School of Materials Science and Engineering, Southeast University, Nanjing, 210096, China.
Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
Sci Rep. 2017 Aug 1;7(1):7076. doi: 10.1038/s41598-017-07669-9.
Strain hardening, originating from defects such as the dislocation, avails conventional metals of high engineering reliability in applications. However, the hardenability of metallic glass is a long-standing concern due to the lack of similar defects. In this work, we carefully examine the stress-strain relationship in three bulk monolithic metallic glasses. The results show that hardening is surely available in metallic glasses if the effective load-bearing area is considered instantly. The hardening is proposed to result from the remelting and ensuing solidification of the shear-band material under a hydrostatic pressure imposed by the normal stress during the shear banding event. This applied-pressure quenching densifies the metallic glass by discharging the free volume. On the other hand, as validated by molecular dynamics simulations, the pressure promotes the icosahedral short-range order. The densification and icosahedral clusters both contribute to the increase of the shear strength and therefore the hardening in metallic glasses.
应变硬化源于位错等缺陷，为传统金属在应用中提供了高工程可靠性。然而，由于缺乏类似的缺陷，金属玻璃的淬透性一直是一个长期存在的问题。在这项工作中，我们仔细研究了三种块状整体金属玻璃的应力-应变关系。结果表明，如果考虑瞬时有效承载面积，金属玻璃中肯定存在硬化现象。提出的硬化机制是由剪切带形成过程中剪切带材料在静水压力下的重熔和随后的凝固引起的，该静水压力由正应力施加。这种外加压力通过排出自由体积使金属玻璃致密化。另一方面，分子动力学模拟验证了压力促进了二十面体短程有序。致密化和二十面体团簇都有助于提高剪切强度，从而使金属玻璃硬化。
