Papers by Keyword: Micro-Structure Evolution

Abstract: The hot power spinning process of TA1 has been studied on the base of isothermal plane compression model in this paper. The microstructures of spun workpieces and plane compression specimens are analyzed and the microstructure evolution mechanism has been investigated. The results reveal that the microstructure evolution has similar mechanism between power spinning and plane compression. Plane strain compression can be used to predict and control the microstructure of as-spun TA1 workpiece.

Abstract: The material undergoes the different deformation stage and the changing history of strain-rate and temperature affects the microstructure evolution during extrusion process. To understand the effect of extrusion process on microstructure evolution, the microstructures of aluminum profile with different wall thickness sections are compared and the variety of strain-rate and temperature are analyzed. The result show that the larger increasing gradient of strain-rate leads to the incomplete recrystallization process in thin wall section during the pocket die stage. The coarse grains are developed by second recrystallization because of the violent strain-rate changes, which is caused by the entrance of bearing-land. The lasting time of high strain-rate and temperature decided the growth of coarse grains, which is affected by bearing-land length.

Abstract: The effect of strain on the microstructure evolution of Fe-32%Ni alloy during multi-axial forging at the temperature of 500°C and a strain rate of 210-2 s-1 was investigated by optical microscope (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scatter diffraction (EBSD) observations. The results show that the austenite grains were greatly refined with increasing cumulative strain, and the microstructure evolution during multi-axial forging can be summarized as such a process that deformation bands crossing each other subdivide the original austenite grain into several sub-grains and then these sub-grains are subdivided into more small ones and gradually angled to new independent grains with their boundaries transformed into large angle boundaries in subsequent compression.

Abstract: Heat-resistant Al-8.5Fe-1.3V-1.7Si alloys were prepared by spray forming technique. The effect of temperature on microstructure and mechanical properties of the alloys was studied by optical microscope(OM), transmission electron microscope(TEM) with energy dispersive spectrometer(EDS), X-ray diffraction(XRD), differential scanning calorimeter(DSC) in this paper. The research results show that the microstructure of the material doesn’t change obviously after being hold for 3 hours at 420°C temperature. When the temperature is over 420°C, the second coarse phases are found in the alloy. The study on the microstructure of the alloy exposed at 400°C for 100 hours shows that the alloy has excellent high temperature stability. And the main second phase in the alloy is spherical a-Al₁₂(Fe,V)₃Si, with a little other phases such as Al₁₃Fe₄, Al₆Fe, Al₉FeSi₃ and so on.

Abstract: The dynamic deformation behavior of an as-extruded Mg-Gd-Y magnesium alloy was studied by using Split Hopkinson Pressure Bar (SHPB) apparatus under high strain rates of 102 s-1 to 103s-1 in the present work, in the mean while the microstructure evolution after deformation were inspected by OM and SEM. The results demonstrated that the material is not sensitive to the strain rate and with increasing the strain rate the yield stress of as-extruded Mg-Gd-Y magnesium alloy has a tendency of increasing. The microstructure observation results shown that several deformation localization areas with the width of 10mm formed in the strain rates of 465s-1 and 2140s-1 along the compression axis respectively, and the grain boundaries within the deformation localization area are parallel with each other and are perpendicular to the compression axis. While increasing the strain rate to 3767s-1 the deformation seems become uniform and all the grains are compressed flat in somewhat. The deformation mechanism of as-extruded Mg-Gd-Y magnesium alloy under high strain rate at room temperature was also discussed.

Abstract: The microstructures of FeCoNiCrCu high entropy alloy were investigated under directional solidification. The results showed that only diffraction peak corresponding to a FCC crystal structure was observed in the directionally solidified FeCoNiCrCu alloy. With increasing solidification rate, the interface morphology would grows in planar, cellular and dendrite. Comparing the potentiodynamic polarization of as-cast and directionally solidified FeCoNiCrCu high entropy alloy in a 3.5%NaCl solution, it is clearly reveals that the corrosion resistance of directionally solidified FeCoNiCrCu alloy is superior to that of the as-cast FeCoNiCrCu alloy.

Abstract: Microstructure evolution behavior of 1235 aluminum alloy under different deformation conditions was studied by hot compression simulation, along with OM, TEM. The law of microstructure evolution at hot deformation was also analyzed. The results showed that the dynamic recrystallization behavior of 1235 aluminum alloy was obvious during hot deformation. At higher deformation temperature or lower strain rate, the grain dislocation density was lower and grain boundaries tended to be straighter, therefore, the grains dynamic recrystallized more adequately. The recrystal grains were smaller and distributed uniformly at deformation temperature for 400°C and stress rate for 0.1s^-1 with the average grain size for 54.03μm.

Abstract: The phase field method has been applied to simulate the microstructural evolution of a commercial single crystal Ni-based superalloy during both, HIP and annealing treatments. The effects of applying high isostatic pressure on the microstructural evolution, which mainly retards the diffusion of the alloying elements causing the loss of the orientational coherency between the phases is demonstrated by the simulation and experimental results

Abstract: The dissolution kinetics of an ultra-fine γ’ precipitation occurring in the γ matrix between the standard secondary precipitates of MC2 Ni-based single crystal superalloy was investigated. Creep-fatigue experiments at 1050°C including an overheating at 1200°C were performed on <111> oriented specimens to study the effects of fine γ’ particles on the plastic deformation. During these experiments, a decrease of the plastic deformation rate was observed just after the temperature peak. This hardening effect disappears once the fine γ’ precipitates had been dissolved. A mean time for this hyperfine precipitation dissolution could then be highlighted. Based on both simple binary diffusion and complex diffusion analysis, the mean time for the dissolution of the fine γ’ precipitates is analyzed and compared to the experimental ones. It is shown that considering only a simple binary diffusion is not sufficient and it should be considered a more complex diffusive analysis involving additional interplays.

Abstract: Complex martensitic microstructure evolution in steels generates enormous curiosity among the materials scientists and especially among the Phase Field (PF) modeling enthusiasts. In the present work PF Microelasticity theory proposed by A.G. Khachaturyan coupled with plasticity is applied for modeling the Martensitic Transformation (MT) by using Finite Element Method (FEM). PF simulations in 3D are performed by considering different cases of MT occurring in a clamped system, i.e. simulation domain with fixed boundaries, of (a) pure elastic material with dilatation (b) pure elastic material without dilatation (c) elastic perfectly plastic material with dilatation having (i) isotropic as well as (ii) anisotropic elastic properties. As input data for the simulations the thermodynamic parameters corresponding to Fe - 0.3% C alloy as well as the physical parameters corresponding to steels acquired from experimental results are considered. The results indicate that elastic strain energy, dilatation and plasticity affect MT whereas anisotropy affects the microstructure.