Mehmet Ceylan

Microstructure and phase analyses of Stellite 6 plus 6 wt.% Mo alloy

Abstract The alloy Stellite-6 was cast with 6% Mo. Then, some pieces of this alloy were cooled in water after annealing at 950°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 μ, R and σ 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 α phase with fee (face centered cubic) structure to ϵ phase with hcp (hexagonal close-packed) structure occurred in the sample cooled in water, the amount of the ϵ 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 α phase to ϵ phase had taken place in the temperature range between the Curie temperature (1121°C) and 1223°C for all of the samples.

Phase investigation of a cobalt base alloy containing Cr, Ni, W and C

Abstract 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 σ 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°C.

An investigation of stellite-6 alloy containing 5.0 wt% silicon

Abstract 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 M 7 C 3 , M 23 C 6 , M 3 C 2 , inter-metallic phases such as μ and σ phases and some silicon compounds such as CrSi 2 , WSi 2 , CoSi 2 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°C depending on the heat treatment applied to the samples.

Investigation of the casting microstructure of a Fe-base, CrNiMo duplex alloy

Abstract 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°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, σ, G , μ, R , χ, Fe 3 C, Fe 3 P, FeS 2 , MnS phases and M 23 C 6 , M 7 C 3 , M 6 C 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°C, and in specimens cooled in liquid nitrogen after annealed at 950°C for 2 h, a phase with a small percentage dissolving at about 310°C. DTA (differential thermal analysis) curves also showed that austenite phase transformed to ferrite phase completely between 1182 and 1220°C. In addition, it was found that the hardness of the specimens were different.

Influence of neutron irradiation on the characteristics of Cu–13%wt.Al–4%wt.Ni shape memory alloy

Abstract Unirradiated and neutron irradiated Cu–13%wt.Al–4%wt.Ni shape memory alloy, SMA, were investigated by differential scanning calorimetry, DSC, and electrical resistivity changes, ERC, measurements, X-ray diffraction, XRD and optical microscopy methods. The forward and reverse temperatures of martensite⇔austenite phase transformation decreased and transformation enthalpies increased after the neutron irradiation of samples. Some changes in the lattice parameters and surface morphologies of sample were also seen after neutron irradiation.

Investigation of the microstructures of iron based wrought CrNiMo duplex alloy

Abstract Samples of duplex stainless steel, consisting of iron-based CrNiMo alloy containing some other elements undergoing various heat treatments after having been wrought at 1150°C, have been investigated using X-ray diffraction, thermal analysis and metallographic techniques. It is determined that some intermetallic phases such as Laves, σ, G, μ, R, χ, 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°C. In samples cooled in liquid nitrogen, it is seen that some dissolving elements in the matrix have accumulated around the σ phases and some precipitation phases have occurred. It is concluded that the use of annealing of this material at 950°C affects the chemical, mechanical and other properties adversely.

The influence of the cooling rate on the microstructure of AlCuSi, AlSi and AlZn alloys

Abstract 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 heating regime in a differential scanning calorimeter.

Effects of irradiation on the activation energies of Li2B4O7 phases

Abstract The effects of X-ray irradiation on the activation energies of Li 2 B 4 O 7 phase transitions have been investigated. Differential scanning calorimetry measurements were taken before and after irradiation. The activation energies of normal and irradiated Li 2 B 4 O 7 are 233 kJ mol −1 and 279 kJ mol −1 , respectively.

Phase investigation of an iron meteorite from Akyumak

Abstract The phase of an iron meteorite which fell near Akyumak, East Anatolia, in 1981 have been investigated by optical and X-ray diffraction. Diffraction peaks of kamacite, teanite, plessite and cementite phases were separated and indexed by the related unit cell parameters of the phases. From the analysis of DSC and DTA curves, some phase transformation are known to have occurred during different heating regimes.

Synthesis of melt-quenched Bi1.7V0.3Sr2Ca2Cu3O10+y superconducting glass-ceramics

A glass in the BSCCO system with Bi17V0.3Sr2Ca2Cu3O10+y nominal composition was prepared by the melt-quenching (glass) method. The suitability of the glass ceramic method has been assessed in terms of physical and electrical properties. Using an analysis developed for non-isothermal crystallization studies, information on some aspects of crystallization has been obtained. The result obtained indicated that substitution of vanadium for bismuth increased the activation energy compared to the unsubstituted BSCCO system but did not enhance the superconducting phase formation. The activation energy for crystallization of glass has been found, Ea=355 kJ mol−1. The crystal structure was found to differ from that in the unsubstituted BSCCO system. Most importantly, the HTc phase was formed by reaction between the constituent phases at lower temperatures and not directly from the glass material. The best electrical properties were obtained at T0=75 K and Jc=12 × 103A cm−2 at 4.2 K.