Abstract
A promising method of improving the densification of powder metallurgical steel components is to blend nanopowder with the otherwise typically used micrometre-sized powder. The higher surface-to-volume ratio of nanopowder is hypothesized to accelerate the sintering process and increase the inter-particle contact area between the powder particles. This is supposed to enhance the material transport and improve the densification. In the present investigation, water-atomized iron powder (− 45 μm) was mixed separately with pure iron and low-carbon steel nanopowder, each at a ratio of 95 to 5 pct. These powder mixes were compacted at different pressures (400, 600 and 800 MPa) and then sintered at 1350 °C in a pure hydrogen atmosphere. The sintering behavior of the powder blend compacts was compared to that of the compact with micrometre-sized powder only. Densification commenced at much lower temperatures in the presence of nanopowder. To understand this, sintering at intermittent temperatures such as 500 °C and 700 °C was conducted. The fracture surface revealed that the nanopowder was sintered at between 500 °C and 700 °C, which in turn contributed to the densification of the powder mix at the lower temperature range. Based on the sintering experiments, an attempt was made to calculate the activation energy and identify the associated sinter mechanism using two different approaches. It was shown that the first approach yielded values in agreement with the grain-boundary diffusion mechanism. As the nanopowder content increased, there was an increase in linear shrinkage during sintering.
Highlights
THE press and sinter route offers cost-effective solutions in the manufacturing of powder metallurgical (PM) steel components for structural applications
There is a constant drive to improve the density of PM steel, which expands its usage in applications demanding higher performance than what it currently delivers
The process of so-called solid-state sinter occurs at temperatures below the melting point of the particles, and the properties of the product are a direct function of the sinter neck development and the degree of SWATHI K
Summary
THE press and sinter route offers cost-effective solutions in the manufacturing of powder metallurgical (PM) steel components for structural applications. 4890—VOLUME 51A, SEPTEMBER 2020 densification.[1] Understanding sintering is important, because the performance of the component largely depends on this process. This largely depends on the sintering temperature and particle size. Surface diffusion mechanisms for material flow facilitate neck formation between the metal particles, whereas bulk diffusion mechanisms are required for the densification of the component.[2] Densification is accomplished by increasing the temperature of the powder compact to enable material transport. The metal particles change their morphology to reduce the total energy of the system This has been explained at both a coarse and fine scale. Grain growth or coarsening occurs during the final stage of sintering as the temperature is sufficient to drive the coarsening process.[3] A promising method of improving densification is the use of bimodal mixes.
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