XRD and XPS studies of surface MMC layers developed by laser alloying Ti6Al4V using a combination of a dilute nitrogen environment and SiC powder

Using a continuous-wave CO2 laser, surface engineering of a Ti-6Al-4V alloy through a combined treatment of laser nitriding and SiC preplacement was undertaken. Under spinning laser beam conditions, a surface alloyed / metal matrix composite (MMC) layer over 300μm in depth and 24mm wide was produced in the alloy by the overlapping of 12 tracks. Microstructural and chemical changes were studied as a function of (a) depth in the laser formed composite layer and (b) of the track position. Using X- ray diffraction (XRD) and X-ray photospectrographic (XPS) techniques, it was shown that the composite layer contained a complex microstructure which changed with depth. At the surface, a non-stoichiometric, cubic TiNx solid solution ( possibly a carbonitride) containing C and Si , where x ≈ 0.65-0.8, was prominent, but was replaced by α′-Ti with increasing depth to 300μm. TiC phase was also identified, and the presence of TiN0.3 and Ti5Si3 phases considered a distinct possibility. 1