Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy ex...Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy exhibits an excellent creep resistance at 700 ℃ and below. When the creep temperature rises to 750 ℃, the creep resistance falls drastically due to the failure of phase transformation strengthening and the precipitation of a large amount of δ phase and σ phase at the grain boundary. The special temperature-sensitive characteristics of Inconel 625 alloy play a very important role in its fracture. When the strain rate is 8.33×10^-3s^-1, the strength of the specimen is higher than that of other parameters attributed to the effect of phase transformation strengthening. With the increase of Ni3(Al, Ti), the phase transformation strengthening inhibits thickening of the stacking faults into twins and improves the overall mechanical properties of the alloy. With the increase of the aging time, the granular Cr-rich M23C6 carbides continue to precipitate at the grain boundary, which hinders the movement of the dislocations and obviously increases the strength of the samples. Especially, the yield strength increases several times.展开更多
Annealing is one of the most efficient heat treatment to refine the grain microstructure in metal alloys.Prior to the annealing,an aging treatment can be implemented to precipitate the second phases for more nucleatio...Annealing is one of the most efficient heat treatment to refine the grain microstructure in metal alloys.Prior to the annealing,an aging treatment can be implemented to precipitate the second phases for more nucleation sites in deformed mixed grains during subsequent recrystallization.However,the underlying mechanism behind the second phases and recrystallization has not yet been fully understood.Taking a typical deformed nickel(Ni)-based(GH4169)superalloy as an exapmle,this research aims to clairfy the connections between the recrystallization and delta(δ)phase(Ni_(3)Nb) during annealing.All deformed samples were also treated by aging and then annealing.The results show that the microstructure and component ofδphase dominated the recrystallization nucleation in the Ni-based alloy.Moreover,there was the presence of theδphase interval limiting nucleation(PILN)andδphase protecting nucleation(PPN),when a high content of close-set phase was precipitated from the matrix.The PILN determined the primary condition for the recrystallization nucleation that happended at the interval ofδphase larger than the critical nucleation size.The peak nucleation occurred in the PPN,where the recrystallization nucleus were free of the penetration by the adjacent grains,before the nucleation incubation time was reached.Thus,a new feasible JNtheory was proposed to determine the maximum domain of recrystallization nucleation under close-set precipitated phases.All the possible nucleation sites were assumed under PPN in the JNtheory.As such,the original microstructure can be expected to design for the annealing via the aging process.A quantitative evaluation of recrystallization nucleation can also achieved in the Ni-based alloys during aging.展开更多
Due to the important role ofδphase's quantity and morphology in the mechanical and fatigue properties of Inconel 718 alloy and its components,it is necessary to renew insights into the effect of cold deformation ...Due to the important role ofδphase's quantity and morphology in the mechanical and fatigue properties of Inconel 718 alloy and its components,it is necessary to renew insights into the effect of cold deformation on theδphase precipitation,especially on the morphology evolution.Therefore,the nucleation and growth behavior ofδphase in cold-rolled Inconel 718 alloy during aging were investigated.The results show that the precipitation rate and volume fraction ofδphase increase with increasing the cold rolling reduction from 10%to 50%.The volume fraction ofδphase reaches equilibrium after 5 h,remaining at 5.98%,6.52%,and 6.79%under different rolling reductions(10%,30%,and 50%),respectively.The nucleation ofδphase mainly occurs on different sites(grain boundaries,new twin boundaries and old twin boundaries)under 10%rolling reduction,whileδphase mainly nucleates on the new grain boundaries of static recrystallization due to 50%rolling reduction.And the growth ofδphase undergoes a process of alternate orientation growth from spherical(nucleation)→short rod(longitudinal orientation growth)→short rod(radial orientation growth)→dynamic equilib-rium.Under 10%rolling reduction,δphase tends to grow into the matrix,while under 50%rolling reduction,the orientation grows faster and is easily affected by the grain boundary curvature.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.51664041,51561021,and 51665032)in part by Longyuan Youth Innovation and Entrepreneurship ProjectsBRICS STI Framework Programme
文摘Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy exhibits an excellent creep resistance at 700 ℃ and below. When the creep temperature rises to 750 ℃, the creep resistance falls drastically due to the failure of phase transformation strengthening and the precipitation of a large amount of δ phase and σ phase at the grain boundary. The special temperature-sensitive characteristics of Inconel 625 alloy play a very important role in its fracture. When the strain rate is 8.33×10^-3s^-1, the strength of the specimen is higher than that of other parameters attributed to the effect of phase transformation strengthening. With the increase of Ni3(Al, Ti), the phase transformation strengthening inhibits thickening of the stacking faults into twins and improves the overall mechanical properties of the alloy. With the increase of the aging time, the granular Cr-rich M23C6 carbides continue to precipitate at the grain boundary, which hinders the movement of the dislocations and obviously increases the strength of the samples. Especially, the yield strength increases several times.
基金the National Natural Science Foundation of China(No.51975593,51775564)the Hunan Provincial Natural Science Foundation of China(No.2020JJ4113)+1 种基金Fundamental Research Funds for the Central Universities of Central South University(No.2021xxts0151)Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20210226)。
文摘Annealing is one of the most efficient heat treatment to refine the grain microstructure in metal alloys.Prior to the annealing,an aging treatment can be implemented to precipitate the second phases for more nucleation sites in deformed mixed grains during subsequent recrystallization.However,the underlying mechanism behind the second phases and recrystallization has not yet been fully understood.Taking a typical deformed nickel(Ni)-based(GH4169)superalloy as an exapmle,this research aims to clairfy the connections between the recrystallization and delta(δ)phase(Ni_(3)Nb) during annealing.All deformed samples were also treated by aging and then annealing.The results show that the microstructure and component ofδphase dominated the recrystallization nucleation in the Ni-based alloy.Moreover,there was the presence of theδphase interval limiting nucleation(PILN)andδphase protecting nucleation(PPN),when a high content of close-set phase was precipitated from the matrix.The PILN determined the primary condition for the recrystallization nucleation that happended at the interval ofδphase larger than the critical nucleation size.The peak nucleation occurred in the PPN,where the recrystallization nucleus were free of the penetration by the adjacent grains,before the nucleation incubation time was reached.Thus,a new feasible JNtheory was proposed to determine the maximum domain of recrystallization nucleation under close-set precipitated phases.All the possible nucleation sites were assumed under PPN in the JNtheory.As such,the original microstructure can be expected to design for the annealing via the aging process.A quantitative evaluation of recrystallization nucleation can also achieved in the Ni-based alloys during aging.
基金The authors are grateful to the Province Natural Science Foundation of Zhejiang(Grant No.LQ19E050004)for financial support.The authors also graciously thank China Airlines Shenyang Liming Aeroengine Co.,Ltd.for aiding in providing the experimental Inconel 718 alloys.
文摘Due to the important role ofδphase's quantity and morphology in the mechanical and fatigue properties of Inconel 718 alloy and its components,it is necessary to renew insights into the effect of cold deformation on theδphase precipitation,especially on the morphology evolution.Therefore,the nucleation and growth behavior ofδphase in cold-rolled Inconel 718 alloy during aging were investigated.The results show that the precipitation rate and volume fraction ofδphase increase with increasing the cold rolling reduction from 10%to 50%.The volume fraction ofδphase reaches equilibrium after 5 h,remaining at 5.98%,6.52%,and 6.79%under different rolling reductions(10%,30%,and 50%),respectively.The nucleation ofδphase mainly occurs on different sites(grain boundaries,new twin boundaries and old twin boundaries)under 10%rolling reduction,whileδphase mainly nucleates on the new grain boundaries of static recrystallization due to 50%rolling reduction.And the growth ofδphase undergoes a process of alternate orientation growth from spherical(nucleation)→short rod(longitudinal orientation growth)→short rod(radial orientation growth)→dynamic equilib-rium.Under 10%rolling reduction,δphase tends to grow into the matrix,while under 50%rolling reduction,the orientation grows faster and is easily affected by the grain boundary curvature.
