The effect of selected laser beam micromilling parameters on the surface layer structure of High Velocity Oxygen Fuel sprayed WC-CoCr coating

Abstract

The effect of laser beam micromilling on the surface layer structure of High Velocity Oxygen Fuel (HVOF) sprayed WC-CoCr coating was investigated. The carbide layer was HVOF sprayed onto flat test samples made of austenitic stainless steel, AISI 316Ti. Ultra fine-grained WC-CoCr (86/10/4) powder, particle size 10 μm, was used for coat spraying application. The surfaces of test pieces were ground and polished after spraying. Then surface ablation was carried out by micromilling pre-set rectangular-shaped recesses with a nanosecond Master Oscillator Power Amplifier pulsed fiber laser. The experiment was planned using the Taguchi method (L9 33 orthogonal array). The process parameters examined were: laser power, pulse duration and laser beam scanning speed. Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy, X-ray Diffraction phase analysis and 3D profilometry were used to evaluate structural changes. The effect of ablation process parameters (laser work parameters) on the treated coating surface condition, removed layer depth, surface roughness after the ablation process and treated coat phase composition was analysed. It was demonstrated that scanning speed reduction and laser pulse duration increase caused the increase of removed material layer thickness at a single beam pass. It was noted that laser treatment resulted in W2C carbide formation on the treated WC-CoCr coating surface and molten material accumulated at the edges of the openings bored affecting their shapes and topography.