Titanium diboride copper-matrix composites

Abstract

Copper-matrix titanium diboride platelet (3–5 μm) composites containing 15–60 vol% TiB2, were fabricated by powder metallurgy, using copper-coated TiB2 (60 vol% TiB2) and various amounts of copper powder. The porosity was ≤0.5% when TiB2 was ≤48 vol%. Above 48 vol% TiB2, the porosity increased abruptly with increasing TiB2 content, reaching 6.7% at 60 vol% TiB2. As a result, the hardness and compressive yield strength dropped precipitously with increasing TiB2 volume fraction beyond 48%. At 48 vol% TiB2, the thermal conductivity was 176 W m-1°C-1, the electrical resistivity was 3.42× 10-6Ωcm, the coefficient of thermal expansion (CTE) was 10.2×10-6°C-1, the compressive yield strength was 659 MPa, and the Brinell hardness was 218. For composites made by conventional powder metallurgy, using a mixture of TiB2 platelets (not coated) and copper powder, the porosity was ≤1.8% when TiB2 was at ≤42 vol%; above 42 vol% TiB2, the porosity increased abruptly and the hardness and compressive yield strength decreased abruptly. The electrical resistivity and thermal conductivity were also affected by the porosity, but less so than the mechanical properties. Composites made using copper-coated TiB2 exhibited lower electrical resistivity, higher thermal conductivity, lower CTE, higher compressive yield strength, greater hardness, greater abrasive wear resistance, greater scratch resistance and lower porosity than the corresponding composites made from uncoated TiB2.