Surface Modification of Ti600 Ti-Alloy with Laser Cladded NiCr/TiAl Coating

The surfaces of Ti600 Ti-alloy,an advanced internal combustion engine material,were modified with the NiCr/TiAl coatings synthesized by laser cladding of the mixture of TiAl and NiCr powders with a mass ratio of 3.5:1.0.The microstructures and tribological behavior of the coatings were characterized with X-ray diffraction,scanning/transmission electron microscopy and conventional mechanical probes.The results show that the NiCr/TiAl coatings significantly improved the tribological behavior.To be specific,the NiCr/TiAl coatings,comprising high density of equiaxed grains,dendritic grains and fine-clusters,considerably decreased the wear-rate,reduced the friction coefficient and increased the hardness to 3 times higher than that of the substrate and with an average of 832 HV.Moreover,the top-down hardness depth profile showed a "spike-plateau-valley" curve.The abrasive wear was found to be responsible for the wear mechanism of the NiCr/TiAl coatings.