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

• Published in: Materials chemistry and physics 2022-03, Vol.279, p.125768, Article 125768
• Main Authors: Zammit, Ann, Attard, Marlon, Subramaniyan, Prabhakaran, Levin, Sebastian, Wagner, Lothar, Cooper, Jack, Espitalier, Laurent, Cassar, Glenn
• Format: Article
• Language: English
• Subjects: Coating; Compressive properties; Compressive residual stress; Crystal dislocations; Diamond films; Diamond-like carbon; Diamond-like carbon films; Dislocation density; Dislocation mobility; Electron backscatter diffraction; Grain growth; Grain orientation; Integrity; Metallurgy; Microstructure; Nanohardness; Physical vapor deposition; PVD coating; Raman spectroscopy; Residual stress; Shot peening; Strain; Stress relaxation; Surface roughness; Titanium alloy; Titanium alloys; Titanium base alloys; Tungsten carbide
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2022.125768

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 °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. •Hybrid surface enhancement technique to improve the wear and fatigue properties.•Surface and near-surface hardening following the hybrid surface modification (HSM).•Observation of lattice misorientation and higher dislocation density after peening.•Average grain size on the surface after hybrid treatment reduced to less than 5 μm.•Raman spectroscopy results indicates beneficial surface compressive residual stress.