As a typical eutectic high-entropy alloy(EHEA),AlCoCrFeNi2.1 exhibits excellent casting properties.However,the imbalance between strength and plasticity hinders its application as an advanced structural material.In or...As a typical eutectic high-entropy alloy(EHEA),AlCoCrFeNi2.1 exhibits excellent casting properties.However,the imbalance between strength and plasticity hinders its application as an advanced structural material.In order to address this challenge,deep cryogenic treatment(DCT)as a new process applied in the field of EHEAs was proposed in this study.The effects of different DCT times on the microstructure and mechanical properties of AlCoCrFeNi2.1 EHEAs were studied,mainly focusing on the flake structure of FCC+B2 layer.The experimental results suggest that with the extension of the DCT time,the dislocation density in the FCC phase increases significantly.The spherical BCC precipitate phase is generated within the B2 phase,and the average size of this newly generated precipitate phase gradually decreases.Increasing the number of dislocations and precipitate phases is of great significance to improve the mechanical properties.The AlCoCrFeNi2.1 EHEA exhibits excellent comprehensive mechanical properties after DCT for 36 h.Compared with the as-cast state,the tensile strength at room temperature reaches 1,034.51 MPa,increased by 5.74%.The plasticity reaches 21.72%,which is increased by 11.79%.The results show that the tensile strength and ductility of AlCoCrFeNi2.1 EHEAs are balanced and improved after DCT,which are more suitable as advanced structural materials.In addition,the introduction of the DCT process to EHEAs solves the problem of environmental pollution caused by traditional heat treatment process.This study provides useful guidance for using the DCT process to strengthen the mechanical properties of“lamellar+block”type EHEAs.展开更多
The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains ...The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains are refined into triangular prism with sound edges via the process of spheroidization,but WC grain size has no evident change compared with that of untreated alloys.The phase transformation of Co phase from α-Co（FCC） to ε-Co（HCP） is observed in the cryogenically treated alloys,which is attributed to the decrease of W solubility in the binder（Co）.Deep cryogenic treatment enhances the hardness and bending strength of the alloys,while it has no significant effects on the density and cobalt magnetic performance.展开更多
Effect of deep cryogenic treatment （DCT） on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co...Effect of deep cryogenic treatment （DCT） on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its x -ε, phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafine- grained WC-12Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of ε-Co in WC-12Co composites after DCT.展开更多
AZ91 magnesium alloy was subjected to a deep cryogenic treatment. X-ray diffraction （XRD）, scanning electronic microscopy （SEM）, and transmission electronic microscopy （TEM） methods were utilized to characterize...AZ91 magnesium alloy was subjected to a deep cryogenic treatment. X-ray diffraction （XRD）, scanning electronic microscopy （SEM）, and transmission electronic microscopy （TEM） methods were utilized to characterize the composition and microstructure of the treated samples. The results show that after two cryogenic treatments, the quantity of the precipitate hardening β phase increases, and the sizes of the precipitates are refined from 8-10μm to 2-4μm. This is expected to be due to the decreased solubility of aluminum in the matrix at low temperature and the significant plastic deformation owing to internal differences in thermal contraction between phases and grains. The polycrystalline matrix is also noticeably refined, with the sizes of the subsequent nanocrystalline grains in the range of 50-100 nm. High density dislocations are observed to pile up at the grain boundaries, inducing the dynamic recrystallization of the microstructure, leading to the generation of a nanocrystalline grain structure. After two deep cryogenic treatments, the tensile strength and elongation are found to be substantially increased, rising from 243 MPa and 4.4% of as-cast state to 299 MPa and 5.1%.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
To further improve the mechanical performance of a new alloyed austempered ductile iron（ADI）, deep cryogenic treatment（DCT） has been adopted to investigate the effect of DCT time on the microstructure and mechanic...To further improve the mechanical performance of a new alloyed austempered ductile iron（ADI）, deep cryogenic treatment（DCT） has been adopted to investigate the effect of DCT time on the microstructure and mechanical behaviors of the alloyed ADI Fe-3.55 C-1.97 Si-3.79 Ni-0.71 Cu-0.92 Mo-0.64 Cr-0.36 Mn-0.30 V（in wt.%）. With increasing the DCT time, more austenite transformed to martensite and very fine carbides precipitated in martensite in the extended period of DCT. The amount of austenite decreased in alloyed ductile irons, while that of martensite and carbide precipitation increased. The alloyed ADI after DCT for 6 h had the highest hardness and compressive strength, which can be attributed to the formation of more plate-like martensite and the finely precipitated carbides. There was a gradual decrease in hardness and compressive strength with increasing the DCT time to 12 h because of the dissolution of M3 C carbide. After tempering, there was a decrease in mechanical properties compared to the direct DCT sample, which was caused by the occurrence of Ostwald ripening of precipitated carbides. The optimum wear resistance was achieved for the alloyed ADI after DCT for 6 h. The wear mechanism of the alloyed ADI in associating with DCT is mainly consisted of micro-cutting wear and some plastic deformation wear.展开更多
The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distributio...The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.展开更多
In this paper we compare the wear behaviour of a vacuum-heat-treated ESR AISI M2 high-speed steel and the same steel that was vacuum heat treated in conjunction with a deep-cryogenic treatment at -196 °C. Four di...In this paper we compare the wear behaviour of a vacuum-heat-treated ESR AISI M2 high-speed steel and the same steel that was vacuum heat treated in conjunction with a deep-cryogenic treatment at -196 °C. Four different tempering temperatures for the specimens austenized at the same austenitizing temperature were carefully selected to obtain various in-advance-determined combinations of the microstructures, the fracture toughness, KIc and the Rockwell-C hardness. Each of the eight specimens was therefore characterised by these microstructures and resulting material properties. The wear study was performed using a reciprocating sliding device under well-controlled contact conditions. Relatively high loads were used to provide enough wear for a comparison of the selected samples. A much harder and dissimilar model counter-material, i.e. silicon nitride ceramic, was used in order to avoid excessive wear of the counter samples and adhesion, which could occur in contacts with similar materials (metals/steels) under such high loads and in non-lubricated conditions. The wear behaviours were then compared and discussed in terms of these microstructures and the related properties. The differences in the wear resistance obtained in our investigation were as high as an order of magnitude. However, the beneficial effects are not a direct result of the type of the treatment, but relate to a proper combination of the resulting fracture toughness and the hardness. The more uniform and moderate values, which, however, tend to be obtained with a deep-cryogenic treatment, are beneficial to the high wear resistance of the selected high-speed steel.展开更多
Cr-Zr-Cu alloy electrodes for resistance spot welding of aluminium alloy are treated by deep cryogenic treatment processes. The Cr-Zr-Cu alloy electrodes are analyzed by transmission electron microscope（ TEM ） , and...Cr-Zr-Cu alloy electrodes for resistance spot welding of aluminium alloy are treated by deep cryogenic treatment processes. The Cr-Zr-Cu alloy electrodes are analyzed by transmission electron microscope（ TEM ） , and results show that the common dislocation in Cr-Zr-Cu alloy electrodes is changed into the dislocation loop, and twin crystal is found after deep cryogenic treatment. The parallel twin crystal band is observed by selected electron diffraction（SED） and the twin crystal plane is marked as （ 111 ）. The Cr-Zr-Cu alloy electrode is studied by X-ray diffraction（ XRD ） and results show that the intensity of diffraction peak is obviously changed after deep cryogenic treatment, and the grain rotates to preferred orientation. The Cr-Zr- Cu alloy electrode is studied by positron annihilation technique （PAT） and results indicate that the amount of vacancy defects is less than that of Cr-Zr-Cu alloy before deep cryogenic treatment. The main elements in Cr-Zr-Cu alloy are studied with X- ray photoelctron spectroscopy（ XPS ） and the intensity of spectrum peak is increased after deep cryogenic treatment.展开更多
The rapid advancements in computer vision(CV)technology have transformed the traditional approaches to material microstructure analysis.This review outlines the history of CV and explores the applications of deep-lear...The rapid advancements in computer vision(CV)technology have transformed the traditional approaches to material microstructure analysis.This review outlines the history of CV and explores the applications of deep-learning(DL)-driven CV in four key areas of materials science:microstructure-based performance prediction,microstructure information generation,microstructure defect detection,and crystal structure-based property prediction.The CV has significantly reduced the cost of traditional experimental methods used in material performance prediction.Moreover,recent progress made in generating microstructure images and detecting microstructural defects using CV has led to increased efficiency and reliability in material performance assessments.The DL-driven CV models can accelerate the design of new materials with optimized performance by integrating predictions based on both crystal and microstructural data,thereby allowing for the discovery and innovation of next-generation materials.Finally,the review provides insights into the rapid interdisciplinary developments in the field of materials science and future prospects.展开更多
Near-eutectic Al-Si alloys are widely used in automotive manufacturing due to their superior wear resistance and high temperature performance.Because of high Si content,the grain refinement of near-eutectic Al-Si allo...Near-eutectic Al-Si alloys are widely used in automotive manufacturing due to their superior wear resistance and high temperature performance.Because of high Si content,the grain refinement of near-eutectic Al-Si alloy has been a problem for many years.In this study,the effect of deep cryogenic treatment(DCT)on the microstructure and mechanical properties of Al-12Si-4Cu-2Ni-Mg alloy with addition of Al-Ti-C-B master alloy was fully investigated.Results show that the average grain size of the alloy is greatly reduced from 0.92 mm to 0.50 mm,and the eutectic Si and Al7Cu4Ni precipitates are spheroidized and refined in Al-12Si-4Cu-2Ni-Mg after DCT for 24 h and aging treatment.Thereby these changes of microstructures result in a significant increment of about 22.5%in elongation and a slight enhancement of about 6.8%in tensile strength.Moreover,the refinement of microstructure also significantly improves the fatigue life of the alloy.展开更多
Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950°C. Phase transition during annealing was stud...Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950°C. Phase transition during annealing was studied using X-ray diffractometry. Transmission electron microscopy and electron backscattered diffraction were used to characterize the martensite transformation and the distribution of austenite grain size after annealing. The recrystallization mechanism during cryogenic rolling was a reversal of martensite into austenite and austenite growth. Cryogenic rolling followed by annealing refined grains to 4.7 μm compared with 8.7 μm achieved under room-temperature rolling, as shown by the electron backscattered diffraction images. Tensile tests showed significantly improved mechanical properties after cryogenic rolling as the yield strength was enhanced by 47% compared with room-temperature rolling.展开更多
To develop a new compound heat treatment process for improving the mechanical properties of die-cast Al alloys,this study investigated the effects of cryogenic,solution and aging compound treatment on the microstructu...To develop a new compound heat treatment process for improving the mechanical properties of die-cast Al alloys,this study investigated the effects of cryogenic,solution and aging compound treatment on the microstructure and mechanical properties of die-cast Al alloys.The characterization methods used were optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),electron backscatter diffraction(EBSD),and tensile tests;and the Image Pro Plus software was used for statistical analysis.The results indicated that compared with T6 heat treatment,the compound heat treatment process consisting of cryogenic treatment(-196.C for 12 h),solid solution treatment(476.C for 22 min),and aging(159.C for 403 min)significantly enhanced the mechanical properties of the diecast Al alloys.For instance,the tensile strength increased from 224.3 to 249.5 MPa;the hardness increased from HV110.5 to HV 124.6,and the elongation increased from6.28%to 7.72%,which in relative terms corresponds to11.2%,12.8%and 22.9%,respectively.The compound heat treatment process of the alloy led to significant refinement of its a-Al phases.In addition,Si phases tended to be more ellipsoidal or granular,while the tips of Fecontaining phases became rounded,which played a key role in enhancing the mechanical properties and microstructure stability of the alloys.展开更多
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 effect of Mn content on the microstructure and cryogenic mechanical properties of a 7% Ni steel was investigated within the Mn content range from 0.13% to 0.36%. The microstructure of the steel as determined by op...The effect of Mn content on the microstructure and cryogenic mechanical properties of a 7% Ni steel was investigated within the Mn content range from 0.13% to 0.36%. The microstructure of the steel as determined by optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscattering diffraction and X-ray diffraction was presented, and the low-temperature mechanical properties were given. The size of prior austenite grain did not change a lot as Mn content increased. Film-like reversed austenite, having high stability, was found mainly in the specimens with lower Mn content; however, in the specimen with the highest Mn content, the role of Mn was not obvious in stabilizing reversed austenite. Besides, with increasing Mn content, the amount of reversed austenite at grain boundaries gradually decreased. The variable Mn content had a significant effect on cryogenic toughness~ but not apparent on cryogenic tensile strength or yield strength. An excellent combination of cryogenic tensile and impact properties was obtained when Mn content of steel was 0.13%.展开更多
Fe-Cr-Mo-Ni-C-Co alloy was quenched in liquid nitrogen and held for 24 h.Hardness tester,OM,XRD,SEM were used to investigate the mechanical properties and microstructures of the alloy.The results show that the hardnes...Fe-Cr-Mo-Ni-C-Co alloy was quenched in liquid nitrogen and held for 24 h.Hardness tester,OM,XRD,SEM were used to investigate the mechanical properties and microstructures of the alloy.The results show that the hardness increases by 1-2(HRC)and the compressive strength decreases slightly after cryogenic treatment.The increase in hardness is attributed to the transformation from austenite to martensite and the precipitation of the very tiny carbideη-Fe2C.The decrease in compressive strength is caused by residual stress.The great amount of carbides,such as Cr7C3 and Fe2MoC,in the alloy and the obvious difference in thermal expansion coefficient between these carbides and the matrix at the cryogenic temperatures lead to this residual stress.The microscopy of cryogenic martensite is different from that of the non-cryogenic martensite.The cryogenic martensite is long and fine;while the non-cryogenic martensite is short and coarse.There is obvious surface relief of the cryogenic martensite transformation.It is not orientational of this kind surface relief and the boundary of this surface relief is smooth and in a shape of butterfly.The surface relief in the non-cryogenic martensite is wide and arranged in parallel,and the boundary of surface relief is not smooth.These characteristics may imply different growth ways of the two kinds of martensite.展开更多
Cryogenic treatment was used to improve the tribological properties of Ti6Al4V artificial hip joint implants.Cryogenic treatment at-196℃with different holding time were carried out on Ti6Al4V specimens fabricated usi...Cryogenic treatment was used to improve the tribological properties of Ti6Al4V artificial hip joint implants.Cryogenic treatment at-196℃with different holding time were carried out on Ti6Al4V specimens fabricated using electron beam melting(EBM),and their microstructure and tribological properties evolution were systematically analyzed by scanning electron microscopy(SEM),vickers hardness,and wear tests.The experimental results show that the as-fabricated specimen consists of lamellarαphase andβcolumnar crystal.While,the thickness of lamellarαphase decreased after cryogenic treatment.In addition,it can be found that the fineαphase was precipitated and dispersed between the lamellarαphase with the holding time increase.Vickers hardness shows a trend of first increasing and then decreasing.The wear rate of the specimen cryogenic treated for 24 h is the minimum and the average friction coefficient is 0.50,which is reduced by 14.61%compared with the as-fabricated.The wear mechanism of the as-fabricated specimen is severe exfoliation,adhesive,abrasive,and slight fatigue wear.However,the specimen cryogenic treated for 24 h shows slight adhesive and abrasive wear.It can be concluded that it is feasibility of utilizing cryogenic treatment to reduce the wear of EBMed Ti6Al4V.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 development of microstructure and texture during cold deep drawing of commercially pure titanium（CP-Ti） was investigated.Three parts,stretching region,drawing region and flange region,were sequentially formed in...The development of microstructure and texture during cold deep drawing of commercially pure titanium（CP-Ti） was investigated.Three parts,stretching region,drawing region and flange region,were sequentially formed in the deep drawing process of the hemispheric surface part,with reference to deformation modes and strain regimes.Results show that the plastic strain is accommodated by dislocation slip and deformation twinning in the whole deep drawing process.The texture of the CP-Ti sheet and its drawn part consists of rolling texture component and recrystallization texture component.The intensity and type of the initial texture varied during the drawing process are related to the production of deformation twinning and dislocation slip.Twinning weakens the initial texture by randomizing the orientations of crystals,especially for the recrystallization texture.The recrystallization texture in the drawing region disappears due to the significant forming of twinning.Furthermore,over drawing would result in the predominance of dislocation slip and the texture is strengthened.展开更多
Combining with the low temperature material properties and the boiling heat transfer coefficient of specimen immersed in the liquid nitrogen, a numerical model based on metallo-thermo-mechanical couple theory was esta...Combining with the low temperature material properties and the boiling heat transfer coefficient of specimen immersed in the liquid nitrogen, a numerical model based on metallo-thermo-mechanical couple theory was established to reproduce the deep cryogenic treatment （DCT） process of a newly developed cold work die steel Cr8Mo2SiV （SDC99）. Moreover, an experimental setup for rapid temperature measurement was designed to validate the simulation results. The investigation suggests that the differences in temperature and cooling rate between the surface and core of specimen are very significant. However, it should be emphasized that the acute temperature and cooling rate changes during DCT are mainly concentrated on the specimen surface region about 1/3 of the sample thickness. Subjected to DCT, the retained austenite of quenched specimen continues to transform to martensite and finally its phase volume fraction reduces to 2.3%. The predicted results are coincident well with the experimental data, which demonstrates that the numerical model employed in this study can accurately capture the variation characteristics of temperature and microstructure fields during DCT and provide a theoretical guidance for making the reasonable DCT procedure.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52301061,52204394)the Joint Fund Project of Science and Technology Plan of Liaoning Province(No.2023-MSLH-250)the Science and the Technology Program of Liaoning Provincial Department of Education(No.JYTQN2023286)。
文摘As a typical eutectic high-entropy alloy(EHEA),AlCoCrFeNi2.1 exhibits excellent casting properties.However,the imbalance between strength and plasticity hinders its application as an advanced structural material.In order to address this challenge,deep cryogenic treatment(DCT)as a new process applied in the field of EHEAs was proposed in this study.The effects of different DCT times on the microstructure and mechanical properties of AlCoCrFeNi2.1 EHEAs were studied,mainly focusing on the flake structure of FCC+B2 layer.The experimental results suggest that with the extension of the DCT time,the dislocation density in the FCC phase increases significantly.The spherical BCC precipitate phase is generated within the B2 phase,and the average size of this newly generated precipitate phase gradually decreases.Increasing the number of dislocations and precipitate phases is of great significance to improve the mechanical properties.The AlCoCrFeNi2.1 EHEA exhibits excellent comprehensive mechanical properties after DCT for 36 h.Compared with the as-cast state,the tensile strength at room temperature reaches 1,034.51 MPa,increased by 5.74%.The plasticity reaches 21.72%,which is increased by 11.79%.The results show that the tensile strength and ductility of AlCoCrFeNi2.1 EHEAs are balanced and improved after DCT,which are more suitable as advanced structural materials.In addition,the introduction of the DCT process to EHEAs solves the problem of environmental pollution caused by traditional heat treatment process.This study provides useful guidance for using the DCT process to strengthen the mechanical properties of“lamellar+block”type EHEAs.
基金Project(12JJ8018)supported by the Natural Science Foundation of Hunan Province,China
文摘The effects of deep cryogenic treatment on the microstructure and properties of WC-11 Co cemented carbides with various carbon contents were investigated.The results show that after deep cryogenic treatment,WC grains are refined into triangular prism with sound edges via the process of spheroidization,but WC grain size has no evident change compared with that of untreated alloys.The phase transformation of Co phase from α-Co（FCC） to ε-Co（HCP） is observed in the cryogenically treated alloys,which is attributed to the decrease of W solubility in the binder（Co）.Deep cryogenic treatment enhances the hardness and bending strength of the alloys,while it has no significant effects on the density and cobalt magnetic performance.
基金financially supported by the Major Special Project,Ministry of Industry and Information Technology,China (No.2012ZX04003061)
文摘Effect of deep cryogenic treatment （DCT） on the microstructures and mechanical behavior of ultrafine-grained WC-12Co cemented carbide was investigated by using XRD, SEM, and DSC. The phase transformations of pure Co and binder phase Co in cemented carbide were analyzed in detail to correlate the strengthening mechanism with its x -ε, phase transition. The results show that DCT resulted in a slight increase in hardness and bending strength of ultrafine- grained WC-12Co cemented carbide. For the ultrafine-grained cemented carbide after DCT, there is no significant change in the microstructure and the elemental distribution of the cemented carbides, but the fractured morphology shows a feature of plastic deformation. In the cases of pure Co and the binder phase Co in WC-12Co cemented carbide, they exhibit different features of phase transformation. The improvement of mechanical property of cemented carbide can be attributed to the increased amount of ε-Co in WC-12Co composites after DCT.
基金financially supported by the National Natural Science Foundation of China(Nos.51001054,51174099,and 51174098)the Natural Science Foundation of Jiangsu Province,China(No.BK2011533)+2 种基金Open Funds of the State Key Laboratory of Metal Matrix Composites of Shanghai Jiao Tong University(No.mmc-kf12-06)the Key Laboratory of Cryogenics,Technical Institute of Physics and Chemistry,Chinese Academy of Sciences(No.CRYO201106)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),China
文摘AZ91 magnesium alloy was subjected to a deep cryogenic treatment. X-ray diffraction （XRD）, scanning electronic microscopy （SEM）, and transmission electronic microscopy （TEM） methods were utilized to characterize the composition and microstructure of the treated samples. The results show that after two cryogenic treatments, the quantity of the precipitate hardening β phase increases, and the sizes of the precipitates are refined from 8-10μm to 2-4μm. This is expected to be due to the decreased solubility of aluminum in the matrix at low temperature and the significant plastic deformation owing to internal differences in thermal contraction between phases and grains. The polycrystalline matrix is also noticeably refined, with the sizes of the subsequent nanocrystalline grains in the range of 50-100 nm. High density dislocations are observed to pile up at the grain boundaries, inducing the dynamic recrystallization of the microstructure, leading to the generation of a nanocrystalline grain structure. After two deep cryogenic treatments, the tensile strength and elongation are found to be substantially increased, rising from 243 MPa and 4.4% of as-cast state to 299 MPa and 5.1%.
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Financial support from the National High Technology Research and Development Program of China(No.2012AA03A508)is greatly appreciated
文摘To further improve the mechanical performance of a new alloyed austempered ductile iron（ADI）, deep cryogenic treatment（DCT） has been adopted to investigate the effect of DCT time on the microstructure and mechanical behaviors of the alloyed ADI Fe-3.55 C-1.97 Si-3.79 Ni-0.71 Cu-0.92 Mo-0.64 Cr-0.36 Mn-0.30 V（in wt.%）. With increasing the DCT time, more austenite transformed to martensite and very fine carbides precipitated in martensite in the extended period of DCT. The amount of austenite decreased in alloyed ductile irons, while that of martensite and carbide precipitation increased. The alloyed ADI after DCT for 6 h had the highest hardness and compressive strength, which can be attributed to the formation of more plate-like martensite and the finely precipitated carbides. There was a gradual decrease in hardness and compressive strength with increasing the DCT time to 12 h because of the dissolution of M3 C carbide. After tempering, there was a decrease in mechanical properties compared to the direct DCT sample, which was caused by the occurrence of Ostwald ripening of precipitated carbides. The optimum wear resistance was achieved for the alloyed ADI after DCT for 6 h. The wear mechanism of the alloyed ADI in associating with DCT is mainly consisted of micro-cutting wear and some plastic deformation wear.
文摘The influence of soaking time in deep cryogenic treatment on the tensile and impact properties of low-alloy medium-carbon HY-TUF steel was investigated in this study. Microstructural studies based on phase distribution mapping by electron backscatter diffraction show that the deep cryogenic process causes a decrease in the content of retained austenite and an increase in the volume fraction of η-carbide with increasing soaking time up to 48 h. The decrease in the content of retained austenite from ~1.23vol% to 0.48vol% suggests an isothermal martensitic transformation at 77 K. The η-type precipitates formed in deep cryogenic-treated martensite over 48 h have the Hirotsu and Nagakura orientation relation with the martensitic matrix. Furthermore, a high coherency between η-carbide and the martensitic matrix is observed by high-resolution transmission electron microscopy. The variations in macrohardness, yield strength, ultimate tensile strength, and ductility with soaking time in the deep cryogenic process show a peak/plateau trend.
文摘In this paper we compare the wear behaviour of a vacuum-heat-treated ESR AISI M2 high-speed steel and the same steel that was vacuum heat treated in conjunction with a deep-cryogenic treatment at -196 °C. Four different tempering temperatures for the specimens austenized at the same austenitizing temperature were carefully selected to obtain various in-advance-determined combinations of the microstructures, the fracture toughness, KIc and the Rockwell-C hardness. Each of the eight specimens was therefore characterised by these microstructures and resulting material properties. The wear study was performed using a reciprocating sliding device under well-controlled contact conditions. Relatively high loads were used to provide enough wear for a comparison of the selected samples. A much harder and dissimilar model counter-material, i.e. silicon nitride ceramic, was used in order to avoid excessive wear of the counter samples and adhesion, which could occur in contacts with similar materials (metals/steels) under such high loads and in non-lubricated conditions. The wear behaviours were then compared and discussed in terms of these microstructures and the related properties. The differences in the wear resistance obtained in our investigation were as high as an order of magnitude. However, the beneficial effects are not a direct result of the type of the treatment, but relate to a proper combination of the resulting fracture toughness and the hardness. The more uniform and moderate values, which, however, tend to be obtained with a deep-cryogenic treatment, are beneficial to the high wear resistance of the selected high-speed steel.
基金This project is supported by Nature Science Foundation of Shanxi Province （ No. 2009011028-2） , Talent Star Special Foundation of Taiyuan （No. 09121013 ）, College Students Innovation Foundation of Shanxi Province（ No. UIT20090065 ）.
文摘Cr-Zr-Cu alloy electrodes for resistance spot welding of aluminium alloy are treated by deep cryogenic treatment processes. The Cr-Zr-Cu alloy electrodes are analyzed by transmission electron microscope（ TEM ） , and results show that the common dislocation in Cr-Zr-Cu alloy electrodes is changed into the dislocation loop, and twin crystal is found after deep cryogenic treatment. The parallel twin crystal band is observed by selected electron diffraction（SED） and the twin crystal plane is marked as （ 111 ）. The Cr-Zr-Cu alloy electrode is studied by X-ray diffraction（ XRD ） and results show that the intensity of diffraction peak is obviously changed after deep cryogenic treatment, and the grain rotates to preferred orientation. The Cr-Zr- Cu alloy electrode is studied by positron annihilation technique （PAT） and results indicate that the amount of vacancy defects is less than that of Cr-Zr-Cu alloy before deep cryogenic treatment. The main elements in Cr-Zr-Cu alloy are studied with X- ray photoelctron spectroscopy（ XPS ） and the intensity of spectrum peak is increased after deep cryogenic treatment.
基金financially supported by the National Science Fund for Distinguished Young Scholars,China(No.52025041)the National Natural Science Foundation of China(Nos.52450003,U2341267,and 52174294)+1 种基金the National Postdoctoral Program for Innovative Talents,China(No.BX20240437)the Fundamental Research Funds for the Central Universities,China(Nos.FRF-IDRY-23-037 and FRF-TP-20-02C2)。
文摘The rapid advancements in computer vision(CV)technology have transformed the traditional approaches to material microstructure analysis.This review outlines the history of CV and explores the applications of deep-learning(DL)-driven CV in four key areas of materials science:microstructure-based performance prediction,microstructure information generation,microstructure defect detection,and crystal structure-based property prediction.The CV has significantly reduced the cost of traditional experimental methods used in material performance prediction.Moreover,recent progress made in generating microstructure images and detecting microstructural defects using CV has led to increased efficiency and reliability in material performance assessments.The DL-driven CV models can accelerate the design of new materials with optimized performance by integrating predictions based on both crystal and microstructural data,thereby allowing for the discovery and innovation of next-generation materials.Finally,the review provides insights into the rapid interdisciplinary developments in the field of materials science and future prospects.
基金financially supported by Shandong Province Aluminum Manufacturing and Application Innovation and Entrepreneurship Community projectShandong Province key Research and Development Plan(2021ZLGX01,2021SFGC1001,2023CXPT024)Shandong Province Youth Taishan project。
文摘Near-eutectic Al-Si alloys are widely used in automotive manufacturing due to their superior wear resistance and high temperature performance.Because of high Si content,the grain refinement of near-eutectic Al-Si alloy has been a problem for many years.In this study,the effect of deep cryogenic treatment(DCT)on the microstructure and mechanical properties of Al-12Si-4Cu-2Ni-Mg alloy with addition of Al-Ti-C-B master alloy was fully investigated.Results show that the average grain size of the alloy is greatly reduced from 0.92 mm to 0.50 mm,and the eutectic Si and Al7Cu4Ni precipitates are spheroidized and refined in Al-12Si-4Cu-2Ni-Mg after DCT for 24 h and aging treatment.Thereby these changes of microstructures result in a significant increment of about 22.5%in elongation and a slight enhancement of about 6.8%in tensile strength.Moreover,the refinement of microstructure also significantly improves the fatigue life of the alloy.
基金financially supported by the National Key Project of Research and Development Program of China (No. 2016YFB0300801)the National Natural Science Foundation of China (No. 51401016)State Key Laboratory for Advanced Metals and Materials of China
文摘Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950°C. Phase transition during annealing was studied using X-ray diffractometry. Transmission electron microscopy and electron backscattered diffraction were used to characterize the martensite transformation and the distribution of austenite grain size after annealing. The recrystallization mechanism during cryogenic rolling was a reversal of martensite into austenite and austenite growth. Cryogenic rolling followed by annealing refined grains to 4.7 μm compared with 8.7 μm achieved under room-temperature rolling, as shown by the electron backscattered diffraction images. Tensile tests showed significantly improved mechanical properties after cryogenic rolling as the yield strength was enhanced by 47% compared with room-temperature rolling.
基金financially supported by the National Natural Science Foundation of China-Youth Project(No.51801076)the Provincial Colleges and Universities Natural Science Research Project of Jiangsu Province(No.18KJB430009)+1 种基金the Postdoctoral Research Support Project of Jiangsu Province(No.1601055C)the Senior Talents Research Startup of Jiangsu University(No.14JDG126)。
文摘To develop a new compound heat treatment process for improving the mechanical properties of die-cast Al alloys,this study investigated the effects of cryogenic,solution and aging compound treatment on the microstructure and mechanical properties of die-cast Al alloys.The characterization methods used were optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),electron backscatter diffraction(EBSD),and tensile tests;and the Image Pro Plus software was used for statistical analysis.The results indicated that compared with T6 heat treatment,the compound heat treatment process consisting of cryogenic treatment(-196.C for 12 h),solid solution treatment(476.C for 22 min),and aging(159.C for 403 min)significantly enhanced the mechanical properties of the diecast Al alloys.For instance,the tensile strength increased from 224.3 to 249.5 MPa;the hardness increased from HV110.5 to HV 124.6,and the elongation increased from6.28%to 7.72%,which in relative terms corresponds to11.2%,12.8%and 22.9%,respectively.The compound heat treatment process of the alloy led to significant refinement of its a-Al phases.In addition,Si phases tended to be more ellipsoidal or granular,while the tips of Fecontaining phases became rounded,which played a key role in enhancing the mechanical properties and microstructure stability of the alloys.
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financially supported by Wuhan Iron and Steel(Group)Corp
文摘The effect of Mn content on the microstructure and cryogenic mechanical properties of a 7% Ni steel was investigated within the Mn content range from 0.13% to 0.36%. The microstructure of the steel as determined by optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscattering diffraction and X-ray diffraction was presented, and the low-temperature mechanical properties were given. The size of prior austenite grain did not change a lot as Mn content increased. Film-like reversed austenite, having high stability, was found mainly in the specimens with lower Mn content; however, in the specimen with the highest Mn content, the role of Mn was not obvious in stabilizing reversed austenite. Besides, with increasing Mn content, the amount of reversed austenite at grain boundaries gradually decreased. The variable Mn content had a significant effect on cryogenic toughness~ but not apparent on cryogenic tensile strength or yield strength. An excellent combination of cryogenic tensile and impact properties was obtained when Mn content of steel was 0.13%.
文摘Fe-Cr-Mo-Ni-C-Co alloy was quenched in liquid nitrogen and held for 24 h.Hardness tester,OM,XRD,SEM were used to investigate the mechanical properties and microstructures of the alloy.The results show that the hardness increases by 1-2(HRC)and the compressive strength decreases slightly after cryogenic treatment.The increase in hardness is attributed to the transformation from austenite to martensite and the precipitation of the very tiny carbideη-Fe2C.The decrease in compressive strength is caused by residual stress.The great amount of carbides,such as Cr7C3 and Fe2MoC,in the alloy and the obvious difference in thermal expansion coefficient between these carbides and the matrix at the cryogenic temperatures lead to this residual stress.The microscopy of cryogenic martensite is different from that of the non-cryogenic martensite.The cryogenic martensite is long and fine;while the non-cryogenic martensite is short and coarse.There is obvious surface relief of the cryogenic martensite transformation.It is not orientational of this kind surface relief and the boundary of this surface relief is smooth and in a shape of butterfly.The surface relief in the non-cryogenic martensite is wide and arranged in parallel,and the boundary of surface relief is not smooth.These characteristics may imply different growth ways of the two kinds of martensite.
基金Funded by the National Natural Science Foundation of China(No.42102345)the Fundamental Research Funds for the Central Universities(No.2023ZKPYJD03)。
文摘Cryogenic treatment was used to improve the tribological properties of Ti6Al4V artificial hip joint implants.Cryogenic treatment at-196℃with different holding time were carried out on Ti6Al4V specimens fabricated using electron beam melting(EBM),and their microstructure and tribological properties evolution were systematically analyzed by scanning electron microscopy(SEM),vickers hardness,and wear tests.The experimental results show that the as-fabricated specimen consists of lamellarαphase andβcolumnar crystal.While,the thickness of lamellarαphase decreased after cryogenic treatment.In addition,it can be found that the fineαphase was precipitated and dispersed between the lamellarαphase with the holding time increase.Vickers hardness shows a trend of first increasing and then decreasing.The wear rate of the specimen cryogenic treated for 24 h is the minimum and the average friction coefficient is 0.50,which is reduced by 14.61%compared with the as-fabricated.The wear mechanism of the as-fabricated specimen is severe exfoliation,adhesive,abrasive,and slight fatigue wear.However,the specimen cryogenic treated for 24 h shows slight adhesive and abrasive wear.It can be concluded that it is feasibility of utilizing cryogenic treatment to reduce the wear of EBMed Ti6Al4V.
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Project(SKLSP200906) supported by the Fund of State Key Laboratory of Solidification Processing in NWPUProject(B08040) supported by Program of Introducing Talents of Discipline in the Project of Advanced Materials and Their Forming Technology
文摘The development of microstructure and texture during cold deep drawing of commercially pure titanium（CP-Ti） was investigated.Three parts,stretching region,drawing region and flange region,were sequentially formed in the deep drawing process of the hemispheric surface part,with reference to deformation modes and strain regimes.Results show that the plastic strain is accommodated by dislocation slip and deformation twinning in the whole deep drawing process.The texture of the CP-Ti sheet and its drawn part consists of rolling texture component and recrystallization texture component.The intensity and type of the initial texture varied during the drawing process are related to the production of deformation twinning and dislocation slip.Twinning weakens the initial texture by randomizing the orientations of crystals,especially for the recrystallization texture.The recrystallization texture in the drawing region disappears due to the significant forming of twinning.Furthermore,over drawing would result in the predominance of dislocation slip and the texture is strengthened.
基金Project (51171104) supported by the National Natural Science Foundation of China
文摘Combining with the low temperature material properties and the boiling heat transfer coefficient of specimen immersed in the liquid nitrogen, a numerical model based on metallo-thermo-mechanical couple theory was established to reproduce the deep cryogenic treatment （DCT） process of a newly developed cold work die steel Cr8Mo2SiV （SDC99）. Moreover, an experimental setup for rapid temperature measurement was designed to validate the simulation results. The investigation suggests that the differences in temperature and cooling rate between the surface and core of specimen are very significant. However, it should be emphasized that the acute temperature and cooling rate changes during DCT are mainly concentrated on the specimen surface region about 1/3 of the sample thickness. Subjected to DCT, the retained austenite of quenched specimen continues to transform to martensite and finally its phase volume fraction reduces to 2.3%. The predicted results are coincident well with the experimental data, which demonstrates that the numerical model employed in this study can accurately capture the variation characteristics of temperature and microstructure fields during DCT and provide a theoretical guidance for making the reasonable DCT procedure.
