Microstructural dependence of mechanical properties in Hf-based bulk metallic glasses and their composites

Hf44.5Cu27Ni13.5Ti5Al10 bulk metallic glasses were prepared by the copper mold casting process. The crystallization behaviors of the amorphous alloys treated at different isothermal annealing temperatures were investigated. The results indicated that the crystallization of the alloy proceeded by the process Am0 (amorphous state) → Am1 + Al16Hf6Ni7 → Am2 + Al16Hf6Ni7 + Ti2Cu3 + Cu3Ti → Am3 + Al16Hf6Ni7 + CuTi2 → CuHf2 + CuTi2. After annealing at 763 K, the sample displayed the highest fracture strength of 2401 MPa with an elastic strain of 3.0%. The nanoscale dimple structure and periodic stripes could be observed on the fracture surface. The spacing between stripes decreased gradually and eventually disappeared with the increase of the annealing temperature.