Simultaneous fabrication of Ti-MoS2 self-lubricating coatings and gradient structures to improve the wear resistance of AZ91D alloys

Magnesium alloys are essential for lightweight manufacturing. Nevertheless, defects such as low hardness and poor wear resistance severely restrict their further applications. Ultrasonic impact treatment (UIT) was used to simultaneously fabricate surface Ti-MoS2 self-lubricating coatings and interior gradient structures on AZ91D magnesium alloy for the first time. The surface morphology and microstructure were investigated, the tribological properties were evaluated at various normal loads, and the formation principles and anti-wear mechanisms of coatings and gradient structures were revealed. The findings indicate that the coatings present a particle-stacking microstructure. The gradient structures were characterized by grain, dislocation, and hardness distribution from greater to lesser along the depth direction. At all loads, the UIT samples exhibited superior anti-wear properties. Compared to untreated samples, the UIT sample's wear volume at 5 N, 15 N, and 25 N loads was reduced by 89.78 %, 84.23 %, and 43.88 %, respectively. The wear surface analysis indicates that the Ti-MoS2 coatings effectively enhance the lubricity of friction surfaces. Additionally, gradient structure works when the coatings fail and reduces the shear deformation, further reducing wear. This work presents a new method for fabricating simultaneously surface coatings and interior gradient structures using UIT, contributing to improving the anti-wear properties of magnesium alloys and enhancing their utilization in lightweight manufacturing fields. [Display omitted] •A new method for simultaneous fabrication of coatings and gradient structures by ultrasonic impact treatment was proposed•Surface Ti-MoS2 self-lubricating coatings and interior gradient structures were prepared on AZ91D alloys•The proposed method effectively improves the wear resistance of AZ91D alloys due to the dual anti-wear mechanism