Formation of surface layers on Ti-6Al-4V titanium alloy by laser alloying

This paper presents the results of the laser surface treatment of Ti-6AI-4V two phase titanium alloy. It was carried out in order to modify the microstructure and properties of the alloyed zone. Laser treatment was performed on samples coated by graphite and BN powders in stream of nitrogen in order to form martensitic phase, titanium nitrides, titanium carbides and borides as a consequence of the laser irradiation. The laser melted zone was examined and its microstructure and phase composition were determined. Microstructural analysis was carried out using Epiphot 300 optical microscope and Novascan 30 scanning electron microscope equipped with an EDS X-ray detector for compositional analysis. The phases were identified by X-ray diffractometry (Philips) with CuK alpha radiation. The Vickers microhardness under the load of 1.96 N and thermoelectric power were measured on the surface of cross-sections. The high hardness level (920-570 HV1.96) can be attributed to the formation of TiN, TiC and TiB phases. The laser melted zone displays ductile fracture.