Water droplet erosion behaviour of gas nitrided Ti6Al4V

• Gas nitriding of Ti6Al4V was achieved at 900 °C and 1050 °C for 5 and 10 h.
• Water droplet erosion performance of nitrided coupons was studied.
• Gas nitriding enhanced the cumulative erosion resistance of Ti6Al4V up to 125%.
• Gas nitriding is more protective at low impact speeds.
• Erosion behaviour is significantly influenced by microstructure.

Ti6Al4V is one of the most commonly used materials for turbine blades and improving its water erosion resistance, a typical reason for the blades' failure, is of great interest. In this work gas nitriding was applied on Ti6Al4V and its influence on water droplet erosion performance was investigated. Nitriding was carried out at 1173 and 1323 K temperatures using two different nitriding atmospheres, N2 and N2–4%H2 for 5 and 10 h. The microstructure of specimens was investigated using optical microscope (OM) and scanning electron microscope (SEM). The phases formed after nitriding treatments were analysed using X-ray Diffraction (XRD). Vickers indenter was used to carry out the surface and profile microhardness measurements. The erosion tests were performed using 464 μm droplets impacting the samples at 300 and 350 m/s speeds. The nitrided specimens at 1173 K, which is below β-transus temperature of Ti6Al4V, displayed the best erosion resistance measured by their corresponding cumulative material loss, about two times higher than non-treated Ti6Al4V. The long exposure to nitriding was not beneficial for the erosion performance. The specimen nitrided in the N2–4%H2 atmosphere showed slightly higher resistance to erosion than those nitrided in N2 atmosphere. The latter is due to the formation of a hard and dense compound layer that was deposited due, in part, to the presence of the reducing environment.