Papers by Keyword: Coarsening

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Authors: Yancy W. Riddle, Thomas H. Jr. Sanders
Authors: Andrew Godfrey, O.V. Mishin, T.B. Yu
Abstract: Some methods for quantitative characterization of the microstructures deformed to large plastic strains both before and after annealing are discussed and illustrated using examples of samples after equal channel angular extrusion and cold-rolling. It is emphasized that the microstructures in such deformed samples exhibit a heterogeneity in the microstructural refinement by high angle boundaries. Based on this, a new parameter describing the fraction of regions containing predominantly low angle boundaries is introduced. This parameter has some advantages over the simpler high angle boundary fraction parameter, in particular with regard to data collected from electron-backscatter diffraction investigations, where boundaries with very low misorientation angles cannot be reliably detected. It is shown how this parameter can be related to the recrystallization behavior. Another parameter, based on mode of the distribution of dislocation cell sizes is outlined, and it is demonstrated how this parameter can be used to investigate the uniformity, or otherwise, of the restoration processes occurring during annealing of metals deformed to large plastic strains.
Authors: Francisco Carlos Robles Hernandez, Leonardo González-Reyes, I. Hernández-Pérez
Abstract: In the present paper TiO2 (anatase) nanoparticles were synthesized by ultrasonic radiation proving the potential of this method. The synthesized anatase is heat treated at a temperature of 500°C in open air to coarse it using times from 1 h to 72 h. The heat treatment conditions were selected to prevent phase transformation and to solely sponsor coarsening of anatase from 6.2 nm to 28.3 nm. The synthesized and heat treated anatase were characterized using Electron Microscopy (Transmission and Scanning), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, UV-vis, Raman and Infrared spectroscopy. In the preset work is presented an analysis of anatase that is complemented by the agreement in the different characterization methods. This helps in the understanding of anatase coarsening as a function of heat treatment time and grain size, being the late a more suitable approach. This work opens up new perspectives to produce synthetic nanoparticulate anatase with potential for various applications.
Authors: Suk Won Kang, Dock Young Lee, Ki Bae Kim
Abstract: In order to produce a high quality and cost effective part in the rheocasting process for an automobile industry it has been important to develop a slurry-on-demand process, which can manufacture the semi-solid slurry having a fine and globular structure of primary solid phase. The morphology of primary solid phase of semi-solid slurry is coarsened and globularized during an isothermal holding process in a solid-liquid region. Accordingly, in this paper, the microstructural evolution of semi-solid slurry during the isothermal holding at a various temperature in solid-liquid region was investigated to examine a coarsening and globularization behavior of primary solid phase. The semi-solid slurry of Al alloy was produced in a slurry maker using a multiplex-type slurry cup that we developed recently. A size of primary solid phase was the finer at the higher holding temperature, but under a constant holding time a roundness degree of primary solid phase was the lower at the lower holding temperature. Also, a coarsening rate of primary solid phase was not considered to be affected significantly by a holding temperature even though a little lower coarsening rate was obtained at the higher holding temperature.
Authors: S. Ashouri, Mahmoud Nili-Ahmadabadi
Abstract: Semi-solid forming (SSF) involves alloys with non-dendrite microstructure that contain spherical solid particles in the liquid matrix. This process is generally divided into three main steps: feedstock manufacturing, reheating and forming. Feedstock has the main effect on the cost and quality of product. Many researches have been carried out to reduce the cost of feedstock manufacturing. Slope plate is a simple semi-solid process that can reduce the cost of feedstock. In this study a Cu plate with water and without water circulation was used to investigate the effect of pouring temperature, cooling rate during casting and solidification in the mold on the microstructure. Cast ingots with optimized microstructure were reheated in various time and temperatures in semi-solid region to obtain kinetics of globularization and solid grain growth.
Authors: S. Hossein Nedjad, Mahmoud Nili-Ahmadabadi, Tadashi Furuhara, Tadashi Maki
Abstract: Fe-Ni-Mn maraging alloys show discontinuous coarsening of fct θ-NiMn precipitates along prior austenite grain boundaries (PAGBs) during isothermal aging. Heavy cold rolling of a solution annealed Fe-10Ni-7Mn (wt. %) maraging alloy and subsequent aging treatment at 773 K led to the formation of a nanostructured material. Hardness measurement and transmission electron microscopy were used to study the aging behaviour and microstructural evolution of the nanostructured alloy. At the early stage of aging, an ultrafine grained structure was observed with fine matrix precipitates. However, at later stages of aging, severe coarsening of precipitates was found. At that stage, a lamellar microstructure composed of finely precipitated ferrite laths and ultrafine ferrite grains were identified. Coarse fct θ-NiMn precipitates were identified at the ultrafine ferritic grain boundaries. Development of the coarsening reaction was found to increase the ultrafine grained ferritic regions with prolonged aging.
Authors: Siri Harboe, Vijenthan Sothyratnam, Michael Modigell, Annalisa Pola
Abstract: In this work, the effect of stirring conditions on agglomeration and coalescence-coarsening in isothermal, globulitic, semisolid AlCu10%wt was investigated. It is shown that for the investigated system, a shear rate regime exists which promotes crystallographic alignment of the agglomerated grains, leading to a rapid coalescence process, thereby the formation of rosettes. It is also experimentally validated that for lower shear rates, the size and porosity of aggregates are increased compared to that at higher level of shear.
Authors: Ming Yue Wang, Jing Jing Wang, Yan Lin He, Xiao Gang Lu, Lin Li
Abstract: The precipitation behavior of carbides in Fe-5.78Cr-0.35C (wt.%) alloy during aging at 850°C was studied. The type, particle size and distribution of carbides were determined and measured by the combination of HRTEM (High Resolution Transmission Electron Microscope), XRD (X-Ray Diffraction) and quantitative metallography technique. Results show that the type of carbides was M7C3 and the obvious coarsening of carbides was observed during aging. In addition, the thermodynamic and kinetic calculation using Thermo-Calc software was conducted to study the precipitation of carbides. The stable phase in the alloy aging at 850°C was M7C3 carbide and austenite which is in accordance with experimental results. According to Ostwald coarsening mechanism, the average interfacial energy between γ phase and M7C3 carbide was calculated as 0.7 J·m-2. Then the precipitation behavior of carbides in Fe-5.78Cr-0.35C alloy during aging was well predicted.
Authors: Galina Kasperovich, Sonja Steinbach, Lorenz Ratke
Abstract: Gradient annealing experiments of a near-eutectic AlCu30 alloy with artificial stirring induced by a rotating magnetic field (RMF) of 6 mT were performed. The specific surface area of the primary phase was measured on metallographic sections perpendicular to the sample axis with a fixed amount of fraction solid. The variation of the specific surface area with fluid flow is compared to flow free experiments: the specific surface area varies as the inverse cube root of annealing time if no RMF is applied, but varies as an inverse forth root at 6 mT. The experimental procedure and results are presented in detail and discussed with models of convective coarsening of dendrites.
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