Development of High Strength Ni–Cu–Zr–Ti–Si–Sn In-Situ Bulk Metallic Glass Composites Reinforced by Hard B2 Phase

In the present study, the influence of atomic ratio of Zr to Ti on the microstructure and mechanical properties of Ni–Cu–Zr–Ti–Si–Sn alloys is investigated. The alloys were designed by fine replacement of Ti for Zr from Ni 39 Cu 20 Zr 36−x Ti x Si 2 Sn 3 . The increase of Ti content enhances glass forming ability of the alloy by suppression of formation of (Ni, Cu) 10 (Zr, Ti) 7 phase during solidification. With further increasing Ti content up to 24 at.%, the B2 phase is introduced in the amorphous matrix with a small amount of B19′ phase from alloy melt. The bulk metallic glass composite containing B2 phase with a volume fraction of ~ 10 vol% exhibits higher fracture strength (~ 2.5 GPa) than that of monolithic bulk metallic glass (~ 2.3 GPa). This improvement is associated to the individual mechanical characteristics of the B2 phase and amorphous matrix. The B2 phase exhibits higher hardness and modulus than those of amorphous matrix as well as effective stress accommodation up to the higher stress level than the yield strength of amorphous matrix. The large stress accommodation capacity of the hard B2 phase plays an important factor to improve the mechanical properties of in situ Ni-based bulk metallic glass composites.