Mechanically tailored surface of titanium based alloy (Ti6Al4V) by laser surface treatment

In this study, laser surface treatment (LST) of Ti6Al4V carried out by melting within a narrow regime of optimum process parameters for the formation of a surface with improved wear and tribo-corrosion resistance is presented. The effect of applied power and shrouding gas on the microstructure, phase, surface hardness, residual stress, dry wear (against tungsten carbide, WC) and tribocorrosion resistance (against ZrO2 in Hank's solution) is established. LST in argon atmosphere leads to the formation of a composite structure consisting of acicular alpha' martensite and alpha. LST in nitrogen atmosphere causes the formation of titanium nitride (TiN and Ti2N) dispersed in alpha matrix. Due to LST, there is an increase in surface microhardness both under argon (435-630 VHN) and nitrogen atmosphere (839-1327 VHN) when compared to untreated Ti6Al4V (278 VHN). There is a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17-5.81 x 10-3 mm3/Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91-4.94 x 10-3 mm3/Nm) as compared to Ti6Al4V (5.93 x 10-3 mm3/Nm). The mechanism of wear is established. On the other hand, the tribo-corrosion rate is found to decrease for laser surface melting (3.5-4.8 x 10-3 mm3/Nm) and nitriding (1.3-3.2 x 10-3 mm3/Nm) as compared to Ti6Al4V (5.7 x 10-3 mm3/Nm). Bioactivity in terms of calcium phosphate deposition followed by dipping in Hank's solution was found to increase due to both melting and nitriding, though nitriding offered a marginally higher bioactivity than only melting.