Nickel based single crystal superalloy is currently widely used as the material for turbine blades in aerospace engines.However,metallurgical defects during the manufacturing process and damage during harsh environmen...Nickel based single crystal superalloy is currently widely used as the material for turbine blades in aerospace engines.However,metallurgical defects during the manufacturing process and damage during harsh environmental service are inevitable challenges for turbine blades.Therefore,bonding techniques play a very important role in the manufacturing and repair of turbine blades.The transient liquid phase(TLP)bonding of DD5 Ni-based single crystal superalloy was performed using the designed H1 interlayer.A new third-generation Ni-based superalloy T1 powder was mixed with H1 powder as another interlayer to improve the mechanical properties of the bonded joints.The res-ults show that,such a designed H1 interlayer is beneficial to the improvement of shear strength of DD5 alloy bonded joints by adjusting the bonding temperature and the prolongation of holding time.The maximum shear strength at room temperature of the joint with H1 interlayer reached 681 MPa when bonded at 1260℃for 3 h.The addition of T1 powder can effectively reduce holding time or relatively lower bond-ing temperature,while maintaining relatively high shear strength.When 1 wt.%T1 powder was mixed into H1 interlayer,the maximum room temperature shear strength of the joint bonded at 1260℃reached 641 MPa,which could be obtained for only 1 h.Considering the bonding temperature and the efficiency,the acceptable process parameter of H1+5 wt.%T1 interlayer was 1240℃/2 h,and the room tem-perature shear strength reached 613 MPa.展开更多
Brazing of a Ni-based single crystal superalloy has been investigated with the additive Ni-based superalloy and filler Ni–Cr–W–B alloy at 1260℃, and attentions were paid to the microstructure evolution during braz...Brazing of a Ni-based single crystal superalloy has been investigated with the additive Ni-based superalloy and filler Ni–Cr–W–B alloy at 1260℃, and attentions were paid to the microstructure evolution during brazing and the stress-rupture behavior at 980℃ of such brazed joints after homogenization. Microstructure in the brazed joint generally includes brazing alloy zone（BAZ）, isothermally solidified zone（ISZ） and diffusion affected zone（DAZ）. Microstructure evolution during this brazing process is discussed at the heating stage, the holding stage and the cooling stage respectively, according to the diffusion path of B atoms. Initially well-distributed γ’/γ’ microstructure in the homogenized bonded zone after heat treatment and substantial γ’ rafts enhance the post-brazed joint to obtain a stress-rupture lifetime of more than 120 h at 980℃/250 MPa. On the other hand, the decreased stress-rupture behavior of post-brazed joint, compared with parenting material, is ascribed to the presence of inside brazing porosity and stray grain boundary, which not only reduces the effective loading-carrying area but also offers preferential sites for creep vacancy aggregation to further soften stray grain boundary. And finally an early fracture of these post-brazed joints through the intergranular microholes aggregation and growth mode under this testing condition was observed.展开更多
Additive manufacturing(AM) of Ni-base superalloy components can lead to a significant reduction of weight in aerospace applications. AM of IN718 by selective laser melting results in a very fine dendritic microstructu...Additive manufacturing(AM) of Ni-base superalloy components can lead to a significant reduction of weight in aerospace applications. AM of IN718 by selective laser melting results in a very fine dendritic microstructure with a high dislocation density due to the fast solidification process. The complex phase composition of this alloy, with three different types of precipitates and high residual stresses, necessitates adjustment of the conventional heat treatment for AM parts. To find an optimized heat treatment, the microstructures and mechanical properties of differently solution heat-treated samples were investigated by transmission and scanning electron microscopy, including electron backscatter diffraction, and compression tests. After a solution heat treatment(SHT), the Nb-rich Laves phase dissolves and the dislocation density is reduced, which eliminates the dendritic substructure. SHT at 930 or 954°C leads to the precipitation of the δ-phase, which reduces the volume fraction of the strengthening γ′-and γ′′-phases formed during the subsequent two stage aging treatment. With a higher SHT temperature of 1000°C, where no δ-phase is precipitated, higher γ′ and γ′′ volume fractions are achieved, which results in the optimum strength of all of the solution heat treated conditions.展开更多
The effect of cooling rate on the cooling γ′ precipitation behaviors was investigated in a Ni-base powder/metallurgy （P/M） superalloy （FGH4096）. The empirical equations were established between the cooling rate ...The effect of cooling rate on the cooling γ′ precipitation behaviors was investigated in a Ni-base powder/metallurgy （P/M） superalloy （FGH4096）. The empirical equations were established between the cooling rate and the average sizes of secondary and tertiary γ′ precipitates within grains and tertiary γ′ precipitates at grain boundaries, as well as the apparent width of grain boundaries. The results show that the average sizes of secondary or tertiary γ′ precipitates are inversely correlated with the cooling rate. The shape of secondary γ′ precipitates within grains changes from butterfly-like to spherical with the increase of cooling rate, but all the tertiaryγ′ precipitates formed are spherical in shape. It is also found that tertiary γ′ may be precipitated in the latter part of the cooling cycle only if the cooling rate is not faster than 4.3℃/s, and the apparent width of grain boundaries decreases linearly with the increase of cooling rate.展开更多
The precipitation behavior of γ′ phase,under various interrupt cooling tests after 1170℃,solution treatment was examined.The results indicate that the size of secondary γ′ precipitates increases with the decrease...The precipitation behavior of γ′ phase,under various interrupt cooling tests after 1170℃,solution treatment was examined.The results indicate that the size of secondary γ′ precipitates increases with the decrease of interrupt temperature,and the shape changes from spherical to butterfly like.The fine tertiary γ′ can form either during the post cool air quenching at high interrupt-temperatures,or during the specified 5℃ min-1cooling.Air quenching at high temperatures cannot suppress further nucleation of tertiary γ′ phase.展开更多
This article makes an investigation into the creep behavior and deformation features of FGH95 powder Ni-base superalloy by means of creep curves and microstructural observation. Results show that this superalloy expos...This article makes an investigation into the creep behavior and deformation features of FGH95 powder Ni-base superalloy by means of creep curves and microstructural observation. Results show that this superalloy exposes obvious sensibility to the applied temperature and stresses in the experimental range. Microstructure of the alloy consists of γ＇ phase of various sizes and dispersed carbide particles precipitated in the wider crystal boundaries between the powder particles. During the creep, the deformation of the alloy occurs in the form of singleor double-oriented slipping inside the grains, and some of the finer carbide particles are precipitated near the slipping traces. The wide grain boundaries might be broken into the finer grains due to severe deformation. The deformation mechanism of the alloy during creep is thought to be the activation of dislocations of double-oriented slipping, including （1/2）〈 110〉 dislocation inside the γ matrix phase and 〈110〉 super-dislocation inside the γ＇phase. The formation of the stacking faults and （1/3）〈112〉 super-Shockleys partial dislocation configuration is attributed to the decomposition of 〈 110〉 super-dislocation in the γ＇ phase.展开更多
基金supported by the National Science and Technology Major Project(2017-VI-0009-0080)the Key-Area Research and Development Program of Guangdong Province(2019B010935001)+1 种基金Shenzhen Science and Technology Plan(Project No.JSGG20210802093205015)Industry and Information Technology Bureau of Shenzhen Municipality(Project No.201806071354163490).
文摘Nickel based single crystal superalloy is currently widely used as the material for turbine blades in aerospace engines.However,metallurgical defects during the manufacturing process and damage during harsh environmental service are inevitable challenges for turbine blades.Therefore,bonding techniques play a very important role in the manufacturing and repair of turbine blades.The transient liquid phase(TLP)bonding of DD5 Ni-based single crystal superalloy was performed using the designed H1 interlayer.A new third-generation Ni-based superalloy T1 powder was mixed with H1 powder as another interlayer to improve the mechanical properties of the bonded joints.The res-ults show that,such a designed H1 interlayer is beneficial to the improvement of shear strength of DD5 alloy bonded joints by adjusting the bonding temperature and the prolongation of holding time.The maximum shear strength at room temperature of the joint with H1 interlayer reached 681 MPa when bonded at 1260℃for 3 h.The addition of T1 powder can effectively reduce holding time or relatively lower bond-ing temperature,while maintaining relatively high shear strength.When 1 wt.%T1 powder was mixed into H1 interlayer,the maximum room temperature shear strength of the joint bonded at 1260℃reached 641 MPa,which could be obtained for only 1 h.Considering the bonding temperature and the efficiency,the acceptable process parameter of H1+5 wt.%T1 interlayer was 1240℃/2 h,and the room tem-perature shear strength reached 613 MPa.
基金financial supports from the National High Technology Research and Development Program of China (“863 Program”, No. 20102014AA041701)the National Natural Science Foundation of China (No. 11332010, No. U1508213, No. 51331005, No. 51401210, No. 51601192, No. 51671188 and No. 51571196)
文摘Brazing of a Ni-based single crystal superalloy has been investigated with the additive Ni-based superalloy and filler Ni–Cr–W–B alloy at 1260℃, and attentions were paid to the microstructure evolution during brazing and the stress-rupture behavior at 980℃ of such brazed joints after homogenization. Microstructure in the brazed joint generally includes brazing alloy zone（BAZ）, isothermally solidified zone（ISZ） and diffusion affected zone（DAZ）. Microstructure evolution during this brazing process is discussed at the heating stage, the holding stage and the cooling stage respectively, according to the diffusion path of B atoms. Initially well-distributed γ’/γ’ microstructure in the homogenized bonded zone after heat treatment and substantial γ’ rafts enhance the post-brazed joint to obtain a stress-rupture lifetime of more than 120 h at 980℃/250 MPa. On the other hand, the decreased stress-rupture behavior of post-brazed joint, compared with parenting material, is ascribed to the presence of inside brazing porosity and stray grain boundary, which not only reduces the effective loading-carrying area but also offers preferential sites for creep vacancy aggregation to further soften stray grain boundary. And finally an early fracture of these post-brazed joints through the intergranular microholes aggregation and growth mode under this testing condition was observed.
文摘Additive manufacturing(AM) of Ni-base superalloy components can lead to a significant reduction of weight in aerospace applications. AM of IN718 by selective laser melting results in a very fine dendritic microstructure with a high dislocation density due to the fast solidification process. The complex phase composition of this alloy, with three different types of precipitates and high residual stresses, necessitates adjustment of the conventional heat treatment for AM parts. To find an optimized heat treatment, the microstructures and mechanical properties of differently solution heat-treated samples were investigated by transmission and scanning electron microscopy, including electron backscatter diffraction, and compression tests. After a solution heat treatment(SHT), the Nb-rich Laves phase dissolves and the dislocation density is reduced, which eliminates the dendritic substructure. SHT at 930 or 954°C leads to the precipitation of the δ-phase, which reduces the volume fraction of the strengthening γ′-and γ′′-phases formed during the subsequent two stage aging treatment. With a higher SHT temperature of 1000°C, where no δ-phase is precipitated, higher γ′ and γ′′ volume fractions are achieved, which results in the optimum strength of all of the solution heat treated conditions.
文摘The effect of cooling rate on the cooling γ′ precipitation behaviors was investigated in a Ni-base powder/metallurgy （P/M） superalloy （FGH4096）. The empirical equations were established between the cooling rate and the average sizes of secondary and tertiary γ′ precipitates within grains and tertiary γ′ precipitates at grain boundaries, as well as the apparent width of grain boundaries. The results show that the average sizes of secondary or tertiary γ′ precipitates are inversely correlated with the cooling rate. The shape of secondary γ′ precipitates within grains changes from butterfly-like to spherical with the increase of cooling rate, but all the tertiaryγ′ precipitates formed are spherical in shape. It is also found that tertiary γ′ may be precipitated in the latter part of the cooling cycle only if the cooling rate is not faster than 4.3℃/s, and the apparent width of grain boundaries decreases linearly with the increase of cooling rate.
基金supported by the Science and Technology Project of Beijing (No. D09080300510901)National High Technology Research and Development Pro-gram of China (No. 2012AA03A514)
文摘The precipitation behavior of γ′ phase,under various interrupt cooling tests after 1170℃,solution treatment was examined.The results indicate that the size of secondary γ′ precipitates increases with the decrease of interrupt temperature,and the shape changes from spherical to butterfly like.The fine tertiary γ′ can form either during the post cool air quenching at high interrupt-temperatures,or during the specified 5℃ min-1cooling.Air quenching at high temperatures cannot suppress further nucleation of tertiary γ′ phase.
文摘This article makes an investigation into the creep behavior and deformation features of FGH95 powder Ni-base superalloy by means of creep curves and microstructural observation. Results show that this superalloy exposes obvious sensibility to the applied temperature and stresses in the experimental range. Microstructure of the alloy consists of γ＇ phase of various sizes and dispersed carbide particles precipitated in the wider crystal boundaries between the powder particles. During the creep, the deformation of the alloy occurs in the form of singleor double-oriented slipping inside the grains, and some of the finer carbide particles are precipitated near the slipping traces. The wide grain boundaries might be broken into the finer grains due to severe deformation. The deformation mechanism of the alloy during creep is thought to be the activation of dislocations of double-oriented slipping, including （1/2）〈 110〉 dislocation inside the γ matrix phase and 〈110〉 super-dislocation inside the γ＇phase. The formation of the stacking faults and （1/3）〈112〉 super-Shockleys partial dislocation configuration is attributed to the decomposition of 〈 110〉 super-dislocation in the γ＇ phase.
