Tribological behaviour and mechanical properties of copper and magnesium based composites treated by severe plastic deformation

Mechanical and wear properties of a series of copper and magnesium based composites with alumina dispersoid nanoparticles were studied. The initial states of the composites were further treated by severe plastic deformation (SPD) in order to achieve microstructures with very fine grains. All states, as–received and SPD treated ones were then characterised and the results compared. Hardness and indentation modulus of elasticity of the experimental materials were measured by instrumented indentation. Microstructure parameters were observed using transmission electron microscopy. Tribological properties were studied by pin–on–disk technique in dry sliding against steel balls at a various temperatures from room temperature up to 873 K (copper) or up to 573 K (magnesium), respectively. For all systems the coefficient of friction and specific wear rates were evaluated. Worn surfaces were studied by scanning electron microscopy and level of oxidation was measured using EDX spectrometry. Damage mechanisms were identified and their relationship with structural characteristics was inferred. Hardness of all materials was higher after SPD. In copper based materials higher temperatures lead to forming hard oxide surface layers and to improvement of wear resistance while the wear resistance of the magnesium based composites at high temperatures decreased.