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Recrystallization in Rolled Uranium Sheet

Description: From Introduction: "To overcome the difficulties another investigation has been carried out wherein the rolling stock was subjected to step reduction and annealing treatments designed to develop a small, uniform grain size prior to the final rolling at room temperature. The results of metallographic, dilatometric, and X-ray diffraction studies of this material are given."
Date: March 1962
Creator: Lloyd, Lowell T. & Mueller, Melvin H.
Partner: UNT Libraries Government Documents Department

The Mechanisms of Grain Boundaries - Slip Transmission, Migration, and Sliding

Description: During the last eight years, we have worked on the general problems associated with grain boundaries in metals with DOE support. This final report summarizes the work that has been performed. At the start of this work, we took a much more atomistic approach to grain boundaries. However, as we performed this research it became clear that such approaches had the drawbacks listed above, and that we were not proceeding toward the more general understanding of grain boundaries that we have hoped to achieve. We then moved toward more macroscopic based experiments that we could use to understand the structure and motion of grain boundaries. From these we were able to begin deducing some of the most important results of this work and to provide information that can be used by others to understand the role of grain boundaries in materials. We thus present this report in a topical way and provide the experimental and theoretical underpinning that is needed at each point as we go forward.
Date: March 2, 2005
Creator: Briant, Clyde L.
Partner: UNT Libraries Government Documents Department

Multiscale Modeling of Recrystallization

Description: We propose a multi length scale approach to modeling recrystallization which links a dislocation model, a cell growth model and a macroscopic model. Although this methodology and linking framework will be applied to recrystallization, it is also applicable to other types of phase transformations in bulk and layered materials. Critical processes such as the dislocation structure evolution, nucleation, the evolution of crystal orientations into a preferred texture, and grain size evolution all operate at different length scales. In this paper we focus on incorporating experimental measurements of dislocation substructures, rnisorientation measurements of dislocation boundaries, and dislocation simulations into a mesoscopic model of cell growth. In particular, we show how feeding information from the dislocation model into the cell growth model can create realistic initial microstructure.
Date: December 7, 1998
Creator: Godfrey, A.W.; Holm, E.A.; Hughes, D.A.; Lesar, R. & Miodownik, M.A.
Partner: UNT Libraries Government Documents Department

Modeling of the recrystallization textures of Al-alloys after hot deformation

Description: The recrystallization textures of Al-alloys can be explained by a growth selection of grains with an approximate 40{degree}<111> orientation relationship out of a limited spectrum of preferentially formed nucleus orientations. Accordingly, recrystallization textures can be modeled by the multiplication of a function f(g){sup nucl} describing the probability of nucleation of the various orientations with a function f(g){sup grow} representing their growth probability. Whereas the growth probability can be accounted for by a 40{degree}<111> transformation of the rolling texture, the nucleation probability of the respective grains is given by the distribution of potential nucleus orientations, which is known from local texture analysis for the most important nucleation sites in rolled Al-alloys, cube-bands, grain boundaries and second-phase particles. The contribution of each of these nucleation sites are determined according to an approach to calculate the number of nuclei forming at each nucleation site, which is based on microstructural investigations on the evolution of the various nucleation sites during deformation. The paper describes the model for recrystallization texture simulation in Al-alloys and gives examples of recrystallization textures of AA3004 deformed in plane strain compression at a variety of different deformation temperatures and strain rates.
Date: December 1, 1998
Creator: Engler, O. & Vatne, H.E.
Partner: UNT Libraries Government Documents Department


Description: The preferred orientation of a relatively small piece of high-purity uranium rod, rolled to an 85% reduction at 300 deg C, has been determined in the as-rolled and in the recrystallized conditions. The 12 different charts obtained indicated that the as-rolled texture could be described as a duplex (041) and (352) with the (041) being the major component and with considerable spread about each component. The recrystallized rod showed approximate (041) and (392) components with considerable spread. These texture components for both the as- rolled and the recrystallized rods are not too different from those previously reported for reactor-grade uranium rod. However, it was noted that the texture appeared to be quite sharp for the reduction used, and the maximum intensity on an inverse pole figure was considerably displaced from the periphery of an (001) standard projection for both the rolled and recrystallized rods. (auth)
Date: April 1, 1959
Creator: Mueller, M.H. & Knott, H.W.
Partner: UNT Libraries Government Documents Department

Thin, High Lifetime Silicon Wafers with No Sawing; Re-crystallization in a Thin Film Capsule

Description: The project fits within the area of renewable energy called photovoltaics (PV), or the generation of electricity directly from sunlight using semiconductor devices. PV has the greatest potential of any renewable energy technology. The vast majority of photovoltaic modules are made on crystalline silicon wafers and these wafers accounts for the largest fraction of the cost of a photovoltaic module. Thus, a method of making high quality, low cost wafers would be extremely beneficial to the PV industry The industry standard technology creates wafers by casting an ingot and then sawing wafers from the ingot. Sawing rendered half of the highly refined silicon feedstock as un-reclaimable dust. Being a brittle material, the sawing is actually a type of grinding operation which is costly both in terms of capital equipment and in terms of consumables costs. The consumables costs associated with the wire sawing technology are particularly burdensome and include the cost of the wire itself (continuously fed, one time use), the abrasive particles, and, waste disposal. The goal of this project was to make wafers directly from molten silicon with no sawing required. The fundamental concept was to create a very low cost (but low quality) wafer of the desired shape and size and then to improve the quality of the wafer by a specialized thermal treatment (called re-crystallization). Others have attempted to create silicon sheet by recrystallization with varying degrees of success. Key among the difficulties encountered by others were: a) difficulty in maintaining the physical shape of the sheet during the recrystallization process and b) difficulty in maintaining the cleanliness of the sheet during recrystallization. Our method solved both of these challenges by encapsulating the preform wafer in a protective capsule prior to recrystallization (see below). The recrystallization method developed in this work was extremely effective at maintaining ...
Date: January 16, 2013
Creator: Buonassisi, Emanuel Sachs Tonio
Partner: UNT Libraries Government Documents Department

Influence of orientation pinning on the Goss-texture in Fe-3%Si electrical steel

Description: Despite a large number of investigations on the formation of the Goss-texture in Fe-3%Si electrical steels, the exact mechanisms leading to the preference of this particular orientation are not completely understood so far. As an alternative to the standard explanation of a favored growth of Goss-oriented grains during secondary recrystallization, recently the concept of orientation pinning has been proposed, which considers that the growth of grains with special orientation relationships corresponding to low-angle and twin grain boundaries is disfavored. The present paper present preliminary EBSD-results on the growth of Goss-grains during secondary recrystallization in high-permeability (HiB) transformer steel sheets. A semi-quantitative model to simulate the effect of orientation pinning on the evolution of the Goss-texture is introduced.
Date: December 1, 1998
Creator: Engler, O. & Friedel, F.
Partner: UNT Libraries Government Documents Department

A simulation of recrystallization based on EBSD orientation microscopy data

Description: The present paper introduces a novel stochastic two-dimensional model to simulate the evolution of microstructure and texture during recrystallization. The model is based on data derived by automated large-scale EBSD local texture analysis, i.e., by orientation microscopy. Each measured point is characterized by its coordinates x and y in the microstructure, its crystallographic orientation g and a parameter q describing the quality of the EBSD-pattern which is affected by lattice strain and hence discloses information on the dislocation density. The concurrent information on the local arrangement of orientations and dislocation densities is utilized to derive conclusions on the nucleation and subsequent growth of the new recrystallized grains. The principles of the model are outlined and three example are shown to illustrate the possibilities of the model to simulate the evolution of microstructure and texture during recrystallization.
Date: December 1, 1998
Creator: Engler, O.
Partner: UNT Libraries Government Documents Department

A coupled Monte Carlo-finite element approach to modeling microstructural evolution during static recrystallization

Description: A novel methodology is presented for modeling static recrystallization in metals, by combining the finite element simulation of cold deformation with the Monte Carlo simulation of recovery and grain growth. A model based on crystal plasticity is used to simulate the deformation of an aggregate of grains, so as to capture the inhomogeneous deformation of individual grains, and the strain hardening and texture evolution in the aggregate. The non- uniform distributions of orientation and stored energy are then mapped onto a Monte Carlo grid for simulating static recrystallization. The method has been applied to compute the kinetics and microstructural evolution after different amounts of cold deformation, and leads to improved predictions due to use of more realistic data in the Monte Carlo simulations.
Date: December 31, 1996
Creator: Sarma, G.; Radhakrishnan, B. & Zacharia, T.
Partner: UNT Libraries Government Documents Department

On the influence of dispersoids on the particle stimulated nucleation of recrystallization

Description: Recrystallization of Al alloys is controlled by precipitates. Whereas large particles are generally assumed to promote recrystallization by particle stimulated nucleation, finely dispersed precipitates, either already present in the as-deformed state or precipitating during the recrystallization anneal, are known to strongly retard the progress of recrystallization. It was the aim of this study to elucidate these concurring effects of large particles, and small dispersoids as well as of a supersaturation of solutes on recrystallization in a ternary Al-Fe-Si model alloy. Samples were prepared with different pre-annealing treatments to produce different states of precipitation and supersaturation. Evolution of the microstructure and of the crystallographic texture was followed during cold rolling and recrystallization. Conclusions were drawn on the efficiency of recrystallization nucleation at the various nucleation sites and, especially, on the influence of dispersoids on recrystallization.
Date: December 31, 1996
Creator: Engler, O.
Partner: UNT Libraries Government Documents Department

Fluctuations during melting

Description: Repetitive melting and recrystallization, of crystals in a solid-liquid mixture in quasi-equilibrium, is reported. The experiments were performed at constant volume and ambient temperature inside a diamond anvil cell. The results, which the authors believed are the first to show the importance of fluctuations during a first order phase transition, can be partially understood on the basis of a recent generalized theory of Ostwald ripening.
Date: October 1, 1995
Creator: Grimsditch, M. & Karpov, V.
Partner: UNT Libraries Government Documents Department

Abnormal grain growth -- The origin of recrystallization nuclei?

Description: The origin of recrystallization nuclei is reviewed with particular emphasis on materials in which well-developed cells are present in the deformed state. Nucleation is discussed in terms of coarsening of the subgrain network that develops on annealing and an analogy is made with abnormal grain growth. The results of a theoretical analysis of abnormal growth are summarized. The Monte Carlo model for grain growth is adapted for variable grain boundary energy and mobility in order to investigate the behavior of individual grains with special properties. The simulation results show that both energy and mobility affect abnormal growth as expected from the theoretical analysis. The results are discussed in terms of the stability that subgrain networks may exhibit depending on their mean misorientation.
Date: August 1, 1997
Creator: Rollett, A.D. & Holm, E.A.
Partner: UNT Libraries Government Documents Department

Use of strain-annealing to evolve the grain boundary character distribution in polycrystalline copper

Description: We have used a two-step (low and high temperature) strain-annealing process to evolve the grain boundary character distribution (GBCD) in fully recrystallized oxygen-free electronic (OFE) Cu bar that was forged and rolled. Orientation imaging microscopy has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries was {similar_to}70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high-temperature process resulted in a reduction in the fraction of special GBs while both the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of the low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher temperature anneal and commensurate increase in the special fraction.
Date: November 6, 1996
Creator: King, W.E. & Schwartz, A.J.
Partner: UNT Libraries Government Documents Department

Capturing recrystallization of metals with a multi-scale materials model

Description: The final report for a Laboratory Directed Research and Development project entitled, ``Capturing Recrystallization of Metals in a Multiscale Materials Model'' is presented. In this project, deformation and recrystallization processes have been followed experimentally and theoretically in order to incorporate essential mechanisms from the defect (dislocation) and grain size length scales. A nonlinear rotational gradient theory has been developed which enables the incorporation of microstructural parameters. The evolution of these parameters during deformation and recrystallization has been characterized qualitatively and quantitatively, applying various electron optic techniques ranging over several length scales. The theoretical and experimental framework developed is general. It has been exemplified by an application to recrystallization in single crystals and bicrystals of aluminum. The recrystallization process has been modeled using a 3-D model for the changes in key structural parameters during recrystallization.
Date: April 1, 2000
Creator: Hughes, D. A.; Bammann, D. J.; Godfrey, A.; Prantil, V. C.; Holm, E. A.; Miodownik, M. A. et al.
Partner: UNT Libraries Government Documents Department

A Method to Improve Activation of Implanted Dopants in SiC

Description: Implantation of dopant ions in SiC has evolved according to the assumption that the best electrical results (i.e., carrier concentrations and mobility) is achieved by using the highest possible processing temperature. This includes implantation at &gt; 600 C followed by furnace annealing at temperatures as high as 1,750 C. Despite such aggressive and extreme processing, implantation suffers because of poor dopant activation, typically ranging between &lt; 2%--50% with p-type dopants represented in the lower portion of this range and n-types in the upper. Additionally, high-temperature processing can led to several problems including changes in the stoichiometry and topography of the surface, as well as degradation of the electrical properties of devices. A novel approach for increasing activation of implanted dopants in SiC and lowering the activation temperature will be discussed. This approach utilizes the manipulation of the ion-induced damage to enhance activation of implanted dopants. It will be shown that nearly amorphous layers containing a small amount of residual crystallinity can be recrystallized at temperatures below 900 C with little residual damage. It will be shown that recrystallization traps a high fraction of the implanted dopant residing within the amorphous phase (prior to annealing) onto substitutional sites within the SiC lattice.
Date: January 16, 2001
Creator: Holland, O.W.
Partner: UNT Libraries Government Documents Department


Description: Single crystals of magnesium-aluminate spinel MgAl{sub 2}O{sub 4} were irradiated with 340 keV Xe{sup 2} ions at {minus}173 C ({approximately} 100 K). A fluence of 1 x 10{sup 20} Xe/m{sup 2} created an amorphous layer at the surface of the samples. The samples were annealed for 1 h at different temperatures ranging from 130 C to 880 C. Recrystallization took place in the temperature interval between 610 C and 855 C. Transmission electron microscopy (TEM) images show two distinct layers near the surface: (1) a polycrystalline layer with columnar grain structure; and (2) a buried damaged layer epitaxial with the substrate. After annealing at 1100 C for 52 days, the profile of implanted Xe ions did not change, which means that Xe ions are not mobile in the spinel structure up to 1100 C. The thickness of the buried damaged layer decreased significantly in the 1100 C annealed sample comparing to the sample annealed for 1 h at 855 C.
Date: April 1, 2000
Creator: AFANASYEV, I. & AL, ET
Partner: UNT Libraries Government Documents Department

Mechanism of Ultrafine Grain Formation During Intense Plastic Straining in an Aluminum Alloy at Intermediate Temperatures

Description: The mechanism of grain formation during equal channel angular extrusion (ECAE) in a 2219 Al alloy has been studied at intermediate and high temperatures. It was shown that continuous dynamic recrystallization (CDRX) occurred during intense plastic straining and resulted in the formation of submicrometer grains at temperatures ranging from 250 C to 300 C. Higher temperatures (&lt; 300 C) hindered CDRX. This is caused by the fact that nucleation controls CDRX in the aluminum alloy. Dislocation rearrangements result in the formation of low angle boundary networks at moderate strain. The density of lattice dislocations determines the rate of subgrain formation. In addition, at lower temperatures a low energy dislocation structure (LEDS) forms concurrently with the subgrain structure and stabilizes it. The stability of the subgrain structure is very important for the resulting conversion of low angle boundaries into high angle ones with strain by extensive accumulation of mobile lattice dislocations. Increasing temperature in the range of intermediate temperatures suppresses LEDS formation and decreases the lattice dislocation density. This reduces the rate of the subgrain formation process and CDRX. As a result, at T = 400 C no recrystallized grains were found. At T = 475 C, the new grains form due to geometric dynamic recrystallization (GRX).
Date: September 21, 2000
Creator: Kaibyshev, R.; Sitdikov, O.; Mazurina, I, & Lesuer, D. R.
Partner: UNT Libraries Government Documents Department

Calculation of the evolution of the fuel microstructure in UMo alloys and implications for fuel swelling.

Description: The evolution of a cellular dislocation structure and subsequent recrystallization have been identified as important aspects of the irradiated UMo alloy microstructure that can have a strong impact on dispersion fuel swelling. Dislocation kinetics depends on the preferential bias of dislocations for interstitial compared to vacancies. This paper presents theoretical calculations for the evolution of a cellular dislocation structure, and recrystallization in U-10Mo. Implications for fuel swelling are discussed.
Date: October 1, 1999
Creator: Rest, J.; Hofman, G. L.; Konovalov, I. & Maslov, A.
Partner: UNT Libraries Government Documents Department

Coupled finite element-Monte Carlo simulation of microstructure and texture evolution during thermomechanical processing

Description: A novel simulation technique for predicting the microstructure and texture evolution during thermomechanical processing is presented. The technique involves coupling a finite element microstructural deformation model based on crystal plasticity with a Monte Carlo simulation of recovery and recrystallization. The finite element model captures the stored energy and the crystallographic orientation distributions in the deformed microstructure. The Monte Carlo simulation captures the microstructural evolution associated with recovery and recrystallization. A unique feature of the Monte Carlo simulation is that it treats recrystallization as a heterogeneous subgrain growth process, thus providing the natural link between nucleation and growth phenomena, and quantifying the role of recovery in these phenomena. Different nucleation mechanisms based on heterogeneous subgrain growth as well as strain induced boundary migration are automatically included in the recrystallization simulation. The simulations are shown to account for the extent of prior deformation on the microstructure and kinetics of recrystallization during subsequent annealing. The simulations also capture the influence of the presence of cube orientations in the initial microstructure, and the operation of non-octahedral slip during deformation of fcc polycrystals, on the recrystallization texture.
Date: November 1, 1998
Creator: Radhakrishnan, B.; Sarma, G. & Zacharia, T.
Partner: UNT Libraries Government Documents Department

Nickel and manganese interaction with calcite

Description: Many divalent metal cations sorb to calcite surfaces and incorporate into calcite to varying degrees. Since calcite may sorb trace elements in the environment, the factors controlling metal-calcite interactions are critical to understanding element cycling. The interaction of divalent metal cations with calcite can be critical to toxic metal immobilization, nutrient cycling, interpretation of past redox conditions, tracing fluid flow, for example. Sorption of Ni and Mn on calcite surfaces was studied by Zachara et al.. At any particular pH, the sorption of Mn on calcite was greater than Ni. This was attributed in part to the similarity of divalent Mn and Ca with respect to ion size. Although direct spectroscopic evidence was not available, sorption/desorption results suggested that Mn quickly forms a surface precipitate or solid solution while Ni forms a hydrated surface complex that may incorporate into calcite much more slowly via recrystallization. Because Mn(II) ionic radius is similar to that of Ca(II) (0.80 versus 1.0{angstrom}), and because MnCO{sub 3} has a structure similar to calcite, it is likely that Mn can substitute directly for Ca in the calcite structure. The ionic radius of Ni(II) is significantly smaller (0.69{angstrom}) and Ni(OH){sub 2} precipitation is likely to be favored in most systems. For Ni, direct substitution for Ca is less likely or may require more significant calcite lattice deformation.
Date: August 9, 1999
Creator: Doner, H & Zavarin, M
Partner: UNT Libraries Government Documents Department

Ultrasonic Studies of the Fundamental Mechanisms of Recrystallization and Sintering of Metals

Description: The purpose of this project was to develop a fundamental understanding of the interaction of an ultrasonic wave with complex media, with specific emphases on recrystallization and sintering of metals. A combined analytical, numerical, and experimental research program was implemented. Theoretical models of elastic wave propagation through these complex materials were developed using stochastic wave field techniques. The numerical simulations focused on finite element wave propagation solutions through complex media. The experimental efforts were focused on corroboration of the models developed and on the development of new experimental techniques. The analytical and numerical research allows the experimental results to be interpreted quantitatively.
Date: November 30, 2005
Creator: Turner, Joseph A.
Partner: UNT Libraries Government Documents Department