Shear bands of as-cast and semi-solid Ti48Zr27Cu6Nb5Be14 bulk metallic glass matrix composites

The as-cast Ti48Zr27Cu6Nb5Be14 bulk metallic glass matrix composites (BMGMCs) were fabricated using a copper mold suction casting method. Then, the semi-solid BMGMC samples were obtained following an isothermal treatment (heating at 900 °C for 10 min, then cooling with water). The microstructure and compression property were investigated by scanning electronic microscopy (SEM) and universal mechanical tester. As a result of the isothermal treatment, the crystal shapes change from fine, granular, and dendritic to spherical or vermicular, and the average crystal size of the as-cast and semi-solid samples is 2.2 µm and 18.1 µm, respectively. The plasticity increases from 5.31% in the as-cast to 10.23% in the semi-solid samples, with an increase of 92.66%. The shear bands from different areas of the side surfaces of as-cast and semisolid compression fracture samples were observed. The characteristic changes of multiplicity, bend, branch and intersection of shear bands in different areas indicate that the deformation of as-cast and semi-solid samples is non-uniform during compression. It is found that poor plasticity of the as-cast samples or good plasticity of the semi-solid samples are reflected by characteristics of the shear bands. The semi-solid isothermal treatment improves the plasticity by forming large crystals which can block the expansion of shear bands and promote the multiplicity of shear bands.