Formation of crystalline phase in the glass matrix of Zr-Co-Al glass-matrix composites and its effect on their mechanical properties

The microstructural evolution and mechanical properties of Zr-Co-Al alloys, with compositions of (Zr₅₀Co₅₀)_x (Zr₅₆Co₂₆Al₁₈)_1-x (x = 1/6, 2/6, 3/6, 4/6, 5/6, 1) and Zr₅₄Co₃₅Al₁₁, (referred to as Z1, Z2, Z3, Z4, Z5, Z6, and Z4.5), were investigated. Alloys Z1-Z3 consisted of crystalline phases, while alloys Z4 and Z4.5 consisted of crystalline phase particles (~3 vol% and ~35 vol%, respectively) embedded within the glassy matrix. Alloys Z5 and Z6 consisted of a monolithic glass phase. The crystalline phase of alloys Z1-Z4.5 consisted of primary B2-ZrCo dendrite and an interdendritic B2-ZrCo/Zr₆CoAl₂ eutectic phase. The B2-ZrCo dendritic phase exhibited a high work-hardening rate, which originated from the deformation-induced B2-to-B33 martensitic transformation. However, when the brittle interdendritic B2-ZrCo/Zr₆CoAl₂ eutectic phase fraction increased, the work-hardening rate significantly decreased. The ductility of the glass-matrix composites was significantly impaired by the presence of the interdendritic eutectic phase in the crystalline phase. The results indicate that the design of the crystalline particle microstructure is important with regard to enhancing the plasticity of glass-matrix composites.