Differences in tribological performance between spark plasma sintering and laser melting deposition for fabrication of Ni₃Al matrix self-lubricating composites

Ni₃Al matrix self-lubricating composites containing multilayer graphene and Ag are successfully prepared by spark plasma sintering (SPS) and laser melting deposition (LMD), which are denoted as NMAS and NMAL, respectively. The sliding wear performances of NMAS and NMAL at 25-500 °C are systematically investigated. NMAL exhibits the lower friction coefficients (0.20-0.40) and considerable wear resistance (2.8-5.0 × 10⁻⁵ mm³ · N⁻¹ · m⁻¹) as compared to NMAS. For the use of spherical prealloyed powders and the manner of layer by layer deposition, the hardness distribution of NMAL is more uniform than that of NMAS. NMAL shows the better tribological properties in comparison to NMAS from 25 to 400 °C because of the good consistency of microhardness. NMAL has excellent tribological behavior at 400-500 °C, while NMAS exhibits poor tribological performance. An explanation for the result is that the lubricating film of NMAL is still intact at 400-500 °C, while the lubricating film of NMAS is cracked and peeled off.