MICROSTRUCTURE AND ELEVATED-TEMPERATURE BEHAVIOR OF A SPRAY-ATOMIZED AND CO-DEPOSITED NI3AL/SIC/TIB2 INTERMETALLIC MATRIX COMPOSITE

This paper discusses preliminary results on the microstructure and elevated temperature creep rupture behavior of a spray-atomized and co-deposited Ni3Al composite reinforced with SiC and TiB2 particulates. Microstructural studies suggest that SiC reacts extensively with Ni3Al, leading to the formation of other carbide phases, e.g. Cr3C2. A well-defined interfacial reaction zone, consisting of two distinct layers, was observed at the Ni3Al/TiB2 interface. The layer I consisted of a chromium segregated Ni3Ti phase and the diffusion of nickel was suggested to be the rate control step in this interfacial reaction. The layer II was a nickel-rich Al3Ni-type phase; the formation of it may be related to the decomposition of the TiB2 and the ensuing diffusion of boron. Regarding the elevated temperature behavior of the hot-extruded materials, the monolithic Ni3Al exhibited longer creep rupture lifetimes compared with that for the Ni3Al/SiC/TiB2 intermetallic matrix composite. This behavior was attributed to the formation of cavities around small carbide particles, resulting from the decomposition of SiC particulates.