Papers by Keyword: α-Phase

Abstract: In this paper, we investigated changes in active slip systems of α-phase of Ti-6Al-4V alloy under a cyclic plastic loading using a crystal plasticity finite element method. In the analyses, a bicrystal model was employed, and the crystallographic orientations were set so as that prismatic <a> or basal slip system was the primary slip system in each grain. The results showed that there was a mechanism where the basal slip systems could reach the stage of activation under the cyclic plastic loading even though the condition was that the prismatic <a> slips initially operate. The reason for the activity changes was due to the changes in the incompatibility between the grains by the work hardening, and the effect of the incompatibility on activities of slip systems appeared even in the perpendicular arrangements of the grains to the loading direction.

Abstract: A new intercalation of Indium and Zinc Phthalocyanine(ZnPc) thin films is developed by using thermal co-evaporation method. Optical characteristics of In-doped ZnPc are studied in comparison with pristine ZnPc, which shows improvement on optical absorption at the visible spectrum. The presence of a new phase transition upon Indium doping is examined and consequently support the idea of the intercalated phase upon doping. A Schottky diode made of Indium doped ZnPc is fabricated in order to measure its electrical properties, its photo-current spectrum confirms the existence of phase transition.

Abstract: Using silicon powders as raw materials, adding nano-silicon nitride as a diluent and NH₄Cl₃ and FeCl₃ as catalysts, α-phase silicon nitride powders were prepared by direct nitridation method. The silicon powders were first milled with 20% α-Si₃N₄ and 4% NH₄Cl₃ for 30 minutes. Then the mixture was heat-treated at 1300°C for 1 hour in the pure nitrogen gas. The phases and their content of the as-prepared product were detected by X-ray diffraction (XRD) and the microstructure was studied by scanning electron microscope (SEM). The results showed that the product mainly consisted ofα-Si₃N₄ with a mass fraction over 92% and were submicron-sized particles．

Abstract: Silicon nitride is one of the major structural ceramics that has been developed following many years of intensive research. It possesses high flexural strength, high fracture resistance, good creep resistance, high hardness and excellent wear resistance. These properties arise from the processing of the ceramic by liquid phase sintering and the development of microstructures in which high aspect ratio grains and intergranular glass phase lead to excellent fracture toughness and high strength. The glass phase softens at high temperature and controls the creep rate of the ceramic. The purpose of this review is to examine the development of silicon nitride and the related sialons and their processing into a range of high-grade structural ceramic materials. The development of knowledge of microstructure–property relationships in silicon nitride materials is outlined, particularly recent advances in understanding the effects of grain boundary chemistry and structure on mechanical properties. This review should be of interest to scientists and engineers concerned with the processing and use of ceramics for structural engineering applications.

Abstract: α-phase forming on the surface layer and precipitation of α-phase inside a Ti-Mo alloy during annealing in air has been investigated thermodynamically. α-phase layer is increased rapidly when annealing temperature exceeds 700°C. When the 850°C solution-treated specimen annealed at 400°C for 1 hour, there is no α-phase precipitates. As annealing temperature increased to 800°C, the amount of α-phase precipitates first increased to a maximum at 600°C, then decreased.

Abstract: It is known that the phase-decomposition process of 60/40 Cu-Zn alloy is so-called the bainitic transformation, and decomposition of α-phase from the β’-phase is as follow: β’ → α9R → αfcc. In this work,decomposition of α-phase from the β’ single phase of Cu-40.26at.%Zn alloy has been investigated by high-resolution transmission electron microscopy (HRTEM) to understand the phase transformation of this alloy. Especially, striations in the α-phase has been focused on the special feature for the change of the structure and hardening of this alloy during annealing. The result of a comparison between this alloy and the Si added alloy is also reported.

Abstract: A new molybdenum hybrid-alloyed steel powder has been developed. The powder is based on a molybdenum prealloyed steel powder to which molybdenum powder particles have been diffusion bonded. The sintered compact made of the developed powder has a finer pore structure than that of the conventional molybdenum prealloyed steel powder, because the ferritic iron phase (α-phase) with a high diffusion coefficient is formed in the sintering necks where molybdenum is concentrated resulting in enhanced sintering. The rolling contact fatigue strength of the sintered and carburized compacts made of this powder improved by a factor of 3.6 compared with that of the conventional molybdenum prealloyed steel powder. The improvement in the rolling contact fatigue strength should result from the fine pore structure without coarse pores acting as stress concentration points.

Abstract: The α-phase in 60/40 brass added Si was investigated by transmission electron microscope (TEM) in order to understand the relationship between the ability of hardening during annealing and phase decomposition. The ability of hardening ( Δ HV), which is the value of difference between the maximum hardness during annealing and the value of as-quenched sample, was obtained measurement from the alloy. As a result, the Si-bearing alloy is higher in ΔHV than a base alloy without Si. The α-phase in the Si-bearing alloy showed fringes in its TEM image like as stacking faults, and extra reflected spots in its selected area diffraction pattern (SADP), which is corresponding to the 9R structure. Streaks were also observed together with spots in its SADP. Extra reflected spots and streaks in SADP became weak or disappeared when the annealing time increased. After 600 ks annealing, SADP obtained from the α-phase could be indexed as FCC lattice. Change in chemical composition of α-phase was also measured by the energy dispersive X-ray spectroscopy (EDS).