Microstructure and wear behavior of laser-cladded Ni-based coatings decorated by graphite particles

In order to improve the anti-friction and wear-resistance properties of 42CrMo steel, Ni-coated graphite composite powder and Ni45 alloy powder were designed to fabricate Ni-based self-lubricating wear-resistant coating with simple process and low cost on 42CrMo steel substrate by laser cladding. The effect of scanning speed on pore defects, graphite particle distribution, microstructure and wear behavior of the coatings were investigated, respectively. Through the synergy between adjusting scanning speed and Ni-coated graphite composite powder, the contradiction among the coating density, the interface bonding strength between graphite and Ni matrix and the excessive loss of graphite caused by ablation and in-situ reaction during laser cladding were resolved. Results showed that Ni-coated layer could effectively prevent the graphite from ablation and delay the reaction between carbon and other components. Ni-based self-lubricating coating with low porosity, uniform microstructure, moderate hardness, low friction coefficient and low wear rate can be prepared at an appropriate scanning speed of 300 mm/s. Its average friction coefficient and wear volume were approximately 0.480 and 6.824 x 10(-6) mm(3)/N.m, respectively. The main wear mechanism is slight abrasive wear and adhesive wear. These results obtained are not only applicable to Ni-based alloy coatings, but also to Ni-based composite coatings reinforced by ceramic particle, and even to other material systems. Particularly, when the reinforcing phase is carbide ceramics, the addition of graphite can also inhibit the dissolution of carbide during laser cladding.