Papers by Keyword: Grain Size

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Authors: Jiao Luo, Miao Quan Li, Y.Q. Hu
Abstract: A constitutive equation has been established to describe the effect of grain size on the deformation behavior of Ti-6.62Al-5.14Sn-1.82Zr alloy during the high temperature. In this paper, firstly a steady flow stress model is proposed, and a function relating to the grain size is introduced to modify the steady flow stress model. Meanwhile, a microstructure model established by the fuzzy neural network method is applied to calculate the grain size of prior α phase during the high temperature deformation of Ti-6.62Al-5.14Sn-1.82Zr alloy. The calculated flow stress using the present constitutive equation shows a good agreement with the experimental flow stress of the Ti-6.62Al-5.14Sn-1.82Zr alloy. The relative maximum error was not more than 15%.
Authors: S. Nadir, M. Drache, J.P. Wignacourt, P. Conflant, M. Lagrenee, B. Mernari
Authors: Marcos Flavio de Campos
Abstract: The effect of crystalline imperfections (as for instance, grain size, inclusions and dislocations) on the coercivity of soft magnetic materials is additive. This only can be explained by an Energy Balance Model. By another hand, the angular dependence of the coercivity only can be explained with a Force Balance Model. Thus both models, Energy Balance and Force Balance have to be invoked for the construction of a general model. The effect of dislocations on the coercivity can be treated as short range magnetostrictive effect. The effect of inclusions needs the consideration of the global magnetostatic energy of the system. The dependence of the coercivity with the grain size can also be explained analyzing the magnetostatic energy. The idea of pinning of domain walls by crystalline defects is reformulated, and it is shown that the coercivity increase due to crystalline defects is principally caused by variations of the magnetostatic energy in the system.
Authors: Miao Quan Li, Jiao Luo
Abstract: Isothermal compression of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy is conducted on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1173 K to 1333 K, the strain rates ranging from 0.001 s-1 to 10.0 s-1 at an interval of an order magnitude and the height reductions ranging from 50% to 70%. The primary grain size is measured at an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software. A multi-scale constitutive model coupling the grain size, volume fraction and dislocation density is established to represent the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation, in which the flow stress is decomposed a thermal stress and an athermal stress. A Kock-Mecking model is adopted to describe the thermally activated stress, and an athermal stress model accounts for the working hardening and Hall-Petch effect. A genetic algorithm (GA)-based objective optimization technique is used for determining material constants in this study. The mean relative difference between the predicted and experimental flow stress is 5.98%, thus it can be concluded that the multi-scale constitutive model with high prediction precision can efficiently predict the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation.
Authors: M.O.H. Amuda, S. Mridha
Abstract: In this work, the preliminary result on the effect of cryogenic cooling on grain growth in weld is reported. Ferritic stainless steel weld produced under TIG torch in argon environment is cooled in liquid nitrogen. The weld structure is characterized using LOM, SEM and EDX spectroscopy. The results suggest that cryogenic cooling reduced the weld width within 2% to 5% and HAZ to 39% relative to those cooled in normal condition. This ensures that the area of the base metal affected and exposed to the weld thermal cycle is reduced and hence probably generates less metallurgical distortion. The cryogenic cooling also generated 14% to 36% grain refinement compared to welds cooled in normal condition.
Authors: Pierpaolo Carlone, Gaetano S. Palazzo
Abstract: In recent years, remarkable interest has been focused on the Friction Stir Welding (FSW) process, by academic as well as industrial research groups. Conceptually, the FSW process is quite simple: a non-consumable rotating tool is plunged between the adjoining edges of the parts to be welded and moved along the desired weld line. Frictional and viscous heat generation increases the work piece temperature, softening the processing material and forcing it to flow around the pin. Although FSW has been effectively applied in welding of several materials, such as copper, steel, magnesium, and titanium, considerable attention is still focused on aluminum welding, in particular for transport applications. Recent literature clearly evidenced microstructural variations in the stir zone, imputable to continuous dynamic recrystallization phenomena, leading to the formation of a finer equiaxed grains. Moreover, depending on the specific alloy, thermal cycles can induce coarsening or dissolution of precipitates in the thermo-mechanically affected zone (TMAZ) and in the heat affected zone (HAZ). The influence of the aforementioned microstructural aspects on mechanical properties and formability of FSWed assemblies is also well recognized. The aim of this paper is to numerically and experimentally investigate the influence of process parameters, namely rotating speed and welding speed, on microstructural aspects in AA2024-T3 friction stir butt welds. A three-dimensional Computational Fluid Dynamic (CFD) model has been implemented to simulate the process. A viscoplastic material model, based on Wright and Sheppard modification of the constitutive model initially proposed by Sellars and Tegart has been implemented in the commercial package ANSYS CFX, considering an Eulerian framework. Tool-workpiece interaction has been modeled assuming partial sticking/sliding condition, and incorporating both frictional and viscous contributions to the heat generation. Microstructural aspects have been numerically predicted using the Zenner-Holloman parameter and experimentally measured by means of conventional metallographic techniques. Satisfactory agreement has been found between simulated and experimental results. The influence of process parameters on mechanical properties has also been highlighted.
Authors: Sang Joo Lee, Seung Min Hyun, Seung Woo Han, Hak Joo Lee, Jang Hyun Kim, Young Il Kim
Abstract: Mechanical behavior of small size materials has been explored due to many industry applications such as MEMs and semiconductors. The accurate measurements for mechanical properties of thin films are very challenge due to several technical difficulties. The proposed solution is the Visual Image Tracing (VIT) strain measurement system coupled with a micro tensile testing unit, which consists of a piezoelectric actuator, load cell, microscope and CCD cameras. This system has shown advantages of real time strain monitoring during the test and ability to measure the Young’s modulus, yiled strength and Poisson’s ratio of the material. Free standing Au films 0.5, 1 and 2 μm thick with average grain sizes of 104, 148 and 219 nm prepared by sputtering were studied using VIT system. The yield stresses of the films are dependent on film thickness and grain size.
Authors: Shi Xing Zhang, Shao Kang Guan, Xin Tian Liu, Chun Li Mo
Abstract: A method of Monte Carlo combined with welding experiments was adopted to study the grain size and microstructure in welding heat affected zone of the ferrite stainless steel. Firstly, the kinetic equation of grain growth was established with the experimental data . Then , a simulation procedure based on the kinetic equation was worked out. Agreement between Monte Carlo simulation result and the real experiment results was obtained.
Authors: Shi Xing Zhang, Gang Yi Cai
Abstract: In this paper, Monte Carlo (MC) technology with welding experiments and thermal simulation experiments were introduced to simulate the grain growth process in welding heat affected zone(HAZ) of 1060 industrial pure aluminum. First, a kinetic model was defined by both experimental and statistics method. Then the thermal cycle was calculated and at the same time the simulation program was worked out based on MC technology. Thirdly, the grain growth process in HAZ was simulated during different welding heat input, which has great influence on grain growth in HAZ. The result of the simulation demonstrates the grain growth process dynamically and embodies the “thermal pin effect”. Good agreement between MC simulation results and the experimental results was obtained which can provide a reliable evidence for evaluating the welding craft and the weldability.
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