The extruded AZ80+0.4%Ce magnesium alloy was twisted in the temperature range of 300-380℃by using a Gleeble 3500 thermal simulation test machine with a torsion unit.The deformed cylindrical specimens were cooled at a...The extruded AZ80+0.4%Ce magnesium alloy was twisted in the temperature range of 300-380℃by using a Gleeble 3500 thermal simulation test machine with a torsion unit.The deformed cylindrical specimens were cooled at a cooling rate of 10℃/s or 0.1℃/s,respectively,and aged at 170℃.The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center(SRPC),and that the strong initial basal texture of the extruded magnesium alloy was weakened.Both continuous and discontinuous dynamic recrystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated.And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300℃.For the specimens deformed at 300℃and 340℃followed by a slow cooling rate(0.1℃/s),precipitates of various shapes(β-Mg_(17)Al_(12)),with the dominant precipitates being on the grains boundaries,appeared on the surface section.For specimen deformed at 380℃,lamellar precipitates(LPS)in the interiors of the grains were predominant.After aging,the LPS still dominated for specimens twisted at 380℃;however,the LPS gradually decreased with decreasing deformation temperatures from 380℃to 300℃.Dynamically precipitatedβ,especially those decorating the grain boundaries,changed the competition pictures for the LPS and precipitates of other shapes after aging.Interestingly,LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures.Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain,reduced precipitates size,decreased lamellar spacing as well as strain hardening.展开更多
The mechanical properties of dual-phase steel (DP1000) over the strain rate range of 10^-3-10^3 s^-1 were studied using an electronic universal testing machine and a high-speed tensile testing machine.The plastic defo...The mechanical properties of dual-phase steel (DP1000) over the strain rate range of 10^-3-10^3 s^-1 were studied using an electronic universal testing machine and a high-speed tensile testing machine.The plastic deformation mechanism was investigated from the perspectives of the strain rate sensitivity index,activation volume and dynamic factors.The results show that the tensile strength and yield strength of DP1000 increase as the strain rate increases.The elongation increases without any change after fracture,and then decreased rapidly when the strain rate reaches 103 s^-1.The true strain curves of DP1000 show three stages:the point of instability decreases in the strain range of 10^-3-10^-1 s^-1;the instability point increases between 100-5×10^2 s^-1;above 5×10^2 s^-1,and the instability strain becomes smaller again.The plastic deformation mechanism of the DP was determined by the competitive contributions of work hardening (strain hardening,strain rate hardening) and softening effects due to the adiabatic temperature rise.展开更多
To investigate the influence of tempering process on microstructural evolutions and mechanical properties of 00Cr13Ni4Mo supermartensitic stainless steel(SMSS),specimens were tempered in the temperature range of 520-7...To investigate the influence of tempering process on microstructural evolutions and mechanical properties of 00Cr13Ni4Mo supermartensitic stainless steel(SMSS),specimens were tempered in the temperature range of 520-720 ℃ for 3 h followed by air cooling and an optimized tempering temperature was chosen to prolong holding time from 3 to 12 h.After heat treatments,microstructure examination was conducted by scanning electron microscope,X-ray diffraction examinations,hardness measurements and tensile tests.The results revealed that the superior mechanical properties were achieved by quenching at 1040 ℃ for 1 h+water cooling and tempering at 600 ℃ for 3 h+air cooling.Increasing isothermal tempering time could improve the toughness notably.It was believed that the property was correlated with the microstructure of tempered lath martensite and retained austenite.More retained austenite content is beneficial to the higher toughness of the SMSS.展开更多
The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of σ phase in the test specimen varied up to a maximum of 6% by thermal ...The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of σ phase in the test specimen varied up to a maximum of 6% by thermal treatment at 850 ℃ for up to 60 min. The results showed that σ phase markedly increased the hardness and decreased the impact toughness of the test steel. But the increasing tendency of the ultimate tensile strength and the yield strength was not obvious, while the total elongation abruptly decreased with the aging time from 5 to 60 min. SEM impact microfractograph analysis revealed that the types of impact fracture changed from ductile mode to transcrystalline mode when the specimens were aged for 5-60 min. Furthermore, the extent of pitting potential reducing was found to be strongly temperature dependent, more pronounced at the higher temperature. During the incubation period of σ phase nucleation, the pitting corrosion test temperature and the aging time had collaborative effects on evidently displacing the pitting potential towards less noble values. After 15 min, the higher temperature contributed more to decreasing the pitting potential than the aging time.展开更多
Effects of compression deformation on the sigma-phase precipitation behavior of B-containing S31254 stainless steel after solution treatment were studied using the Gleeble compression test. The cold and hot processing...Effects of compression deformation on the sigma-phase precipitation behavior of B-containing S31254 stainless steel after solution treatment were studied using the Gleeble compression test. The cold and hot processing characteristics of B-containing S31254 stainless steel were evaluated, and the results show that the speed of compression deformation increased the precipitation rate of the sigma phase, and the location of precipitation extended from the austenite grain boundary to the original hot rolling deformation area. During cold deformation at room temperature, the precipitation rate increased when the deformation reached at 40%. Deformation at 950℃ affected precipitation more obviously. At 1074 ℃, when the deformation reached 20%, the precipitated phases started increasing, and above this deformation range, precipitation began decreasing. Also, at 1074℃ the deformation accelerated the precipitation of sigma phase;but with deformation, there was a change in critical temperature for the sigma-phase excursion. The precipitation position of the sigma phase is strongly related to the area of the original hot rolling deformation. With an increase in the deformation amount, precipitates in this region appeared as coarse-grained, skeletal, and network-like features.展开更多
The dynamic recrystallization(DRX)mechanism of as-cast nickel base superalloy N10276 during primary hot working was investigated by compression tests at temperatures of 1000–1200℃ and strain rates between 0.01 and 1...The dynamic recrystallization(DRX)mechanism of as-cast nickel base superalloy N10276 during primary hot working was investigated by compression tests at temperatures of 1000–1200℃ and strain rates between 0.01 and 10 s^(-1).Optical microscopy,scanning electron microscopy,electron backscattered diffraction technique and transmission electron microscopy were used to characterize the evolution of microstructure.At higher deformation temperature or lower strain rate,the true stress–true strain curves exhibit the characteristic of a peak stress followed by a steady state flow stress under large strains,confirming the occurrence of DRX.The degree of DRX increases with elevating deformation temperature.With the progress of DRX,low angle grain boundaries gradually decrease,while high angle grain boundaries increase continuously.Microstructure studies have shown that discontinuous dynamic recrystallization is the main recrystallization mechanism.Since there are few original grain boundaries and twin boundaries,and lack of second phase particles for particle stimulated nucleation,geometrically necessary boundaries are formed as supplementary nucleation sites through sub-grain boundary rotation and deformation twin boundaries.The annealing twins dominated by Σ3 grain boundaries are generated in large quantities during the growth of recrystallized grains.展开更多
To prepare ultra-high-yield strength twinning-induced plasticity(TWIP)steel and reveal its work hardening mechanism at different strain rates from the microcosmic range,the microstructure evolution mechanism of Fe–2...To prepare ultra-high-yield strength twinning-induced plasticity(TWIP)steel and reveal its work hardening mechanism at different strain rates from the microcosmic range,the microstructure evolution mechanism of Fe–20Mn–0.6C TWIP steel was investigated at strain rates of 10^(-4)–10^(3)s^(-1)using a high-speed tensile testing machine and a transmission electron microscope.The results show that the strain rate and deformation had a significant effect on the twin morphology of TWIP steels.At a strain rate of 10^(2)s^(-1),secondary deformation twins were developed,which intersected with the initial deformation twins and increased the resistance of dislocation movement,as well as the plasticity.TWIP steel at a strain rate of 10^(2)s^(-1)had a higher twin formation speed than that at 10^(0)s^(-1).At the same amount of deformation,the twin boundary fraction was higher and increased linearly at a strain rate of 10^(2)s^(-1),while the rule of twin growth at 10^(0)s^(-1)was conformed to S-curve change of DoseResp model.展开更多
基金supported by key technology research and development project of Shan Xi province(20201102019)Natural science foundation of Shanxi Province(201901D111167)+1 种基金Shanxi Scholarship Council of China(2020–117)JCKY2018408B003Magnesium alloy high-performance XXX multi-directional extrusion technology and XX supporting scientific research project(xxxx-2019-021)。
文摘The extruded AZ80+0.4%Ce magnesium alloy was twisted in the temperature range of 300-380℃by using a Gleeble 3500 thermal simulation test machine with a torsion unit.The deformed cylindrical specimens were cooled at a cooling rate of 10℃/s or 0.1℃/s,respectively,and aged at 170℃.The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center(SRPC),and that the strong initial basal texture of the extruded magnesium alloy was weakened.Both continuous and discontinuous dynamic recrystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated.And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300℃.For the specimens deformed at 300℃and 340℃followed by a slow cooling rate(0.1℃/s),precipitates of various shapes(β-Mg_(17)Al_(12)),with the dominant precipitates being on the grains boundaries,appeared on the surface section.For specimen deformed at 380℃,lamellar precipitates(LPS)in the interiors of the grains were predominant.After aging,the LPS still dominated for specimens twisted at 380℃;however,the LPS gradually decreased with decreasing deformation temperatures from 380℃to 300℃.Dynamically precipitatedβ,especially those decorating the grain boundaries,changed the competition pictures for the LPS and precipitates of other shapes after aging.Interestingly,LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures.Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain,reduced precipitates size,decreased lamellar spacing as well as strain hardening.
基金Funded by the National Natural Science Foundation of China(No.52004122)the State Key Laboratory of Marine Equipment made of Metal Material and Application(No.SKLMEAUSTL-201906)+1 种基金the Guidance plan of Natural Science Foundation of Liaoning Province(No.2019-ZD-0025)the Key Project of Liaoning Education Department(No.2019FWDF03)。
文摘The mechanical properties of dual-phase steel (DP1000) over the strain rate range of 10^-3-10^3 s^-1 were studied using an electronic universal testing machine and a high-speed tensile testing machine.The plastic deformation mechanism was investigated from the perspectives of the strain rate sensitivity index,activation volume and dynamic factors.The results show that the tensile strength and yield strength of DP1000 increase as the strain rate increases.The elongation increases without any change after fracture,and then decreased rapidly when the strain rate reaches 103 s^-1.The true strain curves of DP1000 show three stages:the point of instability decreases in the strain range of 10^-3-10^-1 s^-1;the instability point increases between 100-5×10^2 s^-1;above 5×10^2 s^-1,and the instability strain becomes smaller again.The plastic deformation mechanism of the DP was determined by the competitive contributions of work hardening (strain hardening,strain rate hardening) and softening effects due to the adiabatic temperature rise.
基金Item Sponsored by Special Project of Shaanxi Education Department of China(07JK309)Xi'an University of Architecture and Technology of China(JC0714)
文摘To investigate the influence of tempering process on microstructural evolutions and mechanical properties of 00Cr13Ni4Mo supermartensitic stainless steel(SMSS),specimens were tempered in the temperature range of 520-720 ℃ for 3 h followed by air cooling and an optimized tempering temperature was chosen to prolong holding time from 3 to 12 h.After heat treatments,microstructure examination was conducted by scanning electron microscope,X-ray diffraction examinations,hardness measurements and tensile tests.The results revealed that the superior mechanical properties were achieved by quenching at 1040 ℃ for 1 h+water cooling and tempering at 600 ℃ for 3 h+air cooling.Increasing isothermal tempering time could improve the toughness notably.It was believed that the property was correlated with the microstructure of tempered lath martensite and retained austenite.More retained austenite content is beneficial to the higher toughness of the SMSS.
基金Item Sponsored by Special Project of Education Depart ment of Shaanxi Province of China (07JK309)Project of Science andTechnology Research and Development Program of Shaanxi Province of China (2010K10-13)
文摘The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of σ phase in the test specimen varied up to a maximum of 6% by thermal treatment at 850 ℃ for up to 60 min. The results showed that σ phase markedly increased the hardness and decreased the impact toughness of the test steel. But the increasing tendency of the ultimate tensile strength and the yield strength was not obvious, while the total elongation abruptly decreased with the aging time from 5 to 60 min. SEM impact microfractograph analysis revealed that the types of impact fracture changed from ductile mode to transcrystalline mode when the specimens were aged for 5-60 min. Furthermore, the extent of pitting potential reducing was found to be strongly temperature dependent, more pronounced at the higher temperature. During the incubation period of σ phase nucleation, the pitting corrosion test temperature and the aging time had collaborative effects on evidently displacing the pitting potential towards less noble values. After 15 min, the higher temperature contributed more to decreasing the pitting potential than the aging time.
基金The present work was financially supported by National Natural Science Foundation of China (Grant No. 51371123)the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 2013140211003)+1 种基金Shanxi Natural Science Foundation Project (Grant Nos. 2014011002-1, 201601D202033, 201601D202034)Innovation Project for Graduate Education of Shanxi province (Grant No. 2016JD20).
文摘Effects of compression deformation on the sigma-phase precipitation behavior of B-containing S31254 stainless steel after solution treatment were studied using the Gleeble compression test. The cold and hot processing characteristics of B-containing S31254 stainless steel were evaluated, and the results show that the speed of compression deformation increased the precipitation rate of the sigma phase, and the location of precipitation extended from the austenite grain boundary to the original hot rolling deformation area. During cold deformation at room temperature, the precipitation rate increased when the deformation reached at 40%. Deformation at 950℃ affected precipitation more obviously. At 1074 ℃, when the deformation reached 20%, the precipitated phases started increasing, and above this deformation range, precipitation began decreasing. Also, at 1074℃ the deformation accelerated the precipitation of sigma phase;but with deformation, there was a change in critical temperature for the sigma-phase excursion. The precipitation position of the sigma phase is strongly related to the area of the original hot rolling deformation. With an increase in the deformation amount, precipitates in this region appeared as coarse-grained, skeletal, and network-like features.
基金the Central Government Guided Local Special Funds(YDZX20191400002094)the Key Scientific Research Project in Shanxi Province(20191102006)+1 种基金the Special Project for Research and Development of Key Core Technologies and Common Technologies in Shanxi Province(20201102017)the Shanxi Applied Basic Research Plan(201901d111460).
文摘The dynamic recrystallization(DRX)mechanism of as-cast nickel base superalloy N10276 during primary hot working was investigated by compression tests at temperatures of 1000–1200℃ and strain rates between 0.01 and 10 s^(-1).Optical microscopy,scanning electron microscopy,electron backscattered diffraction technique and transmission electron microscopy were used to characterize the evolution of microstructure.At higher deformation temperature or lower strain rate,the true stress–true strain curves exhibit the characteristic of a peak stress followed by a steady state flow stress under large strains,confirming the occurrence of DRX.The degree of DRX increases with elevating deformation temperature.With the progress of DRX,low angle grain boundaries gradually decrease,while high angle grain boundaries increase continuously.Microstructure studies have shown that discontinuous dynamic recrystallization is the main recrystallization mechanism.Since there are few original grain boundaries and twin boundaries,and lack of second phase particles for particle stimulated nucleation,geometrically necessary boundaries are formed as supplementary nucleation sites through sub-grain boundary rotation and deformation twin boundaries.The annealing twins dominated by Σ3 grain boundaries are generated in large quantities during the growth of recrystallized grains.
基金This work is funded by the National Natural Science Foundation of China(No.U 1860112)the Guidance Plan of Liaoning Natural Science Foundation(No.2019-ZD-0025)+1 种基金the Key Project of Liaoning Education Department(No.2019FWDF03)the Postdoctoral Research Support Project of Hebei(No.B2019003031).
文摘To prepare ultra-high-yield strength twinning-induced plasticity(TWIP)steel and reveal its work hardening mechanism at different strain rates from the microcosmic range,the microstructure evolution mechanism of Fe–20Mn–0.6C TWIP steel was investigated at strain rates of 10^(-4)–10^(3)s^(-1)using a high-speed tensile testing machine and a transmission electron microscope.The results show that the strain rate and deformation had a significant effect on the twin morphology of TWIP steels.At a strain rate of 10^(2)s^(-1),secondary deformation twins were developed,which intersected with the initial deformation twins and increased the resistance of dislocation movement,as well as the plasticity.TWIP steel at a strain rate of 10^(2)s^(-1)had a higher twin formation speed than that at 10^(0)s^(-1).At the same amount of deformation,the twin boundary fraction was higher and increased linearly at a strain rate of 10^(2)s^(-1),while the rule of twin growth at 10^(0)s^(-1)was conformed to S-curve change of DoseResp model.
