Papers by Keyword: Heat Treatment

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Authors: Valentin V. Emtsev, Boris A. Andreev, Gagik A. Oganesyan, D.I. Kryzhkov, Andrzej Misiuk, Charalamos A. Londos, M.S. Potsidi
Abstract: Effects of compressive stress on oxygen agglomeration processes in Czochralski grown silicon heat treated at T= 450OC, used as a reference temperature, and T= 600OC to 800OC are investigated in some detail. Compressive stresses of about P= 1 GPa lead to enhanced formation of Thermal Double Donors in materials annealed over a temperature range of T= 450OC – 600OC. It has been shown that the formation of thermal donors at T= 450OC under normal conditions and compressive stress is accompanied with loss of substitutional boron. In contrast, the concentration of the shallow acceptor states of substitutional boron in silicon annealed under stress at T≥ 600OC remains constant. An enhancement effect of thermal donor formation is gradually weakened at T≥ 700OC. The oxygen diffusivity sensitive to mechanical stress is believed to be responsible for the observed effects in heat-treated silicon.
Authors: Yu Yang, Jian Qiu Guo, Balaji Raghothamachar, Michael Dudley, Swetlana Weit, Andreas N. Danilewsky, Patrick J. McNally, Brian R. Tanner
Abstract: We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate mechanism of swapping of TED pinning points between Frank-Read sources lying on same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on same basal plane.
Authors: F.Z. Boujrhal, El Kebir Hlil, R.Cherkaoui El Moursli, T. El Khoukhi, B. Sghir
Abstract: Comparative radon investigations of two natural materials, crystalline apatite and amorphous oxide, are presented here. The radon retention in the apatite (sedimentary apatite) is more than 70% of the total radon formed in the solid matrix. The amorphous oxide (gel hydrothermal alteration) retains only 7% of radon. The nature of the material which plays an important role in the radon diffusion is confirmed by heat treatment. The major and interesting result of this heat treatment is increasing of crystallite size. This phenomenon induces improvement on radon retention ability. To study these properties one uses a structure band calculations based on the Linear Combinations of Orbital Atomic (LCAO) method convenient numerically for the ionic systems.
Authors: Zhan Qiang Liu, Xing Ai, Zhao Hui Wang
Abstract: This paper presents a comparison study of surface hardening by grinding versus machining. The technological, economical and ecological merits of machining hardening and grind-hardening process for steels are described. The mechanisms of machining hardening and grind-hardening of steels are investigated and compared. The phase transformation, plastic deformation and white layer generation are the principal factors contributing to the hardened surface layer by machining and grinding. The influences of the process parameters on the penetrated hardness are given for both grind-hardening and machining hardening operations. The future development trends of the grind-hardening and machining hardening are also presented.
Authors: Ji Yong Yao, D.A. Graham, Malcolm J. Couper
Authors: Jeong Tae Kim, Chae Ho Lim, Jeong Kil Choi, Young Kook Lee
Abstract: New method for evaluation of heat transfer coefficient is proposed. In general, many researchers have been studied about inverse problem in order to calculate the heat transfer coefficient on three-dimensional heat conduction problem. But they can get the time-dependent heat transfer coefficient only through inverse problem. In order to acquire temperature-dependent heat transfer coefficient, it requires much time for numerous repetitive calculation and inconvenient manual modification. In order to solve these problems, we are using the SQP(Sequential Quadratic Programming) as an optimization algorithm. When the temperature history is given by experiment, the optimization algorithm can evaluate the temperature-dependent heat transfer coefficient with automatic repetitive calculation until difference between calculated temperature history and experimental ones is minimized. Finally, temperature-dependent heat transfer coefficient evaluated by developed program can used on the real heat treatment process of casting product.
Authors: Imre Felde, Imre Czinege, B. Smoljan, Rafael Colás
Abstract: A novel numerical approach for testing and evaluation of quenching media and quenching systems is outlined. The technique proposed is based on determination of heat transfer coefficient from temperature signals recorded and applying it as input for simulation of quenching process. The evaluation method is based on the calculated microstructural and mechanical properties of cylindrical samples.
Authors: Zhao Han, Hong Min Zhu
Abstract: Nano-sized nickel powders were prepared through a wet chemical reduction, of NiCl2 by sodium in liquid ammonia at -45 °C, and a subsequent heat-treatment in vacuum at 300 °C. The prepared product was systematically characterized by X-ray diffraction (XRD), scan electron microscopy (SEM), transmission electron microscopy (TEM), and BET specific surface area measurement. The results show that the product was composed of nano-sized nickel particles, with average particle diameter of about 20 nm, and specific surface area of about 30 m2g-1. The possible formation mechanism of the nano-sized nickel powder was also discussed briefly.
Authors: Rodolfo Franchi, Antonio del Prete, Gabriele Papadia
Abstract: The workpiece distortion that occurs during machining, can lead to a large increase in the number of the scrap parts. Residual stresses are the main cause of these distortions and they are generally present in both forging and casting products. In order to obtain the desired microstructure and mechanical properties, the workpiece is subjected to heat treatment before being worked. Quenching produces residual stresses that exist throughout a large percentage of the casting or forging part. Distortion occurs as a result of removing stressed material from the workpiece. The component will re-equilibrate and distort as each layer of stressed material is machined away. This paper describes a procedure development for distortions numerical analysis on a SAF2507 casting bulk workpiece. A solubilization heat treatment has been simulated, in order to predict the bulk residual stresses distribution. Different metal cutting processes have been considered to measure the numerical distortions induced in the workpiece.
Authors: Roger N. Lumley
Abstract: Until recently, the solution heat treatment of conventional aluminum high pressure die cast (HPDC) parts has been considered impractical because the high temperatures involved cause surface blistering and dimensional instability. Now, a new heat treatment procedure has been developed by the CSIRO Light Metals Flagship in Australia which avoids these problems and, in many cases, allows tensile properties such as 0.2% proof stress to be doubled with little change to ductility. This development has the potential to reduce costs by allowing existing HPDC parts to be re-designed to use less metal and still achieve performance requirements. One issue, however, is the possibility that heat treating die castings to increase tensile properties may have an adverse effect on fracture toughness. This paper reports preliminary results of Kahntype tear tests conducted to assess the fracture resistance of as-cast and heat treated HPDCs. Studies of the alloys A360, A380 and C380 have shown that T4 and underaged (UA) T6 tempers produce an optimal combination of fracture resistance and tear strength. Furthermore, the fracture properties compare well with permanent mold and sand cast aluminium alloys that have similar tensile properties.
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