In the course of thermal treatments, materials are usually subjected to continuous heating and cooling cycles during which microstructural evolution and mechanical interactions occur simultaneously at different length and time scales. Modeling of these processes necessitates dealing with inherent complexities such as large material property variations, complex couplings and boundary conditions, coupled heat and mass transfer mechanisms and phase transformations. In this study, a mathematical framework based on finite element method (FEM) capable of predicting temperature history, evolution of phases and internal stresses during heat treatment of metals and alloys was developed. The model was integrated into the commercial FEA software MSC.Marc&reg / by user subroutines. The accuracy of the model was verified by simulating the quenching of eccentrically drilled steel cylinders. Simulation results were justified via SEM observations and XRD residual stress measurements. According to the results, the model can effectively predict the trends in the distribution of microstructure and residual stresses with a remarkable accuracy.

Many Co-based Heusler alloys with the stoichometric composition X2YZ are ideal candidates for the spintronics applications. So, they have been extensively studied theoretically and experimentally. The aim of this work was to investigate the effect heat treatment on phase stability and magnetic properties for quaternary Co2FeSi1-xGax Heusler alloys with varying Si concentration. The Co2FeSi1-xGax alloy samples were prepared by conventional arc melting technique. The structure of Co2FeSi1-xGax bulk alloys were examined by powder x-ray diffraction and differential scanning calorimetry. It was confirmed that Co2FeSi1-xGax alloys display the L21 type structure for all x compositions based on the annealing temperature. The magnetic ordering transition temperature, Tc, was measured by differential scanning calorimetry. It was found that the order-disorder phase transition temperature from the L21 to the B2 structure, T , decreases while the Curie temperature, Tc, increases with increasing x / however, the value of these temperatures were not influenced by changing heat treatment process. The magnetic properties of Co2FeSi1-xGax alloy were investigated by using vibrating sample magnetometer. Higher saturation value was obtained at the L21 phase than the value obtained at the B2 phase. It was concluded that the Co2FeSi0.2Ga0.8 alloy was chosen optimum composition for spintronics applications because of its highest Curie temperature and phase stability of L21.

The primary objectives of this study were: (1) to verify the effectiveness of ECAE to induce equal amounts of strain and grain refinement in bars of different cross-sectional areas, (2) to determine the effectiveness of ECAE in breaking down the as-cast macrostructure in CDA 101 Cu and in producing a homogeneous material containing micron-scale grains upon recrystallization, and (3) to determine a thermomechanical processing (TMP) schedule (from the ones examined) that produces the best microstructure in terms of grain size and uniformity. The effects of extrus ion route, levels of strain and intermediate heat treatment were investigated. To achieve the first objective, bars having square cross-sections of three different sizes, 19 mm, 25 mm and 50 mm, were processed up to eight ECAE passes through routes A, B, C and E. To achieve the second and third objectives, bars were processed up to eight ECAE passes with and without intermediate heat treatments through routes Bc, C, E and F. ECAE processing was carried out in a 90o extrusion die with sliding walls at an extrusion speed of 2.5 mm/s. Recrystallization studies were carried out on the processed material to evaluate the recrystallization behavior and thermal stability of the material. The as-worked and recrystallized materials were characterized by Vickers microhardness, optical microscopy (OM) and transmission electron microscopy (TEM). Results indicate that similar hardness values, sub-grain morphology and recrystallized grain size are generated in the three bars having different cross-sectional sizes processed through ECAE. ECAE is shown to induce uniform strain in all three billet sizes. ECAE is therefore shown to be effective in scale-up to a size of at least 50 mm, with larger billets giving better load efficiency. Results from the later parts of this study indicate that eight extrusion passes via route Bc produces the best microstructure in terms of grain size and microstructural uniformity. The routes can be arranged in the sequence Bc> E, F> C for their ability to produce a uniform recrystallized microstructure with small average grain size. Macroscopic shear bands are sometimes generated during extrusion depending upon the initial grain morphology and texture of the material.

The purpose of this research is to study the effect of the thermal treatment on the devices. We dissolved polymer light emitting materials in different solvents to discuss the influence on polymer thin film and device efficiency at different thermal conditions. We confirmed that the best thermal condition was changed as that of solvent changes. In this study, we dissolved polymer blue light material¡ÐBP105 in Toluene and o-xylene. The glass transition temperature (Tg) of BP105 is 120.7¢J, and the boiling point of Toluene and o-xylene were 110 and 145¢J. That is namely the boiling point of Toluene and o-xylene are lower and higher, respectively, than the Tg of BP105. This makes us to compares the thermal treatment conditions on different influence from different boiling point of solvents. The interrelations between the thermal treatment temperature, the boiling point of solvents and the glass transition temperature of polymer is an interesting topic to study, because it does affect the surface morphology of polymer thin films and the characteristic of devices. The device structure is as follows: ITO/ PEDOT:PSS/ BP105/ LiF/ Ca/ Al. Known from the experimental results that the spectra and the morphologies of polymer thin films will change in the different thermal treatment condition, and the choice of different solvent will also affect the best thermal treatment condition for device processing. We observed the surface roughness of polymer thin film is one of the important factors to affect the device efficiency in this study. We found that if the boiling point of used solvent was higher than the thermal treatment temperature, which was higher than the Tg of polymer, the surface roughness of polymer thin film is more smooth resulting in higher current injecting and higher stability of the device. The best thermal treatment temperature is 130¢J by using o-xylene as solvent. The surface roughness of polymer thin film is 0.393 nm, and the maximum brightness of the device is 8593 cd/m2 at 12.5 V as a configuration of ITO(1500Å)/PEDOT:PSS(800Å)/BP105(650Å)/LiF(10Å)/ Ca(100Å)/ Al(2000Å). The luminous and the power efficiencies are 3.98 cd/A, and 1.43 lm/W, respectively, at the current density 100 mA/cm2.

Investigations of the production of thin-walled steel alloys through the reduction and subsequent gas carburization of structures made from metal oxide powders were performed. Batch compositions, as well as the heat treatment parameters necessary for the formation of structures were determined through the use of thermogravimetric analysis, dilatometric measurements, and microstructural investigation. Parameters for the high temperature carburization of thin-walled 4140 structures were determined. The research has shown that the amount of carbon in the walls of the structures can be controlled and uniform carbon contents across the cross-sections can be achieved in less than 30 minutes. Heat treatments for carburized samples were performed and subsequent microhardness testing resulted in values similar to conventionally produced 4140 steel. Studies on the decarburization behavior of similar alloys under various conditions were also performed in order to aid in the prediction of the microstructural behavior of samples during carburization and subsequent heat treatment. Low temperature gas carburization of structures with 316 steel composition has also been performed. Hardness variations present through the cross-section of the part after carburization suggest some transfer of carbon, though contents are not as high as anticipated. Suggestions for future work in this area are presented. The results of these investigations yield a novel method for the production of steel parts from metal oxide powders. The speed and low cost of the process, coupled with the proven ability of the process to yield parts with similar microstructural and mechanical characteristics as conventionally made alloys, allows for the techniques presented in this study to be used for the development of alloys which could not be previously done economically.

<p>The aim of this thesis is to investigate the influence of ageing process on the microstructure and mechanical properties of aluminium-silicon alloys. The investigation was carried on Al-9%Si-3%Cu and Al-9%Si-0.4%Mg. To obtain different DAS with low content of oxide films and micro shrinkage, gradient solidification has been used. The specimens were treated according to T6 heat treatment.</p><p>In this thesis it has been shown that solidification rate has great influence on mechanical properties since it controls microstructure. To reach peak level of mechanical properties different times of artificial ageing were used depending on the alloy.</p><p>In peak value condition Yield’s Strength of alloys was 197MPa for Al-Si-Cu alloy and 243MPa for Al-Si-Mg one. These results can be compared to these presented in other papers concerning aluminium silicon alloys. Such comparison shows that when talking about potential of alloy, these results are more or less the same as in other articles in this field.</p><p>The work was conducted within 10 weeks and for this reason not all the necessary data was collected. Further work will be conducted to obtain missing results, like overaged state for Al-Si-Cu alloy.</p>

<p>Abstract</p><p>The purpose of this research is to investigate the influence of Manganese (Mn) on cast aluminum alloys where a substantial amount of Iron (Fe) is included. Ductility and tensile strength need to be improved in recycled aluminum alloys where greater amounts of Fe are found. Fe is a common impurity and is known to be detrimental to mechanical properties and in order to neutralize the effects of Fe; modifiers such as Mn are added. In this investigation, attempts will be carried out aiming to find the optimal amount of Mn. Other related topics that will be discussed are whether there exists a Mn/Fe ratio which clearly modifies the harmful iron- rich phases and improves the properties for a certain alloy or not. Also, will the heat treatment have a significant effect on mechanical properties? These are some of the questions that will be answered in this paper.</p><p>It is hard to find research articles that focus only on the influence of Mn on the microstructure and mechanical properties of Al-Si cast alloys. Much of the work that is already published concerns only a specific alloy and casting method. In this work three different casting processes, sand-, die- and high pressure die-casting, will be simulated by using gradient solidification equipment. Furthermore, the influence of heat treatment on the mechanical properties will be examined.</p><p>The results showed that the solidification rate had the biggest impact on the microstructure and mechanical properties of the alloys, where the fastest cooling rate gave the best results. The effect of Mn seems to influence the samples with coarser microstructures significantly where it had time to modify the Iron-rich needles, also called the β-phase. At higher cooling rates the impact of Mn was impeded. It has been observed that a high content of Mn (around 0.6%) needs to be added before the properties start to improve. UTS (Ultimate Tensile Strength) and YS (Yield Strength) are improved while ductility is lowered. Heat treatment did not seem to have any influence on the effects of Mn.</p>

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第18986号 / 工博第4028号 / 新制||工||1620 / 31937 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 田中 功, 教授 乾 晴行 / 学位規則第4条第1項該当

M. Tech. Metalurgical Engineering. / A research project was launched to produce zinc/ nickel, zinc/ tin and zinc/aluminium alloys at different concentrations and to test zinc pick-up with the typical steels used in South Africa. Results show that the addition of 0.023% Al and 0.06% Ni in the zinc bath can be successfully used to reduce the zinc pick up of commercial grades of steel. Tin improved quality of coating as compared to pure zinc.

No description available.