Oxygen addition for improving the strength and plasticity of TiZr-based amorphous alloy composites

Abstract

The addition of a small amount of oxygen improves the mechanical properties, especially plasticity, of Ti45.7Zr33Ni3Cu5.8Be12.5 amorphous alloy composites (AACs) at room temperature (298 K). Compared to the plasticity of AACs without added O (5%), the plasticity of the composites with 0.73 at.% O (nominal composition) was much higher (11 %). Even at O content higher than 0.73 at.%, the AACs exhibited good plasticity. The highest plasticity of ∼12.3 % was observed with 2.87 at.% O. Two distinct mechanisms are proposed to explain the enhanced plasticity of the AACs. At low O content, although deformation-induced phase transformation was suppressed, a substantial amount of α’’ martensite was formed. The microstructural features of α’’ martensite, such as thinner laths and homogeneous distribution, induced the formation of multiple shear bands in the amorphous matrix. At high O content, deformation-induced phase transformation was seriously suppressed. A dispersed nano ω phase was formed during rapid solidification in AACs with O content higher than 1.45 at.%. This resulted in a weakening in the anisotropy of β dendrites and led to their homogenous deformation. Furthermore, multiple shear bands were formed in the amorphous matrix. Apart from plasticity, the strength of the AACs also increased with an increase in the O content. This phenomenon was explained in terms of three mechanisms, viz. the solid-solution-strengthening effect of O, fine-grain strengthening of β dendrites, and secondary phase strengthening by the nano ω phase.