Effects of V on phase formation and plasticity improvement in Cu–Zr–Al glassy alloys

Vanadium was alloyed to an amorphous Cu–Zr–Al alloy to induce B2-CuZr phase formation in order to improve plasticity. The vanadium addition was based on the fact that it has a positive heat of mixing with the major constituents in the Cu–Zr–Al alloy, thus could cause liquid phase separation. Microstructural examination showed that V was dissolved in the amorphous matrix and promoted the formation of B2-CuZr precipitates in (Cu47.5Zr47.5Al5)99V1, improving the plasticity by doubling the fracture strain to 9.4%. However, when V content is more than 3 at%, brittle intermetallic compound phases (V+Al23V4) form and degrade the plasticity. 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. An energy-balance analysis based on deformation-induced B2 particle coarsening produced an interfacial energy of 0.293 J/m2 for the B2 particle–glassy matrix interface. The result appears to indirectly support the previous idea that plasticity in Cu47.5Zr47.5Al5 is caused by dynamic coarsening of the B2-CuZr particles.