Microstructure and nanomechanical properties of Zr-based bulk metallic glass composites fabricated by laser rapid prototyping

In this study, Zr-Al-Ni-Cu bulk metallic glass composites (BMGCs) were successfully fabricated by laser rapid prototyping and systematically characterized using x-ray diffractometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the studied BMGCs exhibit periodical microstructure along the deposition direction. According to the microstructural characteristics and phase composition, three identified regions are identified, which are classified as the amorphous zone, NiZr2 nanocrystals + amorphous matrix zone and Cu10Zr7 dendrites + CuZr2 nano crystals zone. The nanomechanical behaviors were investigated by nanoindentation and nanoscratch tests. The elastic modulus and nanoindentation hardness are in the following order: NiZr2 nanocrystals + amorphous matrix zone > Cu10Zr7 dendrites + CuZr2 nanocrystals zone > amorphous zone. This is mainly attributed to the structural relaxation and crystallization of BMG caused by the effect of heat treatment during the repeated processes of laser heating. Moreover, NiZr2 nanocrystals can effectively inhibit the movement of shear band in amorphous matrix, resulting in the enhancement of their strength and hardness.