Tribological performance of Ni₃Al matrix self-lubricating composites containing Ag prepared by laser melting deposition

For improving tribological properties of Ni₃Al-based alloy, Ni₃Al matrix self-lubricating composites with 10 wt% Ag are successfully fabricated by spark plasma sintering (SPS) and laser melting deposition (LMD), which are abbreviated as NAS and NAL, respectively. Tribological behavior of NAS and NAL against Si₃N₄ ball under constant load (12 N) and variable speeds (from 0.2 to 1.1 m s^-1, 0.3 m s^-1 in tolerance) are systematically investigated. The results showed that NAL exhibited lower friction coefficients (0.28-0.36) and considerable wear resistance (4.6-5.9 ×10^-5 mm³ N^-1 m^-1) as compared to NAS. It should be noticed that the tribological performance of NAL is excellent at 1.1 m s^-1, while the tribological behavior of NAS is deteriorated significantly. LMD, as a process of layer by layer deposition, results in that each layer is comprised of the freshly deposited materials and the previously solidified materials. The characteristic of LMD is particularly significant for obtaining the stable bonding between layer, leading to the improvement of good interface bonding capability between tribolayer and substrate during the sliding wear process. Furthermore, the stability of the tribolayer is favorable for the reduction of friction coefficient and wear rate. For NAS, the local exfoliation of lubricant layer and the occurrence of naked substrate at the sliding speed of 1.1 m s^-1 is explainable for the poor tribological performance.