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J Shen - One of the best experts on this subject based on the ideXlab platform.
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microstructural mechanisms during multidirectional isothermal forging of as cast ti 6al 4v Alloy with an initial lamellar microstructure
Journal of Alloys and Compounds, 2019Co-Authors: Zhen Zhang, A H Feng, J ShenAbstract:Abstract Microstructural evolution and tensile properties of Ti-6al-4v Alloy with an initial lamellar microstructure during the multidirectional isothermal forging (MDIF) were investigated. After three steps isothermal forging, a homogeneous equiaxed grained microstructure with an average grain size of 1.9 μm was achieved. The grain refinement mechanism included both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). The necklaces of new DDRX grains with high angle grain boundaries (HAGBs) were formed along the initial β grain boundaries. Grain subdivision was through CDRX. The fraction of recrystallization and the homogeneity of microstructure were improved with the isothermal forging steps increasing, the fractions of recrystallization increased from 43% to 63% and the fractions of HAGBs increased from 48% to 71%, respectively. The tensile properties of as-cast Ti-6al-4v Alloy were significantly improved at both room temperature and 400 °C, respectively. The yield strength, ultimate tensile strength and elongation increased 21%, 23%, and 210% at room temperature, respectively. And at 400 °C, the yield strength, ultimate tensile strength and elongation increased 46%, 48%, and 21%, respectively. The fracture mechanism changed from brittle fracture to ductile fracture after the MDIF process.
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achieving grain refinement and enhanced mechanical properties in ti 6al 4v Alloy produced by multidirectional isothermal forging
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Zhen Zhang, A H Feng, J ShenAbstract:Abstract This study investigated the principle of multidirectional isothermal forging (MDIF) and determined the major microstructural evolution features and unique room-temperature mechanical properties of extra-low interstitial-grade Ti–6Al–4V Alloy. The grain refinement mechanism, grain boundary characteristics, and phase transformation during MDIF were explored. After three-step MDIF, a homogeneous microstructure with a grain size of about 0.5 µm was produced. The ultrafine grained Ti–6Al–4V Alloy exhibited high yield strength (1170 MPa), high ultimate tensile strength (1190 MPa), and good ductility (10.4%). The mechanism of grain refinement during MDIF included continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Grain subdivision resulted from CDRX or the transformation of cellular dislocation substructures into new ultrafine grains. The necklace of new DDRX grains formed along the initial grain boundaries of the Ti–6Al–4V Alloy. The main strengthening mechanisms were grain boundary and dislocation strengthening. The strength and grain size followed the typical Hall–Petch relationship.
Zhen Zhang - One of the best experts on this subject based on the ideXlab platform.
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microstructural mechanisms during multidirectional isothermal forging of as cast ti 6al 4v Alloy with an initial lamellar microstructure
Journal of Alloys and Compounds, 2019Co-Authors: Zhen Zhang, A H Feng, J ShenAbstract:Abstract Microstructural evolution and tensile properties of Ti-6al-4v Alloy with an initial lamellar microstructure during the multidirectional isothermal forging (MDIF) were investigated. After three steps isothermal forging, a homogeneous equiaxed grained microstructure with an average grain size of 1.9 μm was achieved. The grain refinement mechanism included both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). The necklaces of new DDRX grains with high angle grain boundaries (HAGBs) were formed along the initial β grain boundaries. Grain subdivision was through CDRX. The fraction of recrystallization and the homogeneity of microstructure were improved with the isothermal forging steps increasing, the fractions of recrystallization increased from 43% to 63% and the fractions of HAGBs increased from 48% to 71%, respectively. The tensile properties of as-cast Ti-6al-4v Alloy were significantly improved at both room temperature and 400 °C, respectively. The yield strength, ultimate tensile strength and elongation increased 21%, 23%, and 210% at room temperature, respectively. And at 400 °C, the yield strength, ultimate tensile strength and elongation increased 46%, 48%, and 21%, respectively. The fracture mechanism changed from brittle fracture to ductile fracture after the MDIF process.
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achieving grain refinement and enhanced mechanical properties in ti 6al 4v Alloy produced by multidirectional isothermal forging
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Zhen Zhang, A H Feng, J ShenAbstract:Abstract This study investigated the principle of multidirectional isothermal forging (MDIF) and determined the major microstructural evolution features and unique room-temperature mechanical properties of extra-low interstitial-grade Ti–6Al–4V Alloy. The grain refinement mechanism, grain boundary characteristics, and phase transformation during MDIF were explored. After three-step MDIF, a homogeneous microstructure with a grain size of about 0.5 µm was produced. The ultrafine grained Ti–6Al–4V Alloy exhibited high yield strength (1170 MPa), high ultimate tensile strength (1190 MPa), and good ductility (10.4%). The mechanism of grain refinement during MDIF included continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Grain subdivision resulted from CDRX or the transformation of cellular dislocation substructures into new ultrafine grains. The necklace of new DDRX grains formed along the initial grain boundaries of the Ti–6Al–4V Alloy. The main strengthening mechanisms were grain boundary and dislocation strengthening. The strength and grain size followed the typical Hall–Petch relationship.
Takayuki Takasugi - One of the best experts on this subject based on the ideXlab platform.
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effects of combined plasma carburizing and shot peening on fatigue and wear properties of ti 6al 4v Alloy
Surface & Coatings Technology, 2009Co-Authors: N Tsuji, S Tanaka, Takayuki TakasugiAbstract:Abstract The effects of combined plasma-carburizing and shot-peening on fatigue and wear properties of Ti–6Al–4V Alloy specimen were investigated. Surface morphology and roughness, microstructure, compressive residual stress, work hardening state, and micro-hardness on the surface modified layer in the Ti–6Al–4V Alloy specimen were measured and analyzed. The shot-peening effectively induces highly compressive residual stress and work hardening states on the surface layer of the plasma-carburized Ti–6Al–4V Alloy specimen. Consequently, the fatigue life of plasma-carburized Ti–6Al–4V Alloy specimen has been significantly improved by subsequent shot-peening. The cracks of both shot-peened and shot-peened carburized specimens initiated on the surface at higher applied stress levels. On the contrary, interior-originating fractures occurred at lower applied stress levels. Corresponding to this behavior, the S – N curves show the shape of two-step stages. The wear resistance of Ti–6Al–4V Alloy specimen was also significantly improved by the hardness increase on the surface layer by combination of plasma-carburizing and shot-peening.
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effect of combined plasma carburizing and deep rolling on notch fatigue property of ti 6al 4v Alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: N Tsuji, S Tanaka, Takayuki TakasugiAbstract:This paper discusses the effects of a combination of plasma-carburizing and deep-rolling on notch fatigue properties of a Ti-6al-4v Alloy. Circumferentially V-notched cylindrical Ti-6al-4v Alloy specimens were plasma-carburized at a relatively low temperature for the improvement of wear resistance, and then, deep-rolled at the notch root for inducing compressive residual stress. Scanning electron microscopy, optical microscopy, laser scanning microscopy, surface roughness tester, and micro-hardness tester were used to characterize the modified surface layer at the notch root. Axial loading fatigue tests (R = 0.1) were performed using a servo-hydraulic testing machine in a laboratory atmosphere at an ambient temperature. The notch fatigue life of the specimen was reduced by plasma-carburizing due to the brittleness caused by the higher hardness in addition to the disappearance of compressive residual stress on the notched surface, but remarkably improved by the subsequent deep-rolling. The surface layer containing the compressive residual stress and the work hardening induced by deep-rolling effectively prevented and delayed the fatigue crack initiation and propagation of deep-rolled carburized specimen.
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evaluation of surface modified ti 6al 4v Alloy by combination of plasma carburizing and deep rolling
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: N Tsuji, S Tanaka, Takayuki TakasugiAbstract:Abstract Plasma surface diffusion processes such as plasma-carburizing and nitriding have been used to improve tribological properties of titanium and its Alloys. However, the improvement of fatigue strength by these processes has not been successful due to brittleness introduced in the high-hardness surface layer and the disappearance of compressive residual stress and grain growth by heating. In this work, a Ti–6Al–4V Alloy sample was plasma-carburized at a relatively low temperature to improve wear resistance, and then, deep-rolled to induce compressive residual stress. Scanning electron microscopy, optical microscopy, laser scanning microscopy, surface roughness tester, X-ray diffractometer, and micro-hardness tester were used to characterize the modified surface layer. The residual stress and work hardening state was analyzed by X-ray diffraction techniques. The effect of deep-rolling on fatigue strength and wear resistance of plasma-carburized Ti–6Al–4V Alloy was also investigated. The fatigue properties and wear resistance of Ti–6Al–4V Alloy modified by a combination of low-temperature plasma-carburizing and deep-rolling were significantly improved in comparison with those of the unmodified Ti–6Al–4V Alloy.
Chong Soo Lee - One of the best experts on this subject based on the ideXlab platform.
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effect of microstructure on deformation behavior of ti 6al 4v Alloy during compressing process
Materials & Design, 2012Co-Authors: Ren Guo Guan, Zhan Yong Zhao, Chong Soo LeeAbstract:Abstract In order to obtain a more quantitative understanding of the formability of Ti–6Al–4V Alloys related to different initial microstructures, hot compression tests were conducted on Alloys with three different initial microstructures, and Ti–6Al–4V Alloy forging process for production of gear reverse idle was also studied. Three different microstructures were first established by combinations of several heat treatments for the first time. Average cooling rate obviously affects α lamellar spacing but does not strongly affect colony size. Measured flow curves for Ti–6Al–4V Alloy exhibited peak flow stresses at relative low strains followed flow softening. For a given temperature and strain rate microstructures with finer lamellar spacing exhibited higher flow stresses. Flow curves for different colony sizes were almost coincident. It is concluded that α lamellar spacing strongly affects flow stress but the effect of colony size on flow stress is weak. Deformation resistances for different microstructures were predicted under various deformation conditions using hyperbolic sine law. The predicted constitutive functions coincided well with the results of hot compression tests. Dynamic recovery, dynamic recrystallization and breakage of lamellar structures result in finer microstructures and flow softening during hot forging processing. Cracks were likely to form with coarser lamellar spacing samples at lower forging temperatures.
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prediction of microstructure evolution in hot backward extrusion of ti 6al 4v Alloy
Journal of Metallurgy, 2012Co-Authors: Jongtaek Yeom, Jeoung Han Kim, Jaekeun Hong, Nhokwang Park, Chong Soo LeeAbstract:Microstructure evolution of Ti-6al-4v Alloy during hot backward extrusion process was simulated with the combined approaches of finite element method (FEM) and microstructure prediction model. From experimental analysis, it can be found that the change of microstructure during hot forming process of titanium Alloy has a close relation to α/β phase transformation and grain growth behaviour. A microstructure prediction model was established by considering the change of volume fractions and grain size of both phases varying with process variables and then implemented into the user-defined subroutine of FEM analysis. In order to demonstrate the reliability of the model, the volume fraction and grain size of primary α phase during the hot backward extrusion process of Ti-6al-4v Alloy were simulated. The simulation results were compared with the experimental ones.
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effects of temperature and initial microstructure on the equal channel angular pressing of ti 6al 4v Alloy
Scripta Materialia, 2003Co-Authors: W S Jung, Dong Hyuk Shin, Chong Soo LeeAbstract:Abstract Equal channel angular pressing of Ti–6Al–4V Alloy was successfully carried out isothermally above 600 °C. The equiaxed microstructure presented more uniform material flow than the Widmanstatten microstructure, which was discussed in relation to flow softening behavior of the two microstructures.
Jiao Luo - One of the best experts on this subject based on the ideXlab platform.
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prediction of flow stress in isothermal compression of ti 6al 4v Alloy using fuzzy neural network
Materials & Design, 2010Co-Authors: Jiao LuoAbstract:Abstract Isothermal compression of Ti–6Al–4V Alloy at the deformation temperatures ranging from 1093 K to 1303 K with an interval 20 K, the strain rates ranging from 0.001 s −1 to 10.0 s −1 and the height reductions ranging from 20% to 60% with an interval 10% were carried out on a Thermecmaster-Z simulator. Based on the experimental results, a model for the flow stress in isothermal compression of Ti–6Al–4V Alloy was established in terms of the fuzzy neural network (FNN) with a back-propagation learning algorithm using strain, strain rate and deformation temperature as inputs. The maximum difference and the average difference between the predicted and the experimental flow stress are 18.7% and 4.76%, respectively. The comparison between the predicted results based on the FNN model for flow stress and those using the regression method has illustrated that the FNN model is more efficient in predicting the flow stress of Ti–6Al–4V Alloy.
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effect of the strain on the deformation behavior of isothermally compressed ti 6al 4v Alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Jiao LuoAbstract:Abstract The deformation behavior of isothermally compressed Ti–6Al–4V Alloy in the deformation temperature range from 1093 K to 1303 K, the strain rate range from 0.001 s −1 to 10.0 s −1 and the height reduction range from 20% to 60% has been investigated in depth. Effect of the strain on the flow stress, the grain size and the apparent activation energy for deformation of isothermally compressed Ti–6Al–4V Alloy is analyzed. The results show that the apparent activation energy for deformation and the grain size of isothermally compressed Ti–6Al–4V Alloy in the α + β two-phase region vary slightly with strain: the activation energy increases with strain after an early drop as the primary α grain size varies with strain. On the other hand, the apparent activation energy for deformation of isothermally compressed Ti–6Al–4V Alloy in the β single-phase region increases firstly with the increasing of strain and then does that slightly in the strain range from 0.3 to 0.7. A processing map of the isothermally compressed Ti–6Al–4V Alloy is constructed at a strain of 0.6. The processing map of isothermally compressed Ti–6Al–4V Alloy exhibits that the optimal processing parameters are the deformation temperature of 1143 K and the strain rate of 0.001 s −1 . Meanwhile, two instability domains in the processing map of isothermally compressed Ti–6Al–4V Alloy are as follows: one is in the deformation temperature range from 1093 K to 1183 K and the strain rate range from 0.011 s −1 to 2.02 s −1 , and another is in the deformation temperature range from 1243 K to 1303 K and the strain rate range from 1.0 s −1 to 10.0 s −1 .