The effect of silicon on the glass forming ability of the Cu47Ti34Zr11Ni8 bulk metallic glass forming alloy during processing of composites

Abstract

Composites of the ${\mathrm{Cu}}_{\mathrm{47}}{\mathrm{Ti}}_{\mathrm{34}}{\mathrm{Zr}}_{\mathrm{11}}{\mathrm{Ni}}_{\mathrm{8}}$ bulk metallic glass, reinforced with up to 30 vol % SiC particles are synthesized and characterized. Results based on x-ray diffraction, optical microscopy, scanning Auger microscopy, and differential scanning calorimetry (DSC) are presented. During processing of the composites, a TiC layer forms around the SiC particles and Si diffuses into the ${\mathrm{Cu}}_{\mathrm{47}}{\mathrm{Ti}}_{\mathrm{34}}{\mathrm{Zr}}_{\mathrm{11}}{\mathrm{Ni}}_{\mathrm{8}}$ matrix stabilizing the supercooled liquid against crystallization. The small Si addition between 0.5 and 1 at. % increases the attainable maximum thickness of glassy ingots from 4 mm for Cu–Ti–Zr–Ni alloys to 7 mm for Cu–Ti–Zr–Ni–Si alloys. DSC analyses show that neither the thermodynamics nor the kinetics of the alloy are affected significantly by the Si addition. This suggests that Si enhances the glass forming ability by chemically passivating impurities such as oxygen and carbon that cause heterogeneous nucleation in the melt.