Enhancing surface integrity of titanium alloy through hybrid surface modification (HSM) treatments

The current study investigates the development of a novel hybrid surface modification (HSM) technique to improve the surface integrity of Ti-6Al-4V alloy. The approach combines the mechanical shot peening (SP) and the deposition by Physical Vapour Deposition (PVD) of a tungsten-doped diamond-like carbon coating (WC/C) on Ti-6Al-4V surfaces. The mechanical shot peening induced high surface roughness increasing the metallurgical bonding sites for the PVD deposition, whereas mainly the grain growth during the deposition, was successfully eliminated. The mechanical SP process induced the high strain lattice misorientations evident for increasing the dislocation density in the crystalline structure. The Electron Backscatter Diffraction (EBSD) results suggest that subjecting the SP specimens to a temperature of 240 degrees C for more than 3 h during coating deposition, results in a reduction of dislocation densities, presumably as a result of dislocation annihilation by heat-activated dislocation mobilisation. Hence, the presented Grain Orientation Spread maps suggest that some degree of macro and micro stress relaxation may have occurred during the coating deposition treatment. Further, the Raman spectroscopy confirms the existence of beneficial compressive residual stresses on both PVD and hybrid (HY) coated surfaces. Comparatively, the HY surfaces show a high hardness of 12.08 GPa and high elasticity indices (H/E ratios) of 0.1.

Automated summary

The current study investigates a novel hybrid surface modification technique to improve the surface integrity of Ti-6Al-4V alloy. Mechanical shot peening and physical vapour deposition were combined to create a tungsten-doped diamond-like carbon coating on the alloy surfaces. The mechanical shot peening increased surface roughness and improved bonding sites for the deposition process, while minimizing grain growth. The study found that subjecting the specimens to a specific temperature during coating deposition reduced dislocation densities and resulted in stress relaxation.