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Jishan Zhang - One of the best experts on this subject based on the ideXlab platform.
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Enhanced grain refinement in AA7050 Al alloy by deformation-Induced Precipitation
Materials Science and Engineering: A, 2012Co-Authors: Yuanhua Cai, Yujing Lang, Lingyong Cao, Jishan ZhangAbstract:Abstract In this study, an improved double-step thermomechanical treatment was proposed for producing fine grain structure of high-strength Al–Zn–Mg–Cu series alloy based on deformation-Induced Precipitation. The new method composed of a low temperature pre-deformation and a traditional hot rolling. Effects of this proposed treatment on microstructure and properties of the alloy were studied using optical microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests. The microstructural analysis results show that the pre-deformation can accelerate both formation and spheroidization of the fine precipitates. Those deformation-Induced precipitates could exert more drag force on migrations of the grain boundaries. So, recovery and coarseness of those deformed grains can be suppressed during subsequent heating and hot rolling, contributing to the final fine-grain structure of the AA7050 alloy. The properties test results reveal that the alloy processed by the double-step thermomechanical treatment displays superior strength and elongation than the conventional hot-rolled alloy because of the fine grain.
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effect of strain Induced Precipitation on the low angle grain boundary in aa7050 aluminum alloy
Materials & Design, 2011Co-Authors: Yujing Lang, Jishan ZhangAbstract:Abstract Effects of the particles Induced by strain on dynamic recrystallization and microstructure of the AA7050 aluminum alloy were investigated during hot deformation using X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD). Experimental results showed that partial recrystallized grains containing little sub-structure were produced during the solution treatment. Numerous particles were successfully obtained by the strain-Induced Precipitation during first-pass deformation at 573 K. The deformation promoted spheroidization and refinement of the precipitate particles. Then these particles pinned dislocations and grain boundaries inhibiting dynamic recrystallization during second-pass high-temperature deformation at 673 K and low angle grain boundary fraction was increased significantly to 83.8%. Furthermore, the tensile test indicated that microstructure with numerous low angle boundaries (LAGBs) and 5 μm sub-grains had increased the strength and ductility of the AA7050 aluminum alloy.
Sebastián F. Medina - One of the best experts on this subject based on the ideXlab platform.
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Model for Strain-Induced Precipitation Kinetics in Microalloyed Steels
Metallurgical and Materials Transactions A, 2013Co-Authors: Sebastián F. Medina, Alberto Quispe, Manuel GómezAbstract:Based on Dutta and Sellars’s expression for the start of strain-Induced Precipitation in microalloyed steels, a new model has been constructed which takes into account the influence of variables such as microalloying element percentages, strain, temperature, strain rate, and grain size. Although the equation given by these authors reproduces the typical “C” shape of the Precipitation start time (Ps) curve well, the expression is not reliable for all cases. Recrystallization–Precipitation–time–temperature diagrams have been plotted thanks to a new experimental study carried out by means of hot torsion tests on approximately twenty microalloyed steels with different Nb, V, and Ti contents. Mathematical analysis of the results recommends the modification of some parameters such as the supersaturation ratio (Ks) and constant B, which is no longer a constant, but a function of Ks when the latter is calculated at the nose temperature (TN) of the Ps curve. The value of parameter B is deduced from the minimum point or nose of the Ps curve, where ∂t0.05/∂T is equal to zero, and it can be demonstrated that B cannot be a constant. The new expressions for these parameters are derived from the latest studies undertaken by the authors and this work represents an attempt to improve the model. The expressions are now more consistent and predict the Precipitation–time–temperature curves with remarkable accuracy. The model for strain-Induced Precipitation kinetics is completed by means of Avrami’s equation.
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Influence of Temperature on Strain Induced Precipitation Kinetics in Microalloyed Steels
Materials Science Forum, 2012Co-Authors: Sebastián F. Medina, Alberto Quispe, Manuel GómezAbstract:Starting from the expression of Dutta and Sellars for the beginning of strain Induced Precipitation in microalloyed steels, the influence of temperature on t0.05 parameter has been studied. Although the equation given by these authors reproduces well the typical “C” shape of the curve of Precipitation start time Ps, the expression is not reliable for all cases. The Precipitation-time-temperature (PTT) diagrams have been plotted thanks to a new experimental study carried out by means of hot torsion tests on approximately twenty microalloyed steels having different contents of Nb, V and Ti. Mathematical analysis of results recommends the modification of some parameters such as supersaturation ratio (Ks) and constant B, which is no longer a constant but a function of Ks when the latter is calculated at the nose temperature (TN) of curve Ps. The value of parameter B is deduced from the minimum point or nose of the Ps curve, where ∂t0.05/∂T is equal to zero, and it can be demonstrated that B cannot be a constant. The new expressions for these parameters derive from the latest studies developed by the authors and this work supposes an attempt to improve the model. The expressions are now more consistent and predict with remarkable accuracy the PTT curves.
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Strain Induced Precipitation effect on austenite static recrystallisation in microalloyed steels
Materials Science and Technology, 2003Co-Authors: Sebastián F. Medina, Alberto Quispe, Manuel GómezAbstract:Abstract Using torsion tests and applying the back extrapolation method, the strain Induced Precipitation effect on austenite static recrystallisation in vanadium and niobium microalloyed steels has been studied and a model has been constructed. This model takes account of Precipitation and its influence on recrystallisation kinetics, in particular on the activation energy, which is increased. The model is applied at temperatures below the temperature at which inhibition of recrystallisation commences owing to the Induced Precipitation. The new values of activation energy can be three times higher than the activation energy before Precipitation has started, depending on the contents of elements responsible for the Precipitation (Nb, V, N, C).
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Recrystallization-Induced Precipitation Interaction in a Medium Carbon Vanadium Microalloyed Steel
ISIJ International, 1997Co-Authors: Alberto Quispe, Sebastián F. Medina, P. VallesAbstract:Using torsion tests, a study has been made of Recrystallization-Precipitation (R-P) interaction in a vanadium microalloyed steel for two strains (0.20 and 0.35). When strain Induced Precipitation starts, the recrystallized fraction deviates from Avrami's equation, giving rise to the formation of a plateau on the curves which represent the recrystallized fraction against time. This makes it possible to know the moment at which Precipitation starts (Ps) and the moment at which it finishes (Pf). After the end of Precipitation, recrystallization continues to progress in accordance with Avrami's law. Recrystallization-Precipitation-Time-Temperature (RPTT) diagrams have been drawn, superposing on them the lines corresponding to different recrystallized fractions. This makes it possible to represent in graph form the Recrystallization-Precipitation interaction and the determination of the static recrystallization critical temperature (SRCT). It is demonstrated that during the interval of time in which Precipitation occurs (Pf - Ps), recrystallization does not advance. The work which has been carried out establishes new aspects in the phenomenon of R-P interaction.
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Influence of Strain on Induced Precipitation Kinetics in Microalloyed Steels
ISIJ International, 1996Co-Authors: Sebastián F. Medina, Alberto QuispeAbstract:Using torsion tests and applying the back extrapolation method, the statically recrystallized fraction of low carbon microalloyed steels containing vanadium, niobium and titanium, respectively, has been determined for different temperatures and strains. From the recrystallized fraction against time curves it is possible to draw Precipitation-time-temperature (PTT) diagrams. These diagrams show that the strain does not affect Precipitation kinetics in an independent manner, but that this influence is related with the microalloy content. The greater the strain applied, the shorter the incubation time of Induced Precipitation, but this influence diminishes as the microalloy content increases. It is also demonstrated that the incubation time is practically independent of the nature of the metal microalloy (V, Ti, Nb). In this sense, new expressions are proposed to relate the incubation and Precipitation end times with the strain and the microalloy content. A model is also established for Precipitation kinetics at the curve nose temperature.
Manuel Gómez - One of the best experts on this subject based on the ideXlab platform.
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Model for Strain-Induced Precipitation Kinetics in Microalloyed Steels
Metallurgical and Materials Transactions A, 2013Co-Authors: Sebastián F. Medina, Alberto Quispe, Manuel GómezAbstract:Based on Dutta and Sellars’s expression for the start of strain-Induced Precipitation in microalloyed steels, a new model has been constructed which takes into account the influence of variables such as microalloying element percentages, strain, temperature, strain rate, and grain size. Although the equation given by these authors reproduces the typical “C” shape of the Precipitation start time (Ps) curve well, the expression is not reliable for all cases. Recrystallization–Precipitation–time–temperature diagrams have been plotted thanks to a new experimental study carried out by means of hot torsion tests on approximately twenty microalloyed steels with different Nb, V, and Ti contents. Mathematical analysis of the results recommends the modification of some parameters such as the supersaturation ratio (Ks) and constant B, which is no longer a constant, but a function of Ks when the latter is calculated at the nose temperature (TN) of the Ps curve. The value of parameter B is deduced from the minimum point or nose of the Ps curve, where ∂t0.05/∂T is equal to zero, and it can be demonstrated that B cannot be a constant. The new expressions for these parameters are derived from the latest studies undertaken by the authors and this work represents an attempt to improve the model. The expressions are now more consistent and predict the Precipitation–time–temperature curves with remarkable accuracy. The model for strain-Induced Precipitation kinetics is completed by means of Avrami’s equation.
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Influence of Temperature on Strain Induced Precipitation Kinetics in Microalloyed Steels
Materials Science Forum, 2012Co-Authors: Sebastián F. Medina, Alberto Quispe, Manuel GómezAbstract:Starting from the expression of Dutta and Sellars for the beginning of strain Induced Precipitation in microalloyed steels, the influence of temperature on t0.05 parameter has been studied. Although the equation given by these authors reproduces well the typical “C” shape of the curve of Precipitation start time Ps, the expression is not reliable for all cases. The Precipitation-time-temperature (PTT) diagrams have been plotted thanks to a new experimental study carried out by means of hot torsion tests on approximately twenty microalloyed steels having different contents of Nb, V and Ti. Mathematical analysis of results recommends the modification of some parameters such as supersaturation ratio (Ks) and constant B, which is no longer a constant but a function of Ks when the latter is calculated at the nose temperature (TN) of curve Ps. The value of parameter B is deduced from the minimum point or nose of the Ps curve, where ∂t0.05/∂T is equal to zero, and it can be demonstrated that B cannot be a constant. The new expressions for these parameters derive from the latest studies developed by the authors and this work supposes an attempt to improve the model. The expressions are now more consistent and predict with remarkable accuracy the PTT curves.
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Strain Induced Precipitation effect on austenite static recrystallisation in microalloyed steels
Materials Science and Technology, 2003Co-Authors: Sebastián F. Medina, Alberto Quispe, Manuel GómezAbstract:Abstract Using torsion tests and applying the back extrapolation method, the strain Induced Precipitation effect on austenite static recrystallisation in vanadium and niobium microalloyed steels has been studied and a model has been constructed. This model takes account of Precipitation and its influence on recrystallisation kinetics, in particular on the activation energy, which is increased. The model is applied at temperatures below the temperature at which inhibition of recrystallisation commences owing to the Induced Precipitation. The new values of activation energy can be three times higher than the activation energy before Precipitation has started, depending on the contents of elements responsible for the Precipitation (Nb, V, N, C).
Yutai Katoh - One of the best experts on this subject based on the ideXlab platform.
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transmutation Induced Precipitation in tungsten irradiated with a mixed energy neutron spectrum
Acta Materialia, 2019Co-Authors: Xunxiang Hu, Chad M Parish, Kun Wang, Takaaki Koyanagi, B P Eftink, Yutai KatohAbstract:Abstract Transmutation-Induced Precipitation in neutron-irradiated tungsten is an important performance concern for its application as plasma facing material in fusion reactors. In this study, segregation and Precipitation of transmutant elements in single crystal and polycrystal tungsten irradiated at 460–1100 °C to 0.02–2.4 displacements per atom (dpa) in the High Flux Isotope Reactor were investigated using transmission electron microscopy. The results indicated that nanoscale W-Re-Os clusters were identified in the low dose regime from 0.02 to 0.44 dpa with irradiation temperature lower than 800 °C while acicular-shape precipitates formed when irradiation dose is higher than 1.5 dpa. A tentative roadmap of the kinetics process of the transmutation-Induced Precipitation in neutron-irradiated tungsten is presented characterizing the defect features (i.e., W-Re-Os clusters and precipitates) consisting of transmutant elements in tungsten irradiated to various doses. All TEM-visible voids were associated with the acicular-shape precipitates. Voids were formed prior to the formation of acicular-shape precipitates and act as strong trapping sites for mobile species involved in the Precipitation together with dislocations. Thermal stability of W-Re-Os clusters was assessed by performing a 2-h anneal at 1200 °C on tungsten irradiated to 0.44 dpa at 705 °C. The kinetics process of transmutant elements and radiation defects are discussed to reveal the underlying mechanisms controlling the formation of precipitates in tungsten.
Eric J. Palmiere - One of the best experts on this subject based on the ideXlab platform.
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Characterisation of strain-Induced Precipitation behaviour in microalloyed steels during thermomechanical controlled processing
Materials Characterization, 2017Co-Authors: Peng Gong, Eric J. Palmiere, W.m. RainforthAbstract:The temperature at which thermomechanical controlled processing is undertaken strongly influences strain-Induced Precipitation (SIP) in microalloyed steels. In this study, the recrystallisation-Precipitation-time-temperature curve was simulated to determine the full recrystallisation temperature, recrystallisation-stop temperature and the temperature where Precipitation would occur at the shortest time. The calculated temperatures were verified by experimental testing for rolling between 1100 °C and 850 °C. On the basis of this a finishing deformation of 850 °C was chosen in order to maximise the precipitate number density formed in a fully unrecrystallised austenite. The orientation relationship between the SIP in austenite, and subsequent transformation to ferrite was identified by calculation from the coordinate transformation matrix, and by electron diffraction in the transmission electron microscope. The NbC formed as coherent/semi-coherent precipitates in the austenite, and remained coherent/semi-coherent in the ferrite, indicating a Kurdjumov-Sachs orientation relationship between the austenite and ferrite on transformation.
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On the Effect of Strain Reversal on Static Recrystallisation and Strain-Induced Precipitation Process Kinetics in Microalloyed Steels
Materials Science Forum, 2012Co-Authors: Krzysztof Muszka, Eric J. Palmiere, L. Sun, Bradley P. Wynne, W.m. RainforthAbstract:Recent observations show that the strain reversal affects significantly and in a complex way both the static recrystallisation (SRX) and strain-Induced Precipitation (PPT) kinetics in Nb-microalloyed steel. It is already known that the recrystallisation stagnation is a consequence of the competition between the driving pressure for recrystallisation and the pinning pressure caused by the strain-Induced Precipitation of Nb (C,N) precipitates. Both of these parameters depend in turn on the local dislocation density. Thus, it is expected that a variation of the local dislocation density due to reversal of the strain will affect at the same time the local driving and the pinning pressures, which will cause the difference in the hardening levels. In the present paper, the influence of strain path change on microstructure evolution and mechanical behaviour in Nb-microalloyed steel (API X-70 grade) was studied. The deformation schedules were designed in order to investigate an effect of strain reversal on both static recrystallisation and strain-Induced Precipitation process kinetics. Flow curves recorded during deformation of X-70 steel showed clear influence of applied strain path on both static recrystallisation kinetics and strain-Induced Precipitation process.
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Strain Induced Precipitation in Model and Conventional Microalloyed Steels during Thermomechanical Processing
Materials Science Forum, 2005Co-Authors: R.m. Poths, Mark W. Rainforth, Eric J. PalmiereAbstract:The finishing rolling of microalloyed steels was simulated by double-deformation plane strain compression testing of both model and conventional steels microalloyed with Nb. The flow behavior following interpass delay times of 1-100s was related to the deformed microstructure, the deformation substructure and the strain-Induced Precipitation. Fe-30wt%Ni is clearly a good model alloy for conventional microalloyed steels, as similar results are observed for both materials. In addition, the location of fine strain-Induced precipitates in relation to the deformation substructure can be determined directly using transmission electron microscopy.
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Modelling Strain Induced Precipitation of Niobium Carbonitride during Multipass Deformation of Austenite
Materials Science Forum, 2005Co-Authors: C.m. Sellars, Eric J. PalmiereAbstract:A new model of strain Induced Precipitation in niobium microalloyed austenite is proposed. This is based on the experimental observation of formation of microbands during hot deformation of iron – 30% nickel, which remains austenitic to room temperature. Precipitates are preferentially nucleated on nodes in the dislocation network in the microbands. This geometry enables features of earlier models to be simply explained, and facilitates extension of the model to multipass deformation. It is shown that the model captures all the essential features of previous experimental observations on microalloyed C – Mn steels. Currently, sensitivity analysis of the model and systematic experimental work are being undertaken to quantitatively validate the model.
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Modelling the kinetics of strain Induced Precipitation in Nb microalloyed steels
Acta Materialia, 2001Co-Authors: B. Dutta, Eric J. Palmiere, C.m. SellarsAbstract:Strain Induced Precipitation is a key phenomenon that controls the microstructure evolution during the finish rolling stages of microalloyed steels. Extensive research has shown that the Precipitation of Nb(CN) delays the onset of recrystallisation. This paper presents a model to describe the Precipitation kinetics during isothermal holding following high temperature deformation in Nb-containing steels. The model is based on the assumption that heterogeneous nucleation of precipitates on dislocations and enhanced coarsening due to pipe diffusion are responsible behind the accelerated kinetics observed in strain Induced Precipitation. Results show a very good agreement between reported experimental observations and predictions of the present model for precipitate size and volume fraction evolution.