Rejuvenation of bulk metallic glass

Abstract

Bulk metallic glass (BMG) has an appealing property to the world, its high strength and high shapability could be used in many applications. However, the brittleness of metallic glass holds off the utilization of it. BMG usually shows brittleness in their as-cast state and lead to catastrophic failure when it is subjected to high loading. Therefore, the researchers have found multiple way to increase the plasticity by rejuvenation, such as shot-peening, cryogenic thermal cycling treatment, plastic deformation, cold rolling, and other methods. In this paper, cryogenic thermal cycling (CTC) treatments were performed on Zr₅₅Cu₃₀Ni₅Al₁₀ BMG. Hardness test, scanning electron microscope (SEM) with energy dispersive x-ray analysis (EDX), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and compression tests were conducted to characterize the effect of CTC and the effect of the increment in the number of CTC. There is no change in thermal stability and mechanical strength after CTC; no observable crystallization can be found in the XRD pattern. The plasticity of Zr₅₅Cu₃₀Ni₅Al₁₀ BMG greatly improved by CTC. Increase in the number of CTC further enhanced the plasticity. However, the relaxation enthalpy showed a "up-and-down" trend, which the ΔHrelax peaked at 10 cycles and decreased with further cycles. This phenomenon might be explained by the chemical heterogeneity of the BMG, or the soft regions and nano-clusters generated during CTC, which is widely adopted theory to explain the mechanism of the plasticity in BMGs. Since the plasticity of a BMG is very important for the industrial and commercial use, which might greatly change the world, it is beneficial to study the effect of CTC of a BMG and support the further researchers with new information and ideas.