In this work, powder metallurgy is used to design new duplex composite stainless steels, aiming at a good compromise between ductility, mechanical properties and corrosion resistance. For this purpose, austenitic and ferritic stainless steel powders (a ductile 316L and a corrosion resistant 410L respectively) were mixed and then sintered by spark plasma sintering (SPS). The SPS process consists in pressing the powder between two punches enclosed in a matrix while heating by Joule effect using a pulsed direct current[1]. The originality of this study is that the characteristic size of each phase will be the one of the initial powder particles, larger than that of the metallurgical grains usually observed in duplex steels elaborated by conventional methods.
Seven powder mixtures with weight proportions of 100%, 90%, 75% and 50% for each material were elaborated. The microstructures of the initial powders and of the sintered materials were characterized by optical microscopy and SEM. The phases were identified by XRD and quantified by the Rietveld method. Morphological characterisations were completed by EDX and EBSD to reveal the distribution of the phases, as well as their orientation. In parallel, dilatometry measurements were performed to help understanding the phase transformation mechanisms and diffusion phenomena. Due to the differences in chemical compositions between the two powders, significant diffusion occurs at the austenite/ferrite interfaces during sintering, which influences the final microstructure of the duplex material[2].
Based on the first results, some powder mixtures were selected and sintered by hot isostatic pressing (HIP). During HIP, the encapsulated powder is consolidated by applying an isostatic pressure with an inert gas, typically argon, at high temperature. One of the advantages of HIP over SPS is the possibility to sinter larger and more complex parts. On the other hand, the process takes more time (several hours compared to several minutes for SPS). The present work was completed by a comparative study of the samples elaborated by SPS and HIP to evaluate the influence of the change in time scale on the diffusion phenomena and the final microstructure.

[1]    P. S. Ninawe, S. Ganesh, P. Sai Karthik, S. B. Chandrasekhar, R. Vijay, Advanced Powder Technology. 2022, 33 (6), 103584.
[2]    M. Campos, A. Bautista, D. Cáceres, J. Abenojar, J. M. Torralba, Journal of the European Ceramic Society. 2003, 23 (15), 2813–2819.