Structural relaxation and its influence on the elastic properties and notch toughness of Mg–Zn–Ca bulk metallic glass

Abstract

Structural relaxation and its influence on the elastic properties and mechanical properties of Mg–Zn–Ca bulk metallic glass (BMG) were investigated. It was found that relaxation can occur spontaneously even at room temperature ( T R) because of the high homologous temperature ( T R/ T g > 0.7) of the BMG. A linear dependence between enthalpy change (Δ H t) and free volume change (Δ v f) for the annealed Mg 66Zn 30Ca 4 BMG over a wide temperature range was discovered. The structural relaxation of the Mg 66Zn 30Ca 4 BMG resulted in increased shear modulus μ (3.4%) and decreased Poisson's ratio ν (1.4%). However, the tested BMG samples exhibited no obvious degradation of notch toughness ( K Q) even after full structural relaxation. The K Q values are 9.0 ± 1.7 MPam 1/2 and 7.1 ± 1.8 MPam 1/2 for the freshly prepared samples (annealed at T R for 1.5 h) and fully relaxed samples (annealed at 373 K for 4 h), respectively. These results indicate that the mechanical properties of the Mg 66Zn 30Ca 4 BMG are not very sensitive to its structural relaxation over a wide temperature and time range. These findings may facilitate the clinical applications of Mg 66Zn 30Ca 4 BMG as a promising implant material for future clinical applications.