Microstructure and Mechanical Performance of Novel Al ₂ O ₃ -Cu-Cr Composites Consolidated by Conventional Powder Metallurgy

Abstract

This study investigates the fabrication, microstructural evolution, and mechanical properties of Al ₂ O ₃ -Cu-Cr ceramic-metal composites containing 2.5 vol.% metallic phase produced by uniaxial pressing followed by free sintering in a reducing atmosphere. The composites were sintered at temperatures ranging from 1200°C to 1400°C in order to evaluate the influence of thermal processing on densification behaviour, phase stability, and mechanical performance. The results demonstrated a strong dependence of physical properties on sintering temperature. Increasing the temperature from 1200°C to 1400°C improved the relative density from 82.85% to 97.99%, while open porosity decreased from 16.57% to 0.09%. Simultaneously, water absorption was reduced from 4.66% to 0.2%, indicating near-complete densification at 1400°C. XRD analysis confirmed the presence of stable α-Al ₂ O ₃ , Cu, and Cr phases without formation of undesirable secondary reaction products. SEM/EDS observations revealed a homogeneous distribution of discrete Cu-Cr metallic regions within the alumina matrix and satisfactory ceramic-metal interfacial bonding. The composites sintered at 1400°C exhibited a hardness of 13.8 ± 1.6 GPa and fracture toughness of 4.41 ± 0.78 MPa·m ^0.5 . Digital image correlation analysis during compression testing demonstrated localized strain evolution preceding brittle fracture. The results indicate that Cr addition may contribute to improved microstructural stability and densification behaviour of Al ₂ O ₃ -Cu composites processed by conventional powder metallurgy routes.