Saddle field fast atom beam source: A new low pressure plasma nitriding method for a alloy Ti–6Al–4V

Abstract

Ti and its alloys (Ti–6Al–4V) have been used in different engineering applications due to their several outstanding properties. Nevertheless, their use in practical applications is limited in many cases due to their poor tribological property. Researches are ongoing on surface modification of Ti based materials by different plasma and ion based techniques to overcome this problem. However, the conventional plasma nitriding techniques have several problems such as formation of an arc, increased possibility of surface contamination due to a comparatively higher operating pressure, production of a very thin nitrided layer after a long processing time, etc. In this present work, the possibility of a new low-pressure plasma nitriding process using a Plasma Enhanced Chemical Vapor Deposition (PECVD) based saddle field fast atom beam source on a Ti–6Al–4V alloy sample is investigated. Plasma nitriding was carried out at 900 °C and at a pressure 0.1 Pa for 8 h by using a beam current 0.5 A. Optical Microscopy investigation of the cross-section of the nitrided sample revealed a compound nitrided layer (thickness approximately 16 μm) followed by a diffusion layer. X-Ray Diffraction (XRD) analysis confirmed the presence of a TiN phase in the nitrided layers. A roughly three fold higher hardness value (1578 HV 0.015) in the top nitriding layer was observed by Vickers microhardness testing compared to hardness value of untreated sample (568 HV 0.015),with a gradually decreasing hardness in the core material. The results show that this is a promising method for low pressure plasma nitriding of Ti alloy within a short processing time compared to the conventional nitriding process.