Electromagnetic field assisted sintering techniques (FAST) demonstrated the possibility to minimize the grain growth, obtaining, at the same time, final densities near to the theoretical ones. Besides the high speed of the process, this can be ascribed also to a series of phenomena, like electromigration, the local increase of the diffusion coefficient or the action of ponderomotive forces. Very soon, among these techniques, microwave (MW) assisted sintering reached a strong experimental evidence of accelerated densification, lower porosity and achievement of peculiar microstructuresin the final products, including metal-based ones [1, 2].

In this work, nanostructured stainless steel powders, obtained by high energy milling have been uniaxially pressed in order to obtain 20 mm diameter cylindrical compacts. Microwave sintering of the green compacts has been performed in a single mode microwave applicator, at 2.45 GHz.

Maximum sintering temperature of each sample, monitored using a sapphire optical fibre, was varied in the 900-1150 °C range. Microwave forward power was varied accordingly, in order to maintain sintering times in the 120- 500 seconds range.

Rapid microwave sintering helps maintaining the nanostructure, despite a non homogenous densification due to the uneven electromagnetic field distribution in the single-mode applicator. A more homogenous multi-mode applicator, as well as the samples movement during sintering helped increasing the homogeneity and simultaneously sintering multiple green parts. Numerical simulation of the electromagnetic field distribution inside the multi-mode applicator allowed to select the best experimental conditions in terms of samples homogeneity and energy efficiency. 

References

[1] R. Roy, D. Agrawal, J. Cheng, S. Gedevanishvili, Full sintering of powdered metal bodies in a microwave field, Nature 399, 1999, 668-670.

[2] C. Leonelli, P. Veronesi, L. Denti, A. Gatto, L. Iuliano, Microwave assisted sintering of green metal parts, J. Mater. Proc. Technol. 205, 2008, 489-496.

1. PRESENTATION: Microwave sintering of nanosctructured metallic powders, PDF document, version 1.5, 1.3MB
2. CV: Note about author(s): Cristina Leonelli, Roberto Rosa, Paolo Veronesi, PDF document, version 1.5, 0MB

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