Wear Resistance and Morphological Characterization of High-power Laser Clad Coatings on Ti-6Al-4V Alloy

Abstract

Ti-Si binary coatings were cladded on Ti-6Al-4V alloy surface for improvement morphological orientation, microstructure and surface properties. The coatings were developed at 2.1 kW power, laser scanning speed of 1.2, 1.6 and 2.0 m/min, spot diameter of 3 mm and 0.5 overlap ratio. An optical microscope was used to magnify and analyse the microstructural arrangement and a microhardness indenter used to measure microhardness at 100gf for 10 seconds. The indent spacing was maintained at 100 µm between adjacent indents. The phase content of the coatings was analyzed with XRD technique. The coating wear resistance was tested at 10N force loading for 7 minutes using a TRB tribometer and characterized using SEM. Clad coatings were observed to exhibit refinement in microstructure with an increase in laser scanning speed where transformation occurred from equiaxed grains with localized smaller grains to refined grain structure. The highest degree of refinement was observed at 2.0 m/min scanning speed. It was also found that the microhardness property was improved by 2.44, 2.60 and 2.64 times the microhardness of Ti-6Al-4Vat 342.3 HV0.1. It is understood that high microhardness values favor improved wear resistance behavior. XRD analysis on the coatings revealed presence of Ti5Si3, Ti, Si and TiSi2 phases where Ti and Si are in matrix capacity and Ti5Si3 and TiSi2 present as intermetallic phases. The reported improvement in microhardness was attributed to the presence of Ti5Si3 and TiSi2. The action of the laser scanning speed was found to influence the clad height where an increase in laser scanning speed resulted in a decrease in clad height in the order 685.9, 491.4 and 291.5 µm for 1.2 m/min, 1.6 m/min and 2.0 m/min respectively. Wear test indicated that the coatings displayed an improved wear resistance by evidence of little material removal exhibited, compared to the substrate material which was dilapidated by severe adhesive wear and further aggravated by plastic deformation.