A team at Tohoku University, Japan, announces a new heat treatment technique in which rapid heating and asymmetrical cooling improve ductility in metallic glass. This technique enabled the team to induce a gradient of local glassy structure, bringing an apparent work hardening behavior. Work hardening is the process by which a material is strengthened via plastic deformation, but is not generally observed in metallic glasses due to their intrinsic random structure.
Although bulk metallic glasses (BMGs) have attracted much attention because of their high strength, wide elastic limit, and excellent thermoplasticity, a major disadvantage has been a lack of ductility due to intrinsic work softening at room temperature.
Dr Wookha Ryu, Assistant Professor Rui Yamada and Professor Junji Saida of the Frontier Research Institute for Interdisciplinary Sciences have now successfully produced unique Zr60Cu30Al10 bulk metallic glass with a 2D gradient rejuvenation state, which leads to excellent ductility and tailored hardening of a monolithic BMG at room temperature.
According to Professor Saida, “We have developed a novel structure-controlling technique with asymmetric cryogenic heat treatment, and produced a unique glassy structure with the 2D gradient rejuvenation state. The BMG exhibits a tailored hardening behavior throughout the overall plastic deformation stage, as well as an excellent ductility at room temperature.”
The local free volume concentration related to the rejuvenation state controls the shear band angle and the maximum effective shear stress. Hence, shear band propagation is prevented, and the formation of a complete shear plane transecting the whole specimen is blocked. The generation of plastic strain is accompanied by an increase in the critical shear stress, which results in a sustainable apparent hardening.
The work was published online in NPG Asia Materials on 31 July 2020.
https://www.tohoku.ac.jp/en/press/tailored_hardening_zrcual.html
Publication Details:
Title: Tailored hardening of ZrCuAl bulk metallic glass induced by 2D gradient rejuvenation
Authors: W.H. Ryu, R. Yamada and J. Saida
Journal: NPG Asia Materials
DOI: 10.1038/s41427-020-0233-8
