In this investigation,we examined the high-temperature corrosion behavior of three nickel-based single-crystal superalloys subjected to a mixed molten salt environment of Na_(2)SO_(4)and NaCl at 700℃,leading to a pre...In this investigation,we examined the high-temperature corrosion behavior of three nickel-based single-crystal superalloys subjected to a mixed molten salt environment of Na_(2)SO_(4)and NaCl at 700℃,leading to a preliminary elucidation of their molten salt corrosion mechanisms.By further comparing the corrosion degree of the three nickel-based single-crystal superalloys combined with the Gibbs free energy calculation of the corrosion products,the influence of alloying elements on the corrosion performance of nickel-based single-crystal superalloys was analyzed.It was established that the corrosion mechanism of these nickel-based single-crystal superalloys predominantly involves a cyclic process of oxide layer formation and decomposition,ultimately resulting in the establishment of a protective layer principally composed of NiO,with a constantly regenerating Al2O3 barrier,impeding further alloy degradation.Furthermore,the inclusion of elements such as Cr,Al,Ta,and notably Re has been found to markedly improve the thermal corrosion resistance of the superalloys.These insights not only enhance our comprehension of the corrosion mechanisms pertinent to nickel-based superalloys,but also provide strategic directions for alloy composition refinement aimed at bolstering their corrosion resilience.展开更多
An experimental study was carried out to investigat e the influence of temperatures on workpiece surface integrity in surface grinding of a cast nickel-based superalloy with alumina abrasive wheels. Temperatur e respo...An experimental study was carried out to investigat e the influence of temperatures on workpiece surface integrity in surface grinding of a cast nickel-based superalloy with alumina abrasive wheels. Temperatur e response at the wheel-workpiece interface was measured using a grindable foil /workpiece thermocouple. Specimens with different grinding temperatures were obt ained through changing grinding conditions including depth of cut, workpiece fee d speed, and coolant supply. Changes in surface roughness, residual stress, meta llographies, ground surface morphology, and micro hardness on the specimens were then analyzed. Bending fatigue tests were separately conducted at room temperat ure and 950oC in an effort to evaluate the influence of temperatures on the serv ice life of the ground specimens. A different burning color was found on the gro und workpiece surfaces when grinding temperatures are over a critical value. Alo ng with the emergence of burning color, roughness of the ground workpiece surfac e increased greatly compared with the surfaces without burning color, which was attributed to the plastically deformed coatings on the workpiece surface with el evated temperatures. Excepting the surface roughness, other items concerning the surface integrity of the ground workpiece were not affected by temperatures pro vided that grinding temperatures are not high enough to cause grinding cracks. B ased on the findings in this study, the grinding of the nickel-based superalloy can be divided into two stages in order to increase production efficiency, in which case the first stage is to reach an high material removal rate without concerning of the presence of burning color, whereas the second stage is to remo ve the plastically deformed coatings in order to decrease surface roughness.展开更多
The single crystal of nickel-base super alloy is widely used for making turbine blades.The microstructure of the alloy,especially the deviation of preferred orientation of single crystal,possesses the most important e...The single crystal of nickel-base super alloy is widely used for making turbine blades.The microstructure of the alloy,especially the deviation of preferred orientation of single crystal,possesses the most important effects on the mechanical properties of the blades.In this study,the single crystal ingot and blade of DZ417G alloy are prepared by means of the spiral crystal selector as well as the directional solidification method,and the effect of the parameters(i.e.,the shape of samples,the withdrawal rate)and the structure of the spiral crystal selector on the formation of single crystal and the crystal orientation are investigated.This method can prepare not only the single crystal ingot with simple shape but also the single crystal blades with the complex shape,the simple with rod-shape can form the single crystal easily with a relatively fast withdrawal rate,but the blade with complex shape requires much slower withdrawal rate to form single crystal.The length of the crystal selector almost has no effect on the crystal orientation.However,the angle of selector plays an obvious role on the orientation;the selector with a smaller angle can effectively reduce the deviation of preferred orientation;the appropriate angle of selector to obtain optimal orientation is found to be around30°and the deviation of preferred orientation is about30°for this selector.展开更多
After a standard heat treatment,the microstructural evolution with time during isothermal aging at 850°C and its effect on the creep rupture properties of the Ni-base superalloy M4706 at 870°C and 370 MPa ar...After a standard heat treatment,the microstructural evolution with time during isothermal aging at 850°C and its effect on the creep rupture properties of the Ni-base superalloy M4706 at 870°C and 370 MPa are investigated.It is found that as the aging time increases from 0 to 5000 h,the average diameter of coarseγ′increases from 241 to 484 nm,and the distribution of the carbides at grain boundaries changes from discontinuous to continuous.Moreover,experimental observations on the microstructures of all the crept specimens reveal that dislocation bypassing controls the creep deformation.Thus,it is concluded that the transitions in the microstructures result in the degeneration of the creep rupture properties of the experimental alloy with aging time.展开更多
The apparent activation energy for deformation(Q)and strain rate sensitivity(m)of GH4586 superalloy are calculated and the variation trend is reasonably explained by the microstructure observations.Constitutive modell...The apparent activation energy for deformation(Q)and strain rate sensitivity(m)of GH4586 superalloy are calculated and the variation trend is reasonably explained by the microstructure observations.Constitutive modelling of this superalloy is established and the processing maps at different strains are constructed.The results show that the Q value is in the range of 751.22−878.29 kJ/mol.At a temperature of 1060°C,strain rate of 0.001 s^(−1),and strain of 0.65,the m value of GH4586 superalloy reaches a maximum of 0.42.The optimal processing parameter of GH4586 superalloy is at a deformation temperature of 1050°C and a strain rate of 0.001 s^(−1).The domains of flow instability notably expand with increasing strain during high temperature deformation of GH4586 superalloy.展开更多
The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces h...The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces has an effective role in the fatigue strength and ductility of the alloys.In the present work,the effect of prior cyclic oxidation on the high temperature low cycle fatigue(HTLCF)properties of nickel-based superalloy Rene®80 has been assessed in the uncoated state and in the Pt-aluminide(Pt-Al)coated condition at 930℃.To apply cyclic oxidation,simulation of engine thermal exposure was carried out by exposing coated and uncoated fatigue specimens in the burner rig(120 cycles at 1100℃).The cyclic oxidation procedure led to a changing in the coating microstructure from the dual-phase(ξ-PtAl_(2)+β-(Ni,Pt)Al)to single phase(β-(Ni,Pt)Al).Results of HTLCF tests showed an improvement in the HTLCF life around 11.5%in the unexposed coated specimen(pre-cyclic oxidation)as compared to unexposed bare specimen,while this rise for exposed coated specimen(post-cyclic oxidation)was only 5%.Although a mixed mode fracture morphology(ductile and brittle)was observed on the fracture surfaces of failed specimens,the wider regions of brittle fracture belonged to exposed coated/uncoated ones.展开更多
Three experimental single crystal superalloys with 0%Nb,0.5%Nb,1.0%Nb were cast in the directionally solidified furnace,while other alloying element contents were basically kept unchanged.The effect of Nb on the micro...Three experimental single crystal superalloys with 0%Nb,0.5%Nb,1.0%Nb were cast in the directionally solidified furnace,while other alloying element contents were basically kept unchanged.The effect of Nb on the microstructure,stability at1100°C and stress rupture properties at 1070°C and 160 MPa of the single crystal superalloy were investigated.The experiment results show that the primary dendrite arm spacing decreases and the volume fraction ofγ/γ′eutectic of the alloy increases with the increase of Nb content in the as-cast microstructures.The size ofγ′phase particles becomes small and uniform and the cubic shape does not obviously change with the increase of Nb content.The precipitating rate and volume fraction of TCP phases increase significantly with the increase of Nb content in the process of long term aging at 1100°C.The stress rupture lives increase and elongation decreases with increasing Nb content at 1070°C/160 MPa.At last,the relationship between the microstructures stability,stress rupture properties of the alloy and Nb content is discussed based on JMat Pro software and the lastest relevant database for single crystal superalloy.展开更多
The effect of electromagnetic stirring on the inner quality of K417 superalloy ingots is studied with EPMA and optical microscope.The results show that while an electromagnetic stirring with 50Hz frequency and 80A cur...The effect of electromagnetic stirring on the inner quality of K417 superalloy ingots is studied with EPMA and optical microscope.The results show that while an electromagnetic stirring with 50Hz frequency and 80A current is imposed,the equiax crystals of K417 superalloy ingots can be effectively refined and increased,and the central shrinkage porosity and the dendritic segregation of K417 superalloy ingots are greatly reduced,so the inner quality of K417 superalloy ingots is obviously improved.展开更多
The oxidation behaviors of Ni-16Cr-xAl （x=4.5%, 9.0%, mass fraction） superalloy foams in air at 1000℃ were investigated. The effects of AI content on the resistance to high temperature oxidation were examined. The ...The oxidation behaviors of Ni-16Cr-xAl （x=4.5%, 9.0%, mass fraction） superalloy foams in air at 1000℃ were investigated. The effects of AI content on the resistance to high temperature oxidation were examined. The oxidation mechanisms of the foams were discussed. The results show that the resistance to the oxidation of the Ni-16Cr-xA1 based alloy at 1 000 ℃ increases with the content of A1 increasing from 4.5% to 9.0%. Complex oxide products are formed on the surface of the superalloy foams after the oxidation. Cr203 and A1203 are the predominant oxides for the scales of the foams with 4.5% A1 and 9% A1, respectively. Excellent high temperature oxidation resistance and superior pore conformation stability for the Ni-16Cr-xA1 based superalloy foam with 9% A1 can be mainly attributed to the formation of relatively continuous and protective A1203 oxides on the surface of the foam.展开更多
Non-metallic inclusions,especially the large ones,within P/M Ni-base superalloy have a major influence on fatigue characteristics,but are not directly measurable by routine inspection.In this paper,a method,automatic ...Non-metallic inclusions,especially the large ones,within P/M Ni-base superalloy have a major influence on fatigue characteristics,but are not directly measurable by routine inspection.In this paper,a method,automatic image analysis,is proposed for estimation of the content,size and amount of non-metallic inclusions in superalloy.The methodology for the practical application of this method is described and the factors affecting the precision of the estimation are discussed.In the experiment,the characteristics of the non-metallic inclusions in Ni-base P/M superalloy are analyzed.展开更多
High-temperature Ni-based alloys are widely used in the aerospace field due to their excellent properties,but the shortcomings of brittle fracture at the grain boundaries and poor plasticity at room temperature also l...High-temperature Ni-based alloys are widely used in the aerospace field due to their excellent properties,but the shortcomings of brittle fracture at the grain boundaries and poor plasticity at room temperature also limit their development to a certain extent.Researchers found that there areγ′precipitation phases similar to Ni_(3)Al in Pt-Al based alloys.In this paper,the CASTEP code of Materials Studio software package is used to simulate the thermal and mechanical properties ofγ′-Pt_(3)Al phase andγ′-Ni_(3)Al phase.By comparing the performance characteristics of the electronic structure,mechanical properties and point defect structure of the two,it is found that the stability,elastic deformation resistance and high temperature creep resistance of theγ′-Pt_(3)Al phase are better than those of theγ′-Ni_(3)Al phase.This will provide theoretical guidance for promoting the development of Pt-Al-based high-temperature materials.展开更多
基金Project(2022QNRC001) supported by the Young Elite Scientists Sponsorship Program by China Association for Science and TechnologyProject supported by the State Key Laboratory of Powder Metallurgy,China。
文摘In this investigation,we examined the high-temperature corrosion behavior of three nickel-based single-crystal superalloys subjected to a mixed molten salt environment of Na_(2)SO_(4)and NaCl at 700℃,leading to a preliminary elucidation of their molten salt corrosion mechanisms.By further comparing the corrosion degree of the three nickel-based single-crystal superalloys combined with the Gibbs free energy calculation of the corrosion products,the influence of alloying elements on the corrosion performance of nickel-based single-crystal superalloys was analyzed.It was established that the corrosion mechanism of these nickel-based single-crystal superalloys predominantly involves a cyclic process of oxide layer formation and decomposition,ultimately resulting in the establishment of a protective layer principally composed of NiO,with a constantly regenerating Al2O3 barrier,impeding further alloy degradation.Furthermore,the inclusion of elements such as Cr,Al,Ta,and notably Re has been found to markedly improve the thermal corrosion resistance of the superalloys.These insights not only enhance our comprehension of the corrosion mechanisms pertinent to nickel-based superalloys,but also provide strategic directions for alloy composition refinement aimed at bolstering their corrosion resilience.
文摘An experimental study was carried out to investigat e the influence of temperatures on workpiece surface integrity in surface grinding of a cast nickel-based superalloy with alumina abrasive wheels. Temperatur e response at the wheel-workpiece interface was measured using a grindable foil /workpiece thermocouple. Specimens with different grinding temperatures were obt ained through changing grinding conditions including depth of cut, workpiece fee d speed, and coolant supply. Changes in surface roughness, residual stress, meta llographies, ground surface morphology, and micro hardness on the specimens were then analyzed. Bending fatigue tests were separately conducted at room temperat ure and 950oC in an effort to evaluate the influence of temperatures on the serv ice life of the ground specimens. A different burning color was found on the gro und workpiece surfaces when grinding temperatures are over a critical value. Alo ng with the emergence of burning color, roughness of the ground workpiece surfac e increased greatly compared with the surfaces without burning color, which was attributed to the plastically deformed coatings on the workpiece surface with el evated temperatures. Excepting the surface roughness, other items concerning the surface integrity of the ground workpiece were not affected by temperatures pro vided that grinding temperatures are not high enough to cause grinding cracks. B ased on the findings in this study, the grinding of the nickel-based superalloy can be divided into two stages in order to increase production efficiency, in which case the first stage is to reach an high material removal rate without concerning of the presence of burning color, whereas the second stage is to remo ve the plastically deformed coatings in order to decrease surface roughness.
基金Project(51074105)supported by the National Natural Science Foundation of ChinaProjects(08DZ1130100,10520706400)supported by the Science and Technology Commission of Shanghai Municipality,ChinaProject(2007CB613606)supported by the National Basic Research Program of China
文摘The single crystal of nickel-base super alloy is widely used for making turbine blades.The microstructure of the alloy,especially the deviation of preferred orientation of single crystal,possesses the most important effects on the mechanical properties of the blades.In this study,the single crystal ingot and blade of DZ417G alloy are prepared by means of the spiral crystal selector as well as the directional solidification method,and the effect of the parameters(i.e.,the shape of samples,the withdrawal rate)and the structure of the spiral crystal selector on the formation of single crystal and the crystal orientation are investigated.This method can prepare not only the single crystal ingot with simple shape but also the single crystal blades with the complex shape,the simple with rod-shape can form the single crystal easily with a relatively fast withdrawal rate,but the blade with complex shape requires much slower withdrawal rate to form single crystal.The length of the crystal selector almost has no effect on the crystal orientation.However,the angle of selector plays an obvious role on the orientation;the selector with a smaller angle can effectively reduce the deviation of preferred orientation;the appropriate angle of selector to obtain optimal orientation is found to be around30°and the deviation of preferred orientation is about30°for this selector.
基金Project(2018BSHQYXMZZ32)supported by the Postdoctoral Science Foundation of Shaanxi Province of ChinaProject(20192109)supported by the State Key Laboratory for Mechanical Behavior of Materials,ChinaProjects(2017M623213,2018M633487)supported by the Postdoctoral Science Foundation of China
文摘After a standard heat treatment,the microstructural evolution with time during isothermal aging at 850°C and its effect on the creep rupture properties of the Ni-base superalloy M4706 at 870°C and 370 MPa are investigated.It is found that as the aging time increases from 0 to 5000 h,the average diameter of coarseγ′increases from 241 to 484 nm,and the distribution of the carbides at grain boundaries changes from discontinuous to continuous.Moreover,experimental observations on the microstructures of all the crept specimens reveal that dislocation bypassing controls the creep deformation.Thus,it is concluded that the transitions in the microstructures result in the degeneration of the creep rupture properties of the experimental alloy with aging time.
基金Project(2020JC-17)supported by the Science Fund for Distinguished Young Scholars from Shaanxi Province,ChinaProject(51705425)+4 种基金supported by the National Natural Science Foundation of ChinaProject(2019-QZ-04)supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),ChinaProjects(3102019PY007,3102019MS0403)supported by the Fundamental Research Funds for the Central Universities,China。
文摘The apparent activation energy for deformation(Q)and strain rate sensitivity(m)of GH4586 superalloy are calculated and the variation trend is reasonably explained by the microstructure observations.Constitutive modelling of this superalloy is established and the processing maps at different strains are constructed.The results show that the Q value is in the range of 751.22−878.29 kJ/mol.At a temperature of 1060°C,strain rate of 0.001 s^(−1),and strain of 0.65,the m value of GH4586 superalloy reaches a maximum of 0.42.The optimal processing parameter of GH4586 superalloy is at a deformation temperature of 1050°C and a strain rate of 0.001 s^(−1).The domains of flow instability notably expand with increasing strain during high temperature deformation of GH4586 superalloy.
文摘The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces has an effective role in the fatigue strength and ductility of the alloys.In the present work,the effect of prior cyclic oxidation on the high temperature low cycle fatigue(HTLCF)properties of nickel-based superalloy Rene®80 has been assessed in the uncoated state and in the Pt-aluminide(Pt-Al)coated condition at 930℃.To apply cyclic oxidation,simulation of engine thermal exposure was carried out by exposing coated and uncoated fatigue specimens in the burner rig(120 cycles at 1100℃).The cyclic oxidation procedure led to a changing in the coating microstructure from the dual-phase(ξ-PtAl_(2)+β-(Ni,Pt)Al)to single phase(β-(Ni,Pt)Al).Results of HTLCF tests showed an improvement in the HTLCF life around 11.5%in the unexposed coated specimen(pre-cyclic oxidation)as compared to unexposed bare specimen,while this rise for exposed coated specimen(post-cyclic oxidation)was only 5%.Although a mixed mode fracture morphology(ductile and brittle)was observed on the fracture surfaces of failed specimens,the wider regions of brittle fracture belonged to exposed coated/uncoated ones.
文摘Three experimental single crystal superalloys with 0%Nb,0.5%Nb,1.0%Nb were cast in the directionally solidified furnace,while other alloying element contents were basically kept unchanged.The effect of Nb on the microstructure,stability at1100°C and stress rupture properties at 1070°C and 160 MPa of the single crystal superalloy were investigated.The experiment results show that the primary dendrite arm spacing decreases and the volume fraction ofγ/γ′eutectic of the alloy increases with the increase of Nb content in the as-cast microstructures.The size ofγ′phase particles becomes small and uniform and the cubic shape does not obviously change with the increase of Nb content.The precipitating rate and volume fraction of TCP phases increase significantly with the increase of Nb content in the process of long term aging at 1100°C.The stress rupture lives increase and elongation decreases with increasing Nb content at 1070°C/160 MPa.At last,the relationship between the microstructures stability,stress rupture properties of the alloy and Nb content is discussed based on JMat Pro software and the lastest relevant database for single crystal superalloy.
文摘The effect of electromagnetic stirring on the inner quality of K417 superalloy ingots is studied with EPMA and optical microscope.The results show that while an electromagnetic stirring with 50Hz frequency and 80A current is imposed,the equiax crystals of K417 superalloy ingots can be effectively refined and increased,and the central shrinkage porosity and the dendritic segregation of K417 superalloy ingots are greatly reduced,so the inner quality of K417 superalloy ingots is obviously improved.
基金Project (51134003) supported by the National Natural Science Foundation of China
文摘The oxidation behaviors of Ni-16Cr-xAl （x=4.5%, 9.0%, mass fraction） superalloy foams in air at 1000℃ were investigated. The effects of AI content on the resistance to high temperature oxidation were examined. The oxidation mechanisms of the foams were discussed. The results show that the resistance to the oxidation of the Ni-16Cr-xA1 based alloy at 1 000 ℃ increases with the content of A1 increasing from 4.5% to 9.0%. Complex oxide products are formed on the surface of the superalloy foams after the oxidation. Cr203 and A1203 are the predominant oxides for the scales of the foams with 4.5% A1 and 9% A1, respectively. Excellent high temperature oxidation resistance and superior pore conformation stability for the Ni-16Cr-xA1 based superalloy foam with 9% A1 can be mainly attributed to the formation of relatively continuous and protective A1203 oxides on the surface of the foam.
文摘Non-metallic inclusions,especially the large ones,within P/M Ni-base superalloy have a major influence on fatigue characteristics,but are not directly measurable by routine inspection.In this paper,a method,automatic image analysis,is proposed for estimation of the content,size and amount of non-metallic inclusions in superalloy.The methodology for the practical application of this method is described and the factors affecting the precision of the estimation are discussed.In the experiment,the characteristics of the non-metallic inclusions in Ni-base P/M superalloy are analyzed.
文摘High-temperature Ni-based alloys are widely used in the aerospace field due to their excellent properties,but the shortcomings of brittle fracture at the grain boundaries and poor plasticity at room temperature also limit their development to a certain extent.Researchers found that there areγ′precipitation phases similar to Ni_(3)Al in Pt-Al based alloys.In this paper,the CASTEP code of Materials Studio software package is used to simulate the thermal and mechanical properties ofγ′-Pt_(3)Al phase andγ′-Ni_(3)Al phase.By comparing the performance characteristics of the electronic structure,mechanical properties and point defect structure of the two,it is found that the stability,elastic deformation resistance and high temperature creep resistance of theγ′-Pt_(3)Al phase are better than those of theγ′-Ni_(3)Al phase.This will provide theoretical guidance for promoting the development of Pt-Al-based high-temperature materials.
