Shape Memory Behaviour of NiTi Alloy Produced by MIM Using Palm Stearin Based Binder

Abstract

In this present work, NiTi alloy has been successfully produced by metal injection moulding (MIM) starting with elemental powders mixture of Nickel (Ni) and Titanium (Ti) mixed with a composite binder of palm stearin (PS) and polyethylene (PE). Two different atomic fractions of Ni-Ti were investigated; 50-50 and 50.8-49.2 and the powder loading used was 65.5vol%. The green parts were successfully injection moulded at an optimum temperature of 130°C. The samples were then underwent solvent extraction using n-heptane solution to remove the primary binder of PS. It was followed by thermal debinding to completely remove the backbone binder of PE and subsequently sintered in high vacuum at 1050°C to allow diffusion of the elemental Ni and Ti powders to form NiTi alloy. The phase constituents of the sintered specimens were characterized by X-Ray Diffraction (XRD) and by Scanning Electron Microscopy (SEM), equipped with EDX analysis under back-scattered electron (BSE) mode. The reversible austenite to martensite phase transformation temperatures (PTTs) correspond to shape memory effect (SME) was determined by Differential Scanning Calorimeter (DSC) with heating and cooling cycle in the range of-50 and 200°C. The influence of Ni-Ti ratio and the processing conditions on phase constituents and SME was then analyzed and discussed.