Strengthening and toughening of Mg-based bulk metallic glass via in-situ formed B2-type AgMg phase

By tuning the composition and melt cooling rate, in situ composites of bulk metallic glass (BMG) with primary phase of B2-type AgMg compound can be fabricated in Mg-Cu-Ag-Y quaternary systems. In the composite, volume fraction of AgMg dendrites dispersed in the glass matrix varies in a range of 20-40%. In contrast to monolithic BMG, Mg52.8Cu19.9Ag19.5Y7.8 composite with AgMg of 40 vol.% dendrites manifest a distinct improvement in the compressive yield strength (~ 1040 MPa), fracture strength (1.2 GPa) and plastic strain (0.4-2%), as well as an apparent work-hardening effect. Moreover, AgMg phase in the composite plays a significant role to suppress the crack propagation, then enhancing the fracture toughness, as indicated by an increment of notch toughness (KQ) from ~ 6 MPa m1/2 of monolithic BMG to ~ 8 MPa m1/2 of the composite. However, since the tiny plastic zone size of glassy matrix is unable to match the microstructural length scales, improvement in the ductility and toughness of Mg-based BMG in situ composite remains limited.