Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel st...Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel steel. The results showed that although the roughness of the original specimen induced by mechanical processing would diminish to some extent in the experiment, the 0.5 - 1.5 μm thick layer of ultrafine microstructure on the original mechanically-processed specimen surface would still become micro-cracks and small spalling pits due to spalling, and would further evolve into fatigue crack source. Additionally, even under the impact of the load that was not adequate to make the material reach fatigue limit, the ferrite in the microstructure underwent plastic deformation, which led the refinement of proeutectoid ferrite grains. During the experiment, the hardening and the refinement caused by plastic deformation consisted with the theory that dislocation gave rise to plastic deformation and grain refinement. The distribution laws of hardness and ferrite grain sizes measured could be explained by the distribution law of the shearing stress in the subsurface.展开更多
A decrease in the weight of aerospace vehicles,large ships,weapons,and high-speed trains will increase the demand for wide-width magnesium alloy plates and their composite parts to replace steel and plastic.An investi...A decrease in the weight of aerospace vehicles,large ships,weapons,and high-speed trains will increase the demand for wide-width magnesium alloy plates and their composite parts to replace steel and plastic.An investigation was conducted to study the variation in deformation behaviors along the transverse direction during the warm rolling of a 1480-mm-wide AZ31B plate.A uniaxial thermal compression test with a 59%reduction was performed at different positions on a 13.7-mm-thick rolled plate along the width direction at a temperature of 220℃ and 270℃ and strain rate of 15 s^(−1).At the same time,the 13.7-mm-thick plate was rolled in a single pass to 5.6 mm on a mill with a 1725-mm-wide roll to confirm the thermal deformation behavior and the dynamic recrystallization(DRX).The results show that the main texture type does not change and the grain size does not have a clear deflection when the magnesium alloy plate reaches a certain value under rolling accumulative reduction.The grain size of a 13.7-mm-thick plate increases with a decrease in the distance to the center layer in the thickness direction.In the width direction,the edge(R6)first decreases and then increases toward the symmetric plane(R1).The critical stress required for dynamic recrystallization in the transition zone R3 of the rolled plate width is minimum,and the average grain size is minimum owing to the relatively complete recrystallization.展开更多
In this paper, the surface microstructure and wear property of D2 wheel steel under sliding wear condition were studied by MRH-30 sliding wear tester. After testing, a transmission electron microscope (TEM), scanning ...In this paper, the surface microstructure and wear property of D2 wheel steel under sliding wear condition were studied by MRH-30 sliding wear tester. After testing, a transmission electron microscope (TEM), scanning electron microscope (SEM) with electron backscatter diffraction (EBSD), and micro-hardness testers were used to characterize the surface microstructure of samples with different cycles. The results show that the wear losss samples are increased as the increase of cycles, and the wear loss of wheel samples is higher than that of rail samples. The surface hardness and thickness of deformation layer of wheel samples are increased as the cycles increase. After sliding wear, the samples surfaces form the white etching layer with the thickness of several microns. Through the analysis of surface microstructure of sample with 12,000 cycles, the lamellar cementite in pearlite is fragment into cementite particles with the decrease of depth from surface, and the cementite is dissolved at surface to lead to the form of white etching layer. The ferrite grains are refined gradually and the fraction of high angle grain boundary is increased with the decrease of depth from surface. The nanosgrains layer of ferrite grains with 5 μm thickness is formed. According to the result of finite element simulation of contact surface temperature, the formation of surface nanograins and the dissolution of cementite are caused by the severe plastic deformation. The fiber structure of samples is formed after sliding wear, with direction of .展开更多
In plants,the genome structure of hybrids changes compared with their parents,but the effects of these changes in hybrids remain elusive.Comparing reciprocal crosses between Col×C24 and C24×Col in Arabidopsi...In plants,the genome structure of hybrids changes compared with their parents,but the effects of these changes in hybrids remain elusive.Comparing reciprocal crosses between Col×C24 and C24×Col in Arabidopsis using high-throughput chromosome conformation capture assay(Hi-C)analysis,we found that hybrid three-dimensional(3D)chromatin organization had more long-distance interactions relative to parents,and this was mainly located in promoter regions and enriched in genes with heterosis-related pathways.The interactions between euchromatin and heterochromatin were increased,and the compartment strength decreased in hybrids.In compartment domain(CD)boundaries,the distal interactions were more in hybrids than their parents.In the hybrids of CURLY LEAF(clf)mutants clfCol×clfC24and clfC24×clfCol,the heterosis phenotype was damaged,and the long-distance interactions in hybrids were fewer than in their parents with lower H3K27me3.ChIP-seq data revealed higher levels of H3K27me3 in the region adjacent to the CD boundary and the same interactional homo-trans sites in the wild-type(WT)hybrids,which may have led to more long-distance interactions.In addition,the differentially expressed genes(DEGs)located in the boundaries of CDs and loop regions changed obviously in WT,and the functional enrichment for DEGs was different between WT and clf in the longdistance interactions and loop regions.Our findings may therefore propose a new epigenetic explanation of heterosis in the Arabidopsis hybrids and provide new insights into crop breeding and yield increase.展开更多
Only a few studies have been conducted on the flow behavior of the novel BTW1/Q345R bimetal,which is widely used in coal equipment.In this work,compression tests were conducted on BTW1/Q345R bimetal at a temperature r...Only a few studies have been conducted on the flow behavior of the novel BTW1/Q345R bimetal,which is widely used in coal equipment.In this work,compression tests were conducted on BTW1/Q345R bimetal at a temperature range of 950°C–1200°C and strain rates of 0.05,0.5,5,and 15 s^−1 by using a Gleeble-3800 thermomechanical simulator.A constitutive equation was validated by referring to the Arrhenius equation during the characterization of hot workability.The computed apparent activation energy of the BTW1/Q345R bimetal was 360 kJ/mol,and processing maps under different strain conditions were drawn.Analysis of the stress-strain relationship revealed that work hardening exerted a dominant effect on the thermal deformation of the BTW1/Q345R bimetal.The processing maps predicted that the optimal processing interval will increase with strain.Results showed that thermal deformation of the BTW1/Q345R bimetal should proceed when the temperature range varies from 1182°C to 1200°C and the strain rate interval is from 4.2 to 15 s^−1.展开更多
文摘Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel steel. The results showed that although the roughness of the original specimen induced by mechanical processing would diminish to some extent in the experiment, the 0.5 - 1.5 μm thick layer of ultrafine microstructure on the original mechanically-processed specimen surface would still become micro-cracks and small spalling pits due to spalling, and would further evolve into fatigue crack source. Additionally, even under the impact of the load that was not adequate to make the material reach fatigue limit, the ferrite in the microstructure underwent plastic deformation, which led the refinement of proeutectoid ferrite grains. During the experiment, the hardening and the refinement caused by plastic deformation consisted with the theory that dislocation gave rise to plastic deformation and grain refinement. The distribution laws of hardness and ferrite grain sizes measured could be explained by the distribution law of the shearing stress in the subsurface.
基金Supported by National Natural Science Foundation of China(Grant Nos.U1910213,U1610253,51604181)Shanxi Provincial Key Research and Development Program of China(Grant Nos.201603D111004,201803D121026).
文摘A decrease in the weight of aerospace vehicles,large ships,weapons,and high-speed trains will increase the demand for wide-width magnesium alloy plates and their composite parts to replace steel and plastic.An investigation was conducted to study the variation in deformation behaviors along the transverse direction during the warm rolling of a 1480-mm-wide AZ31B plate.A uniaxial thermal compression test with a 59%reduction was performed at different positions on a 13.7-mm-thick rolled plate along the width direction at a temperature of 220℃ and 270℃ and strain rate of 15 s^(−1).At the same time,the 13.7-mm-thick plate was rolled in a single pass to 5.6 mm on a mill with a 1725-mm-wide roll to confirm the thermal deformation behavior and the dynamic recrystallization(DRX).The results show that the main texture type does not change and the grain size does not have a clear deflection when the magnesium alloy plate reaches a certain value under rolling accumulative reduction.The grain size of a 13.7-mm-thick plate increases with a decrease in the distance to the center layer in the thickness direction.In the width direction,the edge(R6)first decreases and then increases toward the symmetric plane(R1).The critical stress required for dynamic recrystallization in the transition zone R3 of the rolled plate width is minimum,and the average grain size is minimum owing to the relatively complete recrystallization.
文摘In this paper, the surface microstructure and wear property of D2 wheel steel under sliding wear condition were studied by MRH-30 sliding wear tester. After testing, a transmission electron microscope (TEM), scanning electron microscope (SEM) with electron backscatter diffraction (EBSD), and micro-hardness testers were used to characterize the surface microstructure of samples with different cycles. The results show that the wear losss samples are increased as the increase of cycles, and the wear loss of wheel samples is higher than that of rail samples. The surface hardness and thickness of deformation layer of wheel samples are increased as the cycles increase. After sliding wear, the samples surfaces form the white etching layer with the thickness of several microns. Through the analysis of surface microstructure of sample with 12,000 cycles, the lamellar cementite in pearlite is fragment into cementite particles with the decrease of depth from surface, and the cementite is dissolved at surface to lead to the form of white etching layer. The ferrite grains are refined gradually and the fraction of high angle grain boundary is increased with the decrease of depth from surface. The nanosgrains layer of ferrite grains with 5 μm thickness is formed. According to the result of finite element simulation of contact surface temperature, the formation of surface nanograins and the dissolution of cementite are caused by the severe plastic deformation. The fiber structure of samples is formed after sliding wear, with direction of .
基金supported by the Key Program of National Natural Science Foundation of China(32230006 to D.X.W.)the Shandong Development Fund of Science&Technology+2 种基金the Award of Natural Science Foundation of Shandong Province(ZR2021ZD30)China Postdoctoral Science Foundation(8206300443)Boya Postdoctoral Program of Peking University。
文摘In plants,the genome structure of hybrids changes compared with their parents,but the effects of these changes in hybrids remain elusive.Comparing reciprocal crosses between Col×C24 and C24×Col in Arabidopsis using high-throughput chromosome conformation capture assay(Hi-C)analysis,we found that hybrid three-dimensional(3D)chromatin organization had more long-distance interactions relative to parents,and this was mainly located in promoter regions and enriched in genes with heterosis-related pathways.The interactions between euchromatin and heterochromatin were increased,and the compartment strength decreased in hybrids.In compartment domain(CD)boundaries,the distal interactions were more in hybrids than their parents.In the hybrids of CURLY LEAF(clf)mutants clfCol×clfC24and clfC24×clfCol,the heterosis phenotype was damaged,and the long-distance interactions in hybrids were fewer than in their parents with lower H3K27me3.ChIP-seq data revealed higher levels of H3K27me3 in the region adjacent to the CD boundary and the same interactional homo-trans sites in the wild-type(WT)hybrids,which may have led to more long-distance interactions.In addition,the differentially expressed genes(DEGs)located in the boundaries of CDs and loop regions changed obviously in WT,and the functional enrichment for DEGs was different between WT and clf in the longdistance interactions and loop regions.Our findings may therefore propose a new epigenetic explanation of heterosis in the Arabidopsis hybrids and provide new insights into crop breeding and yield increase.
基金This work was supported by the Applied Basic Research Project of Shanxi Province,China(Grant Nos.201701D121078 and 201701D221143)the National Natural Science Foundation of China(Grant No.U1510131).
文摘Only a few studies have been conducted on the flow behavior of the novel BTW1/Q345R bimetal,which is widely used in coal equipment.In this work,compression tests were conducted on BTW1/Q345R bimetal at a temperature range of 950°C–1200°C and strain rates of 0.05,0.5,5,and 15 s^−1 by using a Gleeble-3800 thermomechanical simulator.A constitutive equation was validated by referring to the Arrhenius equation during the characterization of hot workability.The computed apparent activation energy of the BTW1/Q345R bimetal was 360 kJ/mol,and processing maps under different strain conditions were drawn.Analysis of the stress-strain relationship revealed that work hardening exerted a dominant effect on the thermal deformation of the BTW1/Q345R bimetal.The processing maps predicted that the optimal processing interval will increase with strain.Results showed that thermal deformation of the BTW1/Q345R bimetal should proceed when the temperature range varies from 1182°C to 1200°C and the strain rate interval is from 4.2 to 15 s^−1.