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    Influence of the cooling rate on the microstructure of Al-Cu-Si, Al-Si and Al-Zn alloys
    (Elsevier Science Sa Lausanne, 1997) Ceylan, M; Aksoy, I; Kuzucu, V; Balo, SN
    The dendritic microstructures and solidification morphologies of Al-Cu-Si and Al-Si alloy were explored. Phase comparisons of Al-Zn, Al-Si and Al-Cu-Si alloy samples according to their rapid or slow cooling rate were made by using X-ray diffraction techniques, differences in the crystal structures of each alloy sample not being found. From differential scanning calorimetry investigations it was found that the rapidly solidified Al-Cu-Si sample released greater heat energy than the ingot sample of the same alloy, and the rapidly solidified Al-Si and Al-Zn alloys released less heat energy than the ingot samples of the same alloys during the healing regime in a differential scanning calorimeter. (C) 1997 Elsevier Science S.A.
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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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    Investigation of the casting microstructure of a Fe-base, Cr-Ni-Mo duplex alloy
    (Elsevier Science Sa Lausanne, 1997) Ceylan, M; Kuzucu, V; Aksoy, M; Aksoy, I; Kaplan, M; Yildirim, MM
    The microstructures of Fe-base cast duplex stainless steel specimens, which contain Cr, Ni, Mo and other elements and have been subjected to various heat treatments, were examined with X-ray diffraction, thermal analysis and optical microscopy and their hardnesses were also measured. From the metallographic examinations, it was seen that these specimens included austenite, ferrite, some inter-metallic phases, grain boundary carbides and oxide inclusions. It has been determined that the amount of grain-boundary carbides decreased, and second-phases precipitated in ferrite, in specimens annealed at 950 degrees C for 2 h and then cooled in water and liquid nitrogen. In addition it has been found by X-ray diffraction that the heat treatments applied did not change the types of the phases, but caused lattice deformations in the phases. Furthermore, beside ferrite and austenite, Laves, sigma, G, mu, R, chi, Fe3C, Fe3P, FeS2, MnS phases and M23C6, M7C3, M6C carbides were determined to be in the microstructure. DSC (differential scanning calorimeter) curves showed that some stoichiometry compounds of small amounts occurred between 370 and 470 degrees C, and in specimens cooled in liquid nitrogen after annealed at 950 degrees C for 2 h, a phase with a small percentage dissolving at about 310 degrees C. DTA (differential thermal analysis) curves also showed that austenite phase transformed to ferrite phase completely between 1182 and 1220 degrees C. In addition, it was found that the hardness of the specimens were different. (C) 1997 Elsevier Science S.A.
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    Investigation of the microstructures of iron based wrought Cr-Ni-Mo duplex alloy
    (Elsevier Science Sa Lausanne, 1997) Kuzucu, V; Ceylan, M; Aksoy, M; Aksoy, I; Kaplan, M
    Samples of duplex stainless steel, consisting of iron-based Cr-Ni-Mo ahoy containing some other elements undergoing various heat treatments after having been wrought at 1150 degrees C, have been investigated using X-ray diffraction, thermal analysis and metallographic techniques. It is determined that some intermetallic phases such as Laves, mu, G, mu, R, chi, and some carbide phases as such M23C6, M7C3, M6C may be found in these samples and that the ratio of carbide phases decreased in samples annealed at 950 degrees C. In samples cooled in liquid nitrogen, it is seen that some dissolving elements in the matrix have accumulated around the sigma phases and some precipitation phases have occurred. It is concluded that the use of annealing of this material at 950 degrees C affects the chemical, mechanical and other properties adversely. (C) 1997 Elsevier Science S.A.
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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.