Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-depo...Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-deposited and remelted were developed to refine the microstructure and enhance the oxidation resistance of refractory high entropy alloy using electron beam freeform fabrication(EBF3).Finer and short-range ordering structures were observed in the remelted sample,whereas the Al-deposited sample showcased the formation of silicide and intermetallic phases.High-temperature cyclic and isothermal oxidation tests at 1000℃ were carried out.The total weight gain after 60 h of cyclic oxidation decreased by 17.49%and 30.46%for the remelted and deposited samples,respectively,compared to the as-cast state.Oxidation kinetics reveal an evident lower mass gain and oxidation rate in the treated samples.A multilayer oxide consisting of TiO_(2)+Al_(2)O_(3)+SiO_(2)+AlNbO_(4) was studied for its excellent oxidation resistance.The oxidation behavior of rutile,corundum and other oxides was analyzed using first principles calculations and chemical defect analysis.Overall,this research,which introduces novel treatments,offers promising insights for enhancing the inherent oxidation resistance of refractory high entropy alloys.展开更多
Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects ...Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in 3.5 wt.%NaCl and 5 M HCl solutions,respectively,based on open circuit potential(OCP),potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),static immersion tests and surface analysis.Results indicate that increasing annealing tempe rature endows Ti80 alloy with a higher volume fraction ofβphase and finerαphase,which in turn improves its corrosion resistance.Surface characterization demonstrates thatβphase is more resistant to corrosion thanαphase owing to a higher content of Nb,Mo,and Zr in the former;additionally,the decreased thickness of a phase alleviates segregation of elements to further restrain the micro-galvanic couple effects betweenαandβphases.Meanwhile,the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail.As the formation of a highly compact and stable oxide film on surface,annealed Ti80 alloys exhibit a low corrosion current density(10^(-6)A/cm^(2))and high polarization impedance(10^(6)Ω·cm^(2))in 3.5 wt.%NaCl solution.However,they suffer severe corrosion in 5 M HCl solution,resulting from the breakdown of native oxide films(the conversion of TiO_(2)to aqueous Ti^(3+)),active dissolution of substrate Ti to aqueous Ti^(3+)and existence of micro-galvanic couple effects.Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.展开更多
Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfou...Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in hydrochloric acid(HCl)ranging from 1.37 to 7 M,and temperature ranging from 25 to 55℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCl concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCl at 25℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCl solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCl concentration at which Ti80 alloy can maintain passivation at 25℃can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxedαphase is more susceptible to corrosion compared to intergranularβphase due to a lower content of Nb,Mo,and Zr in the former.展开更多
Ni-advanced weathering steel holds paramount importance in marine atmospheric environments,especially those with heightened Cl^(−)concentrations.The meticulous compositional design plays a crucial role in establishing...Ni-advanced weathering steel holds paramount importance in marine atmospheric environments,especially those with heightened Cl^(−)concentrations.The meticulous compositional design plays a crucial role in establishing a rust layer capable of withstanding intrusion by Cl^(−),making it imperative for the viability of coating-free weathering steel in marine atmospheric environments.This study explores the corrosion evolution and corrosion-resistant mechanisms within a steady-state rust layer in 3Ni weathering steel,with a particular focus on the role of Mo in challenging marine atmospheric conditions.The findings unequivocally demonstrate that the augmentation of the protective properties of the rust layer is directly correlated with an increase in Mo content,transitioning from 0.5 to 1.5 wt.%.This transition is most evident in the reduction of the corrosion rate for the 3Ni-Mo steel,dropping from an initial 1.74 mm a^(−1)to a robust 1.31 mm a^(−1)after 768 h of corrosion exposure.The heightened Mo content expedites the formation of a stable and durable rust layer,significantly enriching the proportion ofα-FeOOH within this protective layer.The stabilized rust layer of 3Ni-Mo weathering steel exhibits a distinct three-layer structure,comprising an outer layer primarily ofγ-FeOOH,an intermediate layer mainly composed of Fe_(2)O_(3)/Fe_(3)O_(4),and an inner layer predominantly composed ofα-FeOOH andβ-FeOOH.Additionally,an alkaline interface enriched with NiFe_(2)O_(4)and CuFe_(2)O_(4)develops between the inner layer and the substrate.Firstly,Mo promotes the deposition of MoO_(2),MoO_(3),and molybdate on both the inner layer and alkaline steel-rust interface to repair corrosion pits and fill cracks.Secondly,Mo facilitates the generation of compounds such as NiFe_(2)O_(4)and CuFe_(2)O_(4),which heightens the electronegativity of the intermediate rust layer and the steel-rust interface,preventing Cl^(−)-induced interface acidification and pitting corrosion.The higher Mo content expedites the formation of this alkaline interface and promotes inner layer densification.Most significantly,Mo creates additional nucleation sites for hydroxide oxides through oxide formation,leading to the formation of nano-sizedα-FeOOH andβ-FeOOH within the inner layer thereby enhancing the stability and compactness of the inner layer.These synergistic effects fortify the resilience of 3Ni-Mo advanced weathering steel in corrosive environments,ultimately strengthening its capacity to withstand environmental challenges.展开更多
Comparative studies on Zr35Cu65and Zr65Cu35amorphous systems were performed using molecular dynamic simulations to explore whether their hydrogenated mechanical behavior depends on the content of hydride-forming eleme...Comparative studies on Zr35Cu65and Zr65Cu35amorphous systems were performed using molecular dynamic simulations to explore whether their hydrogenated mechanical behavior depends on the content of hydride-forming elements.Although both of them present an increased strength and ductility after hydrogen microalloying,we observe the improved mechanical behavior for Zr35Cu65is more pronounced than that for Zr65Cu35.In these two samples,the distribution of configurational potential energy and flexibility volume respectively follows a similar H-induced variation tendency;all of the hydrogenated alloys not just have more stable atoms with smaller flexibility volume,but possess a larger fraction of readily activated atoms.However,the atomic-scale details,based on the local"gradient atomic packing structure"model,indicate minor additions of hydrogen can promote more"soft spots"along with more strengthened"backbones"in the low-Zr alloy than that in the high-Zr sample,which endows the former with much higher strength and deformability after hydrogen microalloying.We regard this finding as a further step forward to distilling the tell-tale metrics of the H-dependent mechanical behavior observed in Zr-based metallic glasses.展开更多
Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal st...Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal stress level to induce the martensitic transformation and experiences premature failure before the formation of martensite during tensile testing.By utilizing in situ characterization technologies,in this study,we demonstrate that by fabricating a NiTi sample with complete<001>_(B2) texture using wire-fed electron beam directed energy deposition,a sluggish martensitic transformation can be achieved to re-tard the initiation of fracture under tensile loading.To discern the origins of this tensile response,we combine experiments with molecular dynamics simulations to systematically analyze the micro-scale de-tails on how internal lattice defects can select the variety of martensite variants.Using both quasi in situ transmission electron microscopy analysis and calculations of the different atomic configurations,our results indicate that the pre-existing precipitates and accumulated dislocation defects,rather than columnar boundaries,can have a positive influence on the sluggish formation of variants that can cou-ple with plastic deformation within a much wider stress interval.Specifically,only the variant favored by both internal strain/stress fluctuations around local defects and external tensile load will overcome the high-energy transition barrier of<001>_(B2)-oriented tension to nucleate and grow sluggishly.The cur-rent findings not only show how the mechanical responses can be controlled in additively manufactured NiTi alloys with<001>_(B2) texture,but also regard this understanding to be a step forward in decoding the salient underlying mechanisms for the correlating texture,defects,and phase transformation of these functional materials.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0609000)National Natural Science Foundation of China(Grant Nos.52171034 and 52101037)Postdoctoral Fellowship Program of CPSFara(No.GZB20230944).
文摘Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-deposited and remelted were developed to refine the microstructure and enhance the oxidation resistance of refractory high entropy alloy using electron beam freeform fabrication(EBF3).Finer and short-range ordering structures were observed in the remelted sample,whereas the Al-deposited sample showcased the formation of silicide and intermetallic phases.High-temperature cyclic and isothermal oxidation tests at 1000℃ were carried out.The total weight gain after 60 h of cyclic oxidation decreased by 17.49%and 30.46%for the remelted and deposited samples,respectively,compared to the as-cast state.Oxidation kinetics reveal an evident lower mass gain and oxidation rate in the treated samples.A multilayer oxide consisting of TiO_(2)+Al_(2)O_(3)+SiO_(2)+AlNbO_(4) was studied for its excellent oxidation resistance.The oxidation behavior of rutile,corundum and other oxides was analyzed using first principles calculations and chemical defect analysis.Overall,this research,which introduces novel treatments,offers promising insights for enhancing the inherent oxidation resistance of refractory high entropy alloys.
基金supported by the National Key Research and Development Program of China(2016YFB0301201)the Yunnan Rare Metal Materials Genetic Engineering Project(2018ZE013)the National Natural Science Foundation of China(51425402 and 51671073)。
文摘Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in 3.5 wt.%NaCl and 5 M HCl solutions,respectively,based on open circuit potential(OCP),potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),static immersion tests and surface analysis.Results indicate that increasing annealing tempe rature endows Ti80 alloy with a higher volume fraction ofβphase and finerαphase,which in turn improves its corrosion resistance.Surface characterization demonstrates thatβphase is more resistant to corrosion thanαphase owing to a higher content of Nb,Mo,and Zr in the former;additionally,the decreased thickness of a phase alleviates segregation of elements to further restrain the micro-galvanic couple effects betweenαandβphases.Meanwhile,the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail.As the formation of a highly compact and stable oxide film on surface,annealed Ti80 alloys exhibit a low corrosion current density(10^(-6)A/cm^(2))and high polarization impedance(10^(6)Ω·cm^(2))in 3.5 wt.%NaCl solution.However,they suffer severe corrosion in 5 M HCl solution,resulting from the breakdown of native oxide films(the conversion of TiO_(2)to aqueous Ti^(3+)),active dissolution of substrate Ti to aqueous Ti^(3+)and existence of micro-galvanic couple effects.Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.
基金the National Key Research and Development Program of China(No.2016YFB0301201)the Yunnan Rare Metal Materials Genetic Engineering Project(No.2018ZE013)the National Natural Science Foundation of China(Nos.51425402 and 51671073)。
文摘Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in hydrochloric acid(HCl)ranging from 1.37 to 7 M,and temperature ranging from 25 to 55℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCl concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCl at 25℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCl solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCl concentration at which Ti80 alloy can maintain passivation at 25℃can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxedαphase is more susceptible to corrosion compared to intergranularβphase due to a lower content of Nb,Mo,and Zr in the former.
基金the National Key R&D Program of China(No.2021YFB3701700)Gang Niu appreciates the support from the National Natural Science Foundation of China(No.52304389)+2 种基金Gang Niu and Huibin Wu appreciate the support from the Fundamental Research Funds for the Central Universities(No.FRFBD-23-01)Gang Niu appreciates the support from the China Postdoctoral Science Foundation(No.2022M720402)Na Gong appreciates the support from the Structural Metal Alloy Program(SMAP),Grant No.A18B1b0061,and Manufacturing of Multi-Material Net-Shape Parts with Heterogeneous Properties(MMNH),Grantno.M22K5a0045 inA∗STAR.
文摘Ni-advanced weathering steel holds paramount importance in marine atmospheric environments,especially those with heightened Cl^(−)concentrations.The meticulous compositional design plays a crucial role in establishing a rust layer capable of withstanding intrusion by Cl^(−),making it imperative for the viability of coating-free weathering steel in marine atmospheric environments.This study explores the corrosion evolution and corrosion-resistant mechanisms within a steady-state rust layer in 3Ni weathering steel,with a particular focus on the role of Mo in challenging marine atmospheric conditions.The findings unequivocally demonstrate that the augmentation of the protective properties of the rust layer is directly correlated with an increase in Mo content,transitioning from 0.5 to 1.5 wt.%.This transition is most evident in the reduction of the corrosion rate for the 3Ni-Mo steel,dropping from an initial 1.74 mm a^(−1)to a robust 1.31 mm a^(−1)after 768 h of corrosion exposure.The heightened Mo content expedites the formation of a stable and durable rust layer,significantly enriching the proportion ofα-FeOOH within this protective layer.The stabilized rust layer of 3Ni-Mo weathering steel exhibits a distinct three-layer structure,comprising an outer layer primarily ofγ-FeOOH,an intermediate layer mainly composed of Fe_(2)O_(3)/Fe_(3)O_(4),and an inner layer predominantly composed ofα-FeOOH andβ-FeOOH.Additionally,an alkaline interface enriched with NiFe_(2)O_(4)and CuFe_(2)O_(4)develops between the inner layer and the substrate.Firstly,Mo promotes the deposition of MoO_(2),MoO_(3),and molybdate on both the inner layer and alkaline steel-rust interface to repair corrosion pits and fill cracks.Secondly,Mo facilitates the generation of compounds such as NiFe_(2)O_(4)and CuFe_(2)O_(4),which heightens the electronegativity of the intermediate rust layer and the steel-rust interface,preventing Cl^(−)-induced interface acidification and pitting corrosion.The higher Mo content expedites the formation of this alkaline interface and promotes inner layer densification.Most significantly,Mo creates additional nucleation sites for hydroxide oxides through oxide formation,leading to the formation of nano-sizedα-FeOOH andβ-FeOOH within the inner layer thereby enhancing the stability and compactness of the inner layer.These synergistic effects fortify the resilience of 3Ni-Mo advanced weathering steel in corrosive environments,ultimately strengthening its capacity to withstand environmental challenges.
基金National Key Research and Development Program of China2016YFB0301201National Natural Science Foundation of China51425402,51371066,51671073。
文摘Comparative studies on Zr35Cu65and Zr65Cu35amorphous systems were performed using molecular dynamic simulations to explore whether their hydrogenated mechanical behavior depends on the content of hydride-forming elements.Although both of them present an increased strength and ductility after hydrogen microalloying,we observe the improved mechanical behavior for Zr35Cu65is more pronounced than that for Zr65Cu35.In these two samples,the distribution of configurational potential energy and flexibility volume respectively follows a similar H-induced variation tendency;all of the hydrogenated alloys not just have more stable atoms with smaller flexibility volume,but possess a larger fraction of readily activated atoms.However,the atomic-scale details,based on the local"gradient atomic packing structure"model,indicate minor additions of hydrogen can promote more"soft spots"along with more strengthened"backbones"in the low-Zr alloy than that in the high-Zr sample,which endows the former with much higher strength and deformability after hydrogen microalloying.We regard this finding as a further step forward to distilling the tell-tale metrics of the H-dependent mechanical behavior observed in Zr-based metallic glasses.
基金supported by the National Natural Science Foundation of China(Nos.52101037,52401040 and 52171034)the Postdoctoral Fellowship Program of CPSF(No.GZB20230944)with the computational resources provided by LvLiang Cloud Comput-ing Center.
文摘Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal stress level to induce the martensitic transformation and experiences premature failure before the formation of martensite during tensile testing.By utilizing in situ characterization technologies,in this study,we demonstrate that by fabricating a NiTi sample with complete<001>_(B2) texture using wire-fed electron beam directed energy deposition,a sluggish martensitic transformation can be achieved to re-tard the initiation of fracture under tensile loading.To discern the origins of this tensile response,we combine experiments with molecular dynamics simulations to systematically analyze the micro-scale de-tails on how internal lattice defects can select the variety of martensite variants.Using both quasi in situ transmission electron microscopy analysis and calculations of the different atomic configurations,our results indicate that the pre-existing precipitates and accumulated dislocation defects,rather than columnar boundaries,can have a positive influence on the sluggish formation of variants that can cou-ple with plastic deformation within a much wider stress interval.Specifically,only the variant favored by both internal strain/stress fluctuations around local defects and external tensile load will overcome the high-energy transition barrier of<001>_(B2)-oriented tension to nucleate and grow sluggishly.The cur-rent findings not only show how the mechanical responses can be controlled in additively manufactured NiTi alloys with<001>_(B2) texture,but also regard this understanding to be a step forward in decoding the salient underlying mechanisms for the correlating texture,defects,and phase transformation of these functional materials.
