Tribological behavior of in-situ nanosized TiB₂ particles reinforced AZ91 matrix composite

To enhance the wear resistance of magnesium alloy to expand its applications, AZ91 matrix composite reinforced with TiB₂ particles was developed by in-situ casting, and its tribological behavior was investigated. The dry sliding wear experiment was carried out with the sliding speeds of 0.25, 0.50 and 0.75 m/s, at different normal loads of 12.5, 25 and 37.5 N respectively. The hardened AISI 52100 bearing steel was selected as counterbody material. The experimental results reveal that the mechanical properties of composite are improved significantly due to grain refinement and numerous dislocations formed near TiB₂ particles. The wear rate of composite reduces with the increase of sliding speeds at all normal loads and wear mechanism is transited from abrasive and mild oxidation wear to delamination and severe oxidation wear, similar to the wear mechanism in various normal loads. However, the mechanically mixed layer formed at higher speeds has a protective effect and the delamination and plastic deformation of subsurface is more severe at higher loads. The wear resistance of composite is greater than that of the matrix at all wear conditions, because TiB₂/AZ91 composite possess improved hardness and strength, as well as increased work hardening capacity of subsurface due to the presence of nanosized TiB₂ particles.