The study focused on investigating the effect of Deep Cryogenic Treatment(DCT)on the mechanical and ballistic properties of AA7075-T6 aluminum alloy.The microstructure,microhardness,tensile strength,and impact strengt...The study focused on investigating the effect of Deep Cryogenic Treatment(DCT)on the mechanical and ballistic properties of AA7075-T6 aluminum alloy.The microstructure,microhardness,tensile strength,and impact strength of the Base Material(BM)and DCT-treated 7075 samples were analyzed through metallographic analysis and mechanical tests.The microstructure of the DCT-treated 7075 samples revealed fine grains and a distribution of secondary phase particles.The tensile strength,impact strength,and microhardness of DCT-treated samples increased by 7.41%,4%,and 9.68%,respectively,compared to the BM samples.The fractography analysis of the tensile samples showed cleavage facets,microvoids,and dimples in both the samples.The ballistic behavior of the BM and DCT target plates were studied by impacting hard steel core projectiles at a velocity of 750±10 m/s.The target plates failed due to petaling and ductile hole enlargement,and the depth of penetration(DOP)of the DCT target was less than that of the BM target,indicating a higher ballistic resistance.The post-ballistic microstructure examination of the target plates showed the formation of an Adiabatic Shear Band(ASB)without any cracks.It was concluded that the DCT treatment improved the mechanical and ballistic properties of the aluminum alloy due to grain refinement and high dislocation density.展开更多
The materials used in variable temperature conditions are required to have excellent thermal fatigue performance.The effects of laser shock processing(LSP),solid solution and aging treatment(T6),and cryogenic treatmen...The materials used in variable temperature conditions are required to have excellent thermal fatigue performance.The effects of laser shock processing(LSP),solid solution and aging treatment(T6),and cryogenic treatment(CT)on both microstructure and thermal fatigue performance of ZCuAl_(10)Fe_(3)Mn_(2) alloys were studied.Microstructure and crack morphology were then examined by scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS).The result showed that,after being subjected to the combination treatment of T6+CT+LSP,the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl_(10)Fe_(3)Mn_(2) alloy with the tensile strength,hardness,and elongation of 720 MPa,300.16 HB,and 16%,respectively,and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm.Moreover,the ZCuAl_(10)Fe_(3)Mn_(2) after combination treatment shows high resistance to oxidation,good adhesion between the matrix and grain boundaries,and dramatically reduced growth rate of crack.During thermal fatigue testing,under the combined action of thermal and alternating stresses,the microstructure around the sample notch oxidized and became loose and porous,which then converted to micro-cracks.Fatigue crack expanded along the grain boundary in the early stage.In the later stage,under the cyclic stress accumulation,the oxidized microstructure separated from the matrix,and the fatigue crack expanded in both intergranular and transgranular ways.The main crack was thick,and the path was meandering.展开更多
The microstructural evolution and corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses(BMGs)after annealing treatment(AT)at different crystallization temperatures and cryogenic treatment(CT)at−100℃are expe...The microstructural evolution and corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses(BMGs)after annealing treatment(AT)at different crystallization temperatures and cryogenic treatment(CT)at−100℃are experimen-tally investigated.Appropriate AT and CT can both improve the thermal stability and comprehensive corrosion resistance of as-cast BMG in 3.5 wt.%NaCl solution.The annealed and cryo-treated BMGs exhibit one more finite diffusion layer loop in the electrical equivalent circuit than the as-cast BMG,indicating the complexity of the corrosion behavior.Superior corrosion resistance is obtained in the cryo-treated BMG because the high degree of amorphization caused by CT reduces the structural inhomogeneity.Lower C_(d)and higher R_(d)values are obtained for the cryo-treated BMG,revealing the formation of a more stable passive film.Among the annealed BMGs,the fully crystallized sample exhibits a higher anti-corrosion performance owing to the existence of Nb-rich oxides in the crystallization products.The passive film is found to be composed mainly of Nb_(2)O_(5)and ZrO_(2),demonstrating that Nb and Zr are conducive to reacting with oxygen to form a passive film.Based on the goal of maintaining a fully amorphous phase,appropriate CT causing structural homogeneity of the BMG is a simple and effective means to improve the comprehensive corrosion resistance.展开更多
The effect of deep cryogenic treatment(DCT)on the electrochemical behavior of Ti-6Al-4V alloy in Hank's solution was experimentally investigated in the present work.Deep cryogenic treatments at-196℃soaking for 24...The effect of deep cryogenic treatment(DCT)on the electrochemical behavior of Ti-6Al-4V alloy in Hank's solution was experimentally investigated in the present work.Deep cryogenic treatments at-196℃soaking for 24(DCT-24) and 48(DCT-48) hours were conducted on the commercial annealed Ti-6Al-4V alloy.The methods of polarization and electrochemical impedance spectroscopy(EIS) were employed to evaluate the electrochemical behavior and corrosion mechanism.Furthermore,atomic force microscopy(AFM) was used to detect the corrosion surface.The results showed that deep cryogenic treatment shifted the corrosion potentials(E_(corr))to the positive direction.The corrosion current densities(i_(corr))of samples treated by DCT-24 and DCT-48decreased from 153.1 nA·cm^(-2) in the untreated(UT)sample to 86.3 nA·cm^(-2) and 43.3 nA·cm^(-2),respectively.Furthermore,the roughness of corrosion surfaces of samples subjected to DCT was smaller than that of the UT sample,which indeed demonstrated the improvement in corrosion resistance of Ti-6Al-4V alloy in Hank's solution.The results of EIS test indicated that deep cryogenic treatment had no influence on the corrosion mechanism of Ti-6Al-4V alloy in Hank's,while enhanced resistance value of outer porous layer R_p,which makes the surface more efficient to prevent the corrosion.The reduction of β-phase particles,improvement in dislocation density and release of residual stress caused by deep cryogenic treatment had great contribution to the improvement in corrosion resistance of Ti-6Al-4V alloy in Hank's solution.展开更多
The effects of traditional heat treatment(quenching and then tempering)and deep cryogenic treatment on the microstructure and mechanical properties of a low-carbon high-alloy martensitic bearing steel were studied by ...The effects of traditional heat treatment(quenching and then tempering)and deep cryogenic treatment on the microstructure and mechanical properties of a low-carbon high-alloy martensitic bearing steel were studied by Rockwell hardness test,X-ray diffractometry,scanning electron microscopy and transmission electron microscopy.The results show that the deep cryogenic treatment promotes the transformation of the retained austenite to martensite during cooling,which leads to the hardness of the sample after deep cryogenic treatment higher than that at the quenched state.Also,the carbon content in the martensite matrix after different treatments was calculated and the results indicated that deep cryogenic treatment can promote the segregation of carbon atoms in martensite to dislocations.The segregated carbon atoms act as and grow into nuclei for the formation of fine carbide particles during subsequent tempering.And this resulted in the fact that the hardness of the tempered experimental steel after deep cryogenic treatment is higher than that without deep cryogenic treatment.展开更多
Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment were investigated.Conventional treatment sample was quenched and tempered at 180℃ for 2 h.Cr...Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment were investigated.Conventional treatment sample was quenched and tempered at 180℃ for 2 h.Cryogenic treatment samples were quenched,cryogenically treated at−80 and−196℃ for 4 h,slowly returned to room temperature and thereafter tempered at 180℃ for 2 h,and finally tempered at 180℃ for 2 h.The scanning electron microscope,electron backscattering diffraction,X-ray diffraction and transmission electron microscope were adopted for microstructure characterization.The results show that cryogenic treatment increases the fraction of high-angle grain boundaries and the precipitation of finely dispersed carbides in the matrix,decreases the volume fraction of inter-lath retained austenite,and hence improves the strength and hardness.Compared with the conventional treatment,the hardness,yield strength and ultimate tensile strength of the steel after cryogenic treatment are increased by 11.7%,12.6%and 18.3%,respectively,while the impact energy is decreased by 9.8%.展开更多
The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms i...The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.展开更多
In this study,the effects of deep cryogenic treatment(DCT)on the mechanical and tribological properties of AISI D3 tool steel were investigated together with a systematic correlation between their hardness and wear re...In this study,the effects of deep cryogenic treatment(DCT)on the mechanical and tribological properties of AISI D3 tool steel were investigated together with a systematic correlation between their hardness and wear resistance.It was found that conventionally heat treated AISI D3 tool steel samples were significantly hardened via an additional DCT,which was attributed to the more retained austenite elimination,more homogenized carbide distribution and more reduction in carbide size in the samples.As a result,the hardened AISI D3 samples exhibited reductions in their friction and wear during rubbing against alumina and 100Cr6 steel balls under different normal loads due to the effectively hindered removal of surface materials.The results clearly showed that the DCT was an effective way to improve the mechanical and tribological properties of the AISI D3 tool steel samples as the tribological performance of the tool steel samples was significantly influenced by their hardness.展开更多
Additively manufactured(AM)metallic materials commonly possess substantial tensile surface residual stress,which is detrimental to the load-bearing service behavior.Recently,we demonstrated that deep cryogenic treatme...Additively manufactured(AM)metallic materials commonly possess substantial tensile surface residual stress,which is detrimental to the load-bearing service behavior.Recently,we demonstrated that deep cryogenic treatment(DCT)is an effective method for improving the tensile properties of CoCrFeMnNi high-entropy alloy(HEA)samples fabricated by laser melting deposition(LMD),by introducing high compressive residual stress and deformation microstructures without destroying the AM shape.However,carrying out the DCT in a single-step mode does not improve the residual stress gradients inherent from the LMD process,which are undesirable as the mechanical properties will not be homogeneous within the sample.In this work,we show that carrying out the DCT in a cyclic mode with repeated cryogenic cooling and reheating can significantly homogenize the residual stress in LMD-fabricated Co Cr Fe Mn Ni HEA,and improve tensile strength and ductility,compared with single-step DCT of the same cryogenic soaking duration.Under cyclic DCT,the thermal stress is re-elevated to a high value at each cryogenic cooling step,leading to the formation of denser and more intersecting reinforcing crystalline defects and hcp phase transformation,compared to single-step DCT of the same total cryogenic soaking duration in which the thermal stress relaxes towards a low value over time.The enhancement of defect formation in the cyclic mode of DCT also leads to more uniform residual stress distribution in the sample after the DCT.The results here provide important insights on optimizing DCT processes for post-fabrication improvement of mechanical properties of AM metallic net shapes.展开更多
The microstructure evolution and the pitting corrosion resistance of a supermartensitic stainless steel after deep cryogenic treatment process were clarified through X-ray diffraction,field emission scanning electron ...The microstructure evolution and the pitting corrosion resistance of a supermartensitic stainless steel after deep cryogenic treatment process were clarified through X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy(TEM)and electrochemical methods.The results showed that the microstructure of supermartensitic stainless steel mainly consisted of reversed austenite,tempered martensite,and M_(23)C_(6)carbides after tempering.The deep cryogenic treatment promoted the refinement of the martensite laths and the precipitation of the carbides in comparison with the traditional process.TEM analysis indicated that the segregation of Si atoms at the boundary was found at the interface between carbide and martensite.The pitting corrosion potential of the specimens subjected to deep cryogenic treatment decreased with the elevated tempering temperature,and the lowest pitting corrosion potential was found at the tempering temperature of 650℃.The sensitivity of the pitting corrosion potential was attributed to the precipitation of M_(23)C_(6)carbides and Si atoms segregation.Si atoms segregation engendered the formation of Cr-depleted zone near M_(23)C_(6)and impeded the recovery of Cr-depleted zone.展开更多
The influence of different cryogenic sequences on the rolling contact fatigue(RCF)life of M50-bearing steel has been studied.The results show that direct cryogenic treatment after quenching can effectively improve RCF...The influence of different cryogenic sequences on the rolling contact fatigue(RCF)life of M50-bearing steel has been studied.The results show that direct cryogenic treatment after quenching can effectively improve RCF life.The L_(10)life is strikingly 5 times longer than that with cryogenic treatment after tem-pering.This is caused by the distinct lattice construction of martensite and the transformation of retained austenite.More secondary nanocarbides and fine twins are formed via cryogenic treatment before tem-pering compared with cryogenic treatment after tempering.The improvement in the RCF life of the steel is attributed to the joint effects of the secondary nanocarbides and twin boundaries with a width of 5-13 nm,which delays significantly crack initiation and propagation.This study highlights a common method to improve the service life of high-carbon and high-alloy steels by adjusting the cryogenic se-quence.展开更多
The effects of acyclic liquid nitrogen(LN)treatment in a temperature range of-196℃to 50℃on the thermal and magnetic stability of Fe78Si9B13 and Fe73.5Si13.5B9Nb3Cu1 glassy ribbons have been studied.The intrinsic het...The effects of acyclic liquid nitrogen(LN)treatment in a temperature range of-196℃to 50℃on the thermal and magnetic stability of Fe78Si9B13 and Fe73.5Si13.5B9Nb3Cu1 glassy ribbons have been studied.The intrinsic heterogeneities of the metallic glasses can be activated through cryogenic thermal cycling,making irreversible structural changes after the treatment and inducing rejuvenation to the materials.The microstructural changes of both Fe-based metallic glass(MG)and nanocrystalline alloy induced by LN treatment were investigated.The experimental results show that the LN treatment could effectively rejuvenate the Fe-Si-B MGs and change their thermomechanical and magnetic properties.Based on the partially-crystallinity and well-known magnetic constants,the increase of the energy at the order of 10m J/g and magnetic domain wall movement and rotation at the order of 5-6μm and 0.5°-0.8°are found for FINEMET-type amorphous alloy after LN treatment.It is also found that LN treatment can contribute a little stored energy to the magnetic domain wall movement and magnetic domain rotation.展开更多
The effect of deep cryogenic cycle treatment(DCT)on Zr_(41.2)Ti_(13.8)Cu_(12.5)Ni_(10)Be_(22.5)(Vit-1)bulk metallic glass(BMG)prepared from high-purity raw materials was investigated.After DCT,no obvious rejuvenation ...The effect of deep cryogenic cycle treatment(DCT)on Zr_(41.2)Ti_(13.8)Cu_(12.5)Ni_(10)Be_(22.5)(Vit-1)bulk metallic glass(BMG)prepared from high-purity raw materials was investigated.After DCT,no obvious rejuvenation of the samples was detected.With an increasing number of cryogenic cycles,the hardness of the samples first decreased and then increased,the room-temperature compression plasticity first increased and then generally remained unchanged,and the impact toughness underwent almost no obvious change.The absence of rejuvenation was attributed to the high fragility index(47-50)and high glass forming ability(GFA)of the material.As lower purity of the raw materials is expected in practical applications,DCT of Vit-1 BMG prepared from low-purity raw materials was also performed.After DCT,the samples prepared with the lower-purity raw materials were clearly rejuvenated,and the room-temperature mechanical properties improved significantly.Both the compression plasticity and impact toughness reached peak values after 5 cryogenic cycles.The initial impurities(including Y and O)had a complex and comprehensive effect on the deformation mechanism of the BMG during DCT.Our findings indicate that the structural heterogeneity,fragility index,and GFA of the BMG alter the effect of DCT.展开更多
文摘The study focused on investigating the effect of Deep Cryogenic Treatment(DCT)on the mechanical and ballistic properties of AA7075-T6 aluminum alloy.The microstructure,microhardness,tensile strength,and impact strength of the Base Material(BM)and DCT-treated 7075 samples were analyzed through metallographic analysis and mechanical tests.The microstructure of the DCT-treated 7075 samples revealed fine grains and a distribution of secondary phase particles.The tensile strength,impact strength,and microhardness of DCT-treated samples increased by 7.41%,4%,and 9.68%,respectively,compared to the BM samples.The fractography analysis of the tensile samples showed cleavage facets,microvoids,and dimples in both the samples.The ballistic behavior of the BM and DCT target plates were studied by impacting hard steel core projectiles at a velocity of 750±10 m/s.The target plates failed due to petaling and ductile hole enlargement,and the depth of penetration(DOP)of the DCT target was less than that of the BM target,indicating a higher ballistic resistance.The post-ballistic microstructure examination of the target plates showed the formation of an Adiabatic Shear Band(ASB)without any cracks.It was concluded that the DCT treatment improved the mechanical and ballistic properties of the aluminum alloy due to grain refinement and high dislocation density.
基金National Natural Science Foundation of China(51801076)Natural Science Research of Jiangsu Higher Education Institutions of China(18KJB430009)+1 种基金Jiangsu Province Postdoctoral Science Foundation(1601055C)Senior Talents Research Startup of Jiangsu University(14JDG126)。
文摘The materials used in variable temperature conditions are required to have excellent thermal fatigue performance.The effects of laser shock processing(LSP),solid solution and aging treatment(T6),and cryogenic treatment(CT)on both microstructure and thermal fatigue performance of ZCuAl_(10)Fe_(3)Mn_(2) alloys were studied.Microstructure and crack morphology were then examined by scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS).The result showed that,after being subjected to the combination treatment of T6+CT+LSP,the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl_(10)Fe_(3)Mn_(2) alloy with the tensile strength,hardness,and elongation of 720 MPa,300.16 HB,and 16%,respectively,and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm.Moreover,the ZCuAl_(10)Fe_(3)Mn_(2) after combination treatment shows high resistance to oxidation,good adhesion between the matrix and grain boundaries,and dramatically reduced growth rate of crack.During thermal fatigue testing,under the combined action of thermal and alternating stresses,the microstructure around the sample notch oxidized and became loose and porous,which then converted to micro-cracks.Fatigue crack expanded along the grain boundary in the early stage.In the later stage,under the cyclic stress accumulation,the oxidized microstructure separated from the matrix,and the fatigue crack expanded in both intergranular and transgranular ways.The main crack was thick,and the path was meandering.
基金the National Natu-ral Science Foundation of China(No.51971102)Open Research Fund of Songshan Lake Materials Laboratory(No.2021SLABFK08)Sci-ence and Technology Program of University of Jinan(No.XKY2117).
文摘The microstructural evolution and corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses(BMGs)after annealing treatment(AT)at different crystallization temperatures and cryogenic treatment(CT)at−100℃are experimen-tally investigated.Appropriate AT and CT can both improve the thermal stability and comprehensive corrosion resistance of as-cast BMG in 3.5 wt.%NaCl solution.The annealed and cryo-treated BMGs exhibit one more finite diffusion layer loop in the electrical equivalent circuit than the as-cast BMG,indicating the complexity of the corrosion behavior.Superior corrosion resistance is obtained in the cryo-treated BMG because the high degree of amorphization caused by CT reduces the structural inhomogeneity.Lower C_(d)and higher R_(d)values are obtained for the cryo-treated BMG,revealing the formation of a more stable passive film.Among the annealed BMGs,the fully crystallized sample exhibits a higher anti-corrosion performance owing to the existence of Nb-rich oxides in the crystallization products.The passive film is found to be composed mainly of Nb_(2)O_(5)and ZrO_(2),demonstrating that Nb and Zr are conducive to reacting with oxygen to form a passive film.Based on the goal of maintaining a fully amorphous phase,appropriate CT causing structural homogeneity of the BMG is a simple and effective means to improve the comprehensive corrosion resistance.
基金financially supported by the Beijing Natural Science Foundation (No.2164072)the Youth Innovation Promotion Association of CAS (No.2016021)the Key Laboratory of Cryogenics,TIPC,CAS (No.CRYOQN201504)。
文摘The effect of deep cryogenic treatment(DCT)on the electrochemical behavior of Ti-6Al-4V alloy in Hank's solution was experimentally investigated in the present work.Deep cryogenic treatments at-196℃soaking for 24(DCT-24) and 48(DCT-48) hours were conducted on the commercial annealed Ti-6Al-4V alloy.The methods of polarization and electrochemical impedance spectroscopy(EIS) were employed to evaluate the electrochemical behavior and corrosion mechanism.Furthermore,atomic force microscopy(AFM) was used to detect the corrosion surface.The results showed that deep cryogenic treatment shifted the corrosion potentials(E_(corr))to the positive direction.The corrosion current densities(i_(corr))of samples treated by DCT-24 and DCT-48decreased from 153.1 nA·cm^(-2) in the untreated(UT)sample to 86.3 nA·cm^(-2) and 43.3 nA·cm^(-2),respectively.Furthermore,the roughness of corrosion surfaces of samples subjected to DCT was smaller than that of the UT sample,which indeed demonstrated the improvement in corrosion resistance of Ti-6Al-4V alloy in Hank's solution.The results of EIS test indicated that deep cryogenic treatment had no influence on the corrosion mechanism of Ti-6Al-4V alloy in Hank's,while enhanced resistance value of outer porous layer R_p,which makes the surface more efficient to prevent the corrosion.The reduction of β-phase particles,improvement in dislocation density and release of residual stress caused by deep cryogenic treatment had great contribution to the improvement in corrosion resistance of Ti-6Al-4V alloy in Hank's solution.
基金The work was financially supported by the National Natural Science Foundation of China(Grant No.51761022).
文摘The effects of traditional heat treatment(quenching and then tempering)and deep cryogenic treatment on the microstructure and mechanical properties of a low-carbon high-alloy martensitic bearing steel were studied by Rockwell hardness test,X-ray diffractometry,scanning electron microscopy and transmission electron microscopy.The results show that the deep cryogenic treatment promotes the transformation of the retained austenite to martensite during cooling,which leads to the hardness of the sample after deep cryogenic treatment higher than that at the quenched state.Also,the carbon content in the martensite matrix after different treatments was calculated and the results indicated that deep cryogenic treatment can promote the segregation of carbon atoms in martensite to dislocations.The segregated carbon atoms act as and grow into nuclei for the formation of fine carbide particles during subsequent tempering.And this resulted in the fact that the hardness of the tempered experimental steel after deep cryogenic treatment is higher than that without deep cryogenic treatment.
基金The authors are grateful to the funding by National High Technology Research and Development Program of China(863 Program,Grant No.2012AA03A503).
文摘Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment were investigated.Conventional treatment sample was quenched and tempered at 180℃ for 2 h.Cryogenic treatment samples were quenched,cryogenically treated at−80 and−196℃ for 4 h,slowly returned to room temperature and thereafter tempered at 180℃ for 2 h,and finally tempered at 180℃ for 2 h.The scanning electron microscope,electron backscattering diffraction,X-ray diffraction and transmission electron microscope were adopted for microstructure characterization.The results show that cryogenic treatment increases the fraction of high-angle grain boundaries and the precipitation of finely dispersed carbides in the matrix,decreases the volume fraction of inter-lath retained austenite,and hence improves the strength and hardness.Compared with the conventional treatment,the hardness,yield strength and ultimate tensile strength of the steel after cryogenic treatment are increased by 11.7%,12.6%and 18.3%,respectively,while the impact energy is decreased by 9.8%.
基金supported by the National Natural Science Foundation of China(No.51871212)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)+1 种基金the Major Scientific and Technological Projects of Jiangxi Province(No.20194ABC28011)the Project to Strengthen Industrial Development at the Grass-roots Level(TC190A4DA/35)。
文摘The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.
文摘In this study,the effects of deep cryogenic treatment(DCT)on the mechanical and tribological properties of AISI D3 tool steel were investigated together with a systematic correlation between their hardness and wear resistance.It was found that conventionally heat treated AISI D3 tool steel samples were significantly hardened via an additional DCT,which was attributed to the more retained austenite elimination,more homogenized carbide distribution and more reduction in carbide size in the samples.As a result,the hardened AISI D3 samples exhibited reductions in their friction and wear during rubbing against alumina and 100Cr6 steel balls under different normal loads due to the effectively hindered removal of surface materials.The results clearly showed that the DCT was an effective way to improve the mechanical and tribological properties of the AISI D3 tool steel samples as the tribological performance of the tool steel samples was significantly influenced by their hardness.
基金the National Natural Science Foundation of China(Nos.52171154,and 51871076)the National Key Research and Development Programs of China(Nos.2018YFB1105200 and 2019YFA0209904)+1 种基金the Guangdong Province Basic and Applied Research Key Projects(Nos.2020190718102)the National Key R&D Programme,Ministry of Science and Technology of China(No.2019YFA0209)。
文摘Additively manufactured(AM)metallic materials commonly possess substantial tensile surface residual stress,which is detrimental to the load-bearing service behavior.Recently,we demonstrated that deep cryogenic treatment(DCT)is an effective method for improving the tensile properties of CoCrFeMnNi high-entropy alloy(HEA)samples fabricated by laser melting deposition(LMD),by introducing high compressive residual stress and deformation microstructures without destroying the AM shape.However,carrying out the DCT in a single-step mode does not improve the residual stress gradients inherent from the LMD process,which are undesirable as the mechanical properties will not be homogeneous within the sample.In this work,we show that carrying out the DCT in a cyclic mode with repeated cryogenic cooling and reheating can significantly homogenize the residual stress in LMD-fabricated Co Cr Fe Mn Ni HEA,and improve tensile strength and ductility,compared with single-step DCT of the same cryogenic soaking duration.Under cyclic DCT,the thermal stress is re-elevated to a high value at each cryogenic cooling step,leading to the formation of denser and more intersecting reinforcing crystalline defects and hcp phase transformation,compared to single-step DCT of the same total cryogenic soaking duration in which the thermal stress relaxes towards a low value over time.The enhancement of defect formation in the cyclic mode of DCT also leads to more uniform residual stress distribution in the sample after the DCT.The results here provide important insights on optimizing DCT processes for post-fabrication improvement of mechanical properties of AM metallic net shapes.
基金The authors gratefully acknowledge the financial support received from the Central Iron and Steel Research Institute and the Research Center for Analysis and Measurement of Kunming University of Science and Technology(No.2017M20152230069).
文摘The microstructure evolution and the pitting corrosion resistance of a supermartensitic stainless steel after deep cryogenic treatment process were clarified through X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy(TEM)and electrochemical methods.The results showed that the microstructure of supermartensitic stainless steel mainly consisted of reversed austenite,tempered martensite,and M_(23)C_(6)carbides after tempering.The deep cryogenic treatment promoted the refinement of the martensite laths and the precipitation of the carbides in comparison with the traditional process.TEM analysis indicated that the segregation of Si atoms at the boundary was found at the interface between carbide and martensite.The pitting corrosion potential of the specimens subjected to deep cryogenic treatment decreased with the elevated tempering temperature,and the lowest pitting corrosion potential was found at the tempering temperature of 650℃.The sensitivity of the pitting corrosion potential was attributed to the precipitation of M_(23)C_(6)carbides and Si atoms segregation.Si atoms segregation engendered the formation of Cr-depleted zone near M_(23)C_(6)and impeded the recovery of Cr-depleted zone.
基金supported by the National Natural Science Foun-dation(Grant No.52031013)the National Key Research and Development Program(Grant No.2018YFA0702900).
文摘The influence of different cryogenic sequences on the rolling contact fatigue(RCF)life of M50-bearing steel has been studied.The results show that direct cryogenic treatment after quenching can effectively improve RCF life.The L_(10)life is strikingly 5 times longer than that with cryogenic treatment after tem-pering.This is caused by the distinct lattice construction of martensite and the transformation of retained austenite.More secondary nanocarbides and fine twins are formed via cryogenic treatment before tem-pering compared with cryogenic treatment after tempering.The improvement in the RCF life of the steel is attributed to the joint effects of the secondary nanocarbides and twin boundaries with a width of 5-13 nm,which delays significantly crack initiation and propagation.This study highlights a common method to improve the service life of high-carbon and high-alloy steels by adjusting the cryogenic se-quence.
基金the National Natural Science Foundation of China(No.51871234)the National Key Research and Development Plan(No.2016YFB0300500)+2 种基金the Open Fund of Key Laboratory of Materials Preparation and Protection for Harsh Environment(Nanjing University of Aeronautics and Astronautics),Ministry of Industry and Information Technology(No.XCA19013-04)the Beijing Municipal Science&Technology Commission(No.Z191100007219006)the Key Research Program of Frontier Sciences,CAS(No.QYZDY-SSW-JSC017)。
文摘The effects of acyclic liquid nitrogen(LN)treatment in a temperature range of-196℃to 50℃on the thermal and magnetic stability of Fe78Si9B13 and Fe73.5Si13.5B9Nb3Cu1 glassy ribbons have been studied.The intrinsic heterogeneities of the metallic glasses can be activated through cryogenic thermal cycling,making irreversible structural changes after the treatment and inducing rejuvenation to the materials.The microstructural changes of both Fe-based metallic glass(MG)and nanocrystalline alloy induced by LN treatment were investigated.The experimental results show that the LN treatment could effectively rejuvenate the Fe-Si-B MGs and change their thermomechanical and magnetic properties.Based on the partially-crystallinity and well-known magnetic constants,the increase of the energy at the order of 10m J/g and magnetic domain wall movement and rotation at the order of 5-6μm and 0.5°-0.8°are found for FINEMET-type amorphous alloy after LN treatment.It is also found that LN treatment can contribute a little stored energy to the magnetic domain wall movement and magnetic domain rotation.
基金financially supported by the National Science Foundation for Distinguished Young Scholars of China(Grant No.51725504)the open funding via State Key Laboratory of Materials Processing and Die&Mould Technology(Grant No.P2019-011)+1 种基金the Guangdong Provincial Natural Science Foundation of China(Grant No.2020A1515011524)the Fundamental Research Funds for the Central Universities,HUST(Grant No.2018KFYRCPT001).
文摘The effect of deep cryogenic cycle treatment(DCT)on Zr_(41.2)Ti_(13.8)Cu_(12.5)Ni_(10)Be_(22.5)(Vit-1)bulk metallic glass(BMG)prepared from high-purity raw materials was investigated.After DCT,no obvious rejuvenation of the samples was detected.With an increasing number of cryogenic cycles,the hardness of the samples first decreased and then increased,the room-temperature compression plasticity first increased and then generally remained unchanged,and the impact toughness underwent almost no obvious change.The absence of rejuvenation was attributed to the high fragility index(47-50)and high glass forming ability(GFA)of the material.As lower purity of the raw materials is expected in practical applications,DCT of Vit-1 BMG prepared from low-purity raw materials was also performed.After DCT,the samples prepared with the lower-purity raw materials were clearly rejuvenated,and the room-temperature mechanical properties improved significantly.Both the compression plasticity and impact toughness reached peak values after 5 cryogenic cycles.The initial impurities(including Y and O)had a complex and comprehensive effect on the deformation mechanism of the BMG during DCT.Our findings indicate that the structural heterogeneity,fragility index,and GFA of the BMG alter the effect of DCT.
