Creep is one of the most typical failure modes for the turbine blades of an aero-engine.The microstructure of the turbine blades after long-term service can be adjusted by rejuvenation heat treatment(RHT)to restore it...Creep is one of the most typical failure modes for the turbine blades of an aero-engine.The microstructure of the turbine blades after long-term service can be adjusted by rejuvenation heat treatment(RHT)to restore its creep properties.In this work,a series of RHT experiments were carried out on a directionally solidified(DS)nickel-based superalloy under different solution temperatures and primary aging temperatures based on the standard heat treatment(SHT)process parameters to investigate the mechanism of temperature influence on DS's microstructure after RHT.It is indicated that a more uniform microstructure can be obtained under higher solution temperatures and lower primary aging temperatures compared to the SHT process.Furthermore,by employing the image processing methods to quantify microstructural parameters,a comprehensive indicator parameter for the RHT effect(marked as Prej)was proposed to characterize the effects of RHT on DS superalloy's microstructure and creep property combined with the entropy weight method.Based on this,a regression model to describe the relationship between RHT process parameters and Prej was constructed by using the response surface methodology(RSM).It is revealed that the optimal solution temperature and primary aging temperature for this DS superalloy are 1283°C and 1095°C,respectively.Then the conclusion was validated through complete creep experiments on the DS superalloy,which showed the creep life after RHT reaches 95.5%of the SHT specimen,and the total life has increased by 20.6%.展开更多
The effects of rejuvenation heat treatment(RHT)on the serrated flow behavior and fracture mode of nickel-based superalloys(R26)were investigated by tensile tests and microstructural characterization.The serrated flow ...The effects of rejuvenation heat treatment(RHT)on the serrated flow behavior and fracture mode of nickel-based superalloys(R26)were investigated by tensile tests and microstructural characterization.The serrated flow activation energies were determined to be 41−72 and 64−81 kJ/mol before and after RHT,respectively.Dynamic strain aging in the alloy is caused by the diffusion of carbon atoms into dislocation channels in the nickel matrix.Before RHT,carbides are concentrated at the grain boundaries.Cracks initiate from these carbides and propagate along the grain boundaries.RHT dissolves carbides at grain boundaries,transferring crack initiation to the precipitated phase group in the grains.RHT increases carbon atom concentration in the nickel matrix,enhancing dynamic strain aging and serrated flow behavior.展开更多
Both surface and internal microstructures of a second-generation Ni-based single crystal(SX) superalloy were studied after creep and rejuvenation heat treatment(RHT).It is indicated that the microstructures,such as th...Both surface and internal microstructures of a second-generation Ni-based single crystal(SX) superalloy were studied after creep and rejuvenation heat treatment(RHT).It is indicated that the microstructures,such as the dislocation network,the γ phase and the γ' phase,can be recovered to those after the standard heat treatment(SHT).It is found that RHT affected zone(RAZ) formed at the surface is composed of theγ'-free layer,the transition layer and the recrystallization(RX),which are less than 20 μm in depth totally.Such depth of the RAZ doesn't affect the properties of the superalloy.The morphology of γ' phase at the RAZ is related to the composition of the elements.The average creep life after RHT is close to the average life after SHT.It is concluded that RHT could effectively repair SX parts and increase the total life of the sample after a damage by creep.展开更多
The morphological evolution ofγ’precipitates for a damaged nickel-based superalloy GTD-111 under different rejuvenation heat treatments(RHTs)was investigated.The degeneratedγ’precipitates can be completely dissolv...The morphological evolution ofγ’precipitates for a damaged nickel-based superalloy GTD-111 under different rejuvenation heat treatments(RHTs)was investigated.The degeneratedγ’precipitates can be completely dissolved into the y matrix under the full solution condition of 1200℃/2 h,and only fineγ’precipitates re-precipitated during the cooling stage of the full solution can be observed,but these fineγ’precipitates cannot grow continuously to be similar as those in virgin alloy during the subsequent long-term aging.It is found that the newly developed RHT schedule,including the full solution,the partial solution,and the aging treatments,can effectively recover the degeneratedγ’precipitates in the GTD-111superalloy to their original state.Moreover,the effects of different RHT cycles on theγ’evolution were investigated.The experimental results show that the degeneratedγ’precipitates can be restored to be analogous with those in virgin alloy by slow cooling after the full solution and an appropriate partial solution followed by the long-term aging.Compared with the different microhardness under various RHT schedules,the microhardness after full solution and partial solution followed by aging is more close to that of the initial alloy.展开更多
The second-generation single-crystal superalloy DD6 with [001] orientation was prepared by screw selecting method in the directionally solidified furnace. The long-term aging of the alloy after full heat treatment was...The second-generation single-crystal superalloy DD6 with [001] orientation was prepared by screw selecting method in the directionally solidified furnace. The long-term aging of the alloy after full heat treatment was performed at1100 °C for 400 h. Then the rejuvenation heat treatment 1300 °C/4 h/AC ？ 1120 °C/4 h/AC ？ 870 °C/24 h/AC was carried out. The stress rupture properties were investigated at 760 °C/800 MPa, 850 °C/550 MPa, 980 °C/250 MPa and1100 °C/140 MPa after different heat treatments. The microstructures of the alloy at different conditions were studied by SEM. The results show that c0 phase of the alloy became very irregular and larger after long-term aging at 1100 °C for 400 h. A very small amount of needle-shaped TCP phase precipitated in the dendrite core. The coarsened c0 phase and TCP phase dissolved entirely after rejuvenation heat treatment. The microstructure was restored and almost same with the original microstructure. The stress rupture life of the alloy decreased in different degrees at various test conditions after long-term aging. The stress rupture life of the alloy after rejuvenation heat treatment all restores to the original specimen more than 80%at different conditions. The microstructure degradation of the alloy during long-term aging includes coarsening of the c0 phase,P-type raft and precipitation of TCP phase, which results in the degeneration of stress rupture property. The rejuvenation heat treatment succeeds in restoring the original microstructure and stress rupture properties of the alloy.展开更多
Rejuvenation heat treatments can restore the microstructures and mechanical properties of the degraded turbine blades in gas turbine engines.Herein we analyze the effects of rejuvenation heat treatments on the microst...Rejuvenation heat treatments can restore the microstructures and mechanical properties of the degraded turbine blades in gas turbine engines.Herein we analyze the effects of rejuvenation heat treatments on the microstructural characteristics and mechanical properties of damaged and undamaged specimens of a Ni-based superalloy,K403.The damaged specimens were found to have degraded microstructures and shorter creep lifetime than the undamaged specimen.The rejuvenation heat treatment proved beneficial,especially for specimens exposed to damage for 50 h.In addition,the microstructure recovery and creep life were found to depend on the predamage durations of the specimens.A y’-precipitate-based creep lifetime model was established to predict the residual lifetime based on the microstructural information.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.52275142)Science Center for Gas Turbine Project(Grant Nos.P2022-AIII-003-001,P2022-B-III-005-001)+1 种基金National Science and Technology Major Project(Grant Nos.J2019-IV-0009-0077,Y2022-IV-0002-0019,J2019-IV-0008-0076)National Basic Scientific Research Project(Grant No.JCKY2021601B204)。
文摘Creep is one of the most typical failure modes for the turbine blades of an aero-engine.The microstructure of the turbine blades after long-term service can be adjusted by rejuvenation heat treatment(RHT)to restore its creep properties.In this work,a series of RHT experiments were carried out on a directionally solidified(DS)nickel-based superalloy under different solution temperatures and primary aging temperatures based on the standard heat treatment(SHT)process parameters to investigate the mechanism of temperature influence on DS's microstructure after RHT.It is indicated that a more uniform microstructure can be obtained under higher solution temperatures and lower primary aging temperatures compared to the SHT process.Furthermore,by employing the image processing methods to quantify microstructural parameters,a comprehensive indicator parameter for the RHT effect(marked as Prej)was proposed to characterize the effects of RHT on DS superalloy's microstructure and creep property combined with the entropy weight method.Based on this,a regression model to describe the relationship between RHT process parameters and Prej was constructed by using the response surface methodology(RSM).It is revealed that the optimal solution temperature and primary aging temperature for this DS superalloy are 1283°C and 1095°C,respectively.Then the conclusion was validated through complete creep experiments on the DS superalloy,which showed the creep life after RHT reaches 95.5%of the SHT specimen,and the total life has increased by 20.6%.
基金supported by the National Natural Science Foundation of China(No.52175286)the Tribology Science Fund of State Key Laboratory of Tribology in Advanced Equipment,Tsinghua University,China(No.SKLTKF20B16).
文摘The effects of rejuvenation heat treatment(RHT)on the serrated flow behavior and fracture mode of nickel-based superalloys(R26)were investigated by tensile tests and microstructural characterization.The serrated flow activation energies were determined to be 41−72 and 64−81 kJ/mol before and after RHT,respectively.Dynamic strain aging in the alloy is caused by the diffusion of carbon atoms into dislocation channels in the nickel matrix.Before RHT,carbides are concentrated at the grain boundaries.Cracks initiate from these carbides and propagate along the grain boundaries.RHT dissolves carbides at grain boundaries,transferring crack initiation to the precipitated phase group in the grains.RHT increases carbon atom concentration in the nickel matrix,enhancing dynamic strain aging and serrated flow behavior.
基金financially supported by the National Science and Technology Major Project(No.2017-VI-0002-0072)the National Key R&D Program of China(Nos.2017YFA0700704,2018YFB110660 and 2017YFB1103800)+2 种基金the National Natural Science Foundation of China(Nos.51601192,51671188,51701210 and 51771190)the Youth Innovation Promotion Association,the Chinese Academy of SciencesState Key Lab of Advanced Metals and Materials Open Fund(No.2018-Z07)。
文摘Both surface and internal microstructures of a second-generation Ni-based single crystal(SX) superalloy were studied after creep and rejuvenation heat treatment(RHT).It is indicated that the microstructures,such as the dislocation network,the γ phase and the γ' phase,can be recovered to those after the standard heat treatment(SHT).It is found that RHT affected zone(RAZ) formed at the surface is composed of theγ'-free layer,the transition layer and the recrystallization(RX),which are less than 20 μm in depth totally.Such depth of the RAZ doesn't affect the properties of the superalloy.The morphology of γ' phase at the RAZ is related to the composition of the elements.The average creep life after RHT is close to the average life after SHT.It is concluded that RHT could effectively repair SX parts and increase the total life of the sample after a damage by creep.
基金financially supported by the University-Industry Cooperation Project from Aviation Industry Corporation of China(No.cxy2010BH06)。
文摘The morphological evolution ofγ’precipitates for a damaged nickel-based superalloy GTD-111 under different rejuvenation heat treatments(RHTs)was investigated.The degeneratedγ’precipitates can be completely dissolved into the y matrix under the full solution condition of 1200℃/2 h,and only fineγ’precipitates re-precipitated during the cooling stage of the full solution can be observed,but these fineγ’precipitates cannot grow continuously to be similar as those in virgin alloy during the subsequent long-term aging.It is found that the newly developed RHT schedule,including the full solution,the partial solution,and the aging treatments,can effectively recover the degeneratedγ’precipitates in the GTD-111superalloy to their original state.Moreover,the effects of different RHT cycles on theγ’evolution were investigated.The experimental results show that the degeneratedγ’precipitates can be restored to be analogous with those in virgin alloy by slow cooling after the full solution and an appropriate partial solution followed by the long-term aging.Compared with the different microhardness under various RHT schedules,the microhardness after full solution and partial solution followed by aging is more close to that of the initial alloy.
文摘The second-generation single-crystal superalloy DD6 with [001] orientation was prepared by screw selecting method in the directionally solidified furnace. The long-term aging of the alloy after full heat treatment was performed at1100 °C for 400 h. Then the rejuvenation heat treatment 1300 °C/4 h/AC ？ 1120 °C/4 h/AC ？ 870 °C/24 h/AC was carried out. The stress rupture properties were investigated at 760 °C/800 MPa, 850 °C/550 MPa, 980 °C/250 MPa and1100 °C/140 MPa after different heat treatments. The microstructures of the alloy at different conditions were studied by SEM. The results show that c0 phase of the alloy became very irregular and larger after long-term aging at 1100 °C for 400 h. A very small amount of needle-shaped TCP phase precipitated in the dendrite core. The coarsened c0 phase and TCP phase dissolved entirely after rejuvenation heat treatment. The microstructure was restored and almost same with the original microstructure. The stress rupture life of the alloy decreased in different degrees at various test conditions after long-term aging. The stress rupture life of the alloy after rejuvenation heat treatment all restores to the original specimen more than 80%at different conditions. The microstructure degradation of the alloy during long-term aging includes coarsening of the c0 phase,P-type raft and precipitation of TCP phase, which results in the degeneration of stress rupture property. The rejuvenation heat treatment succeeds in restoring the original microstructure and stress rupture properties of the alloy.
基金the National Science and Technology Major Project(No.2017-IV-00120049)。
文摘Rejuvenation heat treatments can restore the microstructures and mechanical properties of the degraded turbine blades in gas turbine engines.Herein we analyze the effects of rejuvenation heat treatments on the microstructural characteristics and mechanical properties of damaged and undamaged specimens of a Ni-based superalloy,K403.The damaged specimens were found to have degraded microstructures and shorter creep lifetime than the undamaged specimen.The rejuvenation heat treatment proved beneficial,especially for specimens exposed to damage for 50 h.In addition,the microstructure recovery and creep life were found to depend on the predamage durations of the specimens.A y’-precipitate-based creep lifetime model was established to predict the residual lifetime based on the microstructural information.
