NiTi is categorized as a Shape Memory Alloy (SMA) that has been commercially studied and used in biomedical industry due to two main unique properties, Pseudoelastic (PE) and Shape Memory Effect (SME). Combined with biomimetic properties to human bone, NiTi has the potential to be applied as implants by engineered manufacturing process. The common manufacturing by casting has some challenges in order to obtain intrinsic and miscellaneous design of NiTi parts leash to explore more using powder metallurgy (PM) method that expected to get the porous structure. This paper aims to provide an overview of processing NiTi by conventional PM method which could contribute in focusing porous part that suits for biomedical and implants.

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.

The success of metal injection moulding (MIM) process is significantly influenced by the homogeneity level of the powder-binder mixture (feedstock). This paper highlights some initial characterization of the feedstock containing elemental Ni and Ti powders mixture, (50.8 at.% Ni/ 49.2 at.% Ti) mixed with Palm stearin-based binder system. The feedstock was prepared using an internal mixer, HAAKE Rheomix at a temperature of 160°C for 2 hours. The feedstock was then characterized by Differential Scanning Calorimetry (DSC), Thermogravimetric (TGA), Scanning Electron Microscopy (SEM) and Capillary Rheometer. All the results obtained were analyzed and discussed for further injection moulding process.

This paper presents the processing of Nickel Titanium (NiTi) alloy from elemental powders of Nickel and Titanium by conventional powder metallurgy process. Two batches of feedstock containing 2 different formulations (1) Ti-50.4at% Ni and (2) Ti-50.8at% Ni were prepared. The feedstocks for each composition were warm-pressed and subsequently sintered in vacuum at 1150°C. Based on the XRD result, it clearly showed that the conventional sintering following warm-press method is promising in producing greater amount of the predominant NiTi (B2) phase and a minor fraction of martensitic NiTi (B19’) phase. The reversible phase transformation and the microstructure of the sintered samples have also been observed and discussed.

This paper highlights the influence of Ni-Ti ratio on the phase constituents, the reversible austenite-martensite transformation and mechanical properties produced by metal injection molding (MIM). The binder system used was mainly palm stearin with minor fraction of polyethylene. Injection moulding was done successfully at 130˚C to form tensile shape samples. It was followed by solvent extraction,  thermal debinding at 500oC and subsequently sintered in high vacuum at 1100˚C. The result showed that as the Ni content increased, the fraction of austenite phase also increased owing to greater fraction of transient liquid phase formation during the sintering, thus improved the mechanical tensile properties. However, the reversible austenite to martensite phase transformation temperatures (PTTs) seemed to be broadened with increased Ni content due to formation of metastable R-phase.