The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile...The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile speed mutation method; m reached its maximum value 0.53 at an initial strain rate of 1×10^-4s^-1 at 1253K. The diffusion bonding parameters, including the bonding temperature T, pressure p, and time t, affected the mechanism of joints. When the bonded specimen with 25μm thick nickel foil interlayer was tensile at room temperature, the shear fracture of the joints with nickel foil interlayer took place at the IN718 part. Microstructure study was carried out with the bonded samples. The microstructure shows an excellent bonding at the interfaces. The optimum parameters for the diffusion bonding are: T = 1273-1323K, p = 20-30MPa, t = 45-60min.展开更多
The interaction between thermomechanical parameters and microstructure evolution is so intense that it must be considered during the finite element method (FEM) simulation of the hot plastic working process, for mat...The interaction between thermomechanical parameters and microstructure evolution is so intense that it must be considered during the finite element method (FEM) simulation of the hot plastic working process, for materials that are difficult to deform. Taking the microstructure evolution into account, a novel type of constitutive relationship has been put forward for the IN718 alloy. The microstructure evolution model was first established for the dominant microstructure evolution processes. Then the microstructure evolution models and the method to determine the local flow stress of the corresponding microstructure for current thermomechanical parameters and deformation history were presented. Once the local flow stresses of different structures and their volume contributions were defined, the apparent flow stress of the material could be determined as the weighted sum of the local flow stresses and volume contributions. To validate the proposed method, a thermoviscoplastics and microstructure evolution coupled analysis for a forging process of a critical IN718 disk forging was performed. The predicting results were in close agreement with the experimental data.展开更多
The doping of phosphorus, sulfur and boron in IN718 superalloy can remarkably influence the creep behavior. The modifications of the minor elements seem not to vary the stress exponent and the influences primarily con...The doping of phosphorus, sulfur and boron in IN718 superalloy can remarkably influence the creep behavior. The modifications of the minor elements seem not to vary the stress exponent and the influences primarily concentrate on the effective diffusion coefficient. A pronounced beneficial interaction between P and B and a weaker detrimental interaction between P and S have been obtained. The preexponential frequency constant is proved to be strongly related with the creep activation energy because of the so-called compensation effect. The compensation temperature has been determined to be about 1080 K, which corresponds to the transformation temperature from rapidly coarsened γ'' phase to δ phase. It has been proposed that trace elements can influence the effective diffusion coefficient individually or cooperatively, which in turn either retard or speed the creep process.展开更多
The influence of nitrogen content on the precipitation of secondary phases and the tensile strength of Alloy 718 during gas tungstenarc welding was investigated. Various types of precipitates were characterized using ...The influence of nitrogen content on the precipitation of secondary phases and the tensile strength of Alloy 718 during gas tungstenarc welding was investigated. Various types of precipitates were characterized using scanning electron microscopy and transmission electronmicroscopy. The results showed that in the fusion zone, the volume fraction of Nb-rich phases such as Laves, (Nb,Ti)C, and δ phases, as wellas Ti-rich phases such as (Ti,Nb)CN and (Ti,Nb)N, increased with increase in the nitrogen content due to the microsegregation of Nb and Tiwithin interdendritic areas. Nitrogen was also found to decrease the size of γ′′ particles within γ dendrites. For precipitates in the partiallymelted zone, constitutional liquation was observed for both (Nb,Ti)C and (Ti,Nb)N particles. Based on the results of tensile tests, the weld containing0.015wt% nitrogen exhibited the highest ultimate tensile strength (UTS), whereas more addition of nitrogen led to a decrease in both theUTS and yield strength due to the increased content of brittle Laves phases and decreased size of γ′′.展开更多
The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding(GTAW)of Inconel 718 alloy particularly Nb segregation and subsequent lav...The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding(GTAW)of Inconel 718 alloy particularly Nb segregation and subsequent laves phase evolution in fusion zone.This paper reports the direct effect of magnetically constricted arc traverse speed(MCATS)on bead profile,tensile properties and microstructural evolution of Inconel 718 alloy sheets joined by Gas Tungsten Constricted Arc Welding(GTCAW)process.The mechanism amenable for the microstructural modification and corresponding influence on the tensile properties of joints is investigated both in qualitative and quantitative manner related to the mechanics of arc constriction and pulsing.It is correlated to the solidification conditions during welding.The relationship between MCATS and Arc Constriction Current(ACC)was derived.Its interaction effect on the magnetic arc constriction and joint performance was analysed.Results showed that the joints fabricated using CATS of 70 mm/min exhibited superior tensile properties(98.39% of base metal strength with 31.50% elongation).It is attributed to the grain refinement in fusion zone microstructure leading to the evolution of finer,discrete laves phase in interdendritic areas.展开更多
The volume fraction of δ phase in cold rolled Inconel 718 alloy aged at 910℃ for different times is measured by X ray diffraction techniques, and the influence of cold rolling on the kinetics of δ phase precipitat...The volume fraction of δ phase in cold rolled Inconel 718 alloy aged at 910℃ for different times is measured by X ray diffraction techniques, and the influence of cold rolling on the kinetics of δ phase precipitation is investigated. It has been found that the relation between the volume fraction of δ phase and aging time follows the Avrami equation. With increasing cold rolling reduction, the value of n decreases and the value of a increases.展开更多
Lower content of carbon can further improve the stress rupture life of p-modified DA 718 alloy up to more than 270%. Meanwhile, the ductility of the alloy decreased a little. More boron atoms dissociate due to decreas...Lower content of carbon can further improve the stress rupture life of p-modified DA 718 alloy up to more than 270%. Meanwhile, the ductility of the alloy decreased a little. More boron atoms dissociate due to decreasing carbon content and interact with phosphorus which brings the longer stress rupture life of the alloy. Less carbon may induce more phosphorus segregating in the grain boundary and result in brittleness.展开更多
The anisotropy of the structure and properties caused by the strong epitaxial growth of grains during laser powder bed fusion(L-PBF)significantly affects the mechanical performance of Inconel 718 alloy components such...The anisotropy of the structure and properties caused by the strong epitaxial growth of grains during laser powder bed fusion(L-PBF)significantly affects the mechanical performance of Inconel 718 alloy components such as turbine disks.The defects(lack-of-fusion Lo F)in components processed via L-PBF are detrimental to the strength of the alloy.The purpose of this study is to investigate the effect of laser scanning parameters on the epitaxial grain growth and LoF formation in order to obtain the parameter space in which the microstructure is refined and LoF defect is suppressed.The temperature field of the molten pool and the epitaxial grain growth are simulated using a multiscale model combining the finite element method with the phase-field method.The LoF model is proposed to predict the formation of LoF defects resulting from insufficient melting during L-PBF.Defect mitigation and grain-structure control during L-PBF can be realized simultaneously in the model.The simulation shows the input laser energy density for the as-deposited structure with fine grains and without LoF defects varied from 55.0–62.5 J·mm^(-3)when the interlayer rotation angle was 0°–90°.The optimized process parameters(laser power of 280 W,scanning speed of 1160 mm·s^(-1),and rotation angle of 67°)were computationally screened.In these conditions,the average grain size was 7.0μm,and the ultimate tensile strength and yield strength at room temperature were(1111±3)MPa and(820±7)MPa,respectively,which is 8.8%and10.5%higher than those of reported.The results indicating the proposed multiscale computational approach for predicting grain growth and Lo F defects could allow simultaneous grain-structure control and defect mitigation during L-PBF.展开更多
Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated a...Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h in Alloy 718. In addition to the coalescence of γ′/ γ″ and the amount increasing of δ phase, the existence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore, despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.展开更多
The segregation behavior of sulfur and phosphorus has been studied by means of scanning Auger microprobe (SAM) on microstructural interfaces,such as grain boundaries and carbide/matrix interfaces,The experimental resu...The segregation behavior of sulfur and phosphorus has been studied by means of scanning Auger microprobe (SAM) on microstructural interfaces,such as grain boundaries and carbide/matrix interfaces,The experimental results clearly reveal that sulfur strongly segregates on carbide/matrix interfaces,while phosphorus predominantly distributes on grain boundaries. Molybdenum tends to segregat on grain boundaries.展开更多
Simulating microstructure evolution during forging of superalloys is of great interest for manufacturer of critical components, particularly in aerospace applications. In this research, a phenomenological approach usi...Simulating microstructure evolution during forging of superalloys is of great interest for manufacturer of critical components, particularly in aerospace applications. In this research, a phenomenological approach using a mathematical model was employed into a commercial finite element code, i.e. Abaqus, to study recrystallization and grain growth of IN718 supperalloys during forging. Model validation was performed by compression testing. Results show that the measured recrystallized volume fraction and the grain size were in good agreement with the model predictions. Subsequently, the model was used to simulate the evolution of microstructure in a turbine disc. Finally, a technique based on Tagushi method was used to determine the influence of forging parameters such as forging temperature, ingot height to diameter ratio, and top die velocity on the resultant microstructure. Uniform and refined microstructure of final forging was considered into the objective function. Optimum as well as the poorest parameters combination was attained through analysis. As well the contribution of each parameter on microstructure development was determined through variance analysis.展开更多
The morphology,size,and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718(IN718)superalloy.Due to the deterioration of the substrate zone,the Laves phase...The morphology,size,and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718(IN718)superalloy.Due to the deterioration of the substrate zone,the Laves phase in the laser cladding zone of IN718 superalloy cannot be optimized by a hightemperature solution treatment.In this study,an in situ laser heat-treatment method was proposed to regulate the morphology and size of the Laves phase in the laser cladding zone of IN718 superalloy without impacting the substrate zone.In the in situ laser heat-treatment process,a laser was used to heat previously deposited layers with optimized manufacturing parameters.A thermocouple and an infrared camera were used to analyze thermal cycles and real-time temperature fields,respectively.Microstructures and micro-segregations were observed by optical microscopy,scanning electron microscopy,and electron probe microanalysis.It was found that the in situ laser heat treatment effectively changed the morphology and size of the Laves phase,which was transformed from a continuous striplike shape to a discrete granular shape.The effective temperature range and duration were the two main factors influencing the Laves phase during the in situ laser heat-treatment process.The effective temperature range was determined by the laser linear energy density,and the peak temperature increased with the increase of the linear energy density.In addition,the temperature amplitude could be reduced by simultaneously increasing the laser power and the scanning velocity.Finally,a flow diagram was developed based on the in situ laser heat-treatment process,and the deposition of a single-walled sample with fine and granular Laves phases was detected.展开更多
基金financially supported by the National Natural Science Foundation of China(No.52104372)the Fundamental Research Funds for the Central Universities,China(No.N2107001)the Postdoctoral Research Foundation of China(Nos.2019M651129,2019TQ0053)。
文摘The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile speed mutation method; m reached its maximum value 0.53 at an initial strain rate of 1×10^-4s^-1 at 1253K. The diffusion bonding parameters, including the bonding temperature T, pressure p, and time t, affected the mechanism of joints. When the bonded specimen with 25μm thick nickel foil interlayer was tensile at room temperature, the shear fracture of the joints with nickel foil interlayer took place at the IN718 part. Microstructure study was carried out with the bonded samples. The microstructure shows an excellent bonding at the interfaces. The optimum parameters for the diffusion bonding are: T = 1273-1323K, p = 20-30MPa, t = 45-60min.
基金supported by the National Natural Science Foundation of China (No.59875071).
文摘The interaction between thermomechanical parameters and microstructure evolution is so intense that it must be considered during the finite element method (FEM) simulation of the hot plastic working process, for materials that are difficult to deform. Taking the microstructure evolution into account, a novel type of constitutive relationship has been put forward for the IN718 alloy. The microstructure evolution model was first established for the dominant microstructure evolution processes. Then the microstructure evolution models and the method to determine the local flow stress of the corresponding microstructure for current thermomechanical parameters and deformation history were presented. Once the local flow stresses of different structures and their volume contributions were defined, the apparent flow stress of the material could be determined as the weighted sum of the local flow stresses and volume contributions. To validate the proposed method, a thermoviscoplastics and microstructure evolution coupled analysis for a forging process of a critical IN718 disk forging was performed. The predicting results were in close agreement with the experimental data.
基金supported by the National Natural Science Foundation of China No.59801013 and No.59771056
文摘The doping of phosphorus, sulfur and boron in IN718 superalloy can remarkably influence the creep behavior. The modifications of the minor elements seem not to vary the stress exponent and the influences primarily concentrate on the effective diffusion coefficient. A pronounced beneficial interaction between P and B and a weaker detrimental interaction between P and S have been obtained. The preexponential frequency constant is proved to be strongly related with the creep activation energy because of the so-called compensation effect. The compensation temperature has been determined to be about 1080 K, which corresponds to the transformation temperature from rapidly coarsened γ'' phase to δ phase. It has been proposed that trace elements can influence the effective diffusion coefficient individually or cooperatively, which in turn either retard or speed the creep process.
基金The authors would like to acknowledge Iran University of Science and Technology for financial support。
文摘The influence of nitrogen content on the precipitation of secondary phases and the tensile strength of Alloy 718 during gas tungstenarc welding was investigated. Various types of precipitates were characterized using scanning electron microscopy and transmission electronmicroscopy. The results showed that in the fusion zone, the volume fraction of Nb-rich phases such as Laves, (Nb,Ti)C, and δ phases, as wellas Ti-rich phases such as (Ti,Nb)CN and (Ti,Nb)N, increased with increase in the nitrogen content due to the microsegregation of Nb and Tiwithin interdendritic areas. Nitrogen was also found to decrease the size of γ′′ particles within γ dendrites. For precipitates in the partiallymelted zone, constitutional liquation was observed for both (Nb,Ti)C and (Ti,Nb)N particles. Based on the results of tensile tests, the weld containing0.015wt% nitrogen exhibited the highest ultimate tensile strength (UTS), whereas more addition of nitrogen led to a decrease in both theUTS and yield strength due to the increased content of brittle Laves phases and decreased size of γ′′.
基金funded by Indian Space Research Organization (ISRO) India. Project No. ISRO/RES/3/728/16e17
文摘The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding(GTAW)of Inconel 718 alloy particularly Nb segregation and subsequent laves phase evolution in fusion zone.This paper reports the direct effect of magnetically constricted arc traverse speed(MCATS)on bead profile,tensile properties and microstructural evolution of Inconel 718 alloy sheets joined by Gas Tungsten Constricted Arc Welding(GTCAW)process.The mechanism amenable for the microstructural modification and corresponding influence on the tensile properties of joints is investigated both in qualitative and quantitative manner related to the mechanics of arc constriction and pulsing.It is correlated to the solidification conditions during welding.The relationship between MCATS and Arc Constriction Current(ACC)was derived.Its interaction effect on the magnetic arc constriction and joint performance was analysed.Results showed that the joints fabricated using CATS of 70 mm/min exhibited superior tensile properties(98.39% of base metal strength with 31.50% elongation).It is attributed to the grain refinement in fusion zone microstructure leading to the evolution of finer,discrete laves phase in interdendritic areas.
文摘The volume fraction of δ phase in cold rolled Inconel 718 alloy aged at 910℃ for different times is measured by X ray diffraction techniques, and the influence of cold rolling on the kinetics of δ phase precipitation is investigated. It has been found that the relation between the volume fraction of δ phase and aging time follows the Avrami equation. With increasing cold rolling reduction, the value of n decreases and the value of a increases.
文摘Lower content of carbon can further improve the stress rupture life of p-modified DA 718 alloy up to more than 270%. Meanwhile, the ductility of the alloy decreased a little. More boron atoms dissociate due to decreasing carbon content and interact with phosphorus which brings the longer stress rupture life of the alloy. Less carbon may induce more phosphorus segregating in the grain boundary and result in brittleness.
基金supported by the National Key Research and Development Program of China(No.2021YFB 3700701)the National Natural Science Foundation of China(Nos.52090041,52022011)+1 种基金the National Major Science and Technology Projects of China(No.J2019-VI-00090123)the Key-area Research and Development Program of Guangdong Province(No.2019b010943001)。
文摘The anisotropy of the structure and properties caused by the strong epitaxial growth of grains during laser powder bed fusion(L-PBF)significantly affects the mechanical performance of Inconel 718 alloy components such as turbine disks.The defects(lack-of-fusion Lo F)in components processed via L-PBF are detrimental to the strength of the alloy.The purpose of this study is to investigate the effect of laser scanning parameters on the epitaxial grain growth and LoF formation in order to obtain the parameter space in which the microstructure is refined and LoF defect is suppressed.The temperature field of the molten pool and the epitaxial grain growth are simulated using a multiscale model combining the finite element method with the phase-field method.The LoF model is proposed to predict the formation of LoF defects resulting from insufficient melting during L-PBF.Defect mitigation and grain-structure control during L-PBF can be realized simultaneously in the model.The simulation shows the input laser energy density for the as-deposited structure with fine grains and without LoF defects varied from 55.0–62.5 J·mm^(-3)when the interlayer rotation angle was 0°–90°.The optimized process parameters(laser power of 280 W,scanning speed of 1160 mm·s^(-1),and rotation angle of 67°)were computationally screened.In these conditions,the average grain size was 7.0μm,and the ultimate tensile strength and yield strength at room temperature were(1111±3)MPa and(820±7)MPa,respectively,which is 8.8%and10.5%higher than those of reported.The results indicating the proposed multiscale computational approach for predicting grain growth and Lo F defects could allow simultaneous grain-structure control and defect mitigation during L-PBF.
基金The authors thank Ladish Co.,Inc.to support the test samples for this analysis.And this work was supported by the National Natural Science Foundation of China(No.50171005)the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE to support it.
文摘Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of γ″-Ni3Nb (DO22 structure) and γ′-Ni3(Al,Ti) (L12 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677℃ for 2000h in Alloy 718. In addition to the coalescence of γ′/ γ″ and the amount increasing of δ phase, the existence of a bcc chromium enriched α-Cr phase was observed by SEM, and the weight fraction of α-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed to the interaction of material softening and brittling due to complex structure changes during high temperature exposure. Therefore, despite α-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of α-Cr will be not harmful for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.
文摘The segregation behavior of sulfur and phosphorus has been studied by means of scanning Auger microprobe (SAM) on microstructural interfaces,such as grain boundaries and carbide/matrix interfaces,The experimental results clearly reveal that sulfur strongly segregates on carbide/matrix interfaces,while phosphorus predominantly distributes on grain boundaries. Molybdenum tends to segregat on grain boundaries.
文摘Simulating microstructure evolution during forging of superalloys is of great interest for manufacturer of critical components, particularly in aerospace applications. In this research, a phenomenological approach using a mathematical model was employed into a commercial finite element code, i.e. Abaqus, to study recrystallization and grain growth of IN718 supperalloys during forging. Model validation was performed by compression testing. Results show that the measured recrystallized volume fraction and the grain size were in good agreement with the model predictions. Subsequently, the model was used to simulate the evolution of microstructure in a turbine disc. Finally, a technique based on Tagushi method was used to determine the influence of forging parameters such as forging temperature, ingot height to diameter ratio, and top die velocity on the resultant microstructure. Uniform and refined microstructure of final forging was considered into the objective function. Optimum as well as the poorest parameters combination was attained through analysis. As well the contribution of each parameter on microstructure development was determined through variance analysis.
基金supported by Aero Engine Corporation of China Xi’an Aero-Engine Ltd.(N2018KD040252)the fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University(2020-TS-03)。
文摘The morphology,size,and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718(IN718)superalloy.Due to the deterioration of the substrate zone,the Laves phase in the laser cladding zone of IN718 superalloy cannot be optimized by a hightemperature solution treatment.In this study,an in situ laser heat-treatment method was proposed to regulate the morphology and size of the Laves phase in the laser cladding zone of IN718 superalloy without impacting the substrate zone.In the in situ laser heat-treatment process,a laser was used to heat previously deposited layers with optimized manufacturing parameters.A thermocouple and an infrared camera were used to analyze thermal cycles and real-time temperature fields,respectively.Microstructures and micro-segregations were observed by optical microscopy,scanning electron microscopy,and electron probe microanalysis.It was found that the in situ laser heat treatment effectively changed the morphology and size of the Laves phase,which was transformed from a continuous striplike shape to a discrete granular shape.The effective temperature range and duration were the two main factors influencing the Laves phase during the in situ laser heat-treatment process.The effective temperature range was determined by the laser linear energy density,and the peak temperature increased with the increase of the linear energy density.In addition,the temperature amplitude could be reduced by simultaneously increasing the laser power and the scanning velocity.Finally,a flow diagram was developed based on the in situ laser heat-treatment process,and the deposition of a single-walled sample with fine and granular Laves phases was detected.