The second generation single crystal superalloy DD6 with 0.10%Hf and 0.34%Hf （in mass fraction） was subjected to high-cycle fatigue （HCF） loading at temperatures of 700 ℃ in ambient atmosphere. SEM was used to de...The second generation single crystal superalloy DD6 with 0.10%Hf and 0.34%Hf （in mass fraction） was subjected to high-cycle fatigue （HCF） loading at temperatures of 700 ℃ in ambient atmosphere. SEM was used to determine the initiation site and the failure mechanism. Evolution of the microstructure was investigated by TEM observation. The results show that fatigue limit of DD6 alloy with 0.34%Hf is a little smaller than that of the alloy with 0.10%Hf. The fatigue cracks initiated on the surface or near the surface of the specimens. The crack would propagate along { 111 } octahedral slip planes, rather than perpendicular to the loading axis of specimen. Typical fatigue striation formed in steady propagation of fatigue crack. The fracture mechanisms of the high cycle fatigue of DD6 alloys with 0.10%Hf and 0.34%Hf are quasi-cleavage fracture. Different types of dislocation structures were developed during high cycle fatigue deformation.展开更多
The isothermal oxidation behavior of the second generation single crystal superalloy DD6 was studied at 1050 ℃ and 1100 ℃ in ambient atmosphere.Morphology of oxides was examined by SEM and their composition was anal...The isothermal oxidation behavior of the second generation single crystal superalloy DD6 was studied at 1050 ℃ and 1100 ℃ in ambient atmosphere.Morphology of oxides was examined by SEM and their composition was analyzed by XRD and EDS.The experimental results show that DD6 alloy obeys subparabolic rate law during oxidation of 100 h at 1050 ℃ and 1100 ℃.The oxide scale exposed at 1050 ℃ is made up of an outer NiO layer with a small amount of Al2O3 and an inner Al2O3 layer.The oxide scale exposed at 1100 ℃ is made up of an outer Al2O3 layer with a small amount of NiO,an intermediate layer,mainly composed of Cr2O3 and TaO2,and an inner Al2O3 layer.The γ＇-free layer was formed under the oxide scale at two temperatures.展开更多
Transient Liquid Phase Diffusion bonding (TLP bonding) is an effective method to achieve excellent joint of DD6, which is a new generation single crystal superalloy to manufacture aero-engine turbine blades. In this p...Transient Liquid Phase Diffusion bonding (TLP bonding) is an effective method to achieve excellent joint of DD6, which is a new generation single crystal superalloy to manufacture aero-engine turbine blades. In this paper, the interlayer alloys for DD6 TLP bonding were designed. The alloy foils with thickness 40 μm ~ 60 μm, width 4 mm were prepared by using a single roller rapid solidification apparatus and the TLP bonding of DD6 was conducted. Then the joint microstructure and alloying elements diffusion behaviors were analyzed. The results indicate that microstructures of interlayer alloys prepared are fine and homogeneous, the melting point range of alloys from 1070°C to 1074°C and their melting temperature interval is merely 20°C, when the chemical composition of alloys are 1.5 ~ 2.0Cr, 3.2 ~ 4.0W, 3.7 ~ 4.5Co, 2.2 ~ 3.0Al, 0.7 ~ 1.0Mo, 3.2B, remain Ni (wt%). When the welding parameters are bonding temperature 1200?C, holding time 8.0 hour and welding pressure 0.3 MPa, the compacted joints obtained and the microstructure of TLP bonding seams were similar to base metal. The bonding joint is composed of weld center zone, isothermal solidification zone and diffusion-affected zone. Within joint, the elements diffusion is sufficient and borides in the diffusion zone are fewer.展开更多
Structure and polarity of the Si C single crystal have been analyzed with the four- circle X- ray diffraction method by a double- crystal diffractom eter.The hexagonal{ 10 15 } pole figure shows that this Si C sam pl...Structure and polarity of the Si C single crystal have been analyzed with the four- circle X- ray diffraction method by a double- crystal diffractom eter.The hexagonal{ 10 15 } pole figure shows that this Si C sam ple has a6 H modification.The difference between the integrated intensities m easured byω scan in the triple- axis diffraction set- up finds some convincing evidence that the surface is either a Si- terminated face or C- terminated face.The experi- mental ratios of| F( 0 0 0 L) | 2 / | F( 0 0 0 L) | 2 are in good agreem entwith the calculated ones after the dispersion cor- rections to the atomic scattering factors( L=6 ,12 and18,respectively) .Thus,this m easurem ent technique is con- venient for the application of the materials with remarkable surface polarity.展开更多
The effect of thermal exposure on the microstructure and creep properties of the Ni-based single crystal superalloy in different test conditions was studied.Long-term exposure was performed at 1,000 ℃ and 1,100 ℃ fo...The effect of thermal exposure on the microstructure and creep properties of the Ni-based single crystal superalloy in different test conditions was studied.Long-term exposure was performed at 1,000 ℃ and 1,100 ℃ for 500 h prior to the creep tests.The creep lifetime is found to be improved after the long-term exposure at 1,000 ℃ for 500 h as a result of the formation of secondary M_(23)C_(6) in the interdendritic region.The coarsening of γ’ precipitates accompanied by the formation of TCP phase lead to the degradation of alloy,which is responsible for the reduction of the creep lifetime of Ni-base single crystal superalloy after long-term exposure at 1,100 ℃ for 500 h.The creep lifetime of 1,000 oC thermally exposed sample under the conditions of 1,093 ℃/137 MPa is lower than that of heat-treated state.Thermal exposure at 1,100 ℃ for 500 h causes the creep lifetime to drop drastically.展开更多
Multifunctional lead-free double perovskites demonstrate remarkable potential towards applications in various fields.Herein,an environmentally-friendly,low-cost,high-throughput Cs_(2)NaFeCl_(6) single crystal with exc...Multifunctional lead-free double perovskites demonstrate remarkable potential towards applications in various fields.Herein,an environmentally-friendly,low-cost,high-throughput Cs_(2)NaFeCl_(6) single crystal with exceedingly high thermal stability is designed and grown.It obtains a cubic lattice system in the temperature range of 80-500 K,accompanied by a completely reversible chromatic variation ranging from yellow to black.Importantly,the intriguing thermochromism is proved to own extremely high reproducibility(over 1000 cycles)without a hysteretic effect,originating from its structural flexibility that including(i)the noteworthy distortion/deformation of[NaCl_(6)]5−and[FeCl_(6)]3−octahedra;(ii)order-disorder arrangement transition of[NaCl_(6)]5−and[FeCl6]3−octahedra as the function of temperature.This study paves the way towards a new class of smart windows and camouflage coatings with an unprecedented colour range based on a Cs_(2)NaFeCl_(6) perovskite.展开更多
文摘The second generation single crystal superalloy DD6 with 0.10%Hf and 0.34%Hf （in mass fraction） was subjected to high-cycle fatigue （HCF） loading at temperatures of 700 ℃ in ambient atmosphere. SEM was used to determine the initiation site and the failure mechanism. Evolution of the microstructure was investigated by TEM observation. The results show that fatigue limit of DD6 alloy with 0.34%Hf is a little smaller than that of the alloy with 0.10%Hf. The fatigue cracks initiated on the surface or near the surface of the specimens. The crack would propagate along { 111 } octahedral slip planes, rather than perpendicular to the loading axis of specimen. Typical fatigue striation formed in steady propagation of fatigue crack. The fracture mechanisms of the high cycle fatigue of DD6 alloys with 0.10%Hf and 0.34%Hf are quasi-cleavage fracture. Different types of dislocation structures were developed during high cycle fatigue deformation.
文摘The isothermal oxidation behavior of the second generation single crystal superalloy DD6 was studied at 1050 ℃ and 1100 ℃ in ambient atmosphere.Morphology of oxides was examined by SEM and their composition was analyzed by XRD and EDS.The experimental results show that DD6 alloy obeys subparabolic rate law during oxidation of 100 h at 1050 ℃ and 1100 ℃.The oxide scale exposed at 1050 ℃ is made up of an outer NiO layer with a small amount of Al2O3 and an inner Al2O3 layer.The oxide scale exposed at 1100 ℃ is made up of an outer Al2O3 layer with a small amount of NiO,an intermediate layer,mainly composed of Cr2O3 and TaO2,and an inner Al2O3 layer.The γ＇-free layer was formed under the oxide scale at two temperatures.
文摘Transient Liquid Phase Diffusion bonding (TLP bonding) is an effective method to achieve excellent joint of DD6, which is a new generation single crystal superalloy to manufacture aero-engine turbine blades. In this paper, the interlayer alloys for DD6 TLP bonding were designed. The alloy foils with thickness 40 μm ~ 60 μm, width 4 mm were prepared by using a single roller rapid solidification apparatus and the TLP bonding of DD6 was conducted. Then the joint microstructure and alloying elements diffusion behaviors were analyzed. The results indicate that microstructures of interlayer alloys prepared are fine and homogeneous, the melting point range of alloys from 1070°C to 1074°C and their melting temperature interval is merely 20°C, when the chemical composition of alloys are 1.5 ~ 2.0Cr, 3.2 ~ 4.0W, 3.7 ~ 4.5Co, 2.2 ~ 3.0Al, 0.7 ~ 1.0Mo, 3.2B, remain Ni (wt%). When the welding parameters are bonding temperature 1200?C, holding time 8.0 hour and welding pressure 0.3 MPa, the compacted joints obtained and the microstructure of TLP bonding seams were similar to base metal. The bonding joint is composed of weld center zone, isothermal solidification zone and diffusion-affected zone. Within joint, the elements diffusion is sufficient and borides in the diffusion zone are fewer.
文摘Structure and polarity of the Si C single crystal have been analyzed with the four- circle X- ray diffraction method by a double- crystal diffractom eter.The hexagonal{ 10 15 } pole figure shows that this Si C sam ple has a6 H modification.The difference between the integrated intensities m easured byω scan in the triple- axis diffraction set- up finds some convincing evidence that the surface is either a Si- terminated face or C- terminated face.The experi- mental ratios of| F( 0 0 0 L) | 2 / | F( 0 0 0 L) | 2 are in good agreem entwith the calculated ones after the dispersion cor- rections to the atomic scattering factors( L=6 ,12 and18,respectively) .Thus,this m easurem ent technique is con- venient for the application of the materials with remarkable surface polarity.
基金funded by the Key Laboratory of Advanced High-temperature Structural Materials for National Defense Science and Technology,China(No:6142903180104)。
文摘The effect of thermal exposure on the microstructure and creep properties of the Ni-based single crystal superalloy in different test conditions was studied.Long-term exposure was performed at 1,000 ℃ and 1,100 ℃ for 500 h prior to the creep tests.The creep lifetime is found to be improved after the long-term exposure at 1,000 ℃ for 500 h as a result of the formation of secondary M_(23)C_(6) in the interdendritic region.The coarsening of γ’ precipitates accompanied by the formation of TCP phase lead to the degradation of alloy,which is responsible for the reduction of the creep lifetime of Ni-base single crystal superalloy after long-term exposure at 1,100 ℃ for 500 h.The creep lifetime of 1,000 oC thermally exposed sample under the conditions of 1,093 ℃/137 MPa is lower than that of heat-treated state.Thermal exposure at 1,100 ℃ for 500 h causes the creep lifetime to drop drastically.
基金The research was funded by the National Natural Science Foundation of China(No.51802120,51872126,22075103,51672111)Guangdong Basic and Applied Basic Research Foundation for Distinguished Young Scholar(No.2019B151502030)+7 种基金Natural Science Foundation of Guangdong Province(No.2018030310181)the Science and Technology Plan Project of Guangzhou(No.202002030159)Guangdong Basic and Applied Basic Research Foundation for Young Scholar(No.2020A1515111057)‘100 Talents Program of Hebei Province’(No.E2014100008)the Fundamental Research Funds for the Central Universities(No.21619406)X.Y.thanks for the Special Funds for the Cultivation of Guangdong College Students'Scientific and Technological Innovation("Climbing Program"Special Funds)(No.pdjh2019a0055)J.Fan also thanks for the project support for"Young Top talents"in the Pearl River Talent Project of Guangdong Province(2017GC010424)the Guangdong Provincial Innovation and Entrepreneurship Project(grant 2016ZT06D081).
文摘Multifunctional lead-free double perovskites demonstrate remarkable potential towards applications in various fields.Herein,an environmentally-friendly,low-cost,high-throughput Cs_(2)NaFeCl_(6) single crystal with exceedingly high thermal stability is designed and grown.It obtains a cubic lattice system in the temperature range of 80-500 K,accompanied by a completely reversible chromatic variation ranging from yellow to black.Importantly,the intriguing thermochromism is proved to own extremely high reproducibility(over 1000 cycles)without a hysteretic effect,originating from its structural flexibility that including(i)the noteworthy distortion/deformation of[NaCl_(6)]5−and[FeCl_(6)]3−octahedra;(ii)order-disorder arrangement transition of[NaCl_(6)]5−and[FeCl6]3−octahedra as the function of temperature.This study paves the way towards a new class of smart windows and camouflage coatings with an unprecedented colour range based on a Cs_(2)NaFeCl_(6) perovskite.
