Thermal stability and mechanical properties of spray-formed and melt-spun Al₈₉la₆Ni₅ metallic glass matrix composites

A spray-formed Al₈₉La₆Ni₅ metallic glass matrix composite plate was obtained in thickness of 1 mm and diameter of 200 mm, comprising over 64% primary crystals {e.g. Al₁₁La₃) uniformly dispersed in the glass matrix. The microstructure can not be achieved by annealing corresponding amorphous precursor. The crystals existing in the glass matrix were found to increase the hardness of the composite. Through nanoindentation test, the hardness and modulus of the composite at ambient temperature were found superior than its amorphous ribbon counterpart. The hardness of the composite was estimated with the rule of mixture from the constituents to be 4.4 GPa, which agreed well with the nanoindentation results. From loss modulus measurement and TMA test at elevated temperatures, a weak T₈ signal in the range of 213-240°C was revealed in the as-spray-formed composite. Furthermore, the dimension shrinkage of the composite was only 0.5% during the TMA test, which is much smaller than that of amorphous ribbon counterpart by up to 20%. The enhanced hardness by constituent second phases and the dimension stability of the composite are associated with their inherent microstructure, the primary crystals in particular.