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

There is a constant drive for improvement of the density of powder metallurgy (PM) steels as they are knownto offer cost-effective solutions for structural applications. Increase in the density of PM steels will expand their use inapplications demanding higher performance than what they deliver today. One of the promising ways to improvedensification is through the utilization of powder mixes with different size fractions. Admixing nanopowder cancontribute to higher sinter-density of compacts having micrometer-sized powder as main constituent, typically used formanufacturing PM steel components. The higher surface to volume ratio of nanopowder is hypothesized to contribute todensification by increasing the inter-particle contact area. This is supposed to enhance the material transport path andimprove 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 weightpercent of nanopowder was varied to help understanding the densification provided by the addition. This mixed powderwas compacted at 800 MPa followed by sintering of up to 1350 \u100107 in pure H2 atmosphere. The sintering behavior wasstudied by means of dilatometry and thermal analysis followed by microstructural and fractographic characterization inorder to elucidate the effect of nanopowder on densification. It was shown that the linear shrinkage increased from 1.5 to2.5% when the nanopowder content was increased from 5 to 15 wt. %. Significant changes during the sintering of thecompacts were observed between 500 to 700 \u100107 due to the nanopowder addition