Laser treatment of Ti-6Al-4V alloy prior to plasma nitriding

Ti-6Al-4V alloy suffers from low wear and gall resistance, which in turn limits its use in industrial applications. Laser processing of an alloy surface offers considerable improvement in tribological properties. In the present study, the investigation into surface properties of the duplex treatment (plasma nitriding prior to laser treatment) of Ti-6Al-4V alloy was carried out. Laser treatment was conducted in a nitrogen gas environment, which provided nitrogen diffusion into the substrate. Laser treated workpieces were then plasma nitrided in a plasma nitriding unit operating at -700 V d.c. bias voltage. The surface of the laser treated workpieces was polished before the plasma nitriding process. SEM and XRD were carried out for material characterization and ball-on-disk tests were conducted to measure the friction coefficient of the resulting surfaces. In addition, the microhardness across the workpiece cross-section was measured. It was found that no compound layer at the workpiece surface was observed for the duplex treated workpieces. In this case, the friction coefficient slightly improved as the sliding time progressed. Moreover, no porotic structure and micro-cracks were observed in the surface vicinity after the laser treatment process.