Abstract
Though press and sinter powder metallurgy (PM) steel offers cost-effective solutions for structural applications, there is a constant drive for improvement in their density. Addition of nanopowder to 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 densification behavior. 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 activation energy for sintering decreased with an increase in nanopowder content. This is reflected in the values of work of sintering.
Highlights
To manufacture structural components through powder metallurgy (PM), the press and sinter route has been shown as a cost-effective solution for large volume production
The micrometre sized base powder used were of two kinds; irregularly shaped and correspondingly coarser water-atomized iron powder and finer carbonyl iron powder, while pure nanopowder with particle size of maximum 100 nm was studied as sintering aid
The densification parameter increased with increasing nanopowder content; attributed to the dense grain boundary network promoted by the nanopowder sintering resulting in enhanced densification
Summary
To manufacture structural components through powder metallurgy (PM), the press and sinter route has been shown as a cost-effective solution for large volume production. Its addition can contribute to high interparticle friction decreasing the packing density, and together with agglomeration, inducing defects in green components [5]. Owing to these factors, not many studies have been devoted to exploring the efficacy and impact of nanopowder addition in press and sinter of water atomized powder steel. The authors have studied the influence of addition of nanopowder to micrometre-sized water atomized iron powder in detail elsewhere [6], whereby it was shown that the nanopowder showed shrinkage at temperatures as low as 500 °C. The fractographic analysis on the compacts that were sintered at temperatures like 500 and 700 °C, revealed that the nanopowder in a bimodal powder compact showed no signs of sinter bonding at 500 °C, while significant sinter bond necks had formed at 700 °C
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