The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Baoqi Guo - One of the best experts on this subject based on the ideXlab platform.
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accelerated flow softening and dynamic transformation of ti 6al 4v alloy in two phase Region during hot deformation via coarsening α grain
Journal of Materials Science & Technology, 2020Co-Authors: Baoqi Guo, Fulin Jiang, Jie Teng, Hui Zhang, J J JonasAbstract:Abstract The flow softening is an important phenomenon during hot deformation of metallic materials. In the present work, a more evident flow softening of Ti-6Al-4V alloy when deformed in Two-Phase Region was observed in coarser α grain sample, which was attributed to an accelerated dynamic transformation from harder α phase into β phases. Notably, full β microstructure was observed in coarse grain samples at strain of 1.2, while retained α phase was observed in fine α grain specimens. In the views of thermodynamics and crystallographic analysis, the in-depth mechanisms of dynamic transformation were further investigated.
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Post-dynamic α to β phase transformation and reverse transformation of Ti-5Al-3V alloy after hot deformation in two phase Region
Materials & Design, 2020Co-Authors: Baoqi Guo, Fulin Jiang, Jie Teng, Hui Zhang, John J. JonasAbstract:Abstract The microstructural evolutions and resulted mechanical responses during isothermal holding of multipass hot deformation are essential aspects in the processing of high performance titanium alloys. In this work, isothermal holding testing was performed on a Ti-5Al-3V alloy after hot compression at temperatures of 900 °C, 930 °C and 960 °C, respectively. Stress relaxation, dilatometer measurements, and microstructure examinations (i.e. scanning electron microscope, electron backscatter diffraction and transmission electron microscope) were employed to investigate the phase transformation behaviors. The results showed a flow stress hardening phenomenon during the interrupted isothermal holding in two phase Region. The post-dynamic transformation from α to β phase took place first during the early stage of isothermal holding after hot deformation. With longer isothermal holding time, the reverse transformation of meta-stable β phase to α phase was then observed. Under TEM, the reverse transformed α phases were isolated from quenched α' phases. The in-depth mechanisms of post-dynamic α to β phase transformation and reverse transformation were discussed as well.
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Dynamic transformation of Ti–6Al–4V during torsion in the Two-Phase Region
Journal of Materials Science, 2018Co-Authors: Baoqi Guo, John J. Jonas, S. L. Semiatin, Stephen YueAbstract:Isothermal torsion tests were performed on a Ti–6Al–4V alloy in the Two-Phase Region. The results show that straining leads to an increase in the beta phase fraction, which increases slightly with strain rate. Transformation took place at 880, 940, 960, 980 and 1000 °C. The extent of this type of dynamic transformation (alpha to beta) was increased when the temperature approached the transus temperature. The reverse transformation (beta to alpha) occurred during isothermal holding after torsion and the volume fraction retransformed increased with time. The driving forces promoting dynamic and reverse transformation together with the energy barriers opposing these transformations were derived and compared. The critical stresses required to initiate dynamic transformation are calculated from the flow curves. This analysis confirms that the peak stresses are always higher than the critical stresses at the temperatures employed in the present tests, which makes it possible for the transformation to occur.
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Reverse Transformation Behavior of Ti-6Al-4V After Deformation in the Two-Phase Region
Metallurgical and Materials Transactions A, 2017Co-Authors: Baoqi Guo, Clodualdo Aranas, Binhan Sun, John J. JonasAbstract:Isothermal holding experiments were performed on a Ti-6Al-4V alloy after compression in the Two-Phase Region. The forward transformation took place during compression while the reverse transformation was diffusion controlled when the samples were held after unloading at 940 °C, 970 °C, and 1000 °C. Time-temperature-reverse transformation (TTRT) curves are derived, which indicate that the rate of reverse transformation is independent of temperature when the holding time is 18 seconds. By contrast, it depends on temperature when the holding time is increased to 180 and 1800 seconds.
James S. Harris - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Unstable Two-Phase Region in Wurtzite Group III Nitride Ternary Alloy Using Modified Valence Force Field Model
Japanese Journal of Applied Physics, 2000Co-Authors: Toru Takayama, Masaaki Yuri, Kunio Itoh, Takaaki Baba, James S. HarrisAbstract:The Group III-nitride ternary system is studied with respect to an unstable Two-Phase Region in the phase field. The unstable Two-Phase Region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in InN, GaN, and AlN is also taken into account in our model. According to the calculated results of the interaction parameters, the critical temperature for wurtzite InGaN, InAlN, and GaAlN are found to be 1967 K, 3399 K, and 181 K, respectively. This suggests that, at a typical growth temperature of 800–1000°C a wide unstable Two-Phase Region exists in both InGaN and InAlN. In order to show the validity of our calculation results, we compare the calculated results and the experimental results using the calculation of the interaction parameter for the InGaAs system. The calculated results agree well with the experimental results.
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Theoretical analysis of unstable Two-Phase Region and microscopic structure in wurtzite and zinc-blende InGaN using modified valence force field model
Journal of Applied Physics, 2000Co-Authors: Toru Takayama, Masaaki Yuri, Kunio Itoh, Takaaki Baba, James S. HarrisAbstract:A model to predict material characteristics of the InGaN ternary system, which is useful for blue and green light emitting and laser diodes, with respect to an unstable Two-Phase Region in the phase field and the first neighbor anion–cation bond length is developed. The unstable Region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field (VFF) model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The critical temperatures found in our analysis for wurtzite InGaN and zinc-blende InGaN are 1967 and 1668 K, respectively. This suggests that, at typical growth temperatures around 800 °C, a wide unstable Two-Phase Region exists in both wurtzite and zinc-blende structures. The modified VFF model can also predict the microscopic ...
John J. Jonas - One of the best experts on this subject based on the ideXlab platform.
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Post-dynamic α to β phase transformation and reverse transformation of Ti-5Al-3V alloy after hot deformation in two phase Region
Materials & Design, 2020Co-Authors: Baoqi Guo, Fulin Jiang, Jie Teng, Hui Zhang, John J. JonasAbstract:Abstract The microstructural evolutions and resulted mechanical responses during isothermal holding of multipass hot deformation are essential aspects in the processing of high performance titanium alloys. In this work, isothermal holding testing was performed on a Ti-5Al-3V alloy after hot compression at temperatures of 900 °C, 930 °C and 960 °C, respectively. Stress relaxation, dilatometer measurements, and microstructure examinations (i.e. scanning electron microscope, electron backscatter diffraction and transmission electron microscope) were employed to investigate the phase transformation behaviors. The results showed a flow stress hardening phenomenon during the interrupted isothermal holding in two phase Region. The post-dynamic transformation from α to β phase took place first during the early stage of isothermal holding after hot deformation. With longer isothermal holding time, the reverse transformation of meta-stable β phase to α phase was then observed. Under TEM, the reverse transformed α phases were isolated from quenched α' phases. The in-depth mechanisms of post-dynamic α to β phase transformation and reverse transformation were discussed as well.
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Dynamic transformation of Ti–6Al–4V during torsion in the Two-Phase Region
Journal of Materials Science, 2018Co-Authors: Baoqi Guo, John J. Jonas, S. L. Semiatin, Stephen YueAbstract:Isothermal torsion tests were performed on a Ti–6Al–4V alloy in the Two-Phase Region. The results show that straining leads to an increase in the beta phase fraction, which increases slightly with strain rate. Transformation took place at 880, 940, 960, 980 and 1000 °C. The extent of this type of dynamic transformation (alpha to beta) was increased when the temperature approached the transus temperature. The reverse transformation (beta to alpha) occurred during isothermal holding after torsion and the volume fraction retransformed increased with time. The driving forces promoting dynamic and reverse transformation together with the energy barriers opposing these transformations were derived and compared. The critical stresses required to initiate dynamic transformation are calculated from the flow curves. This analysis confirms that the peak stresses are always higher than the critical stresses at the temperatures employed in the present tests, which makes it possible for the transformation to occur.
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Reverse Transformation Behavior of Ti-6Al-4V After Deformation in the Two-Phase Region
Metallurgical and Materials Transactions A, 2017Co-Authors: Baoqi Guo, Clodualdo Aranas, Binhan Sun, John J. JonasAbstract:Isothermal holding experiments were performed on a Ti-6Al-4V alloy after compression in the Two-Phase Region. The forward transformation took place during compression while the reverse transformation was diffusion controlled when the samples were held after unloading at 940 °C, 970 °C, and 1000 °C. Time-temperature-reverse transformation (TTRT) curves are derived, which indicate that the rate of reverse transformation is independent of temperature when the holding time is 18 seconds. By contrast, it depends on temperature when the holding time is increased to 180 and 1800 seconds.
Toru Takayama - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Unstable Two-Phase Region in Wurtzite Group III Nitride Ternary Alloy Using Modified Valence Force Field Model
Japanese Journal of Applied Physics, 2000Co-Authors: Toru Takayama, Masaaki Yuri, Kunio Itoh, Takaaki Baba, James S. HarrisAbstract:The Group III-nitride ternary system is studied with respect to an unstable Two-Phase Region in the phase field. The unstable Two-Phase Region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in InN, GaN, and AlN is also taken into account in our model. According to the calculated results of the interaction parameters, the critical temperature for wurtzite InGaN, InAlN, and GaAlN are found to be 1967 K, 3399 K, and 181 K, respectively. This suggests that, at a typical growth temperature of 800–1000°C a wide unstable Two-Phase Region exists in both InGaN and InAlN. In order to show the validity of our calculation results, we compare the calculated results and the experimental results using the calculation of the interaction parameter for the InGaAs system. The calculated results agree well with the experimental results.
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Theoretical analysis of unstable Two-Phase Region and microscopic structure in wurtzite and zinc-blende InGaN using modified valence force field model
Journal of Applied Physics, 2000Co-Authors: Toru Takayama, Masaaki Yuri, Kunio Itoh, Takaaki Baba, James S. HarrisAbstract:A model to predict material characteristics of the InGaN ternary system, which is useful for blue and green light emitting and laser diodes, with respect to an unstable Two-Phase Region in the phase field and the first neighbor anion–cation bond length is developed. The unstable Region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field (VFF) model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The critical temperatures found in our analysis for wurtzite InGaN and zinc-blende InGaN are 1967 and 1668 K, respectively. This suggests that, at typical growth temperatures around 800 °C, a wide unstable Two-Phase Region exists in both wurtzite and zinc-blende structures. The modified VFF model can also predict the microscopic ...
Ulrich K. Deiters - One of the best experts on this subject based on the ideXlab platform.
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Adiabatic Processes in the Vapor–Liquid Two-Phase Region. 2. Binary Mixtures
Industrial & Engineering Chemistry Research, 2015Co-Authors: Attila R Imre, Sergio E. Quiñones-cisneros, Ulrich K. DeitersAbstract:The phase equilibrium conditions and entropy balance equations for multicomponent fluid mixtures are expressed with a density-based formalism (“isochoric thermodynamics”), and isentropes in the one- and Two-Phase Region are computed from equations of state; here the Peng–Robinson equation is used as an example. Griffiths’ theorem—one- and Two-Phase isentropes meet at a maxcondenbar point (pressure maximum of an isopleth) with equal slopes—could be confirmed. For chemically similar compounds at subcritical conditions, the resulting isentrope patterns are similar to those of pure fluids. If one of the components is supercritical, it is possible that, along a part of a Two-Phase isentrope, the liquid phase has a higher molar entropy than the vapor phase (“entropic inversion”). The phenomenon not only poses a numerical problem, but is also relevant for the question whether a Two-Phase isentrope can run into the llg three-phase curve.
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Adiabatic Processes in the Liquid–Vapor Two-Phase Region. 1. Pure Fluids
Industrial & Engineering Chemistry Research, 2014Co-Authors: Attila R Imre, Sergio E. Quiñones-cisneros, Ulrich K. DeitersAbstract:Adiabatic processes in the liquid–vapor Two-Phase Region were studied with several equations of state. The comparison of the resulting isentropes, particularly their patterns in quality (fraction of vapor phase) vs temperature diagrams, indicates that there are two different classes of fluids: One class shows a simple pattern where isentropes entering the Two-Phase Region never leave it again; the other shows a more complicated pattern with reentrant isentropes, which may either cross the entire Two-Phase Region or exhibit a retrograde behavior. The existence of these two classes can be related to the shapes of entropy–volume or temperature–entropy curves, and these in turn to the temperature dependence of ideal-gas heat capacities. The Two-Phase isentrope that runs to the critical point approaches it with an infinite slope in the quality–temperature diagram. The slope is positive for reference equations of state, but negative for all other equations of state used in this work.
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adiabatic processes in the liquid vapor two phase Region 1 pure fluids
Industrial & Engineering Chemistry Research, 2014Co-Authors: Attila R Imre, Sergio E Quinonescisneros, Ulrich K. DeitersAbstract:Adiabatic processes in the liquid–vapor Two-Phase Region were studied with several equations of state. The comparison of the resulting isentropes, particularly their patterns in quality (fraction of vapor phase) vs temperature diagrams, indicates that there are two different classes of fluids: One class shows a simple pattern where isentropes entering the Two-Phase Region never leave it again; the other shows a more complicated pattern with reentrant isentropes, which may either cross the entire Two-Phase Region or exhibit a retrograde behavior. The existence of these two classes can be related to the shapes of entropy–volume or temperature–entropy curves, and these in turn to the temperature dependence of ideal-gas heat capacities. The Two-Phase isentrope that runs to the critical point approaches it with an infinite slope in the quality–temperature diagram. The slope is positive for reference equations of state, but negative for all other equations of state used in this work.
