The advent of coarse-grain superplasticity has provided a pathway for novel applications in material forming.This article investigated the underlying deformation mechanisms that enabled achieving superplastic elongati...The advent of coarse-grain superplasticity has provided a pathway for novel applications in material forming.This article investigated the underlying deformation mechanisms that enabled achieving superplastic elongation exceeding 230%in a coarse-grained Ni-Co-based superalloy.The deformed microstructure and fractographic characteristics of the alloy were examined utilizing optical microscopy(OM),scanning electron microscopy(SEM),and electron backscatter diffraction(EBSD).The results of the analysis revealed that below 1100℃,the process of dynamic recrystallization(DRX)occurred at a sluggish rate,resulting in low plasticity and the initiation of severe cracks.Complete DRX occurred when the deformation temperature exceeded 1100℃,leading to a more uniformly deformed microstructure,reduced crack initiation,and enhanced ductility demonstrated by elongation to failure surpassing 230%.The augmented occurrence of the DRX facilitated prolonged plastic-forming periods,which delayed fracture propagation and promoted the deformation flow within the alloy,thereby transitioning the fracture behavior from intergranular-brittle at 1050℃to ductile intergranular at 1140℃.At this temperature,the deformation was predominantly governed by the discontinuous-DRX(DDRX)mechanism and grain growth,facilitated by the formation of twin boundaries.展开更多
The influence of V contents(0.6 wt%,0.8 wt%and 1.0 wt%)on the microstructure and creep behavior of a Nickel-based superalloy was investigated.The results revealed that the V content exerted a significant impact on the...The influence of V contents(0.6 wt%,0.8 wt%and 1.0 wt%)on the microstructure and creep behavior of a Nickel-based superalloy was investigated.The results revealed that the V content exerted a significant impact on the morphology of carbide.Notably,in the alloy containing 0.8 wt%V,coarse blocky M_(6)C carbides formed adjacent to MC carbides,while in the 1.0 wt%V alloy,fine granular M_(6)C carbides exhibited a nearly continuous distribution along grain boundaries(GBs).The influence of V content on creep properties exhibited significant variations depending on temperature.At 650℃/1010 MPa,the 1.0 wt%V alloy,containing a high density of granular M_(6)C carbides,demonstrated enhanced intergranular bonding strength,which contributed to prolonged creep life.In contrast,at higher temperatures(750℃/620 MPa and 800℃/500 MPa),GB mobility was activated,making GB slip the dominant creep mechanism.The near-continuous distribution of M_(6)C carbides in the 1.0 wt%V alloy restricted GB deformation compatibility,promoting stress localization and an increased density of micropores along GBs.As a result,the 0.8 wt%V alloy,with its discrete M_(6)C carbide distribution,exhibited superior creep resistance at elevated temperatures.展开更多
Various cooling scenarios(water,oil,air and furnace)were employed to study the impacts of the solution cooling rate(SCR)on the microstructure and creep behavior of a novel single-crystal(SX)superalloy.The results show...Various cooling scenarios(water,oil,air and furnace)were employed to study the impacts of the solution cooling rate(SCR)on the microstructure and creep behavior of a novel single-crystal(SX)superalloy.The results showed that the cubic degree and size of theγphases were inversely proportional to the SCR.The creep life first increased and then dropped dramatically with a reduction in the SCR.The creep life of the sample cooled with air cooling(AC)was the highest,up to 144.90 h at 800℃/750 MPa and160.15 h at 1100℃/137 MPa.During creep at 800℃/750 MPa,the improved creep life of the AC sample was mainly attributed to the fine cubicγphases,which decreased the rate ofγ-phase coarsening and favoured plastic deformation by promoting the active movement of dislocations.The AC helped theγphases become rich in Al,Ti and Ta while depleted in Co and Cr,which enhanced its stacking fault energy,thus promoting the formation of dislocation locks.Meanwhile,the largest negative lattice misfit caused by AC induced denserγ/γinterface dislocation networks at 1100℃/137 MPa,which efficiently reduced the minimum creep rate.The calculated average dislocation spacing results indicated that the smallest density of excess dislocations corresponded to the AC sample,proving its greatest creep resistance.Interestingly,the size of the secondaryγphases first decreased and then increased sharply with decreasing SCR during creep at 1100℃/137 MPa,when fine secondaryγphases had a positive role in the blockage of dislocation movement in the matrix.Eventually,the comprehensive SCR effect was explored to provide more guidance in the design of Re-free SX superalloys.展开更多
The effects of Ta on the tensile behavior and deformation mechanisms of a Ni-based single crystal superalloy were investigated in this study from room temperature to elevated temperature.The findings demonstrated that...The effects of Ta on the tensile behavior and deformation mechanisms of a Ni-based single crystal superalloy were investigated in this study from room temperature to elevated temperature.The findings demonstrated that the higher content of Ta could improve the tensile properties of the alloy at different temperatures.Due to the different deformation mechanisms at various temperatures,the influence of Ta on tensile deformation varied.At room temperature,the higher content of Ta enhanced the solid solution strengthening,which would enhance the tensile strength of 6.5Ta alloy.After standard heat treatment of 6.5Ta alloy,precipitation of the secondaryγʹphase would hinder the movement of dislocations.When the temperature was elevated to 760℃,the higher content of Ta not only promoted the interaction of stacking faults to form Lomer-Cottrell(L-C)locks that impeded dislocation motion,but also reduced the occurrence of dislocation pile-up groups,thus enhancing the yield strength.At 1120℃,due to the narrowerγchannels and higher APB energy inγʹphase of the alloy with higher Ta addition,the processes of bypassing and shearing of dislocations were hindered,respectively.Meanwhile,the denser and more regular dislocation networks were formed in 6.5Ta alloy;and thus,the tensile strength of 6.5Ta alloy was enhanced.This study systematically investigated the effect of Ta on the tensile behavior at three different temperatures,which provided an important theoretical basis for the design of nickel-based single crystal superalloys in the future.展开更多
基金financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC0140000)the National Science and Technology Major Project(No.J2019-VI-0006-0120)+3 种基金the Science and Technology Major Project of Liaoning Province(No.2024JH1/11700037)the Youth Innovation Promotion Association,CAS(No.2023202)the Natural Science Foundation Project of Liaoning Province(No.2023-MS-024)the National Science and Technology Major Project(No.2024ZD0600600).
文摘The advent of coarse-grain superplasticity has provided a pathway for novel applications in material forming.This article investigated the underlying deformation mechanisms that enabled achieving superplastic elongation exceeding 230%in a coarse-grained Ni-Co-based superalloy.The deformed microstructure and fractographic characteristics of the alloy were examined utilizing optical microscopy(OM),scanning electron microscopy(SEM),and electron backscatter diffraction(EBSD).The results of the analysis revealed that below 1100℃,the process of dynamic recrystallization(DRX)occurred at a sluggish rate,resulting in low plasticity and the initiation of severe cracks.Complete DRX occurred when the deformation temperature exceeded 1100℃,leading to a more uniformly deformed microstructure,reduced crack initiation,and enhanced ductility demonstrated by elongation to failure surpassing 230%.The augmented occurrence of the DRX facilitated prolonged plastic-forming periods,which delayed fracture propagation and promoted the deformation flow within the alloy,thereby transitioning the fracture behavior from intergranular-brittle at 1050℃to ductile intergranular at 1140℃.At this temperature,the deformation was predominantly governed by the discontinuous-DRX(DDRX)mechanism and grain growth,facilitated by the formation of twin boundaries.
基金support from the National Science and Technology Major Project(No.J2019-VI-0006-0120)the National Key R&D Program of China(No.2019YFA0705300)+2 种基金the Youth Innovation Promotion Association,CAS(No.2023202)the Natural Science Foundation Project of Liaoning Province(No.2023-MS-024)the Innovation Program of Institute of Metal Research,Chinese Academy of Sciences(No.2023-PY08).
文摘The influence of V contents(0.6 wt%,0.8 wt%and 1.0 wt%)on the microstructure and creep behavior of a Nickel-based superalloy was investigated.The results revealed that the V content exerted a significant impact on the morphology of carbide.Notably,in the alloy containing 0.8 wt%V,coarse blocky M_(6)C carbides formed adjacent to MC carbides,while in the 1.0 wt%V alloy,fine granular M_(6)C carbides exhibited a nearly continuous distribution along grain boundaries(GBs).The influence of V content on creep properties exhibited significant variations depending on temperature.At 650℃/1010 MPa,the 1.0 wt%V alloy,containing a high density of granular M_(6)C carbides,demonstrated enhanced intergranular bonding strength,which contributed to prolonged creep life.In contrast,at higher temperatures(750℃/620 MPa and 800℃/500 MPa),GB mobility was activated,making GB slip the dominant creep mechanism.The near-continuous distribution of M_(6)C carbides in the 1.0 wt%V alloy restricted GB deformation compatibility,promoting stress localization and an increased density of micropores along GBs.As a result,the 0.8 wt%V alloy,with its discrete M_(6)C carbide distribution,exhibited superior creep resistance at elevated temperatures.
基金financially supported by the National Key R&D Program of China(No.2017YFA0700704)the National Science and Technology Major Project(No.2017-VI-0002-0072)the Youth Innovation Promotion Association,Chinese Academy of Sciences and Innovation Academy for Light-duty Gas Turbine,Chinese Academy of Sciences(No.CXYJJ20-MS-03)。
文摘Various cooling scenarios(water,oil,air and furnace)were employed to study the impacts of the solution cooling rate(SCR)on the microstructure and creep behavior of a novel single-crystal(SX)superalloy.The results showed that the cubic degree and size of theγphases were inversely proportional to the SCR.The creep life first increased and then dropped dramatically with a reduction in the SCR.The creep life of the sample cooled with air cooling(AC)was the highest,up to 144.90 h at 800℃/750 MPa and160.15 h at 1100℃/137 MPa.During creep at 800℃/750 MPa,the improved creep life of the AC sample was mainly attributed to the fine cubicγphases,which decreased the rate ofγ-phase coarsening and favoured plastic deformation by promoting the active movement of dislocations.The AC helped theγphases become rich in Al,Ti and Ta while depleted in Co and Cr,which enhanced its stacking fault energy,thus promoting the formation of dislocation locks.Meanwhile,the largest negative lattice misfit caused by AC induced denserγ/γinterface dislocation networks at 1100℃/137 MPa,which efficiently reduced the minimum creep rate.The calculated average dislocation spacing results indicated that the smallest density of excess dislocations corresponded to the AC sample,proving its greatest creep resistance.Interestingly,the size of the secondaryγphases first decreased and then increased sharply with decreasing SCR during creep at 1100℃/137 MPa,when fine secondaryγphases had a positive role in the blockage of dislocation movement in the matrix.Eventually,the comprehensive SCR effect was explored to provide more guidance in the design of Re-free SX superalloys.
基金supported by the National Key Research and Development Program of China under Grant No.2017YFA0700704the Middle-aged and Youth Talents in Scientific and Technological Innovation Project of Shenyang under Grant No.RC220440the Excellent Youth Foundation of Liaoning Province under Grant No.2021-YQ-02.
文摘The effects of Ta on the tensile behavior and deformation mechanisms of a Ni-based single crystal superalloy were investigated in this study from room temperature to elevated temperature.The findings demonstrated that the higher content of Ta could improve the tensile properties of the alloy at different temperatures.Due to the different deformation mechanisms at various temperatures,the influence of Ta on tensile deformation varied.At room temperature,the higher content of Ta enhanced the solid solution strengthening,which would enhance the tensile strength of 6.5Ta alloy.After standard heat treatment of 6.5Ta alloy,precipitation of the secondaryγʹphase would hinder the movement of dislocations.When the temperature was elevated to 760℃,the higher content of Ta not only promoted the interaction of stacking faults to form Lomer-Cottrell(L-C)locks that impeded dislocation motion,but also reduced the occurrence of dislocation pile-up groups,thus enhancing the yield strength.At 1120℃,due to the narrowerγchannels and higher APB energy inγʹphase of the alloy with higher Ta addition,the processes of bypassing and shearing of dislocations were hindered,respectively.Meanwhile,the denser and more regular dislocation networks were formed in 6.5Ta alloy;and thus,the tensile strength of 6.5Ta alloy was enhanced.This study systematically investigated the effect of Ta on the tensile behavior at three different temperatures,which provided an important theoretical basis for the design of nickel-based single crystal superalloys in the future.
