Phase evolution and microstructure characteristics of ultrafine Ti(C,N)-based cermet by spark plasma sintering

Abstract

Ultrafine Ti(C,N)-based cermet was prepared by spark plasma sintering (SPS). Experimental examination of phase evolution and microstructural characteristics with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected electron diffraction (SED) at temperature ranging from 1050 to 1430 °C were performed in comparison with conventional vacuum sintering (CVS). It was found that SPS remarkably accelerated phase transformation and decreased the end temperature of some phase transformations. At sintering temperature above 1200 °C, WC and Mo were completely dissolved as well as oxides of TiO 2 and WO 3 were effectively reduced. Of which TiO 2 could not be completely remove in a short span of sintering time. The remainder TiO 2 was presented in form of large blocky grain. TiN was dissolved in TiC with extremely rapid rate below 1200 °C and disappeared above 1200 °C. At a very low sintering temperature denitrification had occurred with a lot of nitrogen loss. Above 1350 °C a new graphite phase was formed with band-like grain distribution and penetrated throughout several Ti(C,N) grain. The prepared ultrafine Ti(C,N)-based cermet with mean grain size of 0.42 μm exhibited typical core-rim surrounding structure. The inner rim phase occupied a relatively great volume fraction related to core and outer rim phases. The well developed inner rim phase resulted in grain growth.