This study investigates the microstructural evolution of a novel low-cost second-generation Ni-based single crystal superalloy during long-term thermal exposure at different temperatures(982℃,1038℃,1093℃)and its im...This study investigates the microstructural evolution of a novel low-cost second-generation Ni-based single crystal superalloy during long-term thermal exposure at different temperatures(982℃,1038℃,1093℃)and its impact on the stress rupture properties of alloy.The results reveal that theγ′phase undergoes coarsening and rafting at high temperatures,and its growth behavior follows the Ostwald ripening mechanism.With the increase in aging temperature and extension of aging time,the coarsening rate of theγ′phase increases significantly.Particularly at 1093℃,theγ′phase undergoes the most pronounced growth,leading to a remarkable deterioration of its precipitation strengthening effect.Furthermore,under conditions of higher temperature and longer time,minor amounts of topologically close-packed(TCP)phase precipitate.As the aging temperature rises and time elapses,the precipitation tendency of the TCP phase shows a slight increase.The stress rupture testing at 1100℃/120 MPa demonstrates that the stress rupture life decreases significantly with the increase in thermal exposure temperature and time.This is mainly attributed to the diminished precipitation strengthening effect of theγ′phase and the deteriorating effect of the TCP phase.However,under the same conditions,the stress rupture properties of this alloy are comparable to those of the DD5 alloy.This research provides theoretical support for enhancing the service stability and reliability of single crystal turbine blades,and offers a reference for the development of cost-effective and highperformance turbine blade materials.展开更多
Cyclic thermal exposure tests of infrared heating to 800 ℃ in 120 s followed by compressed air cooling to 150 ℃ in 60 s were performed for the laser deposited Ti60A （Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si） alloy. The ef...Cyclic thermal exposure tests of infrared heating to 800 ℃ in 120 s followed by compressed air cooling to 150 ℃ in 60 s were performed for the laser deposited Ti60A （Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si） alloy. The effects of thermal exposure cycles on length ofβphase, area fraction ofαphase and microhardness of alloy were examined by OM, SEM and EDS. The results indicate that thermal exposure cycles have significant effects on length ofβphase, area fraction ofαphase and microhardness of the alloy. The original fine basket-weaveβand 78.5%αtransform to transient wedge-likeβ, finally leaving granularβand 97.6%coarsenedαwith the increased thermal exposure cycles. The formation mechanism of coarsenedαand broken-upβmicrostructure is discussed. The alloy after 750 thermal exposure cycles has the maximum microhardness, 33.3%higher than that of the as-deposited alloy.展开更多
The effect of thermal exposure at 350 ℃ for 200 h on microstructure and mechanical properties was investigated for Al-Si-Cu-Ni-Mg alloy, which was produced by permanent mold casting(PMC) and high pressure die casting...The effect of thermal exposure at 350 ℃ for 200 h on microstructure and mechanical properties was investigated for Al-Si-Cu-Ni-Mg alloy, which was produced by permanent mold casting(PMC) and high pressure die casting(HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 ℃. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 ℃.展开更多
The effect of thermal exposure on microstructure and creep properties of a fourth-generation nickelbased single crystal superalloy was investigated.The thermal exposure of samples after the full heat treatment was car...The effect of thermal exposure on microstructure and creep properties of a fourth-generation nickelbased single crystal superalloy was investigated.The thermal exposure of samples after the full heat treatment was carried out at 1000℃,1100℃ and 1140℃ for 100 h and 200 h.The γ’ coarsening,γ’ rafting and γ channel widening were observed in samples after thermal exposure.When the thermal exposure time was constant,the morphology of γ’ phase in the alloy evolved significantly with increasing aging temperature.The interracial dislocation networks in aged samples after creep ruptured gradually became irregular and sparse with the increase of exposure temperature.When the higher exposure temperature was used,enla rgement of the defect pores was observed in samples,the microcracks were more likely to initiate and propagate at the corner of these pores.After aging at 1000℃ for 100 h,the creep life at 1140℃/137 MPa was slightly longer than that of heat-treated sample,which could be attributed to the slightly coarsened γ’ phase,homogenization of refractor elements.In contrast,the creep life of sample exposed at 1140℃ for 100 h was greatly decreased.The decrease of creep life was dominated by the rafting of γ’phase,the irregular interfacial dislocation networks as well as the enlargement of homogenization pores.展开更多
The effect of long-term thermal exposure on the tensile behavior of a high W content nickel-based superalloy K416B was investigated.The microstructure and the deformation characteristics were observed by scanning elec...The effect of long-term thermal exposure on the tensile behavior of a high W content nickel-based superalloy K416B was investigated.The microstructure and the deformation characteristics were observed by scanning electron microscopy and transmission electron microscopy,and the phase transformation of the alloy during long-term thermal exposure was analyzed by X-ray diffraction patterns and differential thermal analysis.Results showed that after thermal exposure at 1000℃,the MC carbides in the K416 B alloy decomposed into M_(6)C.During tensile deformation,dislocations slipping inγmatrix crossed over the M_(6)C by Orowan bowing mechanism.With the increase of thermal exposure time,the secondary M_(6)C reduced greatly the yield strength of the alloy at room temperature.Meanwhile,the continuous distribution of the secondary M_(6)C with great brittleness in the grain boundary could become the main source of crack,which might change the fracture characteristic of the alloy from trans-granular to intergranular.展开更多
In this paper,NiCrAlY coating was deposited on TC4 titanium alloy using arc ion plating,and the stability of NiCrAlY coating/TC4 substrate system under pure thermal exposure was analyzed in a wide temperature range.Du...In this paper,NiCrAlY coating was deposited on TC4 titanium alloy using arc ion plating,and the stability of NiCrAlY coating/TC4 substrate system under pure thermal exposure was analyzed in a wide temperature range.During the thermal exposure,β→γ′→γphase transformation takes place in the NiCrAlY coating.The NiCrAlY coating phases totally decompose above the allotropic transformation temperature of TC4.The allotropic transformation ofα-Ti to β-Ti of the substrate significantly influences the stability of NiCrAlY coating/TC4 substrate system.NiCrAlY coating elements are mainly consumed by interfacial reactions below the allotropic transformation temperature of TC4.Above the allotropic transformation temperature of TC4,NiCrAlY coating elements are mainly consumed by element dissolution in β-Ti.The NiCrAlY coating totally degrades for the dissolution of coating elements in the substrate to form thickβ-Ti stabilized layer.展开更多
The effect of thermal exposure on the microstructure and creep properties of the Ni-based single crystal superalloy in different test conditions was studied.Long-term exposure was performed at 1,000 ℃ and 1,100 ℃ fo...The effect of thermal exposure on the microstructure and creep properties of the Ni-based single crystal superalloy in different test conditions was studied.Long-term exposure was performed at 1,000 ℃ and 1,100 ℃ for 500 h prior to the creep tests.The creep lifetime is found to be improved after the long-term exposure at 1,000 ℃ for 500 h as a result of the formation of secondary M_(23)C_(6) in the interdendritic region.The coarsening of γ’ precipitates accompanied by the formation of TCP phase lead to the degradation of alloy,which is responsible for the reduction of the creep lifetime of Ni-base single crystal superalloy after long-term exposure at 1,100 ℃ for 500 h.The creep lifetime of 1,000 oC thermally exposed sample under the conditions of 1,093 ℃/137 MPa is lower than that of heat-treated state.Thermal exposure at 1,100 ℃ for 500 h causes the creep lifetime to drop drastically.展开更多
The microstructure evolution and its effect on the impact toughness of a new Ni-Fe based alloy GH984 G,used in 700℃ ultra-super critical coal-fired power plant,were investigated during thermal exposure at 650℃-750℃...The microstructure evolution and its effect on the impact toughness of a new Ni-Fe based alloy GH984 G,used in 700℃ ultra-super critical coal-fired power plant,were investigated during thermal exposure at 650℃-750℃ for up to 10,000 h.The results show that the impact toughness at room tempe rature drops rapidly at the early stage during thermal exposure at 700℃ and then has no significant change even if after exposure for 10,000 h.The significant decline of the impact toughness is attributed to the coarsening of M_(23)C_(6) carbides at grain boundaries,which weakens the grain boundary strength and leads to the aging-induced grain boundary embrittlement.The M_(23)C_(6) carbides have almost no change with further thermal exposure and the impact toughness also remains stable.Additionally,the impact toughness rises with the increase of thermal exposure temperature.The size of γ' after thermal exposure at 750℃ for10,000 h is much bigger than that at 650℃ and 700℃ for 10,000 h.There fore,the intragranular strength decreases significantly due to the transformation of the interaction between γ' and dislocation from stro ngly coupled dislocation shearing to Orowan bowing.More plastic deformation occurs within grains after thermal exposure at 750℃ for 10,000 h,which increases the impact toughness.展开更多
The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M6 C carbides presented in the solid solution heat treated sample...The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M6 C carbides presented in the solid solution heat treated samples. During long term thermal exposure at 700 C, fine M12 C carbides precipitated preferentially at grain boundaries. These carbides coexisted with the pre-exiting M6 C. The stress rupture life of700 C/1000 h exposed sample under creep testing at 650 C/324 MPa is 93 h. It is much longer than that of the solid solution samples. No noticeable changes could be detected in both the microstructure and stress rupture lives when the samples were exposed for time longer than 1000 h M12 C carbides were found to be beneficial to the creep properties. The cracks initiated at the interface of M6 C carbides and matrix, which led to a lower creep rupture life.展开更多
In this study, the long-term thermal microstructural stability and related stress rupture lives of a new Re-containing Ni-based single-crystal superalloy, DD11, were investigated after high-temperature exposure for di...In this study, the long-term thermal microstructural stability and related stress rupture lives of a new Re-containing Ni-based single-crystal superalloy, DD11, were investigated after high-temperature exposure for different lengths of time. The results show that the γ' precipitates retained a cuboidal morphology and the γ' size increased after short thermal exposure for 50 h at 1,070℃. As the thermal exposure time was prolonged to 500 h, the cuboidal γ' gradually changed into irregular raft-like morphology due to particles coalescence, and the morphology of the microstructure was almost unchanged after further thermal exposure up to 3,000 h. The stress rupture experiments at 1,070℃ and a tensile stress of 140 MPa showed that the rupture lives increased significantly after thermal exposure for 50 h and dropped dramatically with increasing exposure time up to 500 h but decreased slowly after exposure for more than 500 h. These results imply that stress rupture properties did not decrease when the γ' remained cuboidal but degraded to different extents during the γ' coarsening process. The coarsening of the γ' precipitates and change in morphology were regarded as the main factors leading to the degradation of the stress rupture lives. This study provides fundamental information on the high-temperature longterm microstructural stability and mechanical performance, which will be of great help for DD11 alloy optimization and engineering aeroengine applications.展开更多
1Cr15Ni36W3Ti was thermally exposed at 580℃and 680℃,respectively,up to 3000 h.Theγ’phase and intergranular TiC carbides continuously coarsened during exposure.None ofη,laves orσphase was discovered in the expose...1Cr15Ni36W3Ti was thermally exposed at 580℃and 680℃,respectively,up to 3000 h.Theγ’phase and intergranular TiC carbides continuously coarsened during exposure.None ofη,laves orσphase was discovered in the exposed samples,indicating good microstructure stability under the present exposure conditions.The ripening process of theγ’phase could be well modelled utilizing the LSW theory.The evolutions of the yield and tensile strengths were monotonous during exposure at 580℃.However,a transition point in strengths was detected in the tensile samples exposed at 680℃for 300 h.Accordingly,the criticalγ’diameter was measured to be 13-14 nm.Theγ’/dislocations interaction mechanism transformed from shearing to looping with theγ’diameter exceeding the critical point.The combination of the weakly coupled dislocations model and the Orowan looping model yielded a critical diameter of 13.1 nm which coincided well with the measured one,indicating the applicability of these two strengthening models for 1 Cr15Ni36W3Ti.The present exposure conditions did not exert a profound effect on the fracture mode.All the tensile samples underwent a typically ductile fracture with a dimple pattern dominating the fracture surface.The dispersed deformation induced by the prevalence of dislocation looping in the over-aged tensile samples retarded the propagation of intergranular cracks.The declined precipitation hardening increment and the enhanced deformation homogeneity partially recovered the tensile ductility in the over-aged samples exposed at 680℃.展开更多
In the present work,samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550°C.The evolution of surface roughness and microstructure of the alloy durin...In the present work,samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550°C.The evolution of surface roughness and microstructure of the alloy during thermal exposure was studied by combination methods of roughness profiles,optical and scanning electron microscopy as well as XRD analysis.It is found that the roughness and mass of the alloy increase with the raise of the thermal exposure temperature,and the increasing rates of them are slow as the exposure temperature is below 500°C,but accelerates abruptly when the temperature is higher than 500°C.The variation of surface roughness of the alloy is closely related to phase transformation and oxidation during the thermal exposure.展开更多
The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in...The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in cobalt-base superalloys. It is found that M23C6 particles nucleate preferentially at stacking faults （SFs） in the dendritic matrix and grow along the SFs to develop a lamellar character. Additionally, a Cr depletion zone is observed in the vicinity of the lamellar M23C6 carbide, which strongly supports the presence of Suzuki segregation.展开更多
An attempt has been made here to evaluate the effect of thermal exposure on the mechanical behavior and failure mechanisms of carbon fiber composite sandwich panel with pyramidal truss core under axial compression. An...An attempt has been made here to evaluate the effect of thermal exposure on the mechanical behavior and failure mechanisms of carbon fiber composite sandwich panel with pyramidal truss core under axial compression. Analytical formulae for the collapse strength of composite sandwich panel after thermal exposure were derived. Axial compression tests of composite laminates and sandwich panels after thermal exposure were conducted at room temperature to assess the degradation caused by the thermal exposure. Experimental results showed that the failure of sandwich panel are not only temperature dependent, but are time dependent as well. The decrease in residual compressive strength is mainly attributed to the degradation of the matrix and the degradation of fiber-matrix interface, as well as the formation of cracks and pores when specimens are exposed to high temperature. The measured failure loads obtained in the experiments showed reasonable agreement with the analytical predictions.展开更多
In this paper were studied the microstructure and properties of the non-barrier coating compo- sites fabricated by a new technology.The bonding between C and A1 in the composites is quite well, and the composites have...In this paper were studied the microstructure and properties of the non-barrier coating compo- sites fabricated by a new technology.The bonding between C and A1 in the composites is quite well, and the composites have excellent properties.The ion probe and X-ray analyses indicate that there is Al_4C_3 phase in the composites and its amount in the composites increases when the composites are exposed.In the case of exposure the strength of the composites is reduced because of increasing amount of Al_4C_3.展开更多
The thermal stability of microstructures is crucial for determining the performance of alloys in extreme environments.In the present work,the microstructural evolution and precipitation behavior in a high Nb-containin...The thermal stability of microstructures is crucial for determining the performance of alloys in extreme environments.In the present work,the microstructural evolution and precipitation behavior in a high Nb-containing Ti45Al8Nb alloy during thermal exposure at 950°C were investigated.It was found that excessα2 phases in the as-cast microstructure were unstable and tended to decompose during thermal expo-sure.Hexagonal Ti 2 Al phases precipitated at lamellar interfaces and had a[1¯10]_(γ)[11¯20]_(α2)[11¯20]_(Ti2Al),(002)_(γ)(1¯100)_(α2)(1¯100)_(Ti2Al)crystallographic orientation relationship(OR)with the matrix.Stacking faults(SFs)generated inα2 phases during theα2→γphase transformation provided favorable nucleation sites for Ti 2 Al phases.展开更多
The evolution of the microstructure and tensile rupture mechanism of laser welds in UNS N10003 alloy exposed to 700℃are investigated.Fine M_(6)C carbides precipitate around the primary eutectic M_(6)C-γcarbides in t...The evolution of the microstructure and tensile rupture mechanism of laser welds in UNS N10003 alloy exposed to 700℃are investigated.Fine M_(6)C carbides precipitate around the primary eutectic M_(6)C-γcarbides in the fusion zone after 100 h of exposure.During long-term thermal exposure,the size of the fine M_(6)C carbides increased.The eutectic M_(6)C-γcarbides in the as-welded fusion zone transformed into spherical M_(6)C carbides as the exposure time extends to 10000 h.Additionally,the spherical M_(6)C particles exhibit size coarsening with increasing exposure time.The tensile properties of the welded joints are not adversely affected by the evolution of eutectic M_(6)C-γcarbides and the coarsening of M_(6)C carbides.展开更多
The study provided a systematic investigation into the creep behavior of aγʹ-strengthened Co-based single crystal superalloy Co-7Al-8W-1Ta-4Ti(at.%)under compressive creep conditions at 1000℃and 137 MPa.Simultaneous...The study provided a systematic investigation into the creep behavior of aγʹ-strengthened Co-based single crystal superalloy Co-7Al-8W-1Ta-4Ti(at.%)under compressive creep conditions at 1000℃and 137 MPa.Simultaneously,the microstructural changes during thermal exposure at 1000℃ were thor-oughly examined.The microstructure analysis of the creep samples revealed the presence ofγ/γʹrafts,twins,stacking faults,and dislocation networks.Statistical analyses were conducted to assess the dimen-sions and volume fractions ofγʹ,alongside Vickers hardness tests and nanoindentation experiments.Re-sults show thatγʹdissolution in the creep samples with substantially higher dissolution rates compared to thermal exposure.Localized Co depletion and Ti enrichment in twin is observed in creep sample,po-tentially initiating localized phase transformations.Concurrently,lattice rotation occurred during creep,resulting in a progressive deviation of crystal orientation away from the[001]direction.Stacking faults transitioned from network-like structures to parallel configurations,and twins played a significant role in creep deformation,particularly in samples subjected to 382 h creep.The study also explored the evo-lution of Vickers hardness and the elastic modulus,introducing a systematic linear model to describe Vickers hardness changes during both thermal exposure and creep conditions.展开更多
In this paper,the microstructure evolution and tensile behavior of wrought ATI 718 Plus superalloy during long-term thermal exposure(LTTE) were investigated.The γ’ phase evolves from spherical morphology to cuboidal...In this paper,the microstructure evolution and tensile behavior of wrought ATI 718 Plus superalloy during long-term thermal exposure(LTTE) were investigated.The γ’ phase evolves from spherical morphology to cuboidal morphology at 800℃,which is related to increasing γ’/γ misfit because of the increase of elastic energy.The amounts of η phase obviously increased and γ’ precipitate free zones(PFZs) were found in 800-LTTE samples due to the increase of η phase amount by consuming Al,Ti,and Nb.According to the formula of “MC+γ→M_(23)C_(6)+η”,η phase is also related to the decomposition of MC carbide,which involves the diffusion and segregation of Nb and Ti.In addition,some short rod-like and irregular Cr,Mo-rich σ phases were prone to precipitate near η phases after LTTE at 800℃ for 500 and 1000 h.σ phase has a crystallographic relationship with ηphase as(002)_(σ)//(10■0)_(η),[0■0]_(σ)//[01■0]_(η).The deteriorated tensile strength after LTTE is mainly attributed to that:(1) the evident coarsening of γ’ phase results in that the deformation mechanism transforms from stacking faults(SFs) shearing to Orowan looping,which is also convinced by calculated critical resolved shear stress(CRSS);(2) the noticeable increasing number of η phase contributes to stress concentration,resulting in micro-cracks formation;and (3) the apparently increasing number of η phase promotes the PFZs formation.展开更多
High-strength Al-Zn-Mg-Cu alloys are widely utilized,but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures,limiting their applications above 150℃.This study systematic...High-strength Al-Zn-Mg-Cu alloys are widely utilized,but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures,limiting their applications above 150℃.This study systematically investigates the microstructure evolution and its impact on the properties of peak-aged Al-Zn-Mg-Cu alloys with varying Zn/Mg ratios during thermal exposure at a series of temperatures from 150 to 300℃ for 500 h.The results reveal that alloys A1 and A2 with an optimal Zn/Mg ratio(1.50-2.14)and relatively lower(Zn+Mg)content(7.0-8.8 wt.%),exhibit superior heat resistance properties compared to the other three alloys.Despite having lower strength relative to alloys with higher solute content,peak-aged alloys A1 and A2 retain the highest strength after thermal exposure.This performance is attributed to the high proportion(over 80%)of T'/T phases in the precipitates for alloys A1 and A2,which demonstrate better thermal stability in comparison to η'/η phases.Additionally,the lower solute content reduces the driving force for diffusion of Zn and Mg atoms,thus inhibiting the coarsening of precipitates.Moreover,the study elucidates that the coarsening mechanism of precipitates transitions from interfacial diffusion control at 150℃ to matrix diffusion control at 200-300℃.These insights into the composition-dependent coarsening behavior of precipitates in dual-phase strengthened Al-Zn-Mg-Cu alloys offer valuable guidance for designing heat-resistant aluminum alloys with enhanced performance at elevated temperatures.展开更多
文摘This study investigates the microstructural evolution of a novel low-cost second-generation Ni-based single crystal superalloy during long-term thermal exposure at different temperatures(982℃,1038℃,1093℃)and its impact on the stress rupture properties of alloy.The results reveal that theγ′phase undergoes coarsening and rafting at high temperatures,and its growth behavior follows the Ostwald ripening mechanism.With the increase in aging temperature and extension of aging time,the coarsening rate of theγ′phase increases significantly.Particularly at 1093℃,theγ′phase undergoes the most pronounced growth,leading to a remarkable deterioration of its precipitation strengthening effect.Furthermore,under conditions of higher temperature and longer time,minor amounts of topologically close-packed(TCP)phase precipitate.As the aging temperature rises and time elapses,the precipitation tendency of the TCP phase shows a slight increase.The stress rupture testing at 1100℃/120 MPa demonstrates that the stress rupture life decreases significantly with the increase in thermal exposure temperature and time.This is mainly attributed to the diminished precipitation strengthening effect of theγ′phase and the deteriorating effect of the TCP phase.However,under the same conditions,the stress rupture properties of this alloy are comparable to those of the DD5 alloy.This research provides theoretical support for enhancing the service stability and reliability of single crystal turbine blades,and offers a reference for the development of cost-effective and highperformance turbine blade materials.
基金Project(2010CB731705)supported by the National Basic Research Program of China
文摘Cyclic thermal exposure tests of infrared heating to 800 ℃ in 120 s followed by compressed air cooling to 150 ℃ in 60 s were performed for the laser deposited Ti60A （Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si） alloy. The effects of thermal exposure cycles on length ofβphase, area fraction ofαphase and microhardness of alloy were examined by OM, SEM and EDS. The results indicate that thermal exposure cycles have significant effects on length ofβphase, area fraction ofαphase and microhardness of the alloy. The original fine basket-weaveβand 78.5%αtransform to transient wedge-likeβ, finally leaving granularβand 97.6%coarsenedαwith the increased thermal exposure cycles. The formation mechanism of coarsenedαand broken-upβmicrostructure is discussed. The alloy after 750 thermal exposure cycles has the maximum microhardness, 33.3%higher than that of the as-deposited alloy.
基金Projects(2016YFB0700502,2016YFB0301001)supported by the National Key Research and Development Program of China。
文摘The effect of thermal exposure at 350 ℃ for 200 h on microstructure and mechanical properties was investigated for Al-Si-Cu-Ni-Mg alloy, which was produced by permanent mold casting(PMC) and high pressure die casting(HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 ℃. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 ℃.
基金the National Science and Technology Major Project(No.2017-VI-0002-0072)the National Key R&D Program of China(No.2017YFA0700704)+1 种基金the National Natural Science Foundation of China(Nos.51601192 and 51671188)the State Key Lab of Advanced Metals and Materials Open Fund(No.2018-Z07)。
文摘The effect of thermal exposure on microstructure and creep properties of a fourth-generation nickelbased single crystal superalloy was investigated.The thermal exposure of samples after the full heat treatment was carried out at 1000℃,1100℃ and 1140℃ for 100 h and 200 h.The γ’ coarsening,γ’ rafting and γ channel widening were observed in samples after thermal exposure.When the thermal exposure time was constant,the morphology of γ’ phase in the alloy evolved significantly with increasing aging temperature.The interracial dislocation networks in aged samples after creep ruptured gradually became irregular and sparse with the increase of exposure temperature.When the higher exposure temperature was used,enla rgement of the defect pores was observed in samples,the microcracks were more likely to initiate and propagate at the corner of these pores.After aging at 1000℃ for 100 h,the creep life at 1140℃/137 MPa was slightly longer than that of heat-treated sample,which could be attributed to the slightly coarsened γ’ phase,homogenization of refractor elements.In contrast,the creep life of sample exposed at 1140℃ for 100 h was greatly decreased.The decrease of creep life was dominated by the rafting of γ’phase,the irregular interfacial dislocation networks as well as the enlargement of homogenization pores.
基金financially supported by the National Basic Research Program of China(Nos.2010CB631200 and 2010CB631206)the National Natural Science Foundation of China(Nos.51701212,50931004,51571196,51601192 and 51671188)+1 种基金the State Key Laboratory of Solidification Processing in NWPU(SKLSP201747)the Liaoning Provincial Natural Science Foundation of China(No.2019-MS-336)。
文摘The effect of long-term thermal exposure on the tensile behavior of a high W content nickel-based superalloy K416B was investigated.The microstructure and the deformation characteristics were observed by scanning electron microscopy and transmission electron microscopy,and the phase transformation of the alloy during long-term thermal exposure was analyzed by X-ray diffraction patterns and differential thermal analysis.Results showed that after thermal exposure at 1000℃,the MC carbides in the K416 B alloy decomposed into M_(6)C.During tensile deformation,dislocations slipping inγmatrix crossed over the M_(6)C by Orowan bowing mechanism.With the increase of thermal exposure time,the secondary M_(6)C reduced greatly the yield strength of the alloy at room temperature.Meanwhile,the continuous distribution of the secondary M_(6)C with great brittleness in the grain boundary could become the main source of crack,which might change the fracture characteristic of the alloy from trans-granular to intergranular.
基金financially supported by the National Natural Science Foundation of China(No.51101054)the Foundation of State Key Laboratory of Advanced Metals and Materials(No.2012-Z03)Hunan Provincial Natural Science Foundation of China(No.14JJ3132)
文摘In this paper,NiCrAlY coating was deposited on TC4 titanium alloy using arc ion plating,and the stability of NiCrAlY coating/TC4 substrate system under pure thermal exposure was analyzed in a wide temperature range.During the thermal exposure,β→γ′→γphase transformation takes place in the NiCrAlY coating.The NiCrAlY coating phases totally decompose above the allotropic transformation temperature of TC4.The allotropic transformation ofα-Ti to β-Ti of the substrate significantly influences the stability of NiCrAlY coating/TC4 substrate system.NiCrAlY coating elements are mainly consumed by interfacial reactions below the allotropic transformation temperature of TC4.Above the allotropic transformation temperature of TC4,NiCrAlY coating elements are mainly consumed by element dissolution in β-Ti.The NiCrAlY coating totally degrades for the dissolution of coating elements in the substrate to form thickβ-Ti stabilized layer.
基金funded by the Key Laboratory of Advanced High-temperature Structural Materials for National Defense Science and Technology,China(No:6142903180104)。
文摘The effect of thermal exposure on the microstructure and creep properties of the Ni-based single crystal superalloy in different test conditions was studied.Long-term exposure was performed at 1,000 ℃ and 1,100 ℃ for 500 h prior to the creep tests.The creep lifetime is found to be improved after the long-term exposure at 1,000 ℃ for 500 h as a result of the formation of secondary M_(23)C_(6) in the interdendritic region.The coarsening of γ’ precipitates accompanied by the formation of TCP phase lead to the degradation of alloy,which is responsible for the reduction of the creep lifetime of Ni-base single crystal superalloy after long-term exposure at 1,100 ℃ for 500 h.The creep lifetime of 1,000 oC thermally exposed sample under the conditions of 1,093 ℃/137 MPa is lower than that of heat-treated state.Thermal exposure at 1,100 ℃ for 500 h causes the creep lifetime to drop drastically.
基金supported by the National Key Research and Development Program of China(No.2017YFB0305204)the National Natural Science Foundation of China(No.51971216 and No.51871213)LiaoNing Revitalization Talents Program(No.XLYC1807038)。
文摘The microstructure evolution and its effect on the impact toughness of a new Ni-Fe based alloy GH984 G,used in 700℃ ultra-super critical coal-fired power plant,were investigated during thermal exposure at 650℃-750℃ for up to 10,000 h.The results show that the impact toughness at room tempe rature drops rapidly at the early stage during thermal exposure at 700℃ and then has no significant change even if after exposure for 10,000 h.The significant decline of the impact toughness is attributed to the coarsening of M_(23)C_(6) carbides at grain boundaries,which weakens the grain boundary strength and leads to the aging-induced grain boundary embrittlement.The M_(23)C_(6) carbides have almost no change with further thermal exposure and the impact toughness also remains stable.Additionally,the impact toughness rises with the increase of thermal exposure temperature.The size of γ' after thermal exposure at 750℃ for10,000 h is much bigger than that at 650℃ and 700℃ for 10,000 h.There fore,the intragranular strength decreases significantly due to the transformation of the interaction between γ' and dislocation from stro ngly coupled dislocation shearing to Orowan bowing.More plastic deformation occurs within grains after thermal exposure at 750℃ for 10,000 h,which increases the impact toughness.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA020404040)the National High Technology Research and Development Program of China (Grant No. 2012AA03A511)
文摘The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M6 C carbides presented in the solid solution heat treated samples. During long term thermal exposure at 700 C, fine M12 C carbides precipitated preferentially at grain boundaries. These carbides coexisted with the pre-exiting M6 C. The stress rupture life of700 C/1000 h exposed sample under creep testing at 650 C/324 MPa is 93 h. It is much longer than that of the solid solution samples. No noticeable changes could be detected in both the microstructure and stress rupture lives when the samples were exposed for time longer than 1000 h M12 C carbides were found to be beneficial to the creep properties. The cracks initiated at the interface of M6 C carbides and matrix, which led to a lower creep rupture life.
基金funded by the National High Technology Research and Development Program(No.2012AA03A513)
文摘In this study, the long-term thermal microstructural stability and related stress rupture lives of a new Re-containing Ni-based single-crystal superalloy, DD11, were investigated after high-temperature exposure for different lengths of time. The results show that the γ' precipitates retained a cuboidal morphology and the γ' size increased after short thermal exposure for 50 h at 1,070℃. As the thermal exposure time was prolonged to 500 h, the cuboidal γ' gradually changed into irregular raft-like morphology due to particles coalescence, and the morphology of the microstructure was almost unchanged after further thermal exposure up to 3,000 h. The stress rupture experiments at 1,070℃ and a tensile stress of 140 MPa showed that the rupture lives increased significantly after thermal exposure for 50 h and dropped dramatically with increasing exposure time up to 500 h but decreased slowly after exposure for more than 500 h. These results imply that stress rupture properties did not decrease when the γ' remained cuboidal but degraded to different extents during the γ' coarsening process. The coarsening of the γ' precipitates and change in morphology were regarded as the main factors leading to the degradation of the stress rupture lives. This study provides fundamental information on the high-temperature longterm microstructural stability and mechanical performance, which will be of great help for DD11 alloy optimization and engineering aeroengine applications.
基金financially supported by the National Natural Science Foundation of China(No.51801221)。
文摘1Cr15Ni36W3Ti was thermally exposed at 580℃and 680℃,respectively,up to 3000 h.Theγ’phase and intergranular TiC carbides continuously coarsened during exposure.None ofη,laves orσphase was discovered in the exposed samples,indicating good microstructure stability under the present exposure conditions.The ripening process of theγ’phase could be well modelled utilizing the LSW theory.The evolutions of the yield and tensile strengths were monotonous during exposure at 580℃.However,a transition point in strengths was detected in the tensile samples exposed at 680℃for 300 h.Accordingly,the criticalγ’diameter was measured to be 13-14 nm.Theγ’/dislocations interaction mechanism transformed from shearing to looping with theγ’diameter exceeding the critical point.The combination of the weakly coupled dislocations model and the Orowan looping model yielded a critical diameter of 13.1 nm which coincided well with the measured one,indicating the applicability of these two strengthening models for 1 Cr15Ni36W3Ti.The present exposure conditions did not exert a profound effect on the fracture mode.All the tensile samples underwent a typically ductile fracture with a dimple pattern dominating the fracture surface.The dispersed deformation induced by the prevalence of dislocation looping in the over-aged tensile samples retarded the propagation of intergranular cracks.The declined precipitation hardening increment and the enhanced deformation homogeneity partially recovered the tensile ductility in the over-aged samples exposed at 680℃.
基金Project(DLBF2018-KY-JS-066-J)supported by China North Engine Research InstituteProject(XAGDXJJ17008)supported by the Principal Fund of Xi’an Technological University,ChinaProjects(19JK0400,19JK0402)supported by the Education Fund of Shaanxi Province,China。
文摘In the present work,samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550°C.The evolution of surface roughness and microstructure of the alloy during thermal exposure was studied by combination methods of roughness profiles,optical and scanning electron microscopy as well as XRD analysis.It is found that the roughness and mass of the alloy increase with the raise of the thermal exposure temperature,and the increasing rates of them are slow as the exposure temperature is below 500°C,but accelerates abruptly when the temperature is higher than 500°C.The variation of surface roughness of the alloy is closely related to phase transformation and oxidation during the thermal exposure.
基金supported by the National Natural Science Foundation of China (Nos. 51331005, 51601192, 51671188 and 11332010)the High Technology Research and Development Program of China (No. 2014AA041701)
文摘The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in cobalt-base superalloys. It is found that M23C6 particles nucleate preferentially at stacking faults （SFs） in the dendritic matrix and grow along the SFs to develop a lamellar character. Additionally, a Cr depletion zone is observed in the vicinity of the lamellar M23C6 carbide, which strongly supports the presence of Suzuki segregation.
基金financial support of the project from the Major State Basic Research Development Program of China (No. 2011CB610303)the National Natural Science Foundation of China (Nos. 90816024 and 11272105)the Research Fund for the Doctoral Program of Higher Education of China (No. 20092302110006)
文摘An attempt has been made here to evaluate the effect of thermal exposure on the mechanical behavior and failure mechanisms of carbon fiber composite sandwich panel with pyramidal truss core under axial compression. Analytical formulae for the collapse strength of composite sandwich panel after thermal exposure were derived. Axial compression tests of composite laminates and sandwich panels after thermal exposure were conducted at room temperature to assess the degradation caused by the thermal exposure. Experimental results showed that the failure of sandwich panel are not only temperature dependent, but are time dependent as well. The decrease in residual compressive strength is mainly attributed to the degradation of the matrix and the degradation of fiber-matrix interface, as well as the formation of cracks and pores when specimens are exposed to high temperature. The measured failure loads obtained in the experiments showed reasonable agreement with the analytical predictions.
文摘In this paper were studied the microstructure and properties of the non-barrier coating compo- sites fabricated by a new technology.The bonding between C and A1 in the composites is quite well, and the composites have excellent properties.The ion probe and X-ray analyses indicate that there is Al_4C_3 phase in the composites and its amount in the composites increases when the composites are exposed.In the case of exposure the strength of the composites is reduced because of increasing amount of Al_4C_3.
基金support provided by the National Natural Science Foundation of China(NSFC)(No.51371049).
文摘The thermal stability of microstructures is crucial for determining the performance of alloys in extreme environments.In the present work,the microstructural evolution and precipitation behavior in a high Nb-containing Ti45Al8Nb alloy during thermal exposure at 950°C were investigated.It was found that excessα2 phases in the as-cast microstructure were unstable and tended to decompose during thermal expo-sure.Hexagonal Ti 2 Al phases precipitated at lamellar interfaces and had a[1¯10]_(γ)[11¯20]_(α2)[11¯20]_(Ti2Al),(002)_(γ)(1¯100)_(α2)(1¯100)_(Ti2Al)crystallographic orientation relationship(OR)with the matrix.Stacking faults(SFs)generated inα2 phases during theα2→γphase transformation provided favorable nucleation sites for Ti 2 Al phases.
基金supported by the Technology Star of Shanghai Institute of Applied Physics,Chinese Academy of Sciences(No.E2551130)the Youth Innovation Promotion Association,Chinese Academy of Sciences(No.E2292202).
文摘The evolution of the microstructure and tensile rupture mechanism of laser welds in UNS N10003 alloy exposed to 700℃are investigated.Fine M_(6)C carbides precipitate around the primary eutectic M_(6)C-γcarbides in the fusion zone after 100 h of exposure.During long-term thermal exposure,the size of the fine M_(6)C carbides increased.The eutectic M_(6)C-γcarbides in the as-welded fusion zone transformed into spherical M_(6)C carbides as the exposure time extends to 10000 h.Additionally,the spherical M_(6)C particles exhibit size coarsening with increasing exposure time.The tensile properties of the welded joints are not adversely affected by the evolution of eutectic M_(6)C-γcarbides and the coarsening of M_(6)C carbides.
基金supported by the China Post-doctoral Science Foundation(No.2023M731500)the Shen-zhen Science and Technology Innovation Commission,China(Nos.JCYJ20210324104610029,KQTD20170328154443162,and JCYJ20220818100613028)+1 种基金the National Natural Science Foundation of China(No.52250710160),the National Key Research and De-velopment Program of China(No.2017YFB0702901)the Shenzhen Key Laboratory for Additive Manufacturing of High-performance Materials(No.ZDSYS201703031748354)。
文摘The study provided a systematic investigation into the creep behavior of aγʹ-strengthened Co-based single crystal superalloy Co-7Al-8W-1Ta-4Ti(at.%)under compressive creep conditions at 1000℃and 137 MPa.Simultaneously,the microstructural changes during thermal exposure at 1000℃ were thor-oughly examined.The microstructure analysis of the creep samples revealed the presence ofγ/γʹrafts,twins,stacking faults,and dislocation networks.Statistical analyses were conducted to assess the dimen-sions and volume fractions ofγʹ,alongside Vickers hardness tests and nanoindentation experiments.Re-sults show thatγʹdissolution in the creep samples with substantially higher dissolution rates compared to thermal exposure.Localized Co depletion and Ti enrichment in twin is observed in creep sample,po-tentially initiating localized phase transformations.Concurrently,lattice rotation occurred during creep,resulting in a progressive deviation of crystal orientation away from the[001]direction.Stacking faults transitioned from network-like structures to parallel configurations,and twins played a significant role in creep deformation,particularly in samples subjected to 382 h creep.The study also explored the evo-lution of Vickers hardness and the elastic modulus,introducing a systematic linear model to describe Vickers hardness changes during both thermal exposure and creep conditions.
基金supported by the National Natural Science Foundation of China (Grant Nos.52034004,51974201&52122409)。
文摘In this paper,the microstructure evolution and tensile behavior of wrought ATI 718 Plus superalloy during long-term thermal exposure(LTTE) were investigated.The γ’ phase evolves from spherical morphology to cuboidal morphology at 800℃,which is related to increasing γ’/γ misfit because of the increase of elastic energy.The amounts of η phase obviously increased and γ’ precipitate free zones(PFZs) were found in 800-LTTE samples due to the increase of η phase amount by consuming Al,Ti,and Nb.According to the formula of “MC+γ→M_(23)C_(6)+η”,η phase is also related to the decomposition of MC carbide,which involves the diffusion and segregation of Nb and Ti.In addition,some short rod-like and irregular Cr,Mo-rich σ phases were prone to precipitate near η phases after LTTE at 800℃ for 500 and 1000 h.σ phase has a crystallographic relationship with ηphase as(002)_(σ)//(10■0)_(η),[0■0]_(σ)//[01■0]_(η).The deteriorated tensile strength after LTTE is mainly attributed to that:(1) the evident coarsening of γ’ phase results in that the deformation mechanism transforms from stacking faults(SFs) shearing to Orowan looping,which is also convinced by calculated critical resolved shear stress(CRSS);(2) the noticeable increasing number of η phase contributes to stress concentration,resulting in micro-cracks formation;and (3) the apparently increasing number of η phase promotes the PFZs formation.
基金supported by the Natural Science Foundation of Chongqing(Nos.CSTB2022NSCQ-LZX0002 and CSTB2022NSCQ-BHX0624)the Chongqing Key Project for Technological Innovation and Application(No.CSTB2022TIAD-KPX0073)+1 种基金the Opening Project of State Key Laboratory for Advanced Metals and Materials(No.2022-Z03)the Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJQN202200810).
文摘High-strength Al-Zn-Mg-Cu alloys are widely utilized,but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures,limiting their applications above 150℃.This study systematically investigates the microstructure evolution and its impact on the properties of peak-aged Al-Zn-Mg-Cu alloys with varying Zn/Mg ratios during thermal exposure at a series of temperatures from 150 to 300℃ for 500 h.The results reveal that alloys A1 and A2 with an optimal Zn/Mg ratio(1.50-2.14)and relatively lower(Zn+Mg)content(7.0-8.8 wt.%),exhibit superior heat resistance properties compared to the other three alloys.Despite having lower strength relative to alloys with higher solute content,peak-aged alloys A1 and A2 retain the highest strength after thermal exposure.This performance is attributed to the high proportion(over 80%)of T'/T phases in the precipitates for alloys A1 and A2,which demonstrate better thermal stability in comparison to η'/η phases.Additionally,the lower solute content reduces the driving force for diffusion of Zn and Mg atoms,thus inhibiting the coarsening of precipitates.Moreover,the study elucidates that the coarsening mechanism of precipitates transitions from interfacial diffusion control at 150℃ to matrix diffusion control at 200-300℃.These insights into the composition-dependent coarsening behavior of precipitates in dual-phase strengthened Al-Zn-Mg-Cu alloys offer valuable guidance for designing heat-resistant aluminum alloys with enhanced performance at elevated temperatures.
