MICROSTRUCTURE AND FRACTURE TOUGHNESS OF FeNiCr-TiC COMPOSITE PRODUCED BY THERMITE REACTION

The microstructures of the FeNiCr-TiC composite produced by the rapid solidification thermite process were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The effects of aging treatment on the microstructure and fracture toughness of the composite were examined. Results showed that the FeNiCr-TiC composite was composed of ferrite (alpha-FeNiCr), TiC and NiAl (beta phase). TiC particles in the matrix were in the shape of polygon and uniformly distributed, and their size was less than 3 mu m. The beta phase was coherent with the ferrite matrix, and its average size was about 50 nm. The fracture toughness of composite was 22 MPa center dot m(1/2) without aging. When the aging temperature was below 600 degrees C, the fracture toughness of the composite had higher plateau values and reached the maximum of 32 MPa center dot m(1/2) at aging temperature 500 degrees C due to the precipitation of NiAl phase on the nanometer scale. The fracture toughness decreased rapidly aged at 650 degrees C, and then kept homology value in the range of 700 to 900 degrees C, which was attributed to the precipitation of needle-shaped carbide (Cr/Fe)(7)C(3) at the grain boundaries.