Laser gas oxidizing of titanium surface in a dilute oxygen environment

Abstract

Titanium has attracted considerable attention for applications in several industries owing to its low density and high tensile strength ; however, its poor surface hardness and wear rate limit these applications. This study aims to improve the mechanical properties of the titanium surface. A new surface modification process for titanium is proposed, wherein Ar is used to dilute O 2 and laser gas oxidizing is performed on the titanium surface in this dilute O 2 environment. The feasibility of this process was verified at different O 2 /Ar gas flow ratios. The evolution of the molten pool generated by laser irradiation was analyzed using a high-speed camera combined with a welding glass filter. The surface and cross-section of the modified layer were observed by scanning electron microscopy and X-ray diffraction to study its forming characteristics. The microhardness was characterized, and friction and wear tests were carried out to study the properties of the modified layer. The experiments proved that diluting O 2 with Ar can reduce the rate of the reaction between O 2 and titanium and enhance the process controllability; therefore, laser gas oxidizing of the titanium surface in a dilute O 2 environment is feasible. The O 2 to Ar gas flow ratio significantly affected the process controllability, as well as the surface roughness , number of cracks, microhardness, and wear resistance of the modified layer. With a moderate O 2 to Ar gas flow ratio, optimal formation and performance of the modified layer can be achieved. The oxygen content and hardness below the modified layer were lower than those of the modified layer; however, they higher than those of commercially-pure titanium. • Diluting O 2 with Ar reduces Ti oxidation rates and enhances process controllability. • Laser gas oxidizing of Ti surfaces in dilute O 2 is practically feasible. • Moderate O 2 to Ar gas flow ratios are best for modified layer performance. • Hardness and O content below modified layer are higher than in commercial titanium.