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.

Filament extrusion-based additive manufacturing of NiTi shape memory alloys

“…The relatively small shape memory effect reported in this work might be due to severe uptake of oxygen and carbon during sintering at the high temperature of 1290 °C. Typically, lower sintering temperatures are used [60,62,79].…”

Fabrication of nickel-titanium-iron shape memory alloys by powder metallurgy route and analyses of their physical and mechanical behaviour

“…(2) In the solid state technique, the final shape is obtained by powder metallurgy route, and this technique is beneficial due to its simple procedure and low processing cost [19]. The other solid-state methods include selective laser melting [20][21][22], conventional sintering [23], microwave sintering [24], self-propagating high-temperature synthesis [25], spark plasma sintering [26] and metal injection molding [27]. The problem of the liquid state over solid processes is: (1) segregation or extensive grain growth, (2) Not fulfilling the exact composition requirements, and difficulty in manufacturing the complex shapes [28].…”