An unusual solid state amorphization in a TiZr-base bulk metallic glass composite fabricated by laser powder bed fusion

Abstract

In additively manufacturing of bulk metallic glasses (BMCs) and their composites (BMGCs), metallic glass usually forms in the molten pools and a certain crystallization occurs in the heat affected zones. In this work, we report a new phenomenon in laser powder bed fusion of BMCC, where the metastable (Ti,Zr)2Cu intermetallic compound (γ) formed in the solidification of molten pools transforms into metallic glass (MG) phase via a solid-state amorphization manner when it located in the heat affected zones during laser powder bed fusion of a Ti61.75Zr33.25Cu5 BMGC. The thermodynamic mechanisms of this solid-state amorphization are proved by the Molar Gibbs free energy - Component (Gm-X) diagram. The γ phase with the Cu content above 39.8 at.% possesses the higher Gm than the MG phase, which is thermodynamically favorable for the amorphization process. The well-defined interface between the metallic glass and the γ phase reveals a heterogeneous solid-state amorphization nature. The average micro-hardness of the (β + ω) matrix and the (γ + MG) reinforcing phases are 352.47 HV0.05 and 979.27 HV0.05, respectively. The solid-state amorphization will contribute to the increase in the hardness and the fracture toughness of the BMGC.