Effect of TiO2-doping on the microstructure and the wear properties of laser-clad nickel-based coatings

The effects of TiO2-doping on the properties of laser clad nickel-based composite coatings on carbon steel substrates have been studied. It is shown that good finish and crack- and porosity-free coatings can be achieved under a proper amount of TiO2-doping and a suitable laser-scanning speed. Both the cracking sensitivity and the wear resistance are considerably improved at the little expense of a decrease in hardness. This can be attributed to the improvement of the coatings to the refinement of the microstructure both in grain sizes and their homogeneous distribution in the coatings. The microstructural and metallographic analyses by a scanning electron microscopy, energy-dispersive spectrometer and X-ray diffractometer suggest the generation of new phases such as TiB2 and TiC upon the TiO2-doping. Thus, it can be concluded that the refinement in microstructure is due to both an increase in number of nucleation sites by the formation of TiB2 and TiC in the melt pool and an impediment to the growth of larger crystallites by the deposition and insertion of Ti atoms on the grain boundaries.