficient. The experimental result showed a symmetrical effect of applied stress on strengthening and a reduction of the contact pressure at compressive and tensile sides. It was observed that the applied stress plays a negligible effect on creep deformation in as-cast specimen. While for the annealed specimen, creep deformation was facilitated by applied tensile stress and suppressed by applied compressive stress. Strain rate sensitivities (SRS) were calculated from steady-state creep, which were constant for as-cast specimen and strongly correlated with applied stress for the annealed one. The more pronounced effect of applied stress in the 650 K annealed metallic glass could be qualitatively explained through the variation of the shear transformation zone (STZ) size.
为了研究外加应力对金属玻璃力学性能的影响，对具有两种不同结构状态的弹性弯曲Zr-Cu-Ag-Al金属玻璃进行了纳米压痕试验。从球形曲线可知，弹性模量与外加应力无关。对于铸态和650 K退火试样，施加1.5%的拉伸应变时，硬度分别降低了约8%和14%，而在压缩侧硬度略有增加。屈服应力可通过首次压入位置的接触压力与转换系数获得。实验结果表明，外加应力对强化有对称影响，且压缩侧和拉伸侧的接触压力均降低。观察到外加应力对铸态试样的蠕变变形影响可忽略不计。而对于退火试样，外加拉伸应力促进蠕变变形，外加压缩应力抑制蠕变变形。根据稳态蠕变计算应变率敏感性（SRS），铸态试样的SRS恒定，而退火试样的SRS与外加应力密切相关。通过剪切转变区（STZ）尺寸的变化，可以定性地解释外加应力对650 K退火金属玻璃的更显著影响。
