In the present study,a single parameter governing the substructure and the strengthening for martensitic transformation was tentatively explored by detailing the microstructure and the strengthening of a Fe15 wt.%Cr b...In the present study,a single parameter governing the substructure and the strengthening for martensitic transformation was tentatively explored by detailing the microstructure and the strengthening of a Fe15 wt.%Cr binary alloy subjected to thermal cycle under high pressure(cooled at 10℃ s^(-1) from 1050℃ under hydrostatic pressure of 1.0-4.0 GPa).Experimental results show that high pressure makes martensitic transformation occur in a Fe-15Cr alloy that traditionally has no high-temperature austenite under atmospheric pressure.The phase transformation begins with the pairing of twinned variants,and the strengthening is solely dependent upon the density of dislocations and variants.The austenite strength at the transformation temperature governs the substructure and the induced strengthening by influencing:(1)The critical size below which twinned variants are solely allowed;(2)the orientation spreading of the pioneer twinned variants toward Bain pairs;(3)the variant thickness and in turn the strengthening extent.The present study sheds light on tuning the substructure and hardening during martensitic transformation via the austenite strength,showing potential scientific and technological importance.展开更多
A simple powder forging process was presented herein to fabricate an Fe-14 Cr-4.5 Al-2 W-0.4 Ti-0.5 Y_(2)O_(3)ODS Fe Cr Al alloy.The forged alloy exhibits a high density that exceeds 97%of the theoretical density.The ...A simple powder forging process was presented herein to fabricate an Fe-14 Cr-4.5 Al-2 W-0.4 Ti-0.5 Y_(2)O_(3)ODS Fe Cr Al alloy.The forged alloy exhibits a high density that exceeds 97%of the theoretical density.The ODS alloy was investigated in terms of the residual porosity,morphology and phase structure of oxide nanoparticles,impact toughness and tensile properties.It was found that refined grains were obtained during powder forging.A residual porosity less than 1.1%has no impact on the precipitation of oxide nanoparticles.The average diameter of the oxide particles is 7.99 nm,with a number density of 2.75×10^(22)m^(-3).Almost all of the oxides are identified as orthorhombic YAl O3 particles.The refined grains and uniformly distributed oxide nanoparticles enable the alloy to show excellent mechanical strength and ductility below 700℃,and enable the ductile-to-brittle transition temperature to be close to room temperature.However,a slight decrease in strength at 1000℃and the Charpy upper shelf energy has been suggested to be due to the residual porosity.These results indicate that powder forging can be used as a promising technique for the fabrication of ODS alloys.展开更多
A low carbon hypoeutectoid steel(0.19 wt%C)with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding(PISG)at room temperature.The deformation m...A low carbon hypoeutectoid steel(0.19 wt%C)with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding(PISG)at room temperature.The deformation microstructures for each component were systematically characterized along depth,and the patterns of structural evolution toward nanometer regime as well as the governing parameters were addressed.Proeutectoid ferrite grains were refined down to 17 nm,and the pattern covering a length scale of 4–5 orders of magnitude from micron-to nanometer-scale follows:formation of cellular dislocation structure(CDS),elongated dislocation structure(EDS),ultrafine lamellar structure(UFL)and finally the nanolaminated structure(NL).The pearlite experiences the deformation and refinement,and finally the transforming the ultrafine pearlite(UFP)into nanolaminated pearlite(NLP)with the ferrite lamellae as thin as 20 nm.Refinement for both UFL(UFP)and NL(NLP)can be realized via forming novel extended boundaries within ferrite lamellae.A critical lattice curvature of~2.8°is required for forming such extended boundary,corresponding to a minimum strain gradient of 0.25μm^(-1)for a 100 nm-thick lamella.Refinement below size limit(expressed by lamellar thickness d_Tin nm)is correlated with the strain gradient(χ,inμm^(-1))by:d_T=12.5/x.Refinement contributions from strain gradient caused by PISG processing and material heterogeneity were discussed.展开更多
Noble nanometals are of significance in both scientific interest and technological applications,which are usually obtained by conventional wet-chemical synthesis.Organic surfactants are always used in the synthesis to...Noble nanometals are of significance in both scientific interest and technological applications,which are usually obtained by conventional wet-chemical synthesis.Organic surfactants are always used in the synthesis to prevent unexpected overgrowth and aggregation of noble nanometals.However,the surfactants are hard to remove and may interfere with plasmonic and catalytic studies,remaining surfactant-free synthesis of noble nanometals a challenge.Herein,we report an approach to epitaxial growth of sizecontrolled noble nanometals on MXenes.As piloted by density functional theory calculations,along with work function experimental determination,kinetic and spectroscopic studies,epitaxial growth of noble nanometals is initiated via a mechanism that involves an in situ redox reaction.In the redox,MXenes as two-dimensional solid reductants whose work functions are compatible with the reduction potentials of noble metal cations,enable spontaneous donation of electrons from the MXenes to noble metal cations and reduce the cations into nanoscale metallic metals on the outmost surface of MXenes.Neither surfactants nor external reductants are used during the whole synthesis process,which addresses a long-standing interference issue of surfactant and external reductant in the conventional wet-chemical synthesis.Moreover,the MXenes induced noble nanometals are size-controlled.Impressively,noble nanometals firmly anchored on MXenes exhibit excellent performance towards surface enhanced Raman scattering.Our developed strategy will promote the nanostructure-controlled synthesis of noble nanometals,offering new opportunities to further improve advanced functional properties towards practical applications.展开更多
基金supported by the Hundred Outstanding Creative Talents Projects at Hebei University,ChinaThe Natural Science Foundation-Steel and Iron Foundation of Hebei Province(No.E2021203051).
文摘In the present study,a single parameter governing the substructure and the strengthening for martensitic transformation was tentatively explored by detailing the microstructure and the strengthening of a Fe15 wt.%Cr binary alloy subjected to thermal cycle under high pressure(cooled at 10℃ s^(-1) from 1050℃ under hydrostatic pressure of 1.0-4.0 GPa).Experimental results show that high pressure makes martensitic transformation occur in a Fe-15Cr alloy that traditionally has no high-temperature austenite under atmospheric pressure.The phase transformation begins with the pairing of twinned variants,and the strengthening is solely dependent upon the density of dislocations and variants.The austenite strength at the transformation temperature governs the substructure and the induced strengthening by influencing:(1)The critical size below which twinned variants are solely allowed;(2)the orientation spreading of the pioneer twinned variants toward Bain pairs;(3)the variant thickness and in turn the strengthening extent.The present study sheds light on tuning the substructure and hardening during martensitic transformation via the austenite strength,showing potential scientific and technological importance.
基金financially supported by National Defense Science and Technology Industry Nuclear Material Technology Innovation Center Project(No.ICNM-2020-ZH-17)。
文摘A simple powder forging process was presented herein to fabricate an Fe-14 Cr-4.5 Al-2 W-0.4 Ti-0.5 Y_(2)O_(3)ODS Fe Cr Al alloy.The forged alloy exhibits a high density that exceeds 97%of the theoretical density.The ODS alloy was investigated in terms of the residual porosity,morphology and phase structure of oxide nanoparticles,impact toughness and tensile properties.It was found that refined grains were obtained during powder forging.A residual porosity less than 1.1%has no impact on the precipitation of oxide nanoparticles.The average diameter of the oxide particles is 7.99 nm,with a number density of 2.75×10^(22)m^(-3).Almost all of the oxides are identified as orthorhombic YAl O3 particles.The refined grains and uniformly distributed oxide nanoparticles enable the alloy to show excellent mechanical strength and ductility below 700℃,and enable the ductile-to-brittle transition temperature to be close to room temperature.However,a slight decrease in strength at 1000℃and the Charpy upper shelf energy has been suggested to be due to the residual porosity.These results indicate that powder forging can be used as a promising technique for the fabrication of ODS alloys.
基金the Hundred Outstanding Creative Talents Projects in Hebei University,Chinathe Project Program of Heavy Machinery Collaborative Innovation CenterChina and the National Natural Science Foundation of China(No.51171182)。
文摘A low carbon hypoeutectoid steel(0.19 wt%C)with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding(PISG)at room temperature.The deformation microstructures for each component were systematically characterized along depth,and the patterns of structural evolution toward nanometer regime as well as the governing parameters were addressed.Proeutectoid ferrite grains were refined down to 17 nm,and the pattern covering a length scale of 4–5 orders of magnitude from micron-to nanometer-scale follows:formation of cellular dislocation structure(CDS),elongated dislocation structure(EDS),ultrafine lamellar structure(UFL)and finally the nanolaminated structure(NL).The pearlite experiences the deformation and refinement,and finally the transforming the ultrafine pearlite(UFP)into nanolaminated pearlite(NLP)with the ferrite lamellae as thin as 20 nm.Refinement for both UFL(UFP)and NL(NLP)can be realized via forming novel extended boundaries within ferrite lamellae.A critical lattice curvature of~2.8°is required for forming such extended boundary,corresponding to a minimum strain gradient of 0.25μm^(-1)for a 100 nm-thick lamella.Refinement below size limit(expressed by lamellar thickness d_Tin nm)is correlated with the strain gradient(χ,inμm^(-1))by:d_T=12.5/x.Refinement contributions from strain gradient caused by PISG processing and material heterogeneity were discussed.
基金supported by the National Natural Science Foundation of China(No.51972310)the Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences(CAS)+1 种基金the Youth Innovation Promotion Association,CAS(No.2011152)the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase)(No.U1501501).
文摘Noble nanometals are of significance in both scientific interest and technological applications,which are usually obtained by conventional wet-chemical synthesis.Organic surfactants are always used in the synthesis to prevent unexpected overgrowth and aggregation of noble nanometals.However,the surfactants are hard to remove and may interfere with plasmonic and catalytic studies,remaining surfactant-free synthesis of noble nanometals a challenge.Herein,we report an approach to epitaxial growth of sizecontrolled noble nanometals on MXenes.As piloted by density functional theory calculations,along with work function experimental determination,kinetic and spectroscopic studies,epitaxial growth of noble nanometals is initiated via a mechanism that involves an in situ redox reaction.In the redox,MXenes as two-dimensional solid reductants whose work functions are compatible with the reduction potentials of noble metal cations,enable spontaneous donation of electrons from the MXenes to noble metal cations and reduce the cations into nanoscale metallic metals on the outmost surface of MXenes.Neither surfactants nor external reductants are used during the whole synthesis process,which addresses a long-standing interference issue of surfactant and external reductant in the conventional wet-chemical synthesis.Moreover,the MXenes induced noble nanometals are size-controlled.Impressively,noble nanometals firmly anchored on MXenes exhibit excellent performance towards surface enhanced Raman scattering.Our developed strategy will promote the nanostructure-controlled synthesis of noble nanometals,offering new opportunities to further improve advanced functional properties towards practical applications.
