Effect of Powder Loading on Rheology and Dimensional Variability of Porous, Pseudo-Elastic NiTi Alloy Produced by Metal Injection Moulding (MIM) Using a Partly Water Soluble Binder System

摘要

An alternative powder metallurgy route for producing porous NiTi alloy by metal injection moulding (MIM) of elemental Ni and Ti powders is being investigated. This alloy shows pseudo-elastic and shape memory behaviour. Using an atomic ratio of 50.9% Ni, three feedstock batches with different powder loadings ranging from 65.5vol% and 69.5vol% were prepared. The binder used was a partly water soluble system, comprising polyethylene glycol (PEG), polymethyl methacrylate (PMMA) and stearic acid (SA) with a mass ratio of 83/15/2. Rheological analysis was carried out at different temperatures and shear rates in order to investigate the homogeneity and flowability of the mixture. Cylindrical parts were moulded, water leached, to remove the PEG component of the binder, heated in Argon to remove the residual PMMA binder component and sintered at 1250°C for 1 hour in vacuum. The effects of powder loading on the as-sintered properties such as impurity content, dimensional variability, porosity, microstructure and compression behaviour are presented and discussed.