Influence of Iron Nanopowder Addition on Sintering of Water Atomized Iron Powder

Paper in proceeding, 2018

There is a constant drive for improvement of the density of powder metallurgy (PM) steels as they are known
to offer cost-effective solutions for structural applications. Increase in the density of PM steels will expand their use in
applications demanding higher performance than what they deliver today. One of the promising ways to improve
densification is through the utilization of powder mixes with different size fractions. Admixing nanopowder can
contribute to higher sinter-density of compacts having micrometer-sized powder as main constituent, typically used for
manufacturing PM steel components. The higher surface to volume ratio of nanopowder is hypothesized to contribute to
densification by increasing the inter-particle contact area. This is supposed to enhance the material transport path and
improve the densification. In the present investigation, nanopowder (40-60 nm) was added to water atomized iron powder
(-45 μm). This approach was to study the influence of nanopowder addition on the sintering of iron powder. The weight
percent of nanopowder was varied to help understanding the densification provided by the addition. This mixed powder
was compacted at 800 MPa followed by sintering of up to 1350 􀄇 in pure H2 atmosphere. The sintering behavior was
studied by means of dilatometry and thermal analysis followed by microstructural and fractographic characterization in
order to elucidate the effect of nanopowder on densification. It was shown that the linear shrinkage increased from 1.5 to
2.5% when the nanopowder content was increased from 5 to 15 wt. %. Significant changes during the sintering of the
compacts were observed between 500 to 700 􀄇 due to the nanopowder addition.