Plasma nitriding of Ti-6Al-4V alloy to improve some tribological properties

The present study was conducted to investigate the tribological and mechanical properties of plasma-nitrided Ti-6Al-4V alloy. Specimens were nitrided in an H₂-N₂ (1:8 ratio) plasma. The nitrogen concentration along the nitrided zone was obtained using the nuclear reaction analysis technique. The workpiece temperature was varied from 450 to 520°C during the nitriding process. Pin-on-disc wear tests were carried out to evaluate the wear properties of the resultant samples and a ball-on-disc experiment was conducted to measure the friction coefficient. Microhardness tests, Scanning electron microscopy and X-ray diffraction were carried out to investigate the phases developed in the nitrided zone. It was found that the wear resistance improved considerably after the nitriding process. Three distinct layers were identified: (i) an inner layer where δ-TiN + ε-Ti₂N phases formed, (ii) an intermediate layer where α-(TiN) with or without ε phase developed and (iii) an outer layer where precipitations were dominant.