Formation of different phases and their influences on the mechanical and tribological properties of surface alloyed FeCoCrNiAl particles using PTA technique

Abstract

Titanium alloys (Ti–6Al–4V) are attractive in many industries due to their weight ratio, high thermal stability and corrosion resistance. However, their poor tribological properties limit their usage in many applications. In this work, Fe, Co, Cr, Ni and Al powders are mechanically mixed by ball milling and preplaced on the Ti–6Al–4V substrate. Plasma Transferred Arc (PTA) alloying process is performed to fuse the preplaced powder into the substrate surface. X-ray diffraction (XRD), microstructure and microhardness testing is performed to assess the presence of phases, formation of structure and hardness improvement, respectively. Then, the dry sliding pin-on-disc wear testing is conducted on the substrate and PTA alloyed samples. The various wear mechanism and their corresponding roughness were analysed and discussed. XRD result reveals that the ball milled powder and PTA samples possess BCC and FCC phases. However, BCC phases are formed higher than FCC phases due to rapid cooling and controlled heat input. Moreover, broadened BCC phases are observed in the PTA sample at 27°, 36°, 42°, 54° and 70° than that of the ball milled powder. Microstructure of the PTA sample contains both (Ni, Co) rich inter-dendrite and (Al, Fe, Cr) rich needle like dendrite. The microhardness of PTA region has improved with 2.39 times higher than substrate. The wear resistance of the PTA sample has improved by two times compared to substrate. Abrasive, adhesive and plastic deformation were observed on the worn out substrate while PTA sample showed with mild abrasive wear with reduced roughness. The overall results reveal that the various elements are properly alloyed on the Ti–6Al–4V surface through the PTA process and significantly improved the wear resistance. As a result, the PTA process can be used for alloying of other elements to improve the wear resistance of Ti–6Al–4V substrate.