Study on Binder Removal and Green Properties of TungstenCarbide-Nickel Hardmetals Fabricated by Powder Injection Moulding

Abstract

This works aims to investigate the as-injected properties of the tungsten carbide-nickel (WC-Ni) hardmetal powder. Tungsten carbide containing 6wt% nickel blended with a binder mixture of polyethylene glycol (PEG) and polyvinyl butyral (PVB). The powder loadings (the powder to binder mixture ratios) covered 48:52, 50:50 and 52:48 %v/v. The hardmetal powders were initially mixed with PVB in ethanol, followed by PEG, to prepare powder feedstock. Then, the obtained feedstock was injected into a set of steel die at 120-140 oC to get the injected specimens. The green properties, i.e. green strength and density, were examined. Debinding behaviours of PEG by a stagnant water at ambient temperature from 0.5-5 hours were observed. The preliminary study revealed that powder loading governed injection ability as well as injection temperatures. Density of the green specimens depended strongly on powder loading meanwhile the green strength values did not. PEG removal rate of WC-Ni hardmetals were relatively high at the very beginning and became slow with longer debinding times and also affected by powder loadings.