Surface Top Graphology,Corrosion and Microhardness of Oxygen Diffusion Hardened Pure Titanium Alloy TA4 after Laser Surface Melting

In the oxygen diffusion hardened condition,untreated and laser surface melted pure titanium alloy (TA4) by Nd:YAG pulsed laser,are hardened at temperatures of 650 to 700℃ with the end result being a passive,mechanically stable,abrasion resistant oxide ceramic rutile surface layer.The thickness of this surface layer depends on the time,temperature,and the microstructure of the Ti substrate.This paper describes the results of x-ray diffraction analysis,scanning electron microscope (SEM),microhardness measurements,and corrosion resistance measurements of hardened pure and laser treated Ti substrate.The oxygen diffusion hardened titanium alloy after laser surface melted samples (L-TA4) had a more pronounced grain structure and significantly higher roughness values than the untreated pure TA4 (U-TA4)samples.The L-TA4 samples also exhibited at least equivalent corrosion behavior and a definite increase in surface hardness compared to the U-TA4 samples.The results of this work suggest that laser surface melting plays a key role for effective oxygen diffusion hardening at 650-700℃ for pure and laser treated pure Ti alloys.