Effect of c-BN on the microstructure and high temperature wear resistance of laser cladded Ni-based composite coating

In this study, Ni-based Ni60 + Cu/h-BN + MoO3 and Ni60 + Cu/c-BN + MoO3 composite coatings were fabricated by laser cladding on a Q235 substrate. Compare with the addition of h-BN, the effect of c-BN on the microstructure, high temperature hardness and wear resistance properties of the coating from 25 degrees C to 800 degrees C were analyzed. The results show that part of c-BN is decomposed during laser cladding process, resulting in the formation of Cr(Mo)B, Cr5B3, CrN and MoN reinforcements. The periphery of the remaining c-BN particle is allotropic transformed to h-BN under laser irradiation. The content of the reinforcement in the coating is increased and the distribution is more uniform, therefore, the hardness of the coating is increased. This resulted in a reduction of the wear rate from 25 degrees C, 200 degrees C, 400 degrees C, 600 degrees C to 800 degrees C by 77%, 61%, 29%, 46% and 39%, respectively. The abrasive and adhesive wear are released because of the increasing of deformation resistance and interface strength of gamma-(Ni, M) matrix and Cr(Mo)B. In the meantime, the formation of h-BN provides lubricating property over the wide temperature range.