XRD and XPS studies of surface MMC layers developed by laser alloying Ti–6Al–4V using a combination of a dilute nitrogen environment and SiC powder

Abstract

Using a continuous-wave CO 2 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 300 μm in depth and 24 mm 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 TiN x 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 300 μm. TiC phase was also identified, and the presence of TiN 0.3 and Ti 5Si 3 phases considered a distinct possibility.