Microstructural effects on the sliding wear of transparent magnesium-aluminate spinel

Grain size effects have been investigated in the lubricated sliding wear of three transparent magnesium aluminate (MgAl2O4) spinel materials with different grains sizes identified as: Nano, Fine, and Coarse. Only Fine spinel shows classical wear behavior, which is characterized by initial mild wear followed by a sharp transition to severe fracture-controlled wear. Worn surfaces of Fine spinel show extensive grain pullout, consistent with intergranular mode of fracture found in that spinel. Nano and Coarse spinels both show gradual transition from mild wear to severe wear, and both have significantly lower overall wear rates compared to Fine spinel. Worn surfaces in both Nano and Coarse spinels show transgranular fracture and material removal, which is reminiscent of lateral-crack induced chipping. The transgranular fracture mode in Nano spinel can be attributed to stronger grain boundaries in that spinel, which could be due to the Y2O3 sintering additive used for grain refinement. Whilst the large scale of the grains in Coarse spinel could be responsible for the transgranular fracture observed in that spinel.