Effect of Laser Surface Treatment on Plastic Deformation of Industrial-grade Zr-based Bulk Metallic Glasses

Industrial-grade Zr49.7Ti2Cu37.8Al10Er0.5 bulk metallic glasses (BMGs) possess poor plastic deformation ability due to the effect of impurity elements in the raw materials and oxygen elements from the preparation processing. This paper aims to study the effect of the laser surface treatment (LSM) on the microstructure and the plasticity of industrial-grade Zr49.7Ti2Cu37.8Al10Er0.5 BMGs. The master alloy ingots were prepared by arc-melting with low-purity raw materials. The industrial-grade Zr49.7Ti2Cu37.8Al10Er0.5 BMG specimens were prepared by copper mold casting method in a low vacuum environment, and then the specimens were treated by LSM under different parameters. The compressive and tensile properties of the laser treated specimens were investigated with a universal testing machine. The microstructure of the specimens before and after the LSM was characterized with an X-ray diffractometer and an electron microprobe. The morphology of the specimens after the deformation was observed with a scanning electron microscopy (SEM). It was found that the depth of the affected zone induced by the LSM was about 150 μm. The content of copper element dropped in the affected zone compared with the nominal composition. Notably, the laser-affected zone in the near surface and the unaffected zone in the middle of the specimen still exhibited amorphous structure. Before the LSM, the compressive plasticity of the industrial grade Zr49.7Ti2Cu37.8Al10Er0.5 BMG was nearly zero, and the fracture strength was 1 534 MPa. After the LSM, the compressive plastic strain was 1% with the yielding strength 1 478 MPa and the fracture strength 1 562 MPa. The SEM observation demonstrated that there existed numerous shear bands on the laser-treated specimens while it was hard to detect shear bands on the specimens without LSM. The appearance of the shear bands further proved the plastic deformation on the laser-treated specimens. Additionally, the fracture surfaces of all the specimens possessed vein-like patterns typical of BMGs, and the angle between the fracture surface and the loading direction was less than 45°, indicating that the shear failure mode was not affected by the LSM. On the other hand, under the tensile condition, the plastic strain of the specimens before and after the LSM was zero, and there was no obvious change in the fracture strength (1 390 MPa). It was known that the LSM produced the residual stress and the change of amorphous composition. During the loading, the combination of the residual stress and the external stress induced the stress concentration and stress gradient which facilitated the formation of the shear band and prevented its propagation. The difference in amorphous composition lead to the different characteristics of shear bands and intensified the interaction of shear bands. Based on the experimental results, it is confirmed that the LSM can effectively improve the compressive plasticity of the industrial-grade Zr49.7Ti2Cu37.8Al10Er0.5 BMG. Nevertheless, the existence of oxygen and erbium elements are detrimental to the inherent plastic deformability of the industrial-grade Zr49.7Ti2Cu37.8Al10Er0.5 BMG. Accordingly, the compositional change and the residual stress at the present scale cannot counteract the effect of the tensile normal stress on the crack initiation. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.