The formation of core-rim structures in Fe40Al/(TiC-TiN-WC) cermets produced by pressureless melt infiltration

Ti(CN)-based cermets were produced by pressureless melt infiltration of TiC, TiN, and WC mixed powders by Fe-40 at.% Al iron aluminide intermetallic (Fe40Al). Before infiltration, the powder compacts were pre-sintered at different temperatures for different times in order to form hard Ti(CN)-based skeletons with given values of porosity. A core-rim morphology of the solid particles evidenced under SEM characterizes the microstructure of cermets made from pre-sintered Ti(CN) skeletons infiltrated by Fe40Al The mechanism of the core-rim structure formation was studied using XRD. SEM, TEM, and EDS. This core-rim structure is composed of an almost pure Ti(CN) core surrounded by a bi-layer rim of (Ti, W)(CN) solid solution. However, direct infiltration of as-pressed TiC, TiN, and WC powder mixtures by Fe40Al led to mostly Ti(CN) cermets without core-rim structures. The formation of a (Ti,W)(CN) phase during the pre-sintering step determines the existence of the core-rim microstructure. The Ti(CN) core and the (Ti,W)(CN) inner rim formed at the pre-sintering stage by solid state reaction. while the outer rim was formed during the infiltration stage by the dissolution of (Ti,W)(CN) material from the inner rim and precipitation as a solid solution of low W content. (C) 2004 Elsevier B.V. All rights reserved.