Papers by Keyword: Multi-Phase

Abstract: MMCs exhibit a high potential in modern structures due to many positive attributes. One of these attributes is a heightened creep resistance compared to conventional single or multi-phase alloys. The following paper focuses on the creep resistance of a spray-compacted Al-based alloy (DISPAL^® S270). This alloy, designed for high temperature applications like turbochargers, cylinder bore liners or pistons can be subjected to temperatures up to 450°C, which is considerably higher compared to unreinforced Al-alloys. DISPAL^® S270 microscopically consists of Si-particles with round shapes in an Al-rich α solid solution, which is additionally reinforced by complex precipitates, including Al₉FeNi and Al₃Ti, among others. The particle sizes and ratios differ with the heat treatment. The same applies to the precipitates in the matrix. The investigated heat treatments are F (after extrusion) and T6 (additional peak aged). The alloy is tested at 250°C using different loads at constant force with stress values between 125 and 200 MPa. The measured minimal creep rates are in the range of _min. = 10^-5-10^-8 1/s. In comparison to conventional single or multiple phase alloys MMCs reveal some advantages, since the modified threshold stresses and direct strengthening often reduce the minimum creep rate. The stress exponent of the MMCs has higher values ​​compared to aluminum alloys, as known from previous MMC studies. The specimens are analyzed with LM, SEM, EDS and XRD. It could be shown that an additional heat treatment (peak aged T6) enhances the creep properties by introducing very fine precipitates containing the Mg₅Si₆ phase.

Abstract: In the meso-scale machining, feed rate, grain size and tool edge radius are in the same order of magnitude, and cutting process is often carried out in the grain interior and grain boundary. In this paper the meso-cutting process of hot-rolled AISI1045 steel is studied and its metallographic microstructure is analyzed for the establishment of multiphase models which incorporate the effect of ferrite and pearlite grains. In order to discover the applicability of multiphase models to the simulation of meso-cutting, three contrast simulation models including multiphase model with rounded-edge cutting insert (model I), multiphase model with sharp edge cutting insert (model II) and equivalent homogeneous material model with rounded-edge cutting insert (model III) are built up for the meso-orthogonal cutting processes of hot-rolled AISI1045. By comparison with the experiments in terms of chip morphology, cutting force and specific cutting force, the most suitable model is identified. Then the stress distiribution is analyzed. And it is found that multiphase model with tool edge radius can give a more accurate prediction of the global variables and reveal more about these important local variables distribution.

Abstract: This paper adopts the method of multi-phase flow to simulate the extrusion process of single-screw extruder based on different screw speed by using the finite element analysis software, and get the conclusion that the screw speed has a significant effect on the extrusion quality and outlet pressure of the single-screw extruder. With the increase of the screw speed, the extrusion quality of the single-screw extruder gets worse and the outlet pressure of the single-screw extruder increases.

Abstract: The screw edge width is usually selected based on experience when designing screw extruders, and it is difficult to get the best extrusion quality. The extrusion process of screw extruder is a process of multi-phase flow, which includes gas, liquid and solid. Making it simplified to single-phase flow process can cause relatively large error. This paper adopts the method of multi-phase flow to simulate the extrusion process of single-screw extruder based on different screw edge width by using the finite element analysis software, and get the conclusion that increasing the screw edge width appropriately under the condition that the production efficiency is acceptable is helpful to improve the extrusion quality of single-screw extruders.

Abstract: We use quantum-mechanical calculations to study single-crystalline elastic properties of (Ca,Mg)CO₃ crystals with concentrations ranging from calcite CaCO₃ to magnesite MgCO₃. By analyzing results for a dense set of distributions of Ca and Mg atoms within 30-atom supercells, our theoretical study shows that those atomic configurations, that minimize the total energy for a given concentration, are characterized by elastic constants that either increase with the Mg content or remain nearly constants. Employing these ab initio calculated single-crystalline elastic parameters, the polycrystalline elastic properties of (Ca,Mg)CO₃ aggregates are determined using a mean-field self-consistent homogenization method. The computed integral elastic moduli (bulk and shear) show a significant stiffening impact of Mg atoms on calcite crystals. Our analysis also demonstrates that it is not advantageous to use a granular two-phase composite of stoichiometric calcite and magnesite instead of substituting individual Ca and Mg atoms. Such two-phase aggregates are not significantly thermodynamically favorable and do not offer any strong additional stiffening effect.

Abstract: The multi-scale method was applied to solve the multi-phase multi-scale problem in the industrial crystallization process. The fluid dynamics model was considering under the grid scale, and the population balance model was considering under subsystem scale. The macro model was used to interact with the environment. The crystallization process of potassium chloride was simulated by CFD and MATLAB. The result of the simulation shows the distribution of the supersaturation is strongly affected by the distribution of the suspended crystal volume fraction.

Abstract: Four continuous annealing cycles were adopted to get four kinds of multi-phase steels using 0.2C-1.5Si-1.8Mn [wt%] alloyed raw steel and the microstructures and mechanical properties were investigated. The results show that traditional ferrite-martensite dual phase steel has a tensile strength of more than 1000MPa, but has the lowest strength-plastic product of only 18GPa%. The traditional ferrite, bainite and residual austenite TRIP steel has the highest elongation of 31% and hardening exponent of 0.24, but its tensile strength is just over 800MPa. Introducing hard matrix such as acicular bainitc ferrite or martensite to replace the polygonal ferrite matrix, meanwhile introducing metastable austenite, is conducive to obtain high strength and good ductility. Those kinds of modified TRIP steel with hard matrix can reach above 20GPa% of the strength-plastic product on the 1000MPa grade.

Abstract: In this paper a theoretical relationship for the effective thermal conductivity of a multiphase transversely isotropic composite system is obtained. The Generalized Self-Consistent Method and simple energy balance principle is employed to derive a more appropriate model. In the derivation, it is assumed that the orientation of fiber within the transversely isotropic composite system is unidirectional and surrounded by two different phases of porous and matrix phase. A combined effect of these three different phases on the effective thermal conductivity of the composite system in transverse direction is studied. The effect of the interfacial contact conductance between the fibers and porous medium is also considered. Results of effective thermal conductivity are plotted against volume fraction and conductance which shows extremely good agreement.

Abstract: The microstructure and properties of 600MPa grade steels produced by isothermal treatment has been studied. The influence of isothermal treatment temperature on the microstructure of steels has been investigated by the aid of Optical microscopy and TEM. The results show that after various isothermal treatments the microstructure of steels varies with the isothermal temperature. When the temperature is lower than 530°C the microstructure is mainly composed of granular bainite and lath bainite. Whereas when the temperature is higher than 580°C the polygonal ferrite and quasi polygonal ferrite appears and the microstructure consists of ferrite and fine lath bainite. Since the microstructures are complex and the yield ratio of steels under these conditions are all lower than 0.8. The strength of sample for 630°C isothermal treatment is the highest. The yield strength is over than 800MPa and the tensile strength is over than 1000MPa due to the fine precipitates containing copper. These copper containing precipitates formed during the isothermal transformation by the way of inter-phase precipitation.

Abstract: This paper introduces an automatic parameter measurement and analysis system of multi-phase electric machines based on Labview, presents the system hardware configuration, designs the various measuring and analysis modules, discusses the algorithm including automatic measurement, data analysis and report generation and implements the multi-channel and high-performance parallel data acquisition. Compared with the old methods, it has many advantages such as more flexible software application, higher measuring accuracy and simpler hardware configuration.