Study for the Development of Fe-NbC Composites by Advanced PM Techniques

Abstract

The development of Fe-based metal matrix composites (MMCs) with high content of hard phase has been approached by combining the use of advanced powder metallurgy techniques like high-energy milling (HEM), cold isostatic pressing (CIP) and vacuum sintering. The most innovative is the use of HEM for the obtaining of a composite powder avoiding the formation of clusters in the microstructure of the sintered material, and the study of hardenability of sintered materials. A 30 % vol. of NbC particles was mixed with Fe powder by HEM in a planetary mill under Ar atmosphere to prevent oxidation. The optimal milling time was determined by sampling every two hours until 10 hours of milling, characterising the powder by the observation of morphology and microstructure by scanning electron microscopy (SEM), and controlling the carbon content by a LECO analyser. Composite powders were compacted by CIP and then sintered in vacuum at temperatures between 1300 °C and 1375 °C, during 30 min and 60 min. The variation of density, hardness and carbon content with sintering temperature and time, besides the microstructural changes observed, permits to find the optimal conditions of processing. Afterwards, a heat treatment study was performed to study the hardenability of the cermet.