MICROSTRUCTURE AND PHASE ANALYSES OF STELLITE-6 PLUS-6 WT.PERCENT MO ALLOY

The alloy Stellite-6 was cast with 6% Mo. Then, some pieces of this al loy were cooled in water after annealing at 950 degrees C for 2 h. A p iece of the water-cooled samples was cooled in liquid nitrogen again. Later, all of the samples were investigated using metallographic and x -ray diffraction techniques and thermal (DSC and DTA) analysis methods . The hardnesses were also measured as 40, 46 and 49 HRC for samples c ast, cooled in water and cooled in liquid nitrogen, respectively. In a ddition to mu, R and sigma phases, it was determined that various meta l carbides such as MC, M7C3, M23C6, M6C and some other inter-metallic phases may exist in these samples. It was identified by x-ray diffract ion that a phase transformation from alpha phase with fcc (face center ed cubic) structure to epsilon phase with hcp (hexagonal close-packed) structure occurred in the sample cooled in water, the amount of the e psilon phase (martensite phase) increasing in the sample cooled in the liquid nitrogen, and the hardnesses of these samples also increasing. In addition, from the DTA curves it was seen that a second allotropic transformation of cobalt from alpha phase to epsilon phase had taken place in the temperature range between the Curie temperature (1121 deg rees C) and 1223 degrees C for all of the samples. (C) 1997 Elsevier S cience S.A.