In-Situ copper MMCs

Highly Reinforced Copper Matrix Composites

C. Krüger, A. Mortensen (with earlier contributions from V. Laporte and M. Guo)

This project funded by a CTI/industry collaborative grant is an exploration of industrially applicable routes for the production of copper-based composites containing a high fraction of light reinforcement particles, of density lower than that of copper together with attractive mechanical properties. Two routes are explored: infiltration and a new in-situ process.

For higher volume fractions ceramic, on the order of 50-60 %, composites are produced by pressure infiltration. It is shown that aluminium in molten copper causes limited particle rounding. The effect of titanium additions in infiltrated Cu8wt%Al-alumina composites are investigated using two different Al2O3 particles types and four different Ti contents (0, 0.2 ,1, 2 wt%Ti). It is shown that the addition of 0.2wt%Ti leads to the development of a very thin (5-10 nm) layer enriched in Ti at the interface between the alloy and the particles; these composites have the best mechanical properties. Higher Ti-contents lead to formation of a ternary oxide, shown to be Ti3(Cu,Al)3O; this decreases the interface strength. A Young’s modulus near 235 GPa, a density of 5.5 g/cm3, a tensile strength and elongation of 600 MPa and 1% respectively, together with a compressive strength near 1100 MPa reached at 9% strain are obtained with the best combination of particle and matrix.

For lower fractions ceramic, on the order of 30% by volume, a new in-situ process is developed, in which the composites are prepared by coupled reaction and deformation processing, starting from pure metal and oxide powders, free of ball-milling. The evolution of the microstructure is governed by the formation of alumina films; these mitigate the rate of reaction, preventing thermal runaway if samples are processed with sufficient thermal ballast. The resulting alumina being in the form of thin films, it is amenable to subsequent refinement and dispersion by hot working the metal. Cu7wt%Al matrix composites containing 26 vol% homogeneously distributed alumina particles have in the optimal state among conditions explored her a Young’s modulus of 145 GPa, a hardness of 250 HV10, a density near 7 g/cm3, a yield stress near 680 MPa with a UTS of 846±44 MPa and a tensile elongation of 2.2±0.8%. Mechanical properties furthermore degrade little after exposure of the composite to temperatures near the liquidus of its matrix.