Improving the glass-forming ability and plasticity of a TiCu-based bulk metallic glass composite by minor additions of Si

• The effect of minor additions of Si to a Ti–Cu–Ni–Zr metallic glass was studied.
• An optimum glass-forming ability occurs for 0.5 at% Si.
• None of the GFA criteria predicts this optimum.
• It's explained considering the increased thermal stability and formation of Ti5Si3.
• The alloy with 2 at% Si formed composites with enhanced mechanical properties.

In this work, the effect of Si additions on the glass-forming ability (GFA) and the mechanical behaviour of a Ti42.5Cu42.5Ni7.5Zr7.5 alloy is investigated. An optimum GFA occurs for addition of 0.5 at% Si and it is explained based on a balance between two factors: an increased thermal stability of the supercooled liquid and the detrimental effect of Ti5Si3 on vitrification. On rapid cooling, composites consisting mainly of the cubic B2 phase and glass can form. Their plasticity increases with increasing Si additions without sacrificing their high yield strength. A characteristic core–shell microstructure is formed in the rod with 2 at% Si, for which the combination of an amorphous outer surface and a refined dendritic structure in the centre gives rise to a composite with enhanced mechanical properties.