Zr-Cu-Ni-Al-Ta glassy matrix composites with enhanced plasticity

(Zr62Cu15.4Ni12.6) (x=6-12) in situ glassy composites containing uniformly distributed Ta-rich particles were prepared by arc-melting and copper mould casting. The results show that addition of 6-10 at.% Ta to Zr62Cu15.4Ni12.6Al10 results in dissolution of 2.4 to 4.6 at.% Ta in the glassy matrix, which promotes glass-forming ability, and the remaining Ta precipitates out as body-centered cubic (BCC) Ta-rich particles dispersed on the glassy matrix. The critical diameters for the composites with 6, 8, and 10 at.% Ta are 7, 7, and 6 mm, respectively. At 12 at.% Ta addition, the glass-forming ability is dramatically reduced because of the precipitation of secondary dendritic Ta-rich particles and other nanocrystallites from melts during copper mould casting. Also, owing to the solid-liquid reaction during induction heating, some Ta-rich particles formed in the master alloys will redissolve into the glassy matrix, resulting in a smaller volume fraction of Ta-rich particles in the as-cast glassy rods than that of the corresponding ingots. The glassy matrix composites exhibit enhanced plastic strain of about 7.5 to 22.5% at room temperature. The optimum Ta content in the glassy alloys is determined to be 10 at.%, which corresponds to the highest ultimate stress of 2220 MPa and the largest plastic strain of 22.5%. The plastic strain increases with increasing volume fraction of in situ BCC Ta-rich particles. This is apparently ascribed to the impedance of Ta-rich particles to shear bands. Ta-rich particles seed the initiation of multiple shear bands and block the shear band propagation, leading to intensive multiplication and bifurcation of shear bands.