Effects of replacing metal powder with powder space holder on metal foam produced by metal injection moulding

Porous metal has a high strength-to-weight ratio and can be produced by various methods. Powder metallurgy using a powder space holder, which is one of the metal foam fabrication techniques, can produce complex parts with a well-controlled foam structure. This work employed the metal injection moulding method with the use of a powder space holder, which was PMMA. The volume fraction of PMMA was varied from 0% to 50% to replace the metal volume fraction, while the binder volume fraction was kept constant. The results show that when more PMMA is added, the mixture of metal powder, binder and PMMA has higher wettability and became less viscous and more difficult to mix effectively and to inject. In addition, there were two competing shrinkages during sintering, which were the shrinkage due to the consolidation of the powder during sintering, which was always present, and the shrinkage of the foam structure after the power spacer was removed, which was a function of the volume fraction of PMMA. All results can be divided into two regions, which are the first region (0–35% PMMA) and the second region (35–50% PMMA). In the first region, as the volume fraction of PMMA increased, the sintered density and mechanical properties decreased, and the porosity per area decreased. For the second region, the sintered density and mechanical properties improved and the porosity per area increased as more PMMA was added. The original shape of the parts could not be retained in the second region. Microstructural observations supported these findings.