Papers by Keyword: Gamma Phase

Abstract: In this work, lead-free silicon brass (Cu-Si-Zn) with tin addition was studied to investigate on the comparative influence of the adding and non-adding tin on the microstructures and microhardness. In order to produce new alloy compositions, varied amount of silicon (0.5, 1.0, 2.0, 3.0 wt%) were incorporated. The ranges of chemical compositions were copper contents between 58.7 and 60.3 wt%, tin content 0.6 wt% and zinc remaining. The silicon brasses were prepared by melting pure elements with a graphite crucible using an induction furnace. The chemical composition of each alloy has been determined by X-ray fluorescence spectrometry (XRF). Microstructures of the as-cast silicon brass ingots have been observed by optical microscopy and scanning electron microscopy. The respective chemical analysis of the phases was determined by energy dispersive X-ray spectroscopy (EDS) and the hardness was measured by Vickers hardness test. The results revealed that the hardness of 60Cu-0.5Si-39.5Zn brass was 123.4 HV. The higher silicon content improved the higher hardness of samples. Moreover, the addition of tin together with silicon increased amount of beta (β) phase and more uniform dispersive gamma (γ) phase than those of the silicon addition alone. It could be concluded that the tin addition enhanced the hardness of lead-free Cu-Si-Zn brass and trended to be helpful for machining.

Abstract: In the present study the series of the Ni46.2Co5.0Mn36.1In12.6, Ni48.7Co5.2Mn34.4In11.6 and Ni45.6Co4.8Mn36.4In13.2 alloys (at. %) were studied. The influence of the indium addition on structure and phase transitions was studied. All alloys were annealed at 900°C for 24 hours and then slowly cooled in the furnace. After annealing all of the studied alloys showed the macrostructure of radially oriented columnar grains, which lied in the direction perpendicular to the casting axis. For the alloy containing about 13 at. % of indium the monoclinic 14M modulated martensite was stated at room temperature. Apart from the modulated martensite in a1_133 alloy the gamma phase was also observed. For alloy with higher indium content the mixture of cubic L21 parent phase and cubic gamma phase was identified. All studied alloys showed one-step martensitic transformation.

Abstract: Series of the near stoichiometric two phase (martensite + , parent + ) Co2NiGa alloys were studied. Different thermal treatments changing the microstructure were applied. After annealing for 20 h at 9000C large  precipitates were dispersed, they decorated mainly the grain boundaries. For the alloys quenched from the 11000C modulated structures were observed. Furthermore, during aging at the 3500C ' precipitation process occured in the matrix.

Abstract: Effect of the warm processing parameters (the strain rate, forming temperature and deformation degree ) on the γ' metastable phase transformation in 2205 duplex stainless steel has been studied. The γ' metastable phase was located within the ferrite phase. Dynamic recovery took place only within the γ phase, and dynamic recrystallization underwent for the ferrite phase. The γ' metastable phase transformation was affected by the deformation degree and about 15% deformation led to appearance of the γ' metastable phase. γ' metastable phase formation by the precipitation of intragranular γ' was favored by increasing ageing time, and the size and content of γ' metastable phase were related to deformation temperature and strain rates.

Abstract: In the present paper the effect of heat treatment on microstructure, martensitic transformation temperatures and magnetic properties behavior of Co-Ni-Ga pollycrystal was discussed in detail. Microscopic observations revealed two types of two phase polycrystalline alloys: i) martensite with γ-precipitates and ii) parent phase with γ-precipitates. Making use of Xray and electron diffraction methods the crystal structure of martensite phase was identified as bct structure (with co/ao about 1.2). Annealing of Co-Ni-Ga alloy at 1223K/40 min causes a separation of martensitic and magnetic transformation and an increase of the Curie temperature by about 70K, after this annealing any significant structural changes in the parent (martensitic) and γ phase are not observed.