Sintering of bimodal micrometre/nanometre iron powder compacts - A master sintering curve approach

Though press and sinter\ua0powder metallurgy\ua0(PM) steel offers cost-effective solutions for structural applications, there is a constant drive for improvement in their density. Addition of\ua0nanopowder\ua0to the conventional micrometre-sized metal powder is explored to improve the sinter density. In this study, the effect of nanopowder addition in varying amounts has been studied. Carbonyl iron powder (<5 μm) and water atomized iron powder (<45 μm) were used as the base powder to which varying amounts of iron nanopowder (<100 nm) was added. Dilatometric sintering studies under pure hydrogen atmosphere were carried out to analyze the\ua0densification\ua0behavior. The results revealed that the bimodal powder mixture containing 25% nanopowder exhibited the highest green density for both carbonyl and ASC 300 compacts. Master sinter curve for compacts was developed based on the dilatometer data. The apparent\ua0activation energy\ua0for sintering decreased with an increase in nanopowder content. This is reflected in the values of work of sintering