Isothermal compression of TC11 alloy at the deformation temperatures ranging from 1023 to 1323 K with an interval of 20 K, the strain rates of 0.001, 0.1, 1.0, and 10.0 s-1, and the height reductions of 50% and 70% wa...Isothermal compression of TC11 alloy at the deformation temperatures ranging from 1023 to 1323 K with an interval of 20 K, the strain rates of 0.001, 0.1, 1.0, and 10.0 s-1, and the height reductions of 50% and 70% was conducted on a Gleeble-1500D thermomechanical simulator. According to the experimental results, the isothermal compression and the processing maps of TC11 alloy at different strains were drawn by using the dynamic material model (DMM). Based on the processing maps, the proper forging parameters, including a combination of defor-mation temperature and strain rate, vary with the strain in different phases of TC11 alloy.展开更多
High temperature deformation behavior and workability of Mg-8.1 Gd-4.5Y-0.3Zr alloy were studied by compression tests.Arrhenius equation with strain compensation and processing maps were established.The results show t...High temperature deformation behavior and workability of Mg-8.1 Gd-4.5Y-0.3Zr alloy were studied by compression tests.Arrhenius equation with strain compensation and processing maps were established.The results show that the activation energy Q,structure factor a,n and In A varies with the strain,its relationship fit well by fifth order polynomial.The flow stresses predicted by the extracted model are in good agreement with the experimental results.There are five typical domains in the processing map,and the deformation mechanisms in different domains were determined by microstructure analysis.The feasible processing window of the alloy is in the areas of 400-500℃/0.001-0.1 s^(-1).展开更多
ZE20(Mg-2Zn-0.2Ce)^2 is a new wrought magnesium alloy with improved extrudability and mechanical properties[1].To understand the constitutive behavior and workability of this new alloy,Gleeble thermomechanical testing...ZE20(Mg-2Zn-0.2Ce)^2 is a new wrought magnesium alloy with improved extrudability and mechanical properties[1].To understand the constitutive behavior and workability of this new alloy,Gleeble thermomechanical testing has been carried out in this study.The flow stress behavior of ZE20 was investigated between 250℃–450℃ and 10^–3 s^–1–1.0 s^–1 in isothermal compression.Constitutive descriptions of the flow stress are provided.A new general approach at application of the extended Ludwik equation is demonstrated and was found to be more accurate than the hyperbolic sine Arrhenius model while having a similar number of model constants.Processing maps were developed based on the experimental results and are verified with microstructural investigation.A region of safe processing with non-basal texture and high activity of dynamic recrystallization(DRX)was found between 375℃ and 450℃,from 10^–1 s^–1 to 10^–2.5 s^–1.A region of potentially safe processing with annealing that is associated with shear band nucleation of non-basal grains was identified for temperatures as low as 300℃ and rates as high as 10^–1 s^–1.展开更多
Mg-4Zn-1RE-0.5Zr (ZE41) Mg alloy is extensively used in the aerospace and automobile industries.In order to improve the applicability and performance,this alloy was engineered with in-situ Ti B2reinforcement to form T...Mg-4Zn-1RE-0.5Zr (ZE41) Mg alloy is extensively used in the aerospace and automobile industries.In order to improve the applicability and performance,this alloy was engineered with in-situ Ti B2reinforcement to form Ti B2/ZE41 composite.The high temperature deformation behavior and manufacturability of the newly developed Ti B2/ZE41 composite and the parent ZE41 Mg alloy were studied via establishing constitutive modeling of flow stress,deformation activation energy and processing map over a temperature range of 250℃-450℃ and strain rate range of 0.001 s-1-10 s-1.The predicted flow stress behavior of both materials were found to be well consistent with the experimental values.A significant improvement in activation energy was found in Ti B2/ZE41 composite (171.54 k J/mol) as compared to the ZE41 alloy (148.15 k J/mol) due to the dispersed strengthening of in-situ Ti B2particles.The processing maps were developed via dynamic material modeling.A wider workability domain and higher peak efficiency (45%) were observed in Ti B2/ZE41 composite as compared to ZE41 alloy (41%).The Dynamic recrystallization is found to be the dominating deformation mechanism for both materials;however,particle stimulated nucleation was found to be an additional mode of deformation in Ti B2/ZE41 composite.The twinning and stress induced cracks were observed in both the materials at low temperature and high strain rate.A narrow range of instability zone is found in the present Ti B2/ZE41 composite among the existing published literature on Mg based composites.The detailed microstructural characterization was carried out in both workability and instability domains to establish the governing deformation mechanisms.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
Hot deformation behavior of a high Al-low Si transformation-induced plasticity(TRIP) steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–...Hot deformation behavior of a high Al-low Si transformation-induced plasticity(TRIP) steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–10s^(-1). The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves(dynamic recrystallization and dynamic recovery) were observed during the hot compression of the high Al-low Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1s^(-1) and deformation temperature of 1200℃ as compared to other deformation conditions.展开更多
The isothermally compression deformation behavior of an elevated Cu/Li weight ratio Al–Cu–Li alloy was investigated under various deformation conditions.The isothermal compression tests were carried out in a tempera...The isothermally compression deformation behavior of an elevated Cu/Li weight ratio Al–Cu–Li alloy was investigated under various deformation conditions.The isothermal compression tests were carried out in a temperature range from 300 to 500℃ and at a strain rate range from 0.001 to 10 s^-1.The results show that the peak stress level decreases with temperature increasing and strain rate decreasing,which is represented by the Zener–Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 218.5 k J/mol.At low Z value,the dynamic recrystallized grain is well formed with clean high-angle boundaries.At high Z value,a high dislocation density with poorly developed cellularity and considerable fine dynamic precipitates are observed.Based on the experimental data and dynamic material model,the processing maps at strain of 0.3,0.5 and 0.7 were developed to demonstrate the hot workability of the alloy.The results show that the main softening mechanism at high Z value is precipitate coarsening and dynamic recovery;the dynamic recrystallization of the alloy can be easily observed as ln Z ≤ 29.44,with peak efficiency of power dissipation of around 70%.At strains of 0.3,0.5 and 0.7,the flow instability domains are found at higher strain rates,which mainly locate at the upper part of processing maps.In addition,when the strain rate is 0.001 or 0.02 s^-1,there is a particular instability domain at 300–350℃.展开更多
The hot working behavior of Mg-Gd-Y-Nb-Zr alloy was investigated using constitutive model and hot processing maps in this work. Isothermal compression tests were conducted with temperature and strain rate range of 703...The hot working behavior of Mg-Gd-Y-Nb-Zr alloy was investigated using constitutive model and hot processing maps in this work. Isothermal compression tests were conducted with temperature and strain rate range of 703-773 K and 0.01-5 s^(-1), respectively. Improved Arrhenius-type equation incorporated with strain compensations was used to predict flow behavior of the alloy, and the predictability was evaluated using correlation coefficient, root mean square error and absolute relative error. Processing maps were constructed at different strains for Mg-Gd-Y-Nb-Zr alloy based on dynamic materials model.The processing maps are divided into three domains and the corresponding microstructure evolutions are referred to the forming of straight grain boundaries, twinning, dynamic recrystallization and grain growth. Instability occurred mainly at the strain rate range of 0.3s^(-1)-0.5s^(-1). The optimum processing domain is mainly at the temperature range of 703-765 K with the strain rate range of 0.01-0.1 s^(-1).展开更多
Isothermal compression testing of Ti555211 titanium alloys was carried out at deformation temperatures from 750 to 950 °C in 50 °C intervals with a strain rate of0.001-1.000 s^(-1). The high-temperature de...Isothermal compression testing of Ti555211 titanium alloys was carried out at deformation temperatures from 750 to 950 °C in 50 °C intervals with a strain rate of0.001-1.000 s^(-1). The high-temperature deformation behavior of the Ti555211 alloy was characterized by analysis of stress-strain behavior, kinetics and processing maps. A constitutive equation was formulated to describe the flow stress as a function of deformation temperature and strain rate, and the calculated apparent activation energies are found to be 454.50 and 207.52 k J mol^(-1)in the a b-phase and b-phase regions, respectively. A processing map based on the Murty instability criterion was developed at a strain of 0.7. The maps exhibit two domains of peak efficiency from 750 to 950 °C. A *60 % peak efficiency occurs at 800-850 °C/0.001-0.010 s^(-1). The other peak efficiency of *60 % occurs at C950 °C/0.001-0.010 s^(-1), which can be considered to be the optimum condition for high-temperature working of this alloy.However, at strain rates of higher than 1.000 s^(-1)and deformation temperatures of 750 and 950 °C, clear process flow lines and bands of flow localization occur in the hightemperature deformation process, which should be avoided in Ti555211 alloy hot processing. The mechanism in stability domain and instability domain was also discussed.展开更多
Results of an experimental and modelling study of forming processes in the AA2099 Al–Cu–Li alloy, for a wide range of temperatures, strains and strain rates, are presented. The analyses are based on tensile testing ...Results of an experimental and modelling study of forming processes in the AA2099 Al–Cu–Li alloy, for a wide range of temperatures, strains and strain rates, are presented. The analyses are based on tensile testing at 20 °C at a strain rate of 0.02 s-1and uniaxial compression testing in the temperature range 400–550 °C at strain rates ranging from0.001 to 100 s-1, for constant values of true strain of 0.5 and 0.9. The stability of plastic deformation and its relationship with a sensitivity of stress to strain rate are considered. The power dissipation efficiency coefficient, g(%), and the flow instability parameter, n B 0, were determined. The complex processing maps for hot working were determined and quantified, including process frames for basic forging processes: conventional forging and for near-superplastic and isothermal conditions. A significant aspect is the convergence of power dissipation when passing through the 500 °C peak.Deformation, temperature and strain-rate-dependent microstructures at 500 °C for strain rates of 0.1, 1, 10 and 100 s-1are described and analysed for the conventional die forging process frame, corresponding to 465–523 °C and strain rates of50–100 s-1.展开更多
The hot deformation characteristics and processing maps of aged nickel-base UNS N10276 alloy were inves- tigated and compared with those of solution-treated UNS N10276 alloy at temperatures of 950-1250 ℃ and strain r...The hot deformation characteristics and processing maps of aged nickel-base UNS N10276 alloy were inves- tigated and compared with those of solution-treated UNS N10276 alloy at temperatures of 950-1250 ℃ and strain rates between 0.01 and 10 s-1. The dominant precipitated phase in the aged alloy was identified as topologically close-packed (TCP) # phase enriched in Mo and Ni. The precipitates present in the UNS N10276 alloy could significantly facilitate flow softening after peak stress at temperatures lower than 1150 ℃ and strain rates higher than 0.01 s-1. Processing maps at true strains of 0.1-0.9 were developed using the dynamic materials model and experimental flow stress data. Although aging treatment slightly shrank the suitable hot working window of this alloy, the aged alloy showed higher peak efficiencies of power dissipation and smaller unstable regions in comparison with solution-treated alloy. Furthermore, aging treatment eliminated the instability region of processing maps at true strains of 0.2-0.5. The precipitated phase promoted dynamic recrystallization (DRX) by the particle-stimulated nucleation (PSN) mechanism, which resulted in the larger fraction of DRX as well as finer and more uniform grain structure in the aged alloy specimens compared to the solution-treated alloy.展开更多
Isothermal compression tests of as-forged 30Si2MnCrMoVE low-alloying ultra-high-strength steel were carried out on a Gleeble 3500 thermal simulator at the deformation temperatures of 950-1150℃and strain rates of 0.01...Isothermal compression tests of as-forged 30Si2MnCrMoVE low-alloying ultra-high-strength steel were carried out on a Gleeble 3500 thermal simulator at the deformation temperatures of 950-1150℃and strain rates of 0.01-10 s^−1.Based on the classical stress-dislocation density relationship and the kinematics of the dynamic recrystallization,the constitutive equations of the work hardening dynamical recovery period and dynamical recrystallization period were developed by using the work hardening curve and Avrami equation,which shows good agreement with the experimental value.Processing maps at the strain of 0.90 were constructed based on dynamic material model and were analyzed combined with microstructure observation under different conditions.The optimum parameter based on the processing maps was obtained and verified by a supplementary experiment.The power dissipation maps and instability maps at strains of 0.05-0.90 were also constructed,and the evolution law was analyzed in detail.The established constitutive equation and hot processing maps can provide some guidance for hot working process.展开更多
The hot deformation behavior of a Ti-47Al-2Cr-2Nb-0.2W-0.15B (at%) titanium aluminide alloy fabricated by pre-alloyed powder metallurgy has been investigated by using the hot compression tests in the temperature ran...The hot deformation behavior of a Ti-47Al-2Cr-2Nb-0.2W-0.15B (at%) titanium aluminide alloy fabricated by pre-alloyed powder metallurgy has been investigated by using the hot compression tests in the temperature range from 950℃ to 1300℃ and at the strain rates between 10-3 s-1 and 10 s-1. The processing maps have been established to evaluate the optimum hot processing conditions and reveal the instability regions. It is found that the flow stress of the investigated alloy is a strong function of the temperature and the strain rate, The investigated alloy has the optimum hot-working condition at 950℃ and 10-3 s-1, since the material undergoes dynamic recrystallization to produce a fine-grained microstructure. At 1250℃ and 10-3 s-1, the alloy exhibits superplastic deformation. At 2300℃ and 10-1 s-1, the cyclic dynamic recrystallization with high temperature grain coarsening takes place. The material undergoes flow instabilities at lower temperatures and higher strain rates, as predicted by the instability criterion. The processing maps demonstrate that the strain significantly affected the instability regions. The manifestations of the instabilities have been observed in the form of microvoids, wedge cracks, and surface fractures.展开更多
Hot deformation behavior of the Cu-Cr-Zr alloy was investigated using hot compressive tests in the tem- perature range of 650-850℃ and strain rate range of 0.001-10 s-1. The constitutive equation of the alloy based o...Hot deformation behavior of the Cu-Cr-Zr alloy was investigated using hot compressive tests in the tem- perature range of 650-850℃ and strain rate range of 0.001-10 s-1. The constitutive equation of the alloy based on the hyperbolic-sine equation was established to characterize the flow stress as a function of strain rate and deformation temperature. The critical conditions for the occurrence of dynamic recrystallization were determined based on the alloy strain hardening rate curves. Based on the dynamic material model, the processing maps at the strains of 0.3, 0.4 and 0.5 were obtained. When the true strain was 0.5, greater power dissipation efficiency was observed at 800-850 ℃ and under 0.001-0.1 s-1, with the peak efficiency of 47%. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate. Based on the processing maps and microstructure evolution, the optimal hot working conditions for the Cu-Cr-Zr alloy are in the temperature range of 800-850 ℃ and the strain rate range of 0.001-0.1 s-1.展开更多
The hot deformation behavior of Al-Cu-Li alloy was investigated by hot compression tests in the temperature range of 340-500℃ with strain rate of 0.001-10.000 s^(-1).Based on the dynamic materials model(DMM),processi...The hot deformation behavior of Al-Cu-Li alloy was investigated by hot compression tests in the temperature range of 340-500℃ with strain rate of 0.001-10.000 s^(-1).Based on the dynamic materials model(DMM),processing maps of the test alloy were developed for optimizing hot processing parameters.The optimum parameters of hot deformation for Al-Cu-Li alloy are at temperature of 400-430℃and strain rate of about 0.100 s^(-1),with efficiency of power dissipation of around 30%.The microstructural manifestation of the alloy deformed in instability domains is flow localization,and dynamic softening first occurs in flow localizations structure.In stable domains,dynamic recovery(DRV) and dynamic recrystallization(DRX) are the main microstructural evolution mechanism.DRX is gradually strengthened with the increase in deformation temperature and the decrease in strain rate.During hot deformation,the DRX mechanism of Al-Cu-Li alloy is dominated by continuous DRX(CDRX).A DRX model of Al-Cu-Li alloy is proposed based on the microstructural evolution process of the test alloy.展开更多
Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS)was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s-1 using a Gleeble 3500 ther...Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS)was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s-1 using a Gleeble 3500 thermal-mechanical simulator.The true stress-strain curves of the studied HNMSS were measured and corrected to eliminate the effect of friction on the flow stress.The relationship between the flow stress and Zener-Hollomon parameter for the studied HNMSS wsa analyzed in the Arrhenius hyperbolic sine constitutive model by the law of Z=3.76×1015 sinh(0.004979σp)7.5022.The processing maps at different strains of the studied HNMSS were plotted,and its flow instability regions in hot working were also confirmed in combination with the microstructure examination.Moreover,the optimal hot deformation parameters of the studied HNMSS could be suggested at T=1303-1423 K andε=5-10 s-1 or T=1273-1473 K andε=0.005-0.04 s-1.展开更多
The hot deformation characteristics of ductile iron are studied in the temperature range of 973 to 1273K and strain rate range of 0.001 to 1 s-1 by using hot compression tests.Processing maps for hot working are devel...The hot deformation characteristics of ductile iron are studied in the temperature range of 973 to 1273K and strain rate range of 0.001 to 1 s-1 by using hot compression tests.Processing maps for hot working are developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate.The results reveal that the flow stress of ductile iron is sensitive to strain rate.In the processing map under strain of 0.7,a domain is centered at 1273 K and 1 s-1,and the maximum efficiency is more than 36%.According to the maps,the zone with the temperature range of 1173 to 1273 K and strain rate range of 0.1 to 1 s-1 may be considered as the optimum region for hot working.展开更多
The isothermal hot compression tests of Ti-15Al-12Nb alloy under wide range of strain rates(0.01-10.00 s^(-1)and deformation temperatures(950,1000,1050,and 1100℃)were carried out using Gleeble-3500 thermo-simulation ...The isothermal hot compression tests of Ti-15Al-12Nb alloy under wide range of strain rates(0.01-10.00 s^(-1)and deformation temperatures(950,1000,1050,and 1100℃)were carried out using Gleeble-3500 thermo-simulation machine.A constitutive equation represented as a function of temperature,strain rate and true strain was developed,and the hot deformation appar-ent activation energy is calculated to be about 453 kJ·mol^(-1).By employing dynamic material model(DMM),the processing maps of Ti-15Al-12Nb alloy at various strains were established.Maximum efficiency of about 57%for power dissipation is obtained at high temperature and low strain rate.Owing to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization(DRX)zone for metal material,the optimum processing conditions are selected as the temperature range of 1050-1100℃and the strain rate range of 0.01-0.10 s^(-1).Using transmission electron microscopy(TEM)studies,it is found that the dislocation density is directly associated with the value of processing efficiency.It is observed that when the processing effi-ciency is about 22%,the dislocation density is reasonably large.The flow instability region occurs at strain rate of 10.00 s^(-1)with cracks,which should be avoided during hot processing to obtain the required mechanical properties.展开更多
In order to predict flow instability of wear-resistant steel BTW1, the hot compressions of wear-resistant steel BTW1 were firstly performed at the temperature of 900-1150 ℃ and at the strain rate of 0.05-15 s-1. Then...In order to predict flow instability of wear-resistant steel BTW1, the hot compressions of wear-resistant steel BTW1 were firstly performed at the temperature of 900-1150 ℃ and at the strain rate of 0.05-15 s-1. Then, the constitutive relation was established based on Arrhenius-type hyperbolic sine equation. The results demonstrated that the flow stress depended on the deformation temperature and strain rate. When the deformation temperature kept constant, the flow stress increased as the strain rate increased. When the strain rate remained constant, the flow stress decreased as the temperature increased. The flow stresses calculated by constitutive equations were in a good agreement with experimental results. The apparent activation energy for deformation in the above processing region was estimated to be 369 kJ tool-1. A processing map could be obtained by the superimposition of an instability map on a power dissipation map. Based on the analysis of processing map and the microstructures, the theological instability regimes of strain rate and temperature for hot deformation of wear-resistant steel BTWl had been identified.展开更多
The processing maps were used to identify the optimal forging parameters of Ti-24A1- 17Nb-0.5Mo alloy by evaluating the flow data according to the DMM model. The actual local strain rate and strain distribution in the...The processing maps were used to identify the optimal forging parameters of Ti-24A1- 17Nb-0.5Mo alloy by evaluating the flow data according to the DMM model. The actual local strain rate and strain distribution in the samples were obtained by finite element calculations. The local microstructures of the deformed samples were related to the local deformation parameters and correlated with the processing maps at 0.3, 0.4, 0.5 and 0.6 of logarithmic strain. Flow regimes predicted by DMM analysis were then correlated with the local microstructural observations. Five domains of efficient coefficient could be distinguished. Unstable regions were microstructurally related to shear band formation within the (~2~B2 phase deformation field, and to flow localiza- tion at grain boundaries of B2 phase in the near B2 phase deformation field. Stable flow regimes were shown to be associated with dynamic globularization of the plate- like a2 in the a2+B2 phase deformation zone, and with dynamic recrystallization of B2 in the near B2 phase deformation zone.展开更多
基金supported by the National Natural Science Foundation of China (No. 50975234)
文摘Isothermal compression of TC11 alloy at the deformation temperatures ranging from 1023 to 1323 K with an interval of 20 K, the strain rates of 0.001, 0.1, 1.0, and 10.0 s-1, and the height reductions of 50% and 70% was conducted on a Gleeble-1500D thermomechanical simulator. According to the experimental results, the isothermal compression and the processing maps of TC11 alloy at different strains were drawn by using the dynamic material model (DMM). Based on the processing maps, the proper forging parameters, including a combination of defor-mation temperature and strain rate, vary with the strain in different phases of TC11 alloy.
基金the National Natural Science Foundation of China(Grant no.51501015).
文摘High temperature deformation behavior and workability of Mg-8.1 Gd-4.5Y-0.3Zr alloy were studied by compression tests.Arrhenius equation with strain compensation and processing maps were established.The results show that the activation energy Q,structure factor a,n and In A varies with the strain,its relationship fit well by fifth order polynomial.The flow stresses predicted by the extracted model are in good agreement with the experimental results.There are five typical domains in the processing map,and the deformation mechanisms in different domains were determined by microstructure analysis.The feasible processing window of the alloy is in the areas of 400-500℃/0.001-0.1 s^(-1).
基金This work is partially supported by the United States Automotive Materials Partnership(USAMP).
文摘ZE20(Mg-2Zn-0.2Ce)^2 is a new wrought magnesium alloy with improved extrudability and mechanical properties[1].To understand the constitutive behavior and workability of this new alloy,Gleeble thermomechanical testing has been carried out in this study.The flow stress behavior of ZE20 was investigated between 250℃–450℃ and 10^–3 s^–1–1.0 s^–1 in isothermal compression.Constitutive descriptions of the flow stress are provided.A new general approach at application of the extended Ludwik equation is demonstrated and was found to be more accurate than the hyperbolic sine Arrhenius model while having a similar number of model constants.Processing maps were developed based on the experimental results and are verified with microstructural investigation.A region of safe processing with non-basal texture and high activity of dynamic recrystallization(DRX)was found between 375℃ and 450℃,from 10^–1 s^–1 to 10^–2.5 s^–1.A region of potentially safe processing with annealing that is associated with shear band nucleation of non-basal grains was identified for temperatures as low as 300℃ and rates as high as 10^–1 s^–1.
基金Department of Science and Technology, India [grant number of DST/TDT/AMT/ 2017/211(G)] (MEE/18–19/412/DSTX/SUSH) for the financial support and FIST grant, Department of Science and Technology, India [grant number SR/FST/ET11–059/2012 (G)] for funding electron microscope facilitya part of Center of Excellence (Co E) in Applied Magnesium Research (A Vertical of Center for Materials and Manufacturing for Futuristic Mobility), IIT Madrasthe Ministry of Human Resource and Development for funding this CoE through grant number–SB20210992MEMHRD008517。
文摘Mg-4Zn-1RE-0.5Zr (ZE41) Mg alloy is extensively used in the aerospace and automobile industries.In order to improve the applicability and performance,this alloy was engineered with in-situ Ti B2reinforcement to form Ti B2/ZE41 composite.The high temperature deformation behavior and manufacturability of the newly developed Ti B2/ZE41 composite and the parent ZE41 Mg alloy were studied via establishing constitutive modeling of flow stress,deformation activation energy and processing map over a temperature range of 250℃-450℃ and strain rate range of 0.001 s-1-10 s-1.The predicted flow stress behavior of both materials were found to be well consistent with the experimental values.A significant improvement in activation energy was found in Ti B2/ZE41 composite (171.54 k J/mol) as compared to the ZE41 alloy (148.15 k J/mol) due to the dispersed strengthening of in-situ Ti B2particles.The processing maps were developed via dynamic material modeling.A wider workability domain and higher peak efficiency (45%) were observed in Ti B2/ZE41 composite as compared to ZE41 alloy (41%).The Dynamic recrystallization is found to be the dominating deformation mechanism for both materials;however,particle stimulated nucleation was found to be an additional mode of deformation in Ti B2/ZE41 composite.The twinning and stress induced cracks were observed in both the materials at low temperature and high strain rate.A narrow range of instability zone is found in the present Ti B2/ZE41 composite among the existing published literature on Mg based composites.The detailed microstructural characterization was carried out in both workability and instability domains to establish the governing deformation mechanisms.
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financially supported by the National Program on Key Basic Research Project (Grant No. 2011CB606306-2)the National Natural Science Foundation of China (Grant No. 51775102)
文摘Hot deformation behavior of a high Al-low Si transformation-induced plasticity(TRIP) steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–10s^(-1). The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves(dynamic recrystallization and dynamic recovery) were observed during the hot compression of the high Al-low Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1s^(-1) and deformation temperature of 1200℃ as compared to other deformation conditions.
基金supported by the Foundation for Science and Technology Development Project of Shandong (No.2014GGX102006)
文摘The isothermally compression deformation behavior of an elevated Cu/Li weight ratio Al–Cu–Li alloy was investigated under various deformation conditions.The isothermal compression tests were carried out in a temperature range from 300 to 500℃ and at a strain rate range from 0.001 to 10 s^-1.The results show that the peak stress level decreases with temperature increasing and strain rate decreasing,which is represented by the Zener–Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 218.5 k J/mol.At low Z value,the dynamic recrystallized grain is well formed with clean high-angle boundaries.At high Z value,a high dislocation density with poorly developed cellularity and considerable fine dynamic precipitates are observed.Based on the experimental data and dynamic material model,the processing maps at strain of 0.3,0.5 and 0.7 were developed to demonstrate the hot workability of the alloy.The results show that the main softening mechanism at high Z value is precipitate coarsening and dynamic recovery;the dynamic recrystallization of the alloy can be easily observed as ln Z ≤ 29.44,with peak efficiency of power dissipation of around 70%.At strains of 0.3,0.5 and 0.7,the flow instability domains are found at higher strain rates,which mainly locate at the upper part of processing maps.In addition,when the strain rate is 0.001 or 0.02 s^-1,there is a particular instability domain at 300–350℃.
文摘The hot working behavior of Mg-Gd-Y-Nb-Zr alloy was investigated using constitutive model and hot processing maps in this work. Isothermal compression tests were conducted with temperature and strain rate range of 703-773 K and 0.01-5 s^(-1), respectively. Improved Arrhenius-type equation incorporated with strain compensations was used to predict flow behavior of the alloy, and the predictability was evaluated using correlation coefficient, root mean square error and absolute relative error. Processing maps were constructed at different strains for Mg-Gd-Y-Nb-Zr alloy based on dynamic materials model.The processing maps are divided into three domains and the corresponding microstructure evolutions are referred to the forming of straight grain boundaries, twinning, dynamic recrystallization and grain growth. Instability occurred mainly at the strain rate range of 0.3s^(-1)-0.5s^(-1). The optimum processing domain is mainly at the temperature range of 703-765 K with the strain rate range of 0.01-0.1 s^(-1).
基金financially supported by the Project of Introducing Talents of Discipline to Universities‘‘111’’Project(No.B08040)
文摘Isothermal compression testing of Ti555211 titanium alloys was carried out at deformation temperatures from 750 to 950 °C in 50 °C intervals with a strain rate of0.001-1.000 s^(-1). The high-temperature deformation behavior of the Ti555211 alloy was characterized by analysis of stress-strain behavior, kinetics and processing maps. A constitutive equation was formulated to describe the flow stress as a function of deformation temperature and strain rate, and the calculated apparent activation energies are found to be 454.50 and 207.52 k J mol^(-1)in the a b-phase and b-phase regions, respectively. A processing map based on the Murty instability criterion was developed at a strain of 0.7. The maps exhibit two domains of peak efficiency from 750 to 950 °C. A *60 % peak efficiency occurs at 800-850 °C/0.001-0.010 s^(-1). The other peak efficiency of *60 % occurs at C950 °C/0.001-0.010 s^(-1), which can be considered to be the optimum condition for high-temperature working of this alloy.However, at strain rates of higher than 1.000 s^(-1)and deformation temperatures of 750 and 950 °C, clear process flow lines and bands of flow localization occur in the hightemperature deformation process, which should be avoided in Ti555211 alloy hot processing. The mechanism in stability domain and instability domain was also discussed.
基金financed by the Ministry of Science and Higher Education (AGH-UST statutory research project No. 11.11.110.292)
文摘Results of an experimental and modelling study of forming processes in the AA2099 Al–Cu–Li alloy, for a wide range of temperatures, strains and strain rates, are presented. The analyses are based on tensile testing at 20 °C at a strain rate of 0.02 s-1and uniaxial compression testing in the temperature range 400–550 °C at strain rates ranging from0.001 to 100 s-1, for constant values of true strain of 0.5 and 0.9. The stability of plastic deformation and its relationship with a sensitivity of stress to strain rate are considered. The power dissipation efficiency coefficient, g(%), and the flow instability parameter, n B 0, were determined. The complex processing maps for hot working were determined and quantified, including process frames for basic forging processes: conventional forging and for near-superplastic and isothermal conditions. A significant aspect is the convergence of power dissipation when passing through the 500 °C peak.Deformation, temperature and strain-rate-dependent microstructures at 500 °C for strain rates of 0.1, 1, 10 and 100 s-1are described and analysed for the conventional die forging process frame, corresponding to 465–523 °C and strain rates of50–100 s-1.
基金financially supported by the Subproject of National Science and Technology Major Project of China(Grant No.2015ZX06002001-001)
文摘The hot deformation characteristics and processing maps of aged nickel-base UNS N10276 alloy were inves- tigated and compared with those of solution-treated UNS N10276 alloy at temperatures of 950-1250 ℃ and strain rates between 0.01 and 10 s-1. The dominant precipitated phase in the aged alloy was identified as topologically close-packed (TCP) # phase enriched in Mo and Ni. The precipitates present in the UNS N10276 alloy could significantly facilitate flow softening after peak stress at temperatures lower than 1150 ℃ and strain rates higher than 0.01 s-1. Processing maps at true strains of 0.1-0.9 were developed using the dynamic materials model and experimental flow stress data. Although aging treatment slightly shrank the suitable hot working window of this alloy, the aged alloy showed higher peak efficiencies of power dissipation and smaller unstable regions in comparison with solution-treated alloy. Furthermore, aging treatment eliminated the instability region of processing maps at true strains of 0.2-0.5. The precipitated phase promoted dynamic recrystallization (DRX) by the particle-stimulated nucleation (PSN) mechanism, which resulted in the larger fraction of DRX as well as finer and more uniform grain structure in the aged alloy specimens compared to the solution-treated alloy.
基金This work was supported by the Shaanxi Key Research and Development Program(No.S2017-ZDYF-ZDXM-GY-0115)Natural Science Basic Research Plan in Shaanxi Province of China(No.2017JM5010)Fundamental Research Funds for the Central Universities of China(No.3102019ZX004).
文摘Isothermal compression tests of as-forged 30Si2MnCrMoVE low-alloying ultra-high-strength steel were carried out on a Gleeble 3500 thermal simulator at the deformation temperatures of 950-1150℃and strain rates of 0.01-10 s^−1.Based on the classical stress-dislocation density relationship and the kinematics of the dynamic recrystallization,the constitutive equations of the work hardening dynamical recovery period and dynamical recrystallization period were developed by using the work hardening curve and Avrami equation,which shows good agreement with the experimental value.Processing maps at the strain of 0.90 were constructed based on dynamic material model and were analyzed combined with microstructure observation under different conditions.The optimum parameter based on the processing maps was obtained and verified by a supplementary experiment.The power dissipation maps and instability maps at strains of 0.05-0.90 were also constructed,and the evolution law was analyzed in detail.The established constitutive equation and hot processing maps can provide some guidance for hot working process.
文摘The hot deformation behavior of a Ti-47Al-2Cr-2Nb-0.2W-0.15B (at%) titanium aluminide alloy fabricated by pre-alloyed powder metallurgy has been investigated by using the hot compression tests in the temperature range from 950℃ to 1300℃ and at the strain rates between 10-3 s-1 and 10 s-1. The processing maps have been established to evaluate the optimum hot processing conditions and reveal the instability regions. It is found that the flow stress of the investigated alloy is a strong function of the temperature and the strain rate, The investigated alloy has the optimum hot-working condition at 950℃ and 10-3 s-1, since the material undergoes dynamic recrystallization to produce a fine-grained microstructure. At 1250℃ and 10-3 s-1, the alloy exhibits superplastic deformation. At 2300℃ and 10-1 s-1, the cyclic dynamic recrystallization with high temperature grain coarsening takes place. The material undergoes flow instabilities at lower temperatures and higher strain rates, as predicted by the instability criterion. The processing maps demonstrate that the strain significantly affected the instability regions. The manifestations of the instabilities have been observed in the form of microvoids, wedge cracks, and surface fractures.
基金financially supported by the National Natural Science Foundation of China(No.51101052)the National Science Foundation(No.IRES 1358088)
文摘Hot deformation behavior of the Cu-Cr-Zr alloy was investigated using hot compressive tests in the tem- perature range of 650-850℃ and strain rate range of 0.001-10 s-1. The constitutive equation of the alloy based on the hyperbolic-sine equation was established to characterize the flow stress as a function of strain rate and deformation temperature. The critical conditions for the occurrence of dynamic recrystallization were determined based on the alloy strain hardening rate curves. Based on the dynamic material model, the processing maps at the strains of 0.3, 0.4 and 0.5 were obtained. When the true strain was 0.5, greater power dissipation efficiency was observed at 800-850 ℃ and under 0.001-0.1 s-1, with the peak efficiency of 47%. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate. Based on the processing maps and microstructure evolution, the optimal hot working conditions for the Cu-Cr-Zr alloy are in the temperature range of 800-850 ℃ and the strain rate range of 0.001-0.1 s-1.
基金financially supported by the National Program on Key Basic Research Project of China (No.2012CB619504)the National Natural Science Foundation of China (No.51274046)
文摘The hot deformation behavior of Al-Cu-Li alloy was investigated by hot compression tests in the temperature range of 340-500℃ with strain rate of 0.001-10.000 s^(-1).Based on the dynamic materials model(DMM),processing maps of the test alloy were developed for optimizing hot processing parameters.The optimum parameters of hot deformation for Al-Cu-Li alloy are at temperature of 400-430℃and strain rate of about 0.100 s^(-1),with efficiency of power dissipation of around 30%.The microstructural manifestation of the alloy deformed in instability domains is flow localization,and dynamic softening first occurs in flow localizations structure.In stable domains,dynamic recovery(DRV) and dynamic recrystallization(DRX) are the main microstructural evolution mechanism.DRX is gradually strengthened with the increase in deformation temperature and the decrease in strain rate.During hot deformation,the DRX mechanism of Al-Cu-Li alloy is dominated by continuous DRX(CDRX).A DRX model of Al-Cu-Li alloy is proposed based on the microstructural evolution process of the test alloy.
基金supported by the National Natural Science Foundation of China(No.51871212)the 2018 Regional Key Project on the Science and Technology Service from Shanghai Branch of Chinese Academy of Sciences(STS,SHBCAS)the Supporting Project for STS,SHBCAS in Fujian Province
文摘Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS)was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s-1 using a Gleeble 3500 thermal-mechanical simulator.The true stress-strain curves of the studied HNMSS were measured and corrected to eliminate the effect of friction on the flow stress.The relationship between the flow stress and Zener-Hollomon parameter for the studied HNMSS wsa analyzed in the Arrhenius hyperbolic sine constitutive model by the law of Z=3.76×1015 sinh(0.004979σp)7.5022.The processing maps at different strains of the studied HNMSS were plotted,and its flow instability regions in hot working were also confirmed in combination with the microstructure examination.Moreover,the optimal hot deformation parameters of the studied HNMSS could be suggested at T=1303-1423 K andε=5-10 s-1 or T=1273-1473 K andε=0.005-0.04 s-1.
基金Item Sponsored by National Natural Science Foundation of China and Baosteel(50271061,50371074)
文摘The hot deformation characteristics of ductile iron are studied in the temperature range of 973 to 1273K and strain rate range of 0.001 to 1 s-1 by using hot compression tests.Processing maps for hot working are developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate.The results reveal that the flow stress of ductile iron is sensitive to strain rate.In the processing map under strain of 0.7,a domain is centered at 1273 K and 1 s-1,and the maximum efficiency is more than 36%.According to the maps,the zone with the temperature range of 1173 to 1273 K and strain rate range of 0.1 to 1 s-1 may be considered as the optimum region for hot working.
文摘The isothermal hot compression tests of Ti-15Al-12Nb alloy under wide range of strain rates(0.01-10.00 s^(-1)and deformation temperatures(950,1000,1050,and 1100℃)were carried out using Gleeble-3500 thermo-simulation machine.A constitutive equation represented as a function of temperature,strain rate and true strain was developed,and the hot deformation appar-ent activation energy is calculated to be about 453 kJ·mol^(-1).By employing dynamic material model(DMM),the processing maps of Ti-15Al-12Nb alloy at various strains were established.Maximum efficiency of about 57%for power dissipation is obtained at high temperature and low strain rate.Owing to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization(DRX)zone for metal material,the optimum processing conditions are selected as the temperature range of 1050-1100℃and the strain rate range of 0.01-0.10 s^(-1).Using transmission electron microscopy(TEM)studies,it is found that the dislocation density is directly associated with the value of processing efficiency.It is observed that when the processing effi-ciency is about 22%,the dislocation density is reasonably large.The flow instability region occurs at strain rate of 10.00 s^(-1)with cracks,which should be avoided during hot processing to obtain the required mechanical properties.
基金This work was supported by the National Natural Science Foundation of China (No. U1510131) and the Applied Basic Research Project of Shanxi Province (Nos. 201701D121078 and 201701D221143).
文摘In order to predict flow instability of wear-resistant steel BTW1, the hot compressions of wear-resistant steel BTW1 were firstly performed at the temperature of 900-1150 ℃ and at the strain rate of 0.05-15 s-1. Then, the constitutive relation was established based on Arrhenius-type hyperbolic sine equation. The results demonstrated that the flow stress depended on the deformation temperature and strain rate. When the deformation temperature kept constant, the flow stress increased as the strain rate increased. When the strain rate remained constant, the flow stress decreased as the temperature increased. The flow stresses calculated by constitutive equations were in a good agreement with experimental results. The apparent activation energy for deformation in the above processing region was estimated to be 369 kJ tool-1. A processing map could be obtained by the superimposition of an instability map on a power dissipation map. Based on the analysis of processing map and the microstructures, the theological instability regimes of strain rate and temperature for hot deformation of wear-resistant steel BTWl had been identified.
文摘The processing maps were used to identify the optimal forging parameters of Ti-24A1- 17Nb-0.5Mo alloy by evaluating the flow data according to the DMM model. The actual local strain rate and strain distribution in the samples were obtained by finite element calculations. The local microstructures of the deformed samples were related to the local deformation parameters and correlated with the processing maps at 0.3, 0.4, 0.5 and 0.6 of logarithmic strain. Flow regimes predicted by DMM analysis were then correlated with the local microstructural observations. Five domains of efficient coefficient could be distinguished. Unstable regions were microstructurally related to shear band formation within the (~2~B2 phase deformation field, and to flow localiza- tion at grain boundaries of B2 phase in the near B2 phase deformation field. Stable flow regimes were shown to be associated with dynamic globularization of the plate- like a2 in the a2+B2 phase deformation zone, and with dynamic recrystallization of B2 in the near B2 phase deformation zone.