||CuZrAl and CuZrAl-V and CuZrAl-Co amorphous alloys were cast by rapid suction casting. Flow serrations and fracture morphologies of the base monolithic Cu50Zr43Al7 bulk metallic glasses (BMGs) are first studied by compression at a low strain rate and analyzed by an energy release perspective. |
Vanadium or cobalt from 3 to 10 at% is alloyed to the amorphous CuZrAl base alloys to induce precipitation in order to form the bulk metallic glass composites (BMGCs) with micro-sized second phase domains. The V-rich second phase formed during rapid cooling possesses a sharp dendrite shape, inducing stress concentration in the amorphous matrix and lowering the mechanical performance. The Co-rich phase, formed from liquid phase separation, possesses round morphology, lowering the stress concentration and raising or sustaining the mechanical properties.
Meanwhile, 1 at% vanadium was alloyed to the amorphous CuZrAl base alloy to induce nano-sized B2-CuZr phase formation in order to improve compressive plasticity. It was found that the dilute vanadium addition induced B2-CuZr formation and, thus, improved plasticity of the CuZrAl alloy. The role of vanadium on plasticity improvement was discussed in the frame of shear band multiplication, energy dissipation during shear banding, twinning/phase transformation of the B2-CuZr particles during deformation, and deformation induced B2-CuZr particle coarsening.
It was suggested that such transformation induced plasticity would show dependence on the B2 particle size, which in-turn depends on the inlet shape of the suction casting mold in use. It follows that the final task of this research was to examine the effects of the B2 size and distribution, resulted from the sharp or blunt inlet mold, on the mechanical plasticity in the CuZrAl and CuZrAlCo BMGs and BMGCs. It appears that the B2 particles need to be over some critical size to induce the martensitic/twinning transformation into the B19’ phase (sometimes with twins embedded). An analytic model, based on melt flow dynamics with or without vena contraction, is established, and the agreement between experiment and model is satisfactory.