Tungsten Inert Gas Surface Alloying of Commercial Purity Titanium (CP-Ti) with Fe-C-Si Ternary Mixtures

Abstract

Surface modification by means of alloying is a vital process to improve the performance of a material surface which is subjected to wear and corrosion environments without altering the bulk properties. In this study, the surface of commercial purity-titanium (CP-Ti) material was alloyed using pre-placed powder mixture of iron, silicon and carbon at different weight ratios under TIG torch melting technique. The effects of energy input (1080 and 1350 J/mm) in TIG torch on the melt geometry, topography, microstructure and hardness were examined. The results showed that the TIG torch produced melt pools geometry with hemispherical in shape and different geometrical dimensions. Pores were seen to be concentrated at the edges where low melting energies are prominent to entrapped escaped gases upon fast melt solidification. The melt layers with the 1350 J/mm consisted of armed typed of TiC precipitation in the presence of longer solidification time. The sizes of dendrites observed at energy inputs of 1350 J/mm was found to be greater in population and larger in the middle of the melt pool compared to the energy input of 1080 J/mm. The alloyed layer exhibited a maximum hardness of ~ 810 HV which is about 4 times greater than the base hardness of 200 HV. The high hardness observed at particular areas is attributed to the higher population and larger sizes of dendritic microstructure produced using 1350 J/mm TIG arc source compared to 1080 J/mm which was dominated by lesser precipitated TiC resulting lower hardness values in the melt pool. Keywords: Surface modification; TiC; TIG; dendrites; microhardness