This study systematically investigates the hot deformation behavior and microstructural evolution of CoNiV medium-entropy alloy(MEA)in the temperature range of 950-1100℃ and strain rates of 0.001-1 s^(-1).The Arrheni...This study systematically investigates the hot deformation behavior and microstructural evolution of CoNiV medium-entropy alloy(MEA)in the temperature range of 950-1100℃ and strain rates of 0.001-1 s^(-1).The Arrhenius model and machine learning model were developed to forecast flow stresses at various conditions.The predictive capability of both models was assessed using the coefficients of determination(R^(2)),average absolute relative error(AARE),and root mean square error(RMSE).The findings show that the osprey optimization algorithm convolutional neural network(OOA-CNN)model outperforms the Arrhenius model,achieving a high R^(2) value of 0.99959 and lower AARE and RMSE values.The flow stress that the OOA-CNN model predicted was used to generate power dissipation maps and instability maps under different strains.Finally,combining the processing map and microstructure characterization,the ideal processing domain was identified as 1100℃ at strain rates of 0.01-0.1 s^(-1).This study provided key insights into optimizing the hot working process of CoNiV MEA.展开更多
Hot compression experiments were conducted under conditions of deformation temperatures ranging from 950 to 1150℃,strain rates of 0.001-10 s^(-1),and deformation degrees ranging from 20%to 80%.The hot deformation beh...Hot compression experiments were conducted under conditions of deformation temperatures ranging from 950 to 1150℃,strain rates of 0.001-10 s^(-1),and deformation degrees ranging from 20%to 80%.The hot deformation behavior and microstructure evolution of millimeter-grade coarse grains(MCGs)in the as-cast Ti-6Cr-5Mo-5V-4Al(Ti-6554)alloy were studied,and a hot processing map was established.Under compression along the rolling direction(RD),continuous dynamic recrystallization(CDRX)ensues due to the progressive rotation of subgrains within the MCGs.Along the transverse direction(TD),discontinuous dynamic recrystallization(DDRX)resulting from grain boundary bulging or bridging,occurs on the boundaries of the MCGs.With decreasing strain rate,increasing temperature,and higher deformation degree,dynamic recrystallization becomes more pronounced,resulting in a reduction in the original average grain size.The optimal processing parameters fall within a temperature range of 1050-1150℃,a strain rate of 0.01 s^(-1),and a deformation degree between 40%and 60%.展开更多
High strength β titanium alloys are widely used in large load bearing components in the aerospace field. At present, large parts are generally formed by die forging. Different initial microstructures and deformation ...High strength β titanium alloys are widely used in large load bearing components in the aerospace field. At present, large parts are generally formed by die forging. Different initial microstructures and deformation process parameters will significantly affect the flow behavior. To precisely control the microstructures, researchers have conducted many studies to analyze the microstructure evolution law and deformation mechanism during hot compression. This review focuses on the microstructure evolution of high strength β titanium alloys during hot deformation, including dynamic recrystallization and dynamic recovery in the single-phase region and the dynamic evolution of the α phase in the two-phase region. Furthermore, the optimal hot processing regions, instability regions,and the relationship between the efficiency of power dissipation and the deformation mechanism in the hot processing map are summarized. Finally, the problems and development direction of using hot processing maps to optimize process parameters are also emphasized.展开更多
The isothermal compression tests of A1-5Ti- 1B master alloy were conducted on the thermal mechanical simulator Gleeble-1500D at the deformation temperature range of 300-450 ℃,the strain rate range of 0.01- 10.00 s^-l...The isothermal compression tests of A1-5Ti- 1B master alloy were conducted on the thermal mechanical simulator Gleeble-1500D at the deformation temperature range of 300-450 ℃,the strain rate range of 0.01- 10.00 s^-l, and the engineering strain of 50 %. The effects of deformation temperatures and strain rates on the flow stress were analyzed by the true stress-true strain curves. The result indicates that the flow stress increases with the increase of strain rate, while it decreases with the increase of temperature. The hot deformation activation energy of A1-5Ti-IB master alloy is calculated to be 250.9 kJ.mol^-1, and the constitutive equation is established as ε=1.97 x lO^19[sinh（O.O15δ）^11.14exp（-250.9/RT）, and the validity of this constitutive equation is verified. Based on dynamic material model （DMM） criterion, the hot processing map of AI-5Ti-1B master alloy is obtained. The optimum hot extrusion conditions are determined as deformation temperature of 400℃ and strain rate of 1.00 s^-1, and the flow instability only appears at the temperature range of 300-340℃ at the base of the hot processing map.展开更多
In order to describe the deformation behavior and the hot workability of equiatomic NiTi shape memory alloy (SMA) during hot deformation, Arrhenius-type constitutive equation and hot processing map of the alloy were d...In order to describe the deformation behavior and the hot workability of equiatomic NiTi shape memory alloy (SMA) during hot deformation, Arrhenius-type constitutive equation and hot processing map of the alloy were developed by hot compression tests at temperatures ranging from 500 to 1100 °C and strain rates ranging from 0.0005 to 0.5 s?1. The results show that the instability region of the hot processing map increases with the increase of deformation extent. The instability occurs in the low and high temperature regions. The instability region presents the adiabatic shear bands at low temperatures, but it exhibits the abnormal growth of the grains at high temperatures. Consequently, it is necessary to avoid processing the equiatomic NiTi SMA in these regions. It is preferable to process the NiTi SMA at the temperatures ranging from 750 to 900 °C.展开更多
Hot deformation behavior of as-cast Mn18Cr18 N austenitic stainless steel was studied in the temperature range of 950-1200 ℃ and strain rate range of 0.001-1 s^（-1） using isothermal hot compression tests. The true ...Hot deformation behavior of as-cast Mn18Cr18 N austenitic stainless steel was studied in the temperature range of 950-1200 ℃ and strain rate range of 0.001-1 s^（-1） using isothermal hot compression tests. The true stress-strain curves of the steel were characterized by hardening and subsequent softening and varied with temperatures and strain rates. The hot deformation activation energy of the steel was calculated to be 657.4 k J/mol, which was higher than that of the corresponding wrought steel due to its as-cast coarse columnar grains and heterogeneous structure. Hot processing maps were developed at different plastic strains, which exhibited two domains with peak power dissipation efficiencies at 1150 ℃/0.001 s^（-1） and 1200 ℃/1 s^（-1）, respectively. The corresponding microstructures were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, and electron backscatter diffraction（EBSD）. It has been confirmed that dynamic recrystallization（DRX） controlled by dislocation slipping and climbing mechanism occurs in the temperature and strain rate range of 1050-1200 ℃ and 0.001-0.01 s^（-1）; And DRX controlled by twinning mechanism occurs in the temperature and strain rate range of 1100-1200 ℃, 0.1-1 s^（-1）. These two DRX domains can serve as the hot working windows of the as-cast steel at lower strain rates and at higher strain rates, respectively. The processing maps at different strains also exhibit that the instability region decreases with increasing strain. The corresponding microstructures and the less tensile ductility in the instability region imply that the flow instability is attributed to flow localization accelerated by a few layers of very fine recrystallized grains along the original grain boundaries.展开更多
For Gu-Ag alloy, an important parameter called workability in the forming process of materials can be evaluated by processing maps yielded from the stress-strain data generated by hot compression tests at temperatures...For Gu-Ag alloy, an important parameter called workability in the forming process of materials can be evaluated by processing maps yielded from the stress-strain data generated by hot compression tests at temperatures of 700-850 °C and strain rates of 0.01-10 s-1. And at the true strain of 0.15, 0.35 and 0.55, respectively, the responses of strain-rate sensitivity, power dissipation efficiency and instability parameter to temperature and strain rate were studied. Instability maps and power dissipation maps were superimposed to form processing maps, which reveal the determinate regions where individual metallurgical processes occur and the limiting conditions of flow instability regions. Furthermore, the optimal processing parameters for bulk metal working are identified clearly by the processing maps.展开更多
Hot deformation behavior of a new type of M3∶ 2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950-1 150 ℃ and strain rate of 0. ...Hot deformation behavior of a new type of M3∶ 2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950-1 150 ℃ and strain rate of 0. 001-10 s^（-1）. A comprehensive constitutive equation was obtained,which could be used to predict the flow stress at different strains. Processing map was developed on the basis of the flow stress data using the principles of dynamic material model. The results showed that the flow curves were in fair agreement with the dynamic recrystallization model. The flow stresses,which were calculated by the comprehensive constitutive equation,agreed well with the test data at low strain rates（ ≤1 s^（-1））. The material constant（ α）,stress exponent（ n） and the hot deformation activation energy（ Q_（HW）） of the new steel were 0. 006 15 MPa^（-1）,4. 81 and 546 kJ·mol^（-1）,respectively. Analysis of the processing map with an observation of microstructures revealed that hot working processes of the steel could be carried out safely in the domain（ T = 1 050-1 150 ℃,ε = 0. 01- 0. 1 s^（-1））with about 33% peak efficiency of power dissipation（ η）. Cracks was expected in two domains at either lower temperatures（ 〈 1 000 ℃） or low strain rates（ 0. 001 s^（-1）） with different cracking mechanisms. Flow localization occurred when the strain rates exceeded 1 s^（-1） at all testing temperatures.展开更多
The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperat...The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 Kand strain rate range of 0.001-0.5s^（-1）.The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile,the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally,the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 Kand the low strain rate of 0.001-0.1s^（-1） was obtained.展开更多
The hot deformation behavior of a high Ti 6061 aluminum alloy in the temperature range from 350 to 510 ℃ and strain rate range from 0.001 to 10 s^-1 was investigated using stress-strain curve analysis, processing map...The hot deformation behavior of a high Ti 6061 aluminum alloy in the temperature range from 350 to 510 ℃ and strain rate range from 0.001 to 10 s^-1 was investigated using stress-strain curve analysis, processing map, transmission electron microscopy and electron backscatter diffraction analysis. The results show that the peak stress decreases with increasing deformation temperatures and decreasing strain rate. The average deformation activation energy is 185 kJ/mol in the parameter range investigated. The flow stress model was constructed. The main softening mechanism is dynamic recovery. The processing map was obtained using dynamic material model, and the suggested processing window is 400-440℃ and 0.001-0.1 s^-1.展开更多
The high temperature deformation behaviors of α＋β type titanium alloy TC11 （Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） with coarse lamellar starting microstructure were investigated based on the hot compression tests in the tem...The high temperature deformation behaviors of α＋β type titanium alloy TC11 （Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） with coarse lamellar starting microstructure were investigated based on the hot compression tests in the temperature range of 950-1100 ℃ and the strain rate range of 0.001-10 s-1. The processing maps at different strains were then constructed based on the dynamic materials model, and the hot compression process parameters and deformation mechanism were optimized and analyzed, respectively. The results show that the processing maps exhibit two domains with a high efficiency of power dissipation and a flow instability domain with a less efficiency of power dissipation. The types of domains were characterized by convergence and divergence of the efficiency of power dissipation, respectively. The convergent domain in a＋fl phase field is at the temperature of 950-990 ℃ and the strain rate of 0.001-0.01 s^-1, which correspond to a better hot compression process window of α＋β phase field. The peak of efficiency of power dissipation in α＋β phase field is at 950 ℃ and 0.001 s 1, which correspond to the best hot compression process parameters of α＋β phase field. The convergent domain in β phase field is at the temperature of 1020-1080 ℃ and the strain rate of 0.001-0.1 s^-l, which correspond to a better hot compression process window of β phase field. The peak of efficiency of power dissipation in ℃ phase field occurs at 1050 ℃ over the strain rates from 0.001 s^-1 to 0.01 s^-1, which correspond to the best hot compression process parameters of ,8 phase field. The divergence domain occurs at the strain rates above 0.5 s^-1 and in all the tested temperature range, which correspond to flow instability that is manifested as flow localization and indicated by the flow softening phenomenon in stress-- strain curves. The deformation mechanisms of the optimized hot compression process windows in a＋β and β phase fields are identified to be spheroidizing and dynamic recrystallizing controlled by self-diffusion mechanism, respectively. The microstructure observation of the deformed specimens in different domains matches very well with the optimized results.展开更多
To study the hot deformation behavior of a new powder metallurgy nickel-based superalloy,hot compression tests were conducted in the temperature range of 1020−1110℃ with the strain rates of 0.001−1 s^−1.It is found t...To study the hot deformation behavior of a new powder metallurgy nickel-based superalloy,hot compression tests were conducted in the temperature range of 1020−1110℃ with the strain rates of 0.001−1 s^−1.It is found that the flow stress of the superalloy decreases with increasing temperature and decreasing strain rate.An accurate constitutive equation is established using a hyperbolic-sine type expression.Moreover,processing map of the alloy is constructed to optimize its hot forging parameters.Three domains of dynamic recrystallization stability and instability regions are identified from the processing map at a strain of 0.7,respectively.The adiabatic shear band,intergranular crack and a combination of intergranular crack and wedge crack are demonstrated to be responsible for the instabilities.Comprehensively analyzing the processing map and microstructure,the optimal isothermal forging conditions for the superalloy is determined to be t=1075−1105℃ andε&=10^−3−10−2.8 s^−1.展开更多
The hot compression deformation behavior of Cu−3Ti−0.1Zr alloy with the ultra-high strength and good electrical conductivity was investigated on a Gleeble−3500 thermal-mechanical simulator at temperatures from 700 to ...The hot compression deformation behavior of Cu−3Ti−0.1Zr alloy with the ultra-high strength and good electrical conductivity was investigated on a Gleeble−3500 thermal-mechanical simulator at temperatures from 700 to 850℃ with the strain rates between 0.001 and 1 s^−1.The results show that work hardening,dynamic recovery and dynamic recrystallization occur in the alloy during hot deformation.The hot compression constitutive equation at a true strain of 0.8 is constructed and the apparent activation energy of hot compression deformation Q is about 319.56 kJ/mol.The theoretic flow stress calculated by the constructed constitutive equation is consistent with the experimental result,and the hot processing maps are established based on the dynamic material model.The optimal hot deformation temperature range is between 775 and 850℃ and the strain rate range is between 0.001 and 0.01 s^−1.展开更多
A hot compression experiment （1073 1473 K, strain rates of 0. 001-10 s -1 ） of SAS08GR. 4N low alloy steel was performed using a Gleeble-3800 thermal-mechanical simulator, and the hot deformation behavior of the ste...A hot compression experiment （1073 1473 K, strain rates of 0. 001-10 s -1 ） of SAS08GR. 4N low alloy steel was performed using a Gleeble-3800 thermal-mechanical simulator, and the hot deformation behavior of the steel was investigated by analyzing both the true stress true strain curves and its microstructures. The thermal de formation equation and hot deformation activation energy （Q） of SA508GR. 4N steel were obtained by regression with a classic hyperbolic sine function. The hot processing map of SAS08GR. 4N steel was also established. An empirical equation for the stress peak was described for practical applications. The SA508GR. 4N steel showed a critical Zener-Hollomon parameter （lnZc） for dynamic recrystallization （DRX） of 37.44, below which full DRX may occur. The sensitivity of the SA508GR. 4N steel increased linearly with test temperature, such that higher temperatures led to enhanced workability.展开更多
In order to optimize the deformation processing, the hot deformation behavior of Co-Cr-Mo-Cu （here- after named as Co-Cu） alloy was studied in this paper at a deformation temperature range of 950-1150 ℃ and a strai...In order to optimize the deformation processing, the hot deformation behavior of Co-Cr-Mo-Cu （here- after named as Co-Cu） alloy was studied in this paper at a deformation temperature range of 950-1150 ℃ and a strain rate range of 0.008-5 s^-1. Based on the true stress-true strain curves, a constitutive equation in hyperbolic sin function was established and a hot processing map was drawn. It was found that the flow stress of the Co-Cu alloy increased with the increase of the strain rate and decreased with the increase of the deforming temperature. The hot processing map indicated that there were two unstable regions and one well-processing region. The microstructure, the hardness distribution and the electro- chemical properties of the hot deformed sample were investigated in order to reveal the influence of the hot deformation. Microstructure observation indicated that the grain size increased with the increase of the deformation temperature but decreased with the increase of the strain rate. High temperature and low strain rate promoted the crystallization process but increased the grain size, which results in a reduction in the hardness. The hot deformation at high temperature （1100-1150 ℃） would reduce the corrosion resistance slightly. The final optimized deformation process was： a deformation temperature from 1050to 1100 ℃, and a strain rate from 0.008 to 0.2 s^-1, where a completely recrystallized and homogeneously distributed microstructure would be obtained.展开更多
A successful mechanical property data-driven prediction model is the core of the optimal design of hot rolling process for hot-rolled strips. However, the original industrial data, usually unbalanced, are inevitably m...A successful mechanical property data-driven prediction model is the core of the optimal design of hot rolling process for hot-rolled strips. However, the original industrial data, usually unbalanced, are inevitably mixed with fluctuant and abnormal values. Models established on the basis of the data without data processing can cause misleading results, which cannot be used for the optimal design of hot rolling process. Thus, a method of industrial data processing of C-Mn steel was proposed based on the data analysis. The Bayesian neural network was employed to establish the reliable mechanical property prediction models for the optimal design of hot rolling process. By using the multi-objective optimization algorithm and considering the individual requirements of costumers and the constraints of the equipment, the optimal design of hot rolling process was successfully applied to the rolling process design for Q345B steel with 0.017% Nb and 0.046% Ti content removed. The optimal process design results were in good agreement with the industrial trials results, which verify the effectiveness of the optimal design of hot rolling process.展开更多
In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the in...In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the interactive effects of material hardening, recovery and dynamic recrystallization(DRX) on the characteristic deformation behavior were considered by incorporating the evolution laws of viscoplastic flow, dislocation activities, DRX nucleation and boundary migration in a coupled manner. The model parameters were calibrated based on the experimental data analysis and genetic algorithm(GA) based objective optimization. The predicted flow stress, DRX fraction and average grain size match well with experimental results. The proposed model was embedded in the finite element(FE) software DEFORM-3 D via user defined subroutine to simulate the hot compression and equal channel angular extrusion(ECAE) processes. The heterogeneous microstructure distributions at different deformation zones and the dislocation density evolution with competitive deformation mechanisms were captured.This study can provide a theoretical solution for the hot working problems of magnesium alloy.展开更多
The control of microstructure during hot rolling process of steel is of great importance and will affect the properties of the steel products.According to the production line,a three-dimensional multi-field coupled fi...The control of microstructure during hot rolling process of steel is of great importance and will affect the properties of the steel products.According to the production line,a three-dimensional multi-field coupled finite element model of 24-pass continuous hot rolling process of 38CrMoAl steel rod is established using the finite element software MSC.Marc.Based on the recrystallization kinetics model and the grain growth model,a subroutine written in Fortran is introduced to calculate the recrystallization behavior and microstructure evolution of 38CrMoAl steel during the entire rolling process.The distribution and evolution of variables such as strain,temperature and recrystallization fractions during the rolling process are analyzed.The temperature variations and grain sizes at both the center and surface of the tested steel are compared with the experimental results.And it is found that the simulation results are in good agreement with the experimental ones,confirming the reliability of the established model.展开更多
The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that th...The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.展开更多
The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure a...The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of Al Si Ti phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.展开更多
基金supported by the National Natural Science Foundation of China(NSFC)(Grant No.51901078)the Central Guidance for Local Scientific and Technological Development Funding Project(Grant No.236Z1003G)+3 种基金the Science and Technology Plan Project of Tangshan City(Grant No.24130207C)the Natural Science Foundation of Hebei Province(Grant No.E2022209070)the High-level Talent Project of Hebei(Grant No.E2019100007)the Open Project Program of Key Laboratory of Ministry of Education for Modern Metallurgy Technology(Grant No.2024YJKF02).
文摘This study systematically investigates the hot deformation behavior and microstructural evolution of CoNiV medium-entropy alloy(MEA)in the temperature range of 950-1100℃ and strain rates of 0.001-1 s^(-1).The Arrhenius model and machine learning model were developed to forecast flow stresses at various conditions.The predictive capability of both models was assessed using the coefficients of determination(R^(2)),average absolute relative error(AARE),and root mean square error(RMSE).The findings show that the osprey optimization algorithm convolutional neural network(OOA-CNN)model outperforms the Arrhenius model,achieving a high R^(2) value of 0.99959 and lower AARE and RMSE values.The flow stress that the OOA-CNN model predicted was used to generate power dissipation maps and instability maps under different strains.Finally,combining the processing map and microstructure characterization,the ideal processing domain was identified as 1100℃ at strain rates of 0.01-0.1 s^(-1).This study provided key insights into optimizing the hot working process of CoNiV MEA.
基金supported by the National Key Research and Development Program of China(Nos.2022YFB3706901,2022YFB3706903)the National Natural Science Foundation of China(No.52274382)。
文摘Hot compression experiments were conducted under conditions of deformation temperatures ranging from 950 to 1150℃,strain rates of 0.001-10 s^(-1),and deformation degrees ranging from 20%to 80%.The hot deformation behavior and microstructure evolution of millimeter-grade coarse grains(MCGs)in the as-cast Ti-6Cr-5Mo-5V-4Al(Ti-6554)alloy were studied,and a hot processing map was established.Under compression along the rolling direction(RD),continuous dynamic recrystallization(CDRX)ensues due to the progressive rotation of subgrains within the MCGs.Along the transverse direction(TD),discontinuous dynamic recrystallization(DDRX)resulting from grain boundary bulging or bridging,occurs on the boundaries of the MCGs.With decreasing strain rate,increasing temperature,and higher deformation degree,dynamic recrystallization becomes more pronounced,resulting in a reduction in the original average grain size.The optimal processing parameters fall within a temperature range of 1050-1150℃,a strain rate of 0.01 s^(-1),and a deformation degree between 40%and 60%.
基金supported by the Project of National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, China (No. 6142909190207)Shaanxi Key Laboratory of High-performance Precision Forming Technology and Equipment (SKL-HPFTE), China (No. PETE-2019-KF-01)。
文摘High strength β titanium alloys are widely used in large load bearing components in the aerospace field. At present, large parts are generally formed by die forging. Different initial microstructures and deformation process parameters will significantly affect the flow behavior. To precisely control the microstructures, researchers have conducted many studies to analyze the microstructure evolution law and deformation mechanism during hot compression. This review focuses on the microstructure evolution of high strength β titanium alloys during hot deformation, including dynamic recrystallization and dynamic recovery in the single-phase region and the dynamic evolution of the α phase in the two-phase region. Furthermore, the optimal hot processing regions, instability regions,and the relationship between the efficiency of power dissipation and the deformation mechanism in the hot processing map are summarized. Finally, the problems and development direction of using hot processing maps to optimize process parameters are also emphasized.
基金financially supported by the Natural Science Foundation of Heilongjiang Province(No.E201107)
文摘The isothermal compression tests of A1-5Ti- 1B master alloy were conducted on the thermal mechanical simulator Gleeble-1500D at the deformation temperature range of 300-450 ℃,the strain rate range of 0.01- 10.00 s^-l, and the engineering strain of 50 %. The effects of deformation temperatures and strain rates on the flow stress were analyzed by the true stress-true strain curves. The result indicates that the flow stress increases with the increase of strain rate, while it decreases with the increase of temperature. The hot deformation activation energy of A1-5Ti-IB master alloy is calculated to be 250.9 kJ.mol^-1, and the constitutive equation is established as ε=1.97 x lO^19[sinh（O.O15δ）^11.14exp（-250.9/RT）, and the validity of this constitutive equation is verified. Based on dynamic material model （DMM） criterion, the hot processing map of AI-5Ti-1B master alloy is obtained. The optimum hot extrusion conditions are determined as deformation temperature of 400℃ and strain rate of 1.00 s^-1, and the flow instability only appears at the temperature range of 300-340℃ at the base of the hot processing map.
基金Projects(51305091,51305092,51475101)supported by the National Natural Science Foundation of ChinaProject(20132304120025)supported by the Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘In order to describe the deformation behavior and the hot workability of equiatomic NiTi shape memory alloy (SMA) during hot deformation, Arrhenius-type constitutive equation and hot processing map of the alloy were developed by hot compression tests at temperatures ranging from 500 to 1100 °C and strain rates ranging from 0.0005 to 0.5 s?1. The results show that the instability region of the hot processing map increases with the increase of deformation extent. The instability occurs in the low and high temperature regions. The instability region presents the adiabatic shear bands at low temperatures, but it exhibits the abnormal growth of the grains at high temperatures. Consequently, it is necessary to avoid processing the equiatomic NiTi SMA in these regions. It is preferable to process the NiTi SMA at the temperatures ranging from 750 to 900 °C.
基金Funded by the National Natural Science Foundation of China(No.51575372)
文摘Hot deformation behavior of as-cast Mn18Cr18 N austenitic stainless steel was studied in the temperature range of 950-1200 ℃ and strain rate range of 0.001-1 s^（-1） using isothermal hot compression tests. The true stress-strain curves of the steel were characterized by hardening and subsequent softening and varied with temperatures and strain rates. The hot deformation activation energy of the steel was calculated to be 657.4 k J/mol, which was higher than that of the corresponding wrought steel due to its as-cast coarse columnar grains and heterogeneous structure. Hot processing maps were developed at different plastic strains, which exhibited two domains with peak power dissipation efficiencies at 1150 ℃/0.001 s^（-1） and 1200 ℃/1 s^（-1）, respectively. The corresponding microstructures were analyzed by optical microscopy（OM）, scanning electron microscopy（SEM）, and electron backscatter diffraction（EBSD）. It has been confirmed that dynamic recrystallization（DRX） controlled by dislocation slipping and climbing mechanism occurs in the temperature and strain rate range of 1050-1200 ℃ and 0.001-0.01 s^（-1）; And DRX controlled by twinning mechanism occurs in the temperature and strain rate range of 1100-1200 ℃, 0.1-1 s^（-1）. These two DRX domains can serve as the hot working windows of the as-cast steel at lower strain rates and at higher strain rates, respectively. The processing maps at different strains also exhibit that the instability region decreases with increasing strain. The corresponding microstructures and the less tensile ductility in the instability region imply that the flow instability is attributed to flow localization accelerated by a few layers of very fine recrystallized grains along the original grain boundaries.
基金Project(CSTC2009BA4065) supported by the Chongqing Natural Science Foundation,China
文摘For Gu-Ag alloy, an important parameter called workability in the forming process of materials can be evaluated by processing maps yielded from the stress-strain data generated by hot compression tests at temperatures of 700-850 °C and strain rates of 0.01-10 s-1. And at the true strain of 0.15, 0.35 and 0.55, respectively, the responses of strain-rate sensitivity, power dissipation efficiency and instability parameter to temperature and strain rate were studied. Instability maps and power dissipation maps were superimposed to form processing maps, which reveal the determinate regions where individual metallurgical processes occur and the limiting conditions of flow instability regions. Furthermore, the optimal processing parameters for bulk metal working are identified clearly by the processing maps.
基金Item Sponsored by National Basic Research Program of China(2011CB606303)Constructed Project for Key Laboratory of Beijing of China
文摘Hot deformation behavior of a new type of M3∶ 2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950-1 150 ℃ and strain rate of 0. 001-10 s^（-1）. A comprehensive constitutive equation was obtained,which could be used to predict the flow stress at different strains. Processing map was developed on the basis of the flow stress data using the principles of dynamic material model. The results showed that the flow curves were in fair agreement with the dynamic recrystallization model. The flow stresses,which were calculated by the comprehensive constitutive equation,agreed well with the test data at low strain rates（ ≤1 s^（-1））. The material constant（ α）,stress exponent（ n） and the hot deformation activation energy（ Q_（HW）） of the new steel were 0. 006 15 MPa^（-1）,4. 81 and 546 kJ·mol^（-1）,respectively. Analysis of the processing map with an observation of microstructures revealed that hot working processes of the steel could be carried out safely in the domain（ T = 1 050-1 150 ℃,ε = 0. 01- 0. 1 s^（-1））with about 33% peak efficiency of power dissipation（ η）. Cracks was expected in two domains at either lower temperatures（ 〈 1 000 ℃） or low strain rates（ 0. 001 s^（-1）） with different cracking mechanisms. Flow localization occurred when the strain rates exceeded 1 s^（-1） at all testing temperatures.
基金the financial supports from the National Natural Science Foundation of China(Grant Nos.51301157 and 51434007)the National High Technology Research and Development Program of China 863 Program(Grant No.2013AA031103)
文摘The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 Kand strain rate range of 0.001-0.5s^（-1）.The calculated activation energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6kJ/mol based on the constitutive relationship models developed with the Arrhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile,the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally,the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 Kand the low strain rate of 0.001-0.1s^（-1） was obtained.
文摘The hot deformation behavior of a high Ti 6061 aluminum alloy in the temperature range from 350 to 510 ℃ and strain rate range from 0.001 to 10 s^-1 was investigated using stress-strain curve analysis, processing map, transmission electron microscopy and electron backscatter diffraction analysis. The results show that the peak stress decreases with increasing deformation temperatures and decreasing strain rate. The average deformation activation energy is 185 kJ/mol in the parameter range investigated. The flow stress model was constructed. The main softening mechanism is dynamic recovery. The processing map was obtained using dynamic material model, and the suggested processing window is 400-440℃ and 0.001-0.1 s^-1.
基金Project (51005112) supported by the National Natural Science Foundation of ChinaProject (2010ZF56019) supported by the Aviation Science Foundation of China+1 种基金Project (GJJ11156) supported by the Education Commission of Jiangxi Province, ChinaProject(GF200901008) supported by the Open Fund of National Defense Key Disciplines Laboratory of Light Alloy Processing Science and Technology, China
文摘The high temperature deformation behaviors of α＋β type titanium alloy TC11 （Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） with coarse lamellar starting microstructure were investigated based on the hot compression tests in the temperature range of 950-1100 ℃ and the strain rate range of 0.001-10 s-1. The processing maps at different strains were then constructed based on the dynamic materials model, and the hot compression process parameters and deformation mechanism were optimized and analyzed, respectively. The results show that the processing maps exhibit two domains with a high efficiency of power dissipation and a flow instability domain with a less efficiency of power dissipation. The types of domains were characterized by convergence and divergence of the efficiency of power dissipation, respectively. The convergent domain in a＋fl phase field is at the temperature of 950-990 ℃ and the strain rate of 0.001-0.01 s^-1, which correspond to a better hot compression process window of α＋β phase field. The peak of efficiency of power dissipation in α＋β phase field is at 950 ℃ and 0.001 s 1, which correspond to the best hot compression process parameters of α＋β phase field. The convergent domain in β phase field is at the temperature of 1020-1080 ℃ and the strain rate of 0.001-0.1 s^-l, which correspond to a better hot compression process window of β phase field. The peak of efficiency of power dissipation in ℃ phase field occurs at 1050 ℃ over the strain rates from 0.001 s^-1 to 0.01 s^-1, which correspond to the best hot compression process parameters of ,8 phase field. The divergence domain occurs at the strain rates above 0.5 s^-1 and in all the tested temperature range, which correspond to flow instability that is manifested as flow localization and indicated by the flow softening phenomenon in stress-- strain curves. The deformation mechanisms of the optimized hot compression process windows in a＋β and β phase fields are identified to be spheroidizing and dynamic recrystallizing controlled by self-diffusion mechanism, respectively. The microstructure observation of the deformed specimens in different domains matches very well with the optimized results.
基金Project(2016YFB0700300)supported by the National Key Research and Development Program of ChinaProject(51774335)supported by the National Natural Science Foundation of China。
文摘To study the hot deformation behavior of a new powder metallurgy nickel-based superalloy,hot compression tests were conducted in the temperature range of 1020−1110℃ with the strain rates of 0.001−1 s^−1.It is found that the flow stress of the superalloy decreases with increasing temperature and decreasing strain rate.An accurate constitutive equation is established using a hyperbolic-sine type expression.Moreover,processing map of the alloy is constructed to optimize its hot forging parameters.Three domains of dynamic recrystallization stability and instability regions are identified from the processing map at a strain of 0.7,respectively.The adiabatic shear band,intergranular crack and a combination of intergranular crack and wedge crack are demonstrated to be responsible for the instabilities.Comprehensively analyzing the processing map and microstructure,the optimal isothermal forging conditions for the superalloy is determined to be t=1075−1105℃ andε&=10^−3−10−2.8 s^−1.
基金Project(2016YFB0301300)supported by the National Key Research and Development Program of ChinaProject(U1637210)supported by the National Natural Science Foundation of China+1 种基金Project(2019B10088)supported by the Technology Research Program of Ningbo,ChinaProject supported by State Key Laboratory of Powder Metallurgy,Central South University,China。
文摘The hot compression deformation behavior of Cu−3Ti−0.1Zr alloy with the ultra-high strength and good electrical conductivity was investigated on a Gleeble−3500 thermal-mechanical simulator at temperatures from 700 to 850℃ with the strain rates between 0.001 and 1 s^−1.The results show that work hardening,dynamic recovery and dynamic recrystallization occur in the alloy during hot deformation.The hot compression constitutive equation at a true strain of 0.8 is constructed and the apparent activation energy of hot compression deformation Q is about 319.56 kJ/mol.The theoretic flow stress calculated by the constructed constitutive equation is consistent with the experimental result,and the hot processing maps are established based on the dynamic material model.The optimal hot deformation temperature range is between 775 and 850℃ and the strain rate range is between 0.001 and 0.01 s^−1.
基金Item Sponsored by National Energy Application Technology Research and Engineering Demonstrative Project of China(NY201501)
文摘A hot compression experiment （1073 1473 K, strain rates of 0. 001-10 s -1 ） of SAS08GR. 4N low alloy steel was performed using a Gleeble-3800 thermal-mechanical simulator, and the hot deformation behavior of the steel was investigated by analyzing both the true stress true strain curves and its microstructures. The thermal de formation equation and hot deformation activation energy （Q） of SA508GR. 4N steel were obtained by regression with a classic hyperbolic sine function. The hot processing map of SAS08GR. 4N steel was also established. An empirical equation for the stress peak was described for practical applications. The SA508GR. 4N steel showed a critical Zener-Hollomon parameter （lnZc） for dynamic recrystallization （DRX） of 37.44, below which full DRX may occur. The sensitivity of the SA508GR. 4N steel increased linearly with test temperature, such that higher temperatures led to enhanced workability.
基金financially supported by the National Natural Science Foundation of China (Nos. 81071262, 31271024 and 31470930)the Funding from Northeastern University ("985 program", Nos. N141008001 and LZ2014018), China
文摘In order to optimize the deformation processing, the hot deformation behavior of Co-Cr-Mo-Cu （here- after named as Co-Cu） alloy was studied in this paper at a deformation temperature range of 950-1150 ℃ and a strain rate range of 0.008-5 s^-1. Based on the true stress-true strain curves, a constitutive equation in hyperbolic sin function was established and a hot processing map was drawn. It was found that the flow stress of the Co-Cu alloy increased with the increase of the strain rate and decreased with the increase of the deforming temperature. The hot processing map indicated that there were two unstable regions and one well-processing region. The microstructure, the hardness distribution and the electro- chemical properties of the hot deformed sample were investigated in order to reveal the influence of the hot deformation. Microstructure observation indicated that the grain size increased with the increase of the deformation temperature but decreased with the increase of the strain rate. High temperature and low strain rate promoted the crystallization process but increased the grain size, which results in a reduction in the hardness. The hot deformation at high temperature （1100-1150 ℃） would reduce the corrosion resistance slightly. The final optimized deformation process was： a deformation temperature from 1050to 1100 ℃, and a strain rate from 0.008 to 0.2 s^-1, where a completely recrystallized and homogeneously distributed microstructure would be obtained.
文摘A successful mechanical property data-driven prediction model is the core of the optimal design of hot rolling process for hot-rolled strips. However, the original industrial data, usually unbalanced, are inevitably mixed with fluctuant and abnormal values. Models established on the basis of the data without data processing can cause misleading results, which cannot be used for the optimal design of hot rolling process. Thus, a method of industrial data processing of C-Mn steel was proposed based on the data analysis. The Bayesian neural network was employed to establish the reliable mechanical property prediction models for the optimal design of hot rolling process. By using the multi-objective optimization algorithm and considering the individual requirements of costumers and the constraints of the equipment, the optimal design of hot rolling process was successfully applied to the rolling process design for Q345B steel with 0.017% Nb and 0.046% Ti content removed. The optimal process design results were in good agreement with the industrial trials results, which verify the effectiveness of the optimal design of hot rolling process.
基金funding supported by National Natural Science Foundation of China(No.52175285)Beijing Municipal Natural Science Foundation(No.3182025)+1 种基金National Defense Science and Technology Rapid support Project(No.61409230113)Scientific and Technological Innovation Foundation of Shunde Graduate School,USTB and Fundamental Research Funds for the Central Universities(No.FRFBD-20-08A,FRF-TP-20-009A2)。
文摘In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the interactive effects of material hardening, recovery and dynamic recrystallization(DRX) on the characteristic deformation behavior were considered by incorporating the evolution laws of viscoplastic flow, dislocation activities, DRX nucleation and boundary migration in a coupled manner. The model parameters were calibrated based on the experimental data analysis and genetic algorithm(GA) based objective optimization. The predicted flow stress, DRX fraction and average grain size match well with experimental results. The proposed model was embedded in the finite element(FE) software DEFORM-3 D via user defined subroutine to simulate the hot compression and equal channel angular extrusion(ECAE) processes. The heterogeneous microstructure distributions at different deformation zones and the dislocation density evolution with competitive deformation mechanisms were captured.This study can provide a theoretical solution for the hot working problems of magnesium alloy.
基金This research was funded by the National Key Research and Development Program of China(No.2019YFA0705300)the Joint Research Fund of Natural Science Foundation of Liaoning-the State Key Laboratory of Rolling and Automation,Northeastern University(2019KF0506)the Fundamental Research Funds for the Central Universities of China(DUT19JC26).
文摘The control of microstructure during hot rolling process of steel is of great importance and will affect the properties of the steel products.According to the production line,a three-dimensional multi-field coupled finite element model of 24-pass continuous hot rolling process of 38CrMoAl steel rod is established using the finite element software MSC.Marc.Based on the recrystallization kinetics model and the grain growth model,a subroutine written in Fortran is introduced to calculate the recrystallization behavior and microstructure evolution of 38CrMoAl steel during the entire rolling process.The distribution and evolution of variables such as strain,temperature and recrystallization fractions during the rolling process are analyzed.The temperature variations and grain sizes at both the center and surface of the tested steel are compared with the experimental results.And it is found that the simulation results are in good agreement with the experimental ones,confirming the reliability of the established model.
基金supported by National Natural Science Foundation of China (Grant No. 50971092)Innovation Team Plan pf Liaoning Provincical Education Department (Grant no. 2007T132)
文摘The hypereutectic Al-Si alloy was fabricated by hot extrusion process after solidified under electromagnetic stirring,and the microstructure and mechanical properties of the alloy were studied.The results show that the ultimate tensile strength and elongation of the alloy reached 229.5 MPa and 4.6%,respectively with the extrusion ratio of 10,and 263.2 MPa and 5.4%,respectively with extrusion ratio of 20.This indicates that the mechanical properties of the alloy are obviously improved with the increase of extrusion ratio.After hot extruded,the primary Si,eutectic Si,Mg2Si,AlNi,Al7Cu4Ni and Al-Si-Mn-Fe-Cr-Mo phases are refined to different extent,and the efficiency of refinement is obvious more and more with the increase of extrusion ratio.After T6 heat treatment,the sharp corners of these phases become passivated and roundish,and the mechanical properties are improved.The ultimate tensile strength of the extruded alloy after T6 heat treatment reaches 335.3 MPa with extrusion ratio of 10 and 353.6 MPa with extrusion ratio of 20.
基金supported by the National Key Research Project(No.2016YFB0300901)
文摘The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of Al Si Ti phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.
