PLASMA NITRIDING OF TI-6AL-4V ALLOY TO IMPROVE SOME TRIBOLOGICAL PROPERTIES

The present study was conducted to investigate the tribological and me chanical properties of plasma-nitrided Ti-6Al-4V alloy. Specimens were nitrided in an H-2-N-2 (1:8 ratio) plasma. The nitrogen concentration along the nitrided zone was obtained using the nuclear reaction analy sis technique. The workpiece temperature was varied from 450 to 520 de grees C during the nitriding process. Pin-on-disc wear tests were carr ied out to evaluate the wear properties of the resultant samples and a ball-on-disc experiment was conducted to measure the friction coeffic ient. Microhardness tests, Scanning electron microscopy and X-ray diff raction were carried out to investigate the phases developed in the ni trided zone. It was found that the wear resistance improved considerab ly after the nitriding process. Three distinct layers were identified: (i) an inner layer where delta-TiN + epsilon-Ti2N phases formed, (ii) an intermediate layer where alpha-(TiN) with or without epsilon phase developed and (iii) an outer layer where precipitations were dominant .