Mechanical and tribological analysis of 60NiTi manufactured by Press and Sintering

Abstract

The aim of this study was to determine the feasibility of using Powder Metallurgy (PM) to manufacture components for medical and industrial applications using powdered 60 wt.% nickel and 40 wt.% titanium (60NiTi). More specifically, the effects of particle size and sintering temperature on finished products of pre-alloyed (PA) and blended elemental (BE) 60NiTi powders were investigated. Relatively large powder particles were used for the manufacture of PA samples, with particle size was around ten times greater than those of conventional powders used in PM. Samples were manufactured using Press and Sintering (P&S) followed by mechanical and tribological testing. The performance of the PA 60NiTi samples were then compared with that of conventional or similar materials. Additionally, the phase constituents were identified by microstructural analysis. BE powders were produced using nickel (Ni) and titanium (Ti) powders which were mixed to produce 60NiTi. Once the powders were prepared, they were used for the manufacturing of samples which were then subjected to mechanical testing and microstructural analysis. The mechanical performance of the BE samples was then compared with that of similar materials. From the experiments carried out on the PA 60NiTi samples, it was shown that the powder particle size had a large influence on the finished product manufactured using P&S. Large powder particles resulted in porous samples. As such, this methodology is not appropriate for producing materials with properties suitable for bearing applications, although the Coefficient of Friction (CoF) was found to be adequate when compared to that of 316 stainless steel (a conventional bearing material). Analysis of the BE 60NiTi samples showed that sintering temperature has a large effect on the manufactured sample. It was found that low temperatures resulted in incomplete sintering whereas high temperatures resulted in predominantly Ni-rich areas, both of which are undesirable. The porous structure achieved from large PA 60NiTi powders, although not suitable for bearing applications, is ideal for implants where no bearing load is required. Implants such as femoral stems in hip arthroplasty and tibial components in knee arthroplasty can benefit from porous structures as they allow for bone growth into the porous structures.