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    An investigation of stellite-6 alloy containing 5.0 wt% silicon
    (Elsevier Science Sa, 1998) Kuzucu, V; Ceylan, M; Celik, H; Aksoy, I
    Metal microscopy, X-ray diffraction, differential scanning calorimeter and hardness tests were used to examine and analyze the details of the microstructure of a cobalt based alloy with the composition Co-28Cr-5Si-4W-1.1C. The cast sample has a dendritic microstructure. Eutectic carbides such as M7C3, M23C6, M3C2, inter-metallic phases such as mu and sigma phases and some silicon compounds such as CrSi2, WSi2, CoSi2 solidify in the inter-dendritic regions. In the samples cooled in water and liquid nitrogen after annealing, some of the carbide phases and inter-metallic phases disperse in the dendritic grains, their hardnesses being found to be greater than the hardness of the cast sample. In addition, it is seen that the reverse martensitic or ordering transformations occur in the heating regime between 200 and 450 degrees C depending on the heat treatment applied to the samples. (C) 1998 Elsevier Science S.A. All rights reserved.
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    Microstructure and phase analyses of Stellite 6 plus 6 wt.% Mo alloy
    (Elsevier Science Sa Lausanne, 1997) Kuzucu, V; Ceylan, M; Celik, H; Aksoy, I
    The alloy Stellite-6 was cast with 6% Mo. Then, some pieces of this alloy were cooled in water after annealing at 950 degrees C for 2 h. A piece 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 cast, cooled in water and cooled in liquid nitrogen, respectively. In addition to mu, R and sigma phases, it was determined that various metal carbides such as MC, M7C3, M23C6, M6C and some other inter-metallic phases may exist in these samples. It was identified by x-ray diffraction that a phase transformation from alpha phase with fcc (face centered cubic) structure to epsilon phase with hcp (hexagonal close-packed) structure occurred in the sample cooled in water, the amount of the epsilon 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 degrees C) and 1223 degrees C for all of the samples. (C) 1997 Elsevier Science S.A.
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    Phase investigation of a cobalt base alloy containing Cr, Ni, W and C
    (Elsevier Science Sa, 1998) Kuzucu, V; Ceylan, M; Celik, H; Aksoy, I
    A cobalt base alloy with composition Co-27.74Cr-19.27Ni-6.11W-1.1C was cast, some pieces of this alloy being cooled in water and liquid nitrogen after annealing. Metallographic investigations showed that the cast sample had a dendritic microstructure with eutectic carbides solidified in the inter-dendritic regions. In the samples cooled in water and liquid nitrogen, the carbide phases solidified in the inter-dendritic regions in the cast sample dispersed in the dendritic grains, as a result of this dispersion, the dendritic grains becoming smaller and the branches of dendrites becoming thinner. In accordance with these metallographic observations, the hardness measurements showed that the hardness of the samples cooled in water and liquid nitrogen increased according to the cast sample. It was seen from the X-ray diffraction investigations that various carbides such as M7C3, M23C6, M3C2, Co3C, Ni3C, and sigma phase may exist in these samples. In addition, DSC (Differential Scanning Calorimetry) measurements showed that some recovery processes occur in these samples in the heating regime in the temperature region between 238 and 287 degrees C. (C) 1998 Elsevier Science S.A.