Influence of molybdenum on the microstructure and mechanical properties of TiC-TiB2 reinforced metal matrix composite coatings

TiC reinforced nickel-based composite coatings with different molybdenum contents were in-situ fabricated on 316L steel by the pulsed Nd:YAG laser in order to solve the severe wear problem of biomass fired boiler tubes. TiB2 decomposed and formed several borides in composite coatings. The microstructure and phase compositions of coatings were analyzed by means of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffractometry (XRD). It was found that the increase of molybdenum could create new binder phases and lessen deficiencies in the coatings, preventing the reinforcement from being pulled out of the matrices and leading to less delaminations during erosion. Though the addition of molybdenum improved the average hardness of composites, it could not improve the wear resistance. The wear mechanisms of these composite coatings were further discussed in this paper.