Effect of Y2O3 Addition on Microstructural Characteristics and Microhardness of Laser-Cladded Ti-6Al-4V Alloy Coating

In this study, the effect of Y2O3 addition on the quality, microstructure, and microhardness of multi track laser cladded Ti 6Al-4V coating using coaxial powder feeding was investigated. These parameters were characterised via dye penetration, x-ray diffractometry, scanning electron microscopy, energy dispersive spectrometry, electron probe microanalysis, microhardness measurements, and ball-on-disc tribometer. It is observed that Y2O3 addition improved the coating quality by completely eliminating the formation of pores in multi-tracked Ti-6Al-4V coatings. The microstructure of the coating without and with Y2O3 primarily consists of acicular martensite (x'-Ti). Furthermore, the continuity of original beta-Ti grain boundary is broken by the introduction of Y2O3. In addition, the Y2O3 is adsorbed and pinned at the original beta-Ti grain boundaries resulting in the refinement of the beta-Ti grains. It is believed that the refinement in the original beta-Ti grains occurs via inhibition of the movement of the grain solid-liquid interface through dragging action. This phenomenon hinders grain growth by acting as a heterogeneous nucleus rather than increasing nucleation rate because it exhibits high lattice misfit degree. Compared with the coating without the Y2O3, the microhardness and wear stability of the Y2O3-supplemented coating was improved because of grain boundary strengthening, fine-grained strengthening, addition of high hardness Y2O3, and elimination of pores.