Tribological behavior and wear mechanisms of MoSi2-base composites sliding against AA6063 alloy at elevated temperature

Intermetallic Mo(Si,Al)2, Mo(Si,Al)2/Al2O3, Mo(Si,Al)2/SiC and Mo(Si,Al)2/ZrO2 composites produced by spark plasma sintering of mechanically alloyed powders were tested on a block-on-cylinder apparatus, sliding against an AA6063 alloy cylinder at elevated temperature. Abrasion, micro-fracture and surface tribochemical reactions were found to be the operative wear mechanisms, producing severe wear in the investigated alloys. Abrasive wear by pull-out of Al2O3 and micro-fracture of Mo(Si,Al)2 particles promotes severe wear in the Mo(Si,Al)2/Al2O3 composite. In the Mo(Si,Al)2/SiC composites, hard SiC inclusions suppressed the abrasive wear, but a tribochemical reaction was found to be the dominant wear mechanism. A combination of abrasion by pull-out of Al2O3 particles and a tribochemical reaction was revealed to be the main wear mechanism in the Mo(Si,Al)2/ZrO2 materials. The brittleness index B = H/K1C was applicable for prediction of the relative wear resistance. In agreement with the suggested model, the lowest wear rate, corresponding to B = 5.5–6.5 μm−1/2, was found in the Mo(Si,Al)2/30 vol.% SiC and Mo(Si,Al)2/30 vol.% ZrO2 composites.