The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvem...The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvements in strength and hardness. The ultimate tensile strength increases up to 340 MPa and 390 MPa for the 30% and 50% cryorolled samples, respectively. The cryorolled samples, with 30% and 50% reduction, were subjected to Charpy impact testing at various temperatures from 190℃ to 100℃. It is observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility. Annealing of samples after cryorolling shows remarkable increment in impact toughness through recovery and recrystallization. The average grain size of the 50% cryorolled sample （14 μm） after annealing at 350℃ for 1 h is found to be finer than that of the 30% cryorolled sample （25 μm）. The scanning electron microscopy （SEM） analysis of fractured surfaces shows a large-size dimpled morphology, resembling the ductile fracture mechanism in the starting material and fibrous structure with very fine dimples in cryorolled samples corresponding to the brittle fracture mechanism.展开更多
To investigate the effect of post cryorolling treatments on simultaneous enhancement in strength and ductility of ultrafine grained material （UFG）, AI 6061 alloy was subjected to cryorolling followed by warm rolling...To investigate the effect of post cryorolling treatments on simultaneous enhancement in strength and ductility of ultrafine grained material （UFG）, AI 6061 alloy was subjected to cryorolling followed by warm rolling （CR ＋ WR） and compared with cryorolling followed by short annealing （CR ＋ SA） at the same temperature. Transmission electron microscopy （TEM） was used to characterize the microstructural features of the processed material. The mechanical properties were investigated through Vickers hardness testing and tensile testing at room temperature. TEM, X-ray diffraction （XRD） and differential scanning calorimetry （DSC） were used to investigate the precipitation evolution in UFG material. Results indicated that the alloy subjected to CR ＋ WR has shown improved mechanical properties （114 HV, ultimate tensile strength （UTS）： 350 MPa） as compared to that in the case of CR ＋ SA （105 HV, UTS： 285 MPa）. The size of the precipitates observed in CR ＋ WR sample after peak ageing treatment is finer than that of peak aged CR ＋ SA sample. The UTS of peak aged CR ＋ WR sample （UTS： 390 MPa） was found to be higher than that of peak aged CR ＋ SA sample （UTS： 355 MPa）, without decrease in ductility.展开更多
An Al−3.6Cu−1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties.The microstructure and aging characteristics of the ro...An Al−3.6Cu−1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties.The microstructure and aging characteristics of the room temperature-rolled and the cryorolled alloys with 70%and 90%of thickness reductions were studied by microstructure analysis and mechanical tests.The samples subjected to cryorolling with 90%of thickness reduction have high strength and good toughness.This is mainly due to the inhibition of dynamic recovery and the accumulation of high-density dislocations in cryorolled samples.In addition,the artificial aging reveals that the temperature at which peak hardness is attained is inversely proportional to the deformation amount and directly proportional to the rolling temperature.Moreover,bright field images of cryorolled samples after aging indicate the existence of T1(Al2CuLi)precipitates.This suggests that the high stored strain energy enhances the aging kinetics of the alloy,which further promotes the nucleation of T1 phases.展开更多
Cu−0.5wt.%Cr alloy with high strength and high conductivity was processed by cryorolling(CR)and room temperature rolling(RTR),respectively.The microstructure,mechanical property and electrical conductivity of Cu−0.5Cr...Cu−0.5wt.%Cr alloy with high strength and high conductivity was processed by cryorolling(CR)and room temperature rolling(RTR),respectively.The microstructure,mechanical property and electrical conductivity of Cu−0.5Cr alloy after CR/RTR and aging treatment were investigated.The results indicate that obvious dislocation entanglement can be observed in matrix of CR alloy.The Cr particles in the alloy after CR and aging treatment possess finer particle size and exhibit dispersive distribution.The peak hardness of CR alloy is HV 167.4,significantly higher than that of RTR alloy.The optimum mechanical property of CR alloy is obtained after aging at 450℃ for 120 min.The conductivity of CR Cu−0.5Cr alloy reaches 92.5%IACS after aging at 450℃ for 120 min,which is slightly higher than that of RTR alloy.展开更多
Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples wer...Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples were examined via transmission electron microscopy,and their mechanical properties were measured via tensile and microhardness testing.Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling,and the grain size became finer with reducing rolling temperature.The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm,respectively,via subsequent cold rolling or cryorolling(83 K).Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.展开更多
The microstructure, mechanical properties and electrical conductivity of the room-temperature and cryogenically rolled Cu-0.2wt.%Mg alloy were investigated by transmission electron microscopy (TEM), electron backscatt...The microstructure, mechanical properties and electrical conductivity of the room-temperature and cryogenically rolled Cu-0.2wt.%Mg alloy were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD), hardness measurement, tensile tests and electrical conductivity measurement. The results show that for the cryorolled sample, the grain size is decreased by 41% compared with the sample processed at room temperature. With increasing thickness reduction, the microhardness of the alloy continuously increases and the electrical conductivity decreases. For the sample with 90% thickness reduction rolled at cryogenic temperature, the tensile strength and the electrical conductivity are 726 MPa and 74.5% IACS, respectively. The improved tensile strength can be mainly attributed to the grain boundaries strengthening and dislocation strengthening.展开更多
Ultra fine-grained pure metals and their alloys have high strength and low ductility.In this study,cryorolling under different strains followed by low-temperature short-time annealing was used to fabricate pure nickel...Ultra fine-grained pure metals and their alloys have high strength and low ductility.In this study,cryorolling under different strains followed by low-temperature short-time annealing was used to fabricate pure nickel sheets combining high strength with good ductility.The results show that,for different cryorolling strains,the uniform elongation was greatly increased without sacrificing the strength after annealing.A yield strength of 607 MPa and a uniform elongation of 11.7%were obtained after annealing at a small cryorolling strain(ε=0.22),while annealing at a large cryorolling strain(ε=1.6)resulted in a yield strength of 990 MPa and a uniform elongation of 6.4%.X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),and electron backscattered diffraction(EBSD)were used to characterize the microstructure of the specimens and showed that the high strength could be attributed to strain hardening during cryorolling,with an additional contribution from grain refinement and the formation of dislocation walls.The high ductility could be attributed to annealing twins and micro-shear bands during stretching,which improved the strain hardening capacity.The results show that the synergistic effect of strength and ductility can be regulated through low-temperature short-time annealing with different cryorolling strains,which provides a new reference for the design of future thermo-mechanical processes.展开更多
To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760℃and 830℃with different strain rate.The evolution of grain and micro structure has been...To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760℃and 830℃with different strain rate.The evolution of grain and micro structure has been studied using transmission electron microscopy and electron backscatter diffraction.When the tensile temperature was 760℃(<0.5T_(m),T_(m)is absolute melting point of alloy.)and the strain rate was 5×10^(-4)s^(-1),the fracture elongation of the sample reached 385%,showing good low-temperature superplasticity.Compared with the tensile temperature of 760℃,the fracture elongation of the s ample at 830℃was lower due to grain coarsening and oxidation.The strain rate sensitivity value m of all samples was larger than0.3,which confirmed that the cryorolled Ti-6A1-4V titanium alloy with a non-equiaxed grains structure can achieve high superplasticity at a temperature lower than 0.5T_(m),and indicated that the main deformation mechanisms in the tensile test at760-830℃were grain rotation and grain boundary sliding.After the tensile test,the average grain size of all samples was less than 5μm,in which significant dynamic recrystallization and recovery occurred.展开更多
Ultra-high strength Al alloy system was developed by cryorolling and the contribution of various strengthening mechanisms to the overall yield strength of the system was evaluated. Cryorolling of Al-4%Cu-3%TiB2 in sit...Ultra-high strength Al alloy system was developed by cryorolling and the contribution of various strengthening mechanisms to the overall yield strength of the system was evaluated. Cryorolling of Al-4%Cu-3%TiB2 in situ composite followed by short annealing at 175 ℃ and ageing at 125℃ resulted in an ultra-high yield strength of about 800 MPa with 9%total elongation. The strengthening contributions form solid solution strengthening, grain refinement, dislocation strengthening, precipitation hardening and dispersion strengthening were evaluated using standard equations. It was estimated that the maximum contribution was from grain refinement due to cryorolling followed by precipitation and dispersion strengthening.展开更多
The influence of cryorolling(CR),room temperature rolling(RTR)and post annealing on precipitation,microstructuralevolution(recovery,recrystallisation and grain growth),mechanical and corrosion behavior,was investigate...The influence of cryorolling(CR),room temperature rolling(RTR)and post annealing on precipitation,microstructuralevolution(recovery,recrystallisation and grain growth),mechanical and corrosion behavior,was investigated in the present work.The precipitation kinetics and microstructural morphology of CR,RTR,and post annealed samples were investigated by differentialscanning calorimetry(DSC),transmission electron microscopy(TEM),and electron back scattered diffraction(EBSD)to elucidatethe observed mechanical properties.After annealing at200°C,UTS and hardness of CR samples(345MPa and HV127)wereimproved as compared to RTR samples(320MPa and HV115).The increase in hardness and UTS of CR samples after annealing at200°C was due to precipitation ofβ''from Al matrix,which imparted higher Zener drag effect as compared to RTR samples.Theimprovement in corrosion and pitting potentials was observed for CR samples(?1.321V and?700mV)as compared to RTRsamples(?1.335V and?710mV).In CR samples,heavy dislocation density and dissolution of Mg4Al3Si4-precipitates in the Almatrix have improved corrosion resistance of the alloy through formation of protective passive layer and suppression of galvanic cell,respectively.展开更多
AISI 310S stable austenitic stainless steel was subjected to 90%cryorolling and then annealed at 800 ℃ for 2-60 min.The effect of annealing time on the microstructure and mechanical properties was studied by optical ...AISI 310S stable austenitic stainless steel was subjected to 90%cryorolling and then annealed at 800 ℃ for 2-60 min.The effect of annealing time on the microstructure and mechanical properties was studied by optical microscopy,scanning electron microscopy,transmission electron microscopy,microhardness and tensile test.The results show that the grain size of AISI 310S stainless steel is refined to the nanometer level after 90%cryorolling,and the grain size is approximately 20 nm.With the increase in annealing time,the degree of grain recrystallization occurs more fully and completely,as the grain begins to grow and then tends to stabilize.The strength and hardness of the annealed specimens decrease with increasing annealing time,while elongation tends to increase.When the annealing time is 10 min,the yield strength increases by about 2 times compared to that of the original austenite(unrolled),and the elongation is also above 20%,which is the best preparation process for ultra-fine grain austenitic stainless steel under this experimental condition.As the annealing time treatment increases,the fracture morphology changes from mixed quasi-cleavage and ductile fracture(after cryorolling)to ductile fracture(after annealing).展开更多
AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scann...AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.展开更多
The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling(-100 ° C,-190 ℃) or hot rolling(400 ℃) and subsequent aging at 160 ℃ for different times were investigated. The dy...The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling(-100 ° C,-190 ℃) or hot rolling(400 ℃) and subsequent aging at 160 ℃ for different times were investigated. The dynamic precipitation and dislocation characterizations were examined via transmission electron microscopy and X-ray diffraction. The grain morphologies and the fracture-surface morphologies were studied via optical microscopy and scanning electron microscopy. Samples subjected to cryorolling followed by aging exhibited relatively high dislocation densities and a large number of precipitates compared with hot-rolled samples. The samples cryorolled at-190 ℃ and then aged for 15 h presented the highest ultimate tensile strength(586 MPa), while the alloy processed via hot rolling followed by 10 h aging exhibited the highest uniform elongation rate(11.5%). The size of precipitates increased with the aging time, which has significant effects on the interaction mechanism between dislocations and precipitates. Bowing is the main interaction method between the deformation-induced dislocations and coarsened precipitates during tensile tests, leading to the decline of the mechanical properties of the alloy during overaging. These interesting findings can provide significant insights into the development of materials possessing both excellent strength and high ductility.展开更多
In order to obtain good strength−plasticity synergy for a medium entropy alloy(MEA)CrCoNi,cold rolling,asymmetric rolling,cryorolling and asymmetric-cryorolling with subsequent annealing at different temperatures were...In order to obtain good strength−plasticity synergy for a medium entropy alloy(MEA)CrCoNi,cold rolling,asymmetric rolling,cryorolling and asymmetric-cryorolling with subsequent annealing at different temperatures were conducted.The results showed that the asymmetric-cryorolled alloy achieved a high strength of over 1.6 GPa.After annealing at 1073 K,it retained a high strength of~1 GPa while the elongation reached nearly 60%.After annealing,the heterogeneous characteristics were formed in asymmetric-cryorolled samples,which were found to be more distinct than those of the samples subjected to asymmetric rolling.This resulted in the generation of high strength and ductility.展开更多
基金One of the authors (R. Jayaganthan) thanks DST,New Delhi for the financial support of this work throughgrant No. DST-462-MMD
文摘The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvements in strength and hardness. The ultimate tensile strength increases up to 340 MPa and 390 MPa for the 30% and 50% cryorolled samples, respectively. The cryorolled samples, with 30% and 50% reduction, were subjected to Charpy impact testing at various temperatures from 190℃ to 100℃. It is observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility. Annealing of samples after cryorolling shows remarkable increment in impact toughness through recovery and recrystallization. The average grain size of the 50% cryorolled sample （14 μm） after annealing at 350℃ for 1 h is found to be finer than that of the 30% cryorolled sample （25 μm）. The scanning electron microscopy （SEM） analysis of fractured surfaces shows a large-size dimpled morphology, resembling the ductile fracture mechanism in the starting material and fibrous structure with very fine dimples in cryorolled samples corresponding to the brittle fracture mechanism.
文摘To investigate the effect of post cryorolling treatments on simultaneous enhancement in strength and ductility of ultrafine grained material （UFG）, AI 6061 alloy was subjected to cryorolling followed by warm rolling （CR ＋ WR） and compared with cryorolling followed by short annealing （CR ＋ SA） at the same temperature. Transmission electron microscopy （TEM） was used to characterize the microstructural features of the processed material. The mechanical properties were investigated through Vickers hardness testing and tensile testing at room temperature. TEM, X-ray diffraction （XRD） and differential scanning calorimetry （DSC） were used to investigate the precipitation evolution in UFG material. Results indicated that the alloy subjected to CR ＋ WR has shown improved mechanical properties （114 HV, ultimate tensile strength （UTS）： 350 MPa） as compared to that in the case of CR ＋ SA （105 HV, UTS： 285 MPa）. The size of the precipitates observed in CR ＋ WR sample after peak ageing treatment is finer than that of peak aged CR ＋ SA sample. The UTS of peak aged CR ＋ WR sample （UTS： 390 MPa） was found to be higher than that of peak aged CR ＋ SA sample （UTS： 355 MPa）, without decrease in ductility.
基金Project(2019YFB2006500)supported by the National Key Research and Development Program of ChinaProject(51674303)supported by the National Natural Science Foundation of China+2 种基金Project(2018RS3015)supported by the Huxiang High-Level Talent Gathering Project of Hunan Province,ChinaProject(2019CX006)supported by the Innovation Driven Program of Central South University,ChinaProject supported by the Research Fund of the Key Laboratory of High Performance Complex Manufacturing at Central South University,China。
文摘An Al−3.6Cu−1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties.The microstructure and aging characteristics of the room temperature-rolled and the cryorolled alloys with 70%and 90%of thickness reductions were studied by microstructure analysis and mechanical tests.The samples subjected to cryorolling with 90%of thickness reduction have high strength and good toughness.This is mainly due to the inhibition of dynamic recovery and the accumulation of high-density dislocations in cryorolled samples.In addition,the artificial aging reveals that the temperature at which peak hardness is attained is inversely proportional to the deformation amount and directly proportional to the rolling temperature.Moreover,bright field images of cryorolled samples after aging indicate the existence of T1(Al2CuLi)precipitates.This suggests that the high stored strain energy enhances the aging kinetics of the alloy,which further promotes the nucleation of T1 phases.
基金Project(2016YFB0101206)supported by the National Key Research and Development Program of ChinaProject(3132019328)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Cu−0.5wt.%Cr alloy with high strength and high conductivity was processed by cryorolling(CR)and room temperature rolling(RTR),respectively.The microstructure,mechanical property and electrical conductivity of Cu−0.5Cr alloy after CR/RTR and aging treatment were investigated.The results indicate that obvious dislocation entanglement can be observed in matrix of CR alloy.The Cr particles in the alloy after CR and aging treatment possess finer particle size and exhibit dispersive distribution.The peak hardness of CR alloy is HV 167.4,significantly higher than that of RTR alloy.The optimum mechanical property of CR alloy is obtained after aging at 450℃ for 120 min.The conductivity of CR Cu−0.5Cr alloy reaches 92.5%IACS after aging at 450℃ for 120 min,which is slightly higher than that of RTR alloy.
基金financial supports from the National Key Research and Development Program of China (No. 2019YFB2006500)the National Natural Science Foundation of China (No. 51674303)+2 种基金the Huxiang High-level Talent Gathering Project of Hunan Province, China (No. 2018RS3015)the Innovation Driven Program of Central South University, China (No. 2019CX006)the Research Fund of the Key Laboratory of High Performance Complex Manufacturing at Central South University, China。
文摘Ultrafine-grained(UFG)AA1060 sheets were fabricated via five-cycle accumulative roll bonding(ARB)and subsequent three-pass cold rolling(298 K),or cryorolling(83 K and 173 K).Microstructures of the aluminum samples were examined via transmission electron microscopy,and their mechanical properties were measured via tensile and microhardness testing.Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling,and the grain size became finer with reducing rolling temperature.The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm,respectively,via subsequent cold rolling or cryorolling(83 K).Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.
基金Project(51671064) supported by the National Natural Science Foundation of ChinaProject(HEUCFG201836) supported by the Fundamental Research Funds for the Central Universities,ChinaProject supported by the Key Laboratory of Superlight Materials & Surface Technology(Harbin Engineering University),Ministry of Education,China
文摘The microstructure, mechanical properties and electrical conductivity of the room-temperature and cryogenically rolled Cu-0.2wt.%Mg alloy were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD), hardness measurement, tensile tests and electrical conductivity measurement. The results show that for the cryorolled sample, the grain size is decreased by 41% compared with the sample processed at room temperature. With increasing thickness reduction, the microhardness of the alloy continuously increases and the electrical conductivity decreases. For the sample with 90% thickness reduction rolled at cryogenic temperature, the tensile strength and the electrical conductivity are 726 MPa and 74.5% IACS, respectively. The improved tensile strength can be mainly attributed to the grain boundaries strengthening and dislocation strengthening.
基金the financial support from the High-Tech Industry Technology Innovation Leading Plan of Hunan Province,China(2020GK2032)the Innovation Driven Program of Central South University(CSU)(2019CX006)the Research Fund of the Key Laboratory of High Performance Complex Manufacturing at CSU。
文摘Ultra fine-grained pure metals and their alloys have high strength and low ductility.In this study,cryorolling under different strains followed by low-temperature short-time annealing was used to fabricate pure nickel sheets combining high strength with good ductility.The results show that,for different cryorolling strains,the uniform elongation was greatly increased without sacrificing the strength after annealing.A yield strength of 607 MPa and a uniform elongation of 11.7%were obtained after annealing at a small cryorolling strain(ε=0.22),while annealing at a large cryorolling strain(ε=1.6)resulted in a yield strength of 990 MPa and a uniform elongation of 6.4%.X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),and electron backscattered diffraction(EBSD)were used to characterize the microstructure of the specimens and showed that the high strength could be attributed to strain hardening during cryorolling,with an additional contribution from grain refinement and the formation of dislocation walls.The high ductility could be attributed to annealing twins and micro-shear bands during stretching,which improved the strain hardening capacity.The results show that the synergistic effect of strength and ductility can be regulated through low-temperature short-time annealing with different cryorolling strains,which provides a new reference for the design of future thermo-mechanical processes.
基金financial support from the High-tech Industry Technology Innovation Leading Plan of Hunan Province(Grant No.:2020GK2032)the Research Fund of the Key Laboratory of High-Performance Complex Manufacturing at Central South University。
文摘To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760℃and 830℃with different strain rate.The evolution of grain and micro structure has been studied using transmission electron microscopy and electron backscatter diffraction.When the tensile temperature was 760℃(<0.5T_(m),T_(m)is absolute melting point of alloy.)and the strain rate was 5×10^(-4)s^(-1),the fracture elongation of the sample reached 385%,showing good low-temperature superplasticity.Compared with the tensile temperature of 760℃,the fracture elongation of the s ample at 830℃was lower due to grain coarsening and oxidation.The strain rate sensitivity value m of all samples was larger than0.3,which confirmed that the cryorolled Ti-6A1-4V titanium alloy with a non-equiaxed grains structure can achieve high superplasticity at a temperature lower than 0.5T_(m),and indicated that the main deformation mechanisms in the tensile test at760-830℃were grain rotation and grain boundary sliding.After the tensile test,the average grain size of all samples was less than 5μm,in which significant dynamic recrystallization and recovery occurred.
基金the Department of Science & Technology (DST) for their financial support for carrying out this research through Fast Track Scheme (DST Sanction No: SR/FT/ET-005/2008)Technical Education Quality Improvement Programme (TEQIP)
文摘Ultra-high strength Al alloy system was developed by cryorolling and the contribution of various strengthening mechanisms to the overall yield strength of the system was evaluated. Cryorolling of Al-4%Cu-3%TiB2 in situ composite followed by short annealing at 175 ℃ and ageing at 125℃ resulted in an ultra-high yield strength of about 800 MPa with 9%total elongation. The strengthening contributions form solid solution strengthening, grain refinement, dislocation strengthening, precipitation hardening and dispersion strengthening were evaluated using standard equations. It was estimated that the maximum contribution was from grain refinement due to cryorolling followed by precipitation and dispersion strengthening.
文摘The influence of cryorolling(CR),room temperature rolling(RTR)and post annealing on precipitation,microstructuralevolution(recovery,recrystallisation and grain growth),mechanical and corrosion behavior,was investigated in the present work.The precipitation kinetics and microstructural morphology of CR,RTR,and post annealed samples were investigated by differentialscanning calorimetry(DSC),transmission electron microscopy(TEM),and electron back scattered diffraction(EBSD)to elucidatethe observed mechanical properties.After annealing at200°C,UTS and hardness of CR samples(345MPa and HV127)wereimproved as compared to RTR samples(320MPa and HV115).The increase in hardness and UTS of CR samples after annealing at200°C was due to precipitation ofβ''from Al matrix,which imparted higher Zener drag effect as compared to RTR samples.Theimprovement in corrosion and pitting potentials was observed for CR samples(?1.321V and?700mV)as compared to RTRsamples(?1.335V and?710mV).In CR samples,heavy dislocation density and dissolution of Mg4Al3Si4-precipitates in the Almatrix have improved corrosion resistance of the alloy through formation of protective passive layer and suppression of galvanic cell,respectively.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.U1804146,52111530068 and 51905153)the Science and Technology Innovation Team of Henan University of Science and Technology(Grant No.2015XTD006)the Foreign Experts Introduction Project of Henan Province(Grant No.HNGD2020009).
文摘AISI 310S stable austenitic stainless steel was subjected to 90%cryorolling and then annealed at 800 ℃ for 2-60 min.The effect of annealing time on the microstructure and mechanical properties was studied by optical microscopy,scanning electron microscopy,transmission electron microscopy,microhardness and tensile test.The results show that the grain size of AISI 310S stainless steel is refined to the nanometer level after 90%cryorolling,and the grain size is approximately 20 nm.With the increase in annealing time,the degree of grain recrystallization occurs more fully and completely,as the grain begins to grow and then tends to stabilize.The strength and hardness of the annealed specimens decrease with increasing annealing time,while elongation tends to increase.When the annealing time is 10 min,the yield strength increases by about 2 times compared to that of the original austenite(unrolled),and the elongation is also above 20%,which is the best preparation process for ultra-fine grain austenitic stainless steel under this experimental condition.As the annealing time treatment increases,the fracture morphology changes from mixed quasi-cleavage and ductile fracture(after cryorolling)to ductile fracture(after annealing).
基金financially supported by the National Natural Science Foundation of China(No.51401019)the China Postdoctoral Science Foundation(No.2014M550612)+1 种基金the Fundamental Research Funds for the Central Universities(Nos.FRF-TP-14-048A1 and FRF-TP-15-055A2)the Common Construction Project from Beijing Municipal Commission of Education(No.FRF-SD-13-005B)
文摘AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.
基金Project(2019YFB2006500) supported by the National Key Research and Development Program,ChinaProject(51674303) supported by the National Natural Science Foundation of China+3 种基金Project(2020GK2032) supported by Hunan High-tech Industry Science and Technology Innovation Leading Plan,ChinaProject (2018RS3015) supported by the Huxiang High-level Talent Gathering Project of Hunan Province,ChinaProject(2017YFA0700700) supported by the Ministry of Science&Technology of ChinaProject(2019CX006) supported by Innovation Driven Program of Central South University,China。
文摘The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling(-100 ° C,-190 ℃) or hot rolling(400 ℃) and subsequent aging at 160 ℃ for different times were investigated. The dynamic precipitation and dislocation characterizations were examined via transmission electron microscopy and X-ray diffraction. The grain morphologies and the fracture-surface morphologies were studied via optical microscopy and scanning electron microscopy. Samples subjected to cryorolling followed by aging exhibited relatively high dislocation densities and a large number of precipitates compared with hot-rolled samples. The samples cryorolled at-190 ℃ and then aged for 15 h presented the highest ultimate tensile strength(586 MPa), while the alloy processed via hot rolling followed by 10 h aging exhibited the highest uniform elongation rate(11.5%). The size of precipitates increased with the aging time, which has significant effects on the interaction mechanism between dislocations and precipitates. Bowing is the main interaction method between the deformation-induced dislocations and coarsened precipitates during tensile tests, leading to the decline of the mechanical properties of the alloy during overaging. These interesting findings can provide significant insights into the development of materials possessing both excellent strength and high ductility.
基金supported by the Hunan High-Tech Industry Science and Technology Innovation Leading Plan,China(No.2020GK2032)the Huxiang High-Level Talent Gathering Project of Hunan Province,China(No.2018RS3015)+1 种基金the Innovation Driven Program of Central South University,China(No.2019CX006)the Research Fund of the Key Laboratory of High Performance Complex Manufacturing at Central South University,China。
文摘In order to obtain good strength−plasticity synergy for a medium entropy alloy(MEA)CrCoNi,cold rolling,asymmetric rolling,cryorolling and asymmetric-cryorolling with subsequent annealing at different temperatures were conducted.The results showed that the asymmetric-cryorolled alloy achieved a high strength of over 1.6 GPa.After annealing at 1073 K,it retained a high strength of~1 GPa while the elongation reached nearly 60%.After annealing,the heterogeneous characteristics were formed in asymmetric-cryorolled samples,which were found to be more distinct than those of the samples subjected to asymmetric rolling.This resulted in the generation of high strength and ductility.
