Dry sliding wear of aluminum-silicon (A356) matrix composites with carbon fibre or graphite/silicon carbide reinforcement.

The unlubricated sliding wear of two reinforced A356 (Al-7%Si-0.3%Mg) metal matrix composites was studied using a block on ring wear machine with an AISI 52100 steel counterface (63 HRC). One composite was discontinuously reinforced with 4 $\pm$ 1 vol% non-graphitic carbon fibres coated with nickel. The composites were tested such that the fibres were either normal or parallel to the contact surface. The second composite was a hybrid composite with 20% SiC particulate and 3 or 10 vol% graphite particles. In the wear tests, the applied normal load varied from 5 to 441 N. Sliding speed ranged from 0.1 to 1 m/s with the majority of tests performed at 0.5 m/s. The wear resistance of the A35-Carbon Fibre (CF) reinforced composites was superior to the unreinforced alloy over the entire load range tested. The improved wear resistance was related to an improvement in load carrying capability of the composites as a result of the carbon fibre addition and an interfacial reaction which produced a nickel aluminide intermetallic. These composites demonstrated regions of mild and severe wear. Mild wear was characterized by surface grooves, plastic deformation and loose debris in the form of particulates and flakes. The A356-Gr-SiC composites did not experience severe wear resulting in good wear resistance at high loads. This was due to a reduction in frictional heating and the formation of a tribolayer on the surface which consisted of iron, iron oxides, graphite, SiC and aluminum. Graphite addition resulted in a reduction in counterface wear. Higher graphite concentrations led to higher wear resistance at loads below 10 N. In the load range from 20 to 300 N the 10% graphite composite experienced wear rates 2 to 4 times that of the hybrid composite with only 3% graphite possibly due to a decrease in the load carrying ability due to higher graphite content. Source: Masters Abstracts International, Volume: 33-04, page: 1318. Adviser: A. T. Alpas. Thesis (M.Sc.A.)--University of Windsor (Canada), 1994