Characterization investigations of mechanically alloyed and sintered Al – 4 wt% Cu matrix composites reinforced with mechanochemically synthesized chromium boride/nitride particles

Chromium boride/nitride powders were mechanochemically synthesized via two different routes. In the first route, Cr and BN powder blends in stoichiometric ratios were milled for 8 h and annealed at 1500 °C for 12 h. In the second route, powder blends containing stoichiometric amounts of Cr₂O₃, B₂O₃, Mg and BN were milled for 8 h, annealed at 1500 °C for 12 h and leached in an HCl solution. Synthesized powders of both routes were incorporated into Al - 4 wt% Cu matrix alloy (Al4Cu) powders (premilled for 8 h) with various amounts (5, 10 and 15 wt%), and the resultant powder mixtures were further milled for 1 h. Milled powders containing Al4Cu matrix alloy and chromium boride/nitride powders were pressed at 450 MPa and sintered at 550 °C for 2 h to produce Al4Cu-x (Cr boride/nitride) (_{x = 5,10,15}) composites. Characterization investigations were carried on the synthesized powders of both routes, on the Al4Cu matrix alloy and composite powders and on their sintered composites. For a given reinforcement amount, density and mechanical properties of the Al4Cu composites reinforced with powders of the first route were found to be better than those reinforced with the powders of the second route. The Al4Cu composite reinforced with the powders of the first route by 15 wt% had a microhardness of about 2 GPa and a compression strength of about 323 MPa. The lowest wear rate (1.02 × 10⁻³ mm³/Nm) was achieved for the Al4Cu composite reinforced with 10 wt% Cr boride/nitride powders synthesized from the first route.