This study focuses on the effects of different cold-drawing deformations and aging treatments of solid solution A286 superalloy.The grain configuration,texture,precipitates and tensile strength of A286 superalloy afte...This study focuses on the effects of different cold-drawing deformations and aging treatments of solid solution A286 superalloy.The grain configuration,texture,precipitates and tensile strength of A286 superalloy after different deformations and aging treatments were investigated by optical microscopy(OM),field emission scanning electron microscopy(FESEM),electron back-scattered diffraction(EBSD)and mechanical testing machine.The grain size and configuration of A286 alloy can hardly be changed during aging process.The initially equiaxial and twinned crystals are obvious when deformation is less than30%,while the grain boundaries become blurry and slip bands appear after 35% deformation or more.γ’ phase and Cr-rich carbide are the precipitates of A286 alloy.For each deformation,γ’ phase plays a major role during aging and its amount increases gradually when the aging temperature changes from 650 to 680℃,and a maximum tensile strength appears when following two-stage aging.With deformation increasing,the amounts of γ’ phase and Crrich carbide increase in varying degrees.Meanwhile,the<111>wire textures become more obvious,the tensile strength is enhanced and the kernel average misorientation(KAM)increases gradually;the higher KAM of crystal lattices diffuses from the grain boundary to the matrix gradually.展开更多
The present study deals with the effect of cold deformation and subsequent aging on the microstructure and mechanical properties of AI-Cu-Si-Mg alloy. Differential scanning calorimetry indicates that precipitation occ...The present study deals with the effect of cold deformation and subsequent aging on the microstructure and mechanical properties of AI-Cu-Si-Mg alloy. Differential scanning calorimetry indicates that precipitation occurs in the temperature range of 258-272℃ for the as quenched wrought alloy. The activation energy value estimated by Kissinger method for the aforesaid precipitation reaction is obtained as 106 kJ/mol. 45% cold deformation prior to aging indicates the first dissolution reaction at about 50℃ and the precipitation reaction at a temperature of about 82℃. Microstructural investigations have revealed the formation of fine precipitates within the matrix after aging of the cold deformed sample. As-quenched alloy reveals prominently the aging response, The increase in hardness, yield and tensile strength with simultaneous decrease in elongation in the deformed alloy is found to be primarily due to the deformation strengthening and not due to the precipitation hardening.展开更多
Ag-Cu alloys are extensively used in sliding electric contacts due to their superior electrical conductivity,but their limited wear resistance reduces component longevity.Surface severe plastic deformation(SSPD)has em...Ag-Cu alloys are extensively used in sliding electric contacts due to their superior electrical conductivity,but their limited wear resistance reduces component longevity.Surface severe plastic deformation(SSPD)has emerged as a promising method to enhance wear resistance and reduce friction of metals without altering the matrix composition.In this study,an Ag-20 wt.%Cu alloy was subjected to SSPD for various durations,with the aim of improving tribological performance.The microstructure,hardness,and current-carrying tribological performance under different currents were systematically investigated,along with an exploration of the underlying mechanisms.The results show that in addition to introducing a high density of dislocations on the surface,SSPD also encourages the formation of(111)texture,and particularly disperses the initially long strips of Curich phase into short strips and fine particles.It promotes a tribo-film composed primarily of a mixture of Cu_(2)O and CuO that forms on the worn surface of the surface-treated sample under the 1 A current,thus significantly reducing the friction coefficient and electrical noise.Under the 10 A current,the sample treated for 60 min possesses the optimal friction coefficient(0.429),wear rate(0.791×10^(−6)mm^(3)/(N m)),and electrical noise(0.240 V).In contrast to the Ag/Cu layered structure observed on the worn subsurface of the untreated sample,a single-phase Ag(Cu)solid solution forms on the worn subsurface of the 60-min treated sample,which improves the current-carrying tribological performance.This work provides valuable insights for the development and application of electrical contact alloys with excellent performance.展开更多
Tensile properties at room temperature of a new casting Ni-base superalloy during aging at 800℃ for0-1000 h were investigated.During aging,granular M23C6 carbides presented at grain boundaries and kept growing from d...Tensile properties at room temperature of a new casting Ni-base superalloy during aging at 800℃ for0-1000 h were investigated.During aging,granular M23C6 carbides presented at grain boundaries and kept growing from dispersed particles to continuous networks.The γ’ phase significantly coarsened,with the morphology of some γ’ phase changed from spherical to rounded cubic shape after 1000 h.Three deformation mechanisms in relation to the γ’ diameter(dγ’) were identified:(ⅰ) weakly coupled dislocations(WCD) connected by anti-phase boundary(APB) traveled in pair across the γ/γ’ structure when dγ’ was small in the under-aged alloys;(ⅱ) strongly coupled dislocations(SCD) with reduced spacing compared to(ⅰ) sheared γ’ phase when dγ’ increased in the over-aged alloys;(ⅲ) dislocations occasionally by-passed γ’ phase when dγ’ was larger than 97 nm after aging for more than 300 h.The alloy obtained the peak strength when 20 h-aged with dγ’=44 nm which was in the transition between(ⅰ) and(ⅱ).The aginginduced variation in yield strength was correlated to the coarsening of γ’ phase using a theoretical model of precipitation strengthening in terms of the formation of APB.The calculated results suggested that the γ’ phase with a volume fraction of 23% contributed more than 61% of the peak-aged yield strength.Observation after fracture revealed that the alloys usually fractured at grain boundaries.High stress concentration around carbides resulted in cracks by carbides self-cracking and the initiation of cavities.The undesirable agglomeration of M23C6 at grain boundaries was harmful to the properties of the overaged alloys.展开更多
The influence of pre-deformation on aging precipitates of three near peak-aged Al–Cu–Li alloys,1460 alloy with a low Cu/Li ratio（1.46）,2050 alloy with a high Cu/Li ratio（4.51） and 2A96 alloy with a medium Cu/Li ...The influence of pre-deformation on aging precipitates of three near peak-aged Al–Cu–Li alloys,1460 alloy with a low Cu/Li ratio（1.46）,2050 alloy with a high Cu/Li ratio（4.51） and 2A96 alloy with a medium Cu/Li ratio（2.97）,was investigated.The strength of the aged alloys is enhanced by the pre-deformation.The effectiveness of pre-deformation on precipitates is dependent on the alloy＇s composition.With increasing the pre-deformation,the population density of T1（Al2Cu Li） precipitates increases in all three Al–Cu–Li alloys and their diameter decreases in 2050 and 2A96 alloys,and the greatest effectiveness is observed in 2A96 alloy.The pre-deformation also increases the population density of θ＇（Al2Cu）precipitates and decreases their diameter in 2050 and 2A96 Al–Li alloys,but the effectiveness is smaller compared to that on T1 precipitates.In 1460 alloy subjected to two-step aging at 130 ℃ for 20 h followed by 160 ℃ for 12 h,the main precipitates are δ＇（Al3Li）.At 2%–6% pre-deformation,GP-I zones form and pre-deformation displays little influence.Eight percentage pre-deformation promotes θ＇＇/θ＇ precipitation and increases their population density.展开更多
The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） h...The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） high nitrogen austenitic stainless steels was investigated. The results show that the ＂nose＂ temperatures and incubation periods of the initial time-temperature-precipitation （TTP） curves of aged HNSs are found to be 850 ℃, 60 s; 850 ℃, 45 s; 850 ℃, 60 s and 900 ℃, 90 s, respectively. Based on the analysis of SAD patterns, the coarse cellular Cr2N precipitate which presents a lamellar structure has a hexagonal structure of a=0.478 nm and c=0.444 nm. The Z phase corresponding to a composition of Fe36Cr^2Mo10, is determined to be a body-centered cubic structure ofa=0.892 nm. The precipitating sensitivity presents no more difference with the nitrogen content increasing from 0.77% to 0.96%, but exhibits so obviously that the cellular precipitates nearly overspread the whole field. The addition of Mo element can restrain the TTP curves moving left and down, which means decreasing the sensitivity of aging precipitation. With increasing the cold deformation, the sensitivity of precipitation increases obviously.展开更多
The aging of bitumen has a significant impact on the mechanical behavior of asphalt. This aging is carried out at the mixing operation with the aggregates generally at 163°C in the case of pure mixtures or at tem...The aging of bitumen has a significant impact on the mechanical behavior of asphalt. This aging is carried out at the mixing operation with the aggregates generally at 163°C in the case of pure mixtures or at temperatures higher than in the case of the modification by polymers or industrial waste. This paper presents experimental results of a study of the rheological behavior of a class of bitumen 40/50 to the artificial aging. Three aging temperatures were selected: 163°C, 173°C and 183°C. From obtained results, a study of the risk of deformation of asphalt is performed, based on the results of correlation between the behavior of the coated and his binder deducted SHRP specifications and technical advice French. These results show that the stiffness of the aged binders increases with aging temperature. Moreover, there is no risk of rutting and fatigue cracking for thermal coated projected.展开更多
The influences of artificial aging on the microstructures and mechanical properties of an Al-1.01Mg-0.68Si-1.78Cu alloy were investigated. The detailed fracture surfaces, precipitates, and dislocation structures were ...The influences of artificial aging on the microstructures and mechanical properties of an Al-1.01Mg-0.68Si-1.78Cu alloy were investigated. The detailed fracture surfaces, precipitates, and dislocation structures were also examined through scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that the tensile strengths exhibit two peak values and reach saturated values with increasing aging time, while the elongation decreases sharply to the minimum value and changes slightly later. The deformation and fracture behaviors are also closely related to the aging conditions.展开更多
The effect of deformation and aging treatment on the electrical conductivity of Cu-Cr alloy was studied. The results show that deformation can reduce the electrical conductivity of Cu-Cr alloy, but deformation followe...The effect of deformation and aging treatment on the electrical conductivity of Cu-Cr alloy was studied. The results show that deformation can reduce the electrical conductivity of Cu-Cr alloy, but deformation followed by optimum aging treatment can effectively improve the electrical conductivity of Cu-Cr alloy, under the condition of 0～70% deformation, and the electrical conductivity of Cu-Cr alloy by aging treatment increases and the aging time of obtaining much better electrical conductivity of Cu-Cr alloy decreases with increase in deformation quantity of Cu-Cr alloy. The best electrical conductivity of Cu-Cr alloy after deformation can be obtained by aging treatment at 500 ℃. And also the reasons for the variations of alloy's electrical conductivity and the function of adding RE were analyzed.展开更多
Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitiz...Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitizing at 1 150℃ and water quench, deformation 10% and 30% respectively, and then thermal aging at 500℃ for different period of time. The microstructure of the specimens was analyzed in details using transmission electron microscopy （TEM）. The micro-hardness test results showed that all the hardness curves of undeformed, 10% pre-deformed and 30% pre-deformed specimens have two micro-hardness peaks with the first peak value corresponding to different thermal aging time of 1 hour, 5 hours and 10 hours, respectively. It was revealed that the hardness curves were influenced by the precipitation of Cu-rich precipitates （CRPs） and carbides, deposition of martensite and work hardening.展开更多
The extruded AZ80+0.4%Ce magnesium alloy was twisted in the temperature range of 300-380℃by using a Gleeble 3500 thermal simulation test machine with a torsion unit.The deformed cylindrical specimens were cooled at a...The extruded AZ80+0.4%Ce magnesium alloy was twisted in the temperature range of 300-380℃by using a Gleeble 3500 thermal simulation test machine with a torsion unit.The deformed cylindrical specimens were cooled at a cooling rate of 10℃/s or 0.1℃/s,respectively,and aged at 170℃.The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center(SRPC),and that the strong initial basal texture of the extruded magnesium alloy was weakened.Both continuous and discontinuous dynamic recrystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated.And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300℃.For the specimens deformed at 300℃and 340℃followed by a slow cooling rate(0.1℃/s),precipitates of various shapes(β-Mg_(17)Al_(12)),with the dominant precipitates being on the grains boundaries,appeared on the surface section.For specimen deformed at 380℃,lamellar precipitates(LPS)in the interiors of the grains were predominant.After aging,the LPS still dominated for specimens twisted at 380℃;however,the LPS gradually decreased with decreasing deformation temperatures from 380℃to 300℃.Dynamically precipitatedβ,especially those decorating the grain boundaries,changed the competition pictures for the LPS and precipitates of other shapes after aging.Interestingly,LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures.Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain,reduced precipitates size,decreased lamellar spacing as well as strain hardening.展开更多
The combined effects of pre-deformation and pre-aging on the mechanical properties of AlCu-Mg alloy with Sc and Zr addition were investigated. It is revealed that the introduction of pre-deformation can enhance the pe...The combined effects of pre-deformation and pre-aging on the mechanical properties of AlCu-Mg alloy with Sc and Zr addition were investigated. It is revealed that the introduction of pre-deformation can enhance the peak-aging strength, as well as tensile and yield strength, effectively due to the formation of finer and more dispersive precipitation. Pre-aging process before pre-deformation can increase the elongation while maintaining higher strength with a discontinuous distribution of precipitates at grain boundary. The precipitates of bean-like Al3（Sc, Zr） particles further strengthen the alloy via pinning the dislocations which are formed during pre-deformation process and hindering the dislocation motion. Furthermore, pre-deformation and pre-aging accelerate the kinetics of precipitation due to preferential sites provided by the dislocation and the increase of GPB zones＇ size and distribution. The synergism of pre-deformation and pre-aging achieves a combination of better mechanical properties and shorter peak-aging time.展开更多
Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes.T...Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes.This study aims to comprehensively investigate the strengthening of aluminium alloy 7005 through the imposition of severe plastic deformation supplemented by two different ageing treatments:pre-deformation artificial ageing or postdeformation natural ageing.For this purpose,microstructure evolutions of the alloy processed through mentioned procedures were studied using X-ray diffraction and scanning electron microscopy while the alloy strengthening was evaluated using Vickers hardness measurement.Results show that a superlative strengthening is obtained through the imposition of severe plastic deformation supplemented by post-deformation natural ageing.For instance,the yield strength of the alloy increases to more than 400 MPa,about one-third greater than the counterpart amount after the usual T6 treatment.This superlative strength mainly occurs due to refinement of grains,an increase of dislocation density and an increase of volume fraction of the precipitates that appeared during natural ageing.Considering the applied models,it is inferred that the increase of volume fraction of precipitates that appeared during natural ageing has a determinative role in the strengthening of the alloy.展开更多
The deformation behaviour of a casting Mg-3.6% Er magnesium alloy after T6 treatment was studied in tensile tests from room temperature to 450 ℃ under different strain rates ranging from 1.0 ×10^-4 to 6.0 ×...The deformation behaviour of a casting Mg-3.6% Er magnesium alloy after T6 treatment was studied in tensile tests from room temperature to 450 ℃ under different strain rates ranging from 1.0 ×10^-4 to 6.0 × 10^-3 S^-1 Obtained local plateau in the temperature dependence of the ultimate strength （σb） and yield strength （σ0.2） under constant strain rate indicated the presence of dynamic strain ageing （DSA）. Serrated flow was observed at the temperature of 200, 250, and 300 ℃. The observed negative strain rate sensitivity suggested that the serrated flow behavior arose from DSA. The temperature and strain rate dependence of the critical strain for the onset of serrated flow was analyzed using a phenomenological DSA equation, and the apparent activation energy Q for the serrated flow was obtained by calculation.展开更多
Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a com...Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was investigated by Split Hopkinson Pressure Bar(SHPB)with the strain rates of 1000-25000 s^(-1),high-speed hydraulic servo material testing machine with the strain rates of 1-500 s^(-1).The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with;(111)_(Cu)//(111)_(Ag):(^(-)111)_(Cu)//(^(-)111)_(Ag):(^(-)200)_(Cu)//(^(-)200)_(Ag) and [0^(-)11]_(Cu)//[0^(-)11]_(Ag) with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.展开更多
Effect of large cold deformation on the age-hardening characteristics of 2024 aluminum alloys was investigated. The results reveal: 1) the aging response is accelerated after large cold deformation, and the peak stren...Effect of large cold deformation on the age-hardening characteristics of 2024 aluminum alloys was investigated. The results reveal: 1) the aging response is accelerated after large cold deformation, and the peak strength is attained after aging for 40 min; 2) double aging peaks can be found in the age-hardening curves, and the first peak appears when aged for 40 min. The corresponding peak tensile strength (sb) and elongation are up to 580 MPa and 9.2% respectively, the second peak appears when aged for 120 min, but the peak tensile strength(520 MPa) is lower than the first one; 3) in early stage of aging (<40 min), elongation slightly increases from 8% with prolonging aging time of the alloy. Elongation markedly decreases to 2% after aging for 60 min, and shows a plateau with the prolonging of aging time on the age-elongation curve. It is indicated that the high density of dislocation introduced by large deformation accelerates the precipitation of GP zones and the aging response of the alloy. The first aging peak is due to the formation of GP zones and the deformation strengthening caused by the high density of dislocation. And the second peak present in the aging curve is attributed to the nucleation and growth of S’ phase. The offset between dislocation density decreases and precipitation S’-phase finally results in the phenomenon of double aging peaks when aged at 190 ℃. Moreover, it is suggested that the formation of PFZ and coarse equilibrium phase accompanied by the precipitation of S’ phase decrease the elongation.展开更多
The frequent occurrence of hitherto unknown phase Pre-θ′-2 and unusual 1.5 cθ′thick θ′precipitate was observed by atomic-resolution scanning transmission electron microscopy in the well-studied Al-Cu alloys. Thi...The frequent occurrence of hitherto unknown phase Pre-θ′-2 and unusual 1.5 cθ′thick θ′precipitate was observed by atomic-resolution scanning transmission electron microscopy in the well-studied Al-Cu alloys. This phenomenon is associated with heterogeneous precipitate nucleation and growth on preexisting dislocations introduced by slight deformation prior to aging. In this study, the precise structure details of Pre-θ′-2 was determined by atomic scale imaging, image simulation based on image forming theories and first principle calculations. Pre-θ′-2 has a well-defined ordered structure sandwiched between two 2 aAl(~1.5 cθ′) spaced Cu layers on {200}Alplanes. The strong structural similarities between Pre-θ′-2 and 1.5 cθ′ thick θ′ in terms of interfacial structure and thickness, coupled with energetic calculations and preliminary in-situ observations, lead us to propose a new precipitation path toward key strengthening phase θ′展开更多
By a detailed investigation of geometry and kinematics of the Shangma （商麻） fault in Dabieshan （大别山）, three different crust levels of extension movement have been recognized in sequence from the deep to the sh...By a detailed investigation of geometry and kinematics of the Shangma （商麻） fault in Dabieshan （大别山）, three different crust levels of extension movement have been recognized in sequence from the deep to the shallow：① low-angle ductile detachment shearing with top to the NW; ② low-angle normal fault with top to the NW or NWW in brittle or brittle-ductile transition domain; ③ high-angle brittle normal fault with top to the W or NWW. Two samples were chosen for zircon U-Pb age dating to constrain the activity age of the Shangma fault. A bedding intrusive granitoid pegmatite vein that is parallel to the foliation of the low-angle ductile detachment shear zone of the country rock exhibits a lotus-joint type of boudinage deformation, showing syn-tectonic emplacing at the end of the ductile deformation period and deformation in the brittle-ductile transition domain. The zircon U-Pb dating of this granitoid pegmatite vein gives an age of （125.9±4.2） Ma, which expresses the extension in the brittle-ductile transition domain of the Shangma fault. The other sample, which is collected from a granite pluton cutting the foliation of the low-angle ductile detachment shear zone, gives a zircon U-Pb age of （118.8±4.1） Ma, constraining the end of the ductile detachment shearing. Then the transformation age from ductile to brittle deformation can be constrained between 126-119 Ma. Combined with the previous researches, the formation of the Luotian （罗田） dome, which is locatedto the east of the Shangma fault, can be constrained during 150-126 Ma. This study gives a new time constraint to the evolution of the Dabie orogenic belt.展开更多
Precipitates in the conventionally processed （solution treatment followed by aging） AZ80 alloy are coarse, cellular, and incoherent. They nucleate and grow on the basal planes of the matrix or distribute discontinuo...Precipitates in the conventionally processed （solution treatment followed by aging） AZ80 alloy are coarse, cellular, and incoherent. They nucleate and grow on the basal planes of the matrix or distribute discontinuously in the alloy. Their unique morphology and undesired distribution make them ineffective for precipitation strengthening. This condition, however, can be modified by applying selected deforma-tion and heat treatment conditions. The effect of deformation and heat treatment on the morphology and distribution of precipitates has been studied. Deformation was introduced by hot extrusion, cold rolling, or equal channel angular pressing （ECAP）. The microstructures were characterized using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that cold de-formation improved precipitation more significantly than hot deformation, and twinning promoted precipitation more effectively than slip. When ECAP was applied, the Bc-route induced more precipitates than the A-route.展开更多
The Cu-10 %Fe-1.5 %Ag in situ composite with high strength, high conductivity and low cost was prepared, and its hot deformation behavior was investi- gated by isothermal compression test with true strain of 0.69, tem...The Cu-10 %Fe-1.5 %Ag in situ composite with high strength, high conductivity and low cost was prepared, and its hot deformation behavior was investi- gated by isothermal compression test with true strain of 0.69, temperature range of 750-950℃ and strain rate of 0.002-1.000 s-1. The flow stress-strain response shows the characterization of dynamic recrystallization （DRX）, and the peak stress increases gradually with deformation tem- perature decreasing and strain rate increasing. The defor- mation activation energy of the composite for DRX is calculated as 241.864 kJ.mo1-1. The constitutive relation of the composite was got by Arrhenius equation. Further- more, according to the dynamic material modeling and Kumar-Prasad＇s instability criteria, the processing map was constructed and the unsafe regions for hot deformation were analyzed. Based on the processing map and microstructural evolution, the optimal parameter range for hot deformation processing is 750-863℃ at the strain rate of 0.002-0.013 s-1.展开更多
基金financially supported by the National Natural Science Foundation of China(No. 11502285)
文摘This study focuses on the effects of different cold-drawing deformations and aging treatments of solid solution A286 superalloy.The grain configuration,texture,precipitates and tensile strength of A286 superalloy after different deformations and aging treatments were investigated by optical microscopy(OM),field emission scanning electron microscopy(FESEM),electron back-scattered diffraction(EBSD)and mechanical testing machine.The grain size and configuration of A286 alloy can hardly be changed during aging process.The initially equiaxial and twinned crystals are obvious when deformation is less than30%,while the grain boundaries become blurry and slip bands appear after 35% deformation or more.γ’ phase and Cr-rich carbide are the precipitates of A286 alloy.For each deformation,γ’ phase plays a major role during aging and its amount increases gradually when the aging temperature changes from 650 to 680℃,and a maximum tensile strength appears when following two-stage aging.With deformation increasing,the amounts of γ’ phase and Crrich carbide increase in varying degrees.Meanwhile,the<111>wire textures become more obvious,the tensile strength is enhanced and the kernel average misorientation(KAM)increases gradually;the higher KAM of crystal lattices diffuses from the grain boundary to the matrix gradually.
文摘The present study deals with the effect of cold deformation and subsequent aging on the microstructure and mechanical properties of AI-Cu-Si-Mg alloy. Differential scanning calorimetry indicates that precipitation occurs in the temperature range of 258-272℃ for the as quenched wrought alloy. The activation energy value estimated by Kissinger method for the aforesaid precipitation reaction is obtained as 106 kJ/mol. 45% cold deformation prior to aging indicates the first dissolution reaction at about 50℃ and the precipitation reaction at a temperature of about 82℃. Microstructural investigations have revealed the formation of fine precipitates within the matrix after aging of the cold deformed sample. As-quenched alloy reveals prominently the aging response, The increase in hardness, yield and tensile strength with simultaneous decrease in elongation in the deformed alloy is found to be primarily due to the deformation strengthening and not due to the precipitation hardening.
文摘Ag-Cu alloys are extensively used in sliding electric contacts due to their superior electrical conductivity,but their limited wear resistance reduces component longevity.Surface severe plastic deformation(SSPD)has emerged as a promising method to enhance wear resistance and reduce friction of metals without altering the matrix composition.In this study,an Ag-20 wt.%Cu alloy was subjected to SSPD for various durations,with the aim of improving tribological performance.The microstructure,hardness,and current-carrying tribological performance under different currents were systematically investigated,along with an exploration of the underlying mechanisms.The results show that in addition to introducing a high density of dislocations on the surface,SSPD also encourages the formation of(111)texture,and particularly disperses the initially long strips of Curich phase into short strips and fine particles.It promotes a tribo-film composed primarily of a mixture of Cu_(2)O and CuO that forms on the worn surface of the surface-treated sample under the 1 A current,thus significantly reducing the friction coefficient and electrical noise.Under the 10 A current,the sample treated for 60 min possesses the optimal friction coefficient(0.429),wear rate(0.791×10^(−6)mm^(3)/(N m)),and electrical noise(0.240 V).In contrast to the Ag/Cu layered structure observed on the worn subsurface of the untreated sample,a single-phase Ag(Cu)solid solution forms on the worn subsurface of the 60-min treated sample,which improves the current-carrying tribological performance.This work provides valuable insights for the development and application of electrical contact alloys with excellent performance.
文摘Tensile properties at room temperature of a new casting Ni-base superalloy during aging at 800℃ for0-1000 h were investigated.During aging,granular M23C6 carbides presented at grain boundaries and kept growing from dispersed particles to continuous networks.The γ’ phase significantly coarsened,with the morphology of some γ’ phase changed from spherical to rounded cubic shape after 1000 h.Three deformation mechanisms in relation to the γ’ diameter(dγ’) were identified:(ⅰ) weakly coupled dislocations(WCD) connected by anti-phase boundary(APB) traveled in pair across the γ/γ’ structure when dγ’ was small in the under-aged alloys;(ⅱ) strongly coupled dislocations(SCD) with reduced spacing compared to(ⅰ) sheared γ’ phase when dγ’ increased in the over-aged alloys;(ⅲ) dislocations occasionally by-passed γ’ phase when dγ’ was larger than 97 nm after aging for more than 300 h.The alloy obtained the peak strength when 20 h-aged with dγ’=44 nm which was in the transition between(ⅰ) and(ⅱ).The aginginduced variation in yield strength was correlated to the coarsening of γ’ phase using a theoretical model of precipitation strengthening in terms of the formation of APB.The calculated results suggested that the γ’ phase with a volume fraction of 23% contributed more than 61% of the peak-aged yield strength.Observation after fracture revealed that the alloys usually fractured at grain boundaries.High stress concentration around carbides resulted in cracks by carbides self-cracking and the initiation of cavities.The undesirable agglomeration of M23C6 at grain boundaries was harmful to the properties of the overaged alloys.
基金the National High Technology Research and Development Program of China(No.2013AA032401)Teacher’s Research Foundation of Central South University(No.2013JSJJ 001) for the financial supportNonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Centre
文摘The influence of pre-deformation on aging precipitates of three near peak-aged Al–Cu–Li alloys,1460 alloy with a low Cu/Li ratio（1.46）,2050 alloy with a high Cu/Li ratio（4.51） and 2A96 alloy with a medium Cu/Li ratio（2.97）,was investigated.The strength of the aged alloys is enhanced by the pre-deformation.The effectiveness of pre-deformation on precipitates is dependent on the alloy＇s composition.With increasing the pre-deformation,the population density of T1（Al2Cu Li） precipitates increases in all three Al–Cu–Li alloys and their diameter decreases in 2050 and 2A96 alloys,and the greatest effectiveness is observed in 2A96 alloy.The pre-deformation also increases the population density of θ＇（Al2Cu）precipitates and decreases their diameter in 2050 and 2A96 Al–Li alloys,but the effectiveness is smaller compared to that on T1 precipitates.In 1460 alloy subjected to two-step aging at 130 ℃ for 20 h followed by 160 ℃ for 12 h,the main precipitates are δ＇（Al3Li）.At 2%–6% pre-deformation,GP-I zones form and pre-deformation displays little influence.Eight percentage pre-deformation promotes θ＇＇/θ＇ precipitation and increases their population density.
基金Project(51304041) supported by the National Natural Science Foundation of ChinaProject(N100402015) supported by Fundamental Research Funds for the Central Universities of China+1 种基金Project(2012AA03A502) supported by the National High Technology Research and Development Program of ChinaProject supported by Program for Liaoning Innovative Research Team in University,China
文摘The influence of chemical composition and cold deformation on aging precipitation behavior of 18Cr-16Mn-2Mo-I.IN （HNS-A）, 18Cr-16Mn-I.3N （HNS-B）, 18Cr-18Mn-2Mo-0.96N （HNS-C） and 18Cr-18Mn-2Mo-0.77N （I-INS-D） high nitrogen austenitic stainless steels was investigated. The results show that the ＂nose＂ temperatures and incubation periods of the initial time-temperature-precipitation （TTP） curves of aged HNSs are found to be 850 ℃, 60 s; 850 ℃, 45 s; 850 ℃, 60 s and 900 ℃, 90 s, respectively. Based on the analysis of SAD patterns, the coarse cellular Cr2N precipitate which presents a lamellar structure has a hexagonal structure of a=0.478 nm and c=0.444 nm. The Z phase corresponding to a composition of Fe36Cr^2Mo10, is determined to be a body-centered cubic structure ofa=0.892 nm. The precipitating sensitivity presents no more difference with the nitrogen content increasing from 0.77% to 0.96%, but exhibits so obviously that the cellular precipitates nearly overspread the whole field. The addition of Mo element can restrain the TTP curves moving left and down, which means decreasing the sensitivity of aging precipitation. With increasing the cold deformation, the sensitivity of precipitation increases obviously.
文摘The aging of bitumen has a significant impact on the mechanical behavior of asphalt. This aging is carried out at the mixing operation with the aggregates generally at 163°C in the case of pure mixtures or at temperatures higher than in the case of the modification by polymers or industrial waste. This paper presents experimental results of a study of the rheological behavior of a class of bitumen 40/50 to the artificial aging. Three aging temperatures were selected: 163°C, 173°C and 183°C. From obtained results, a study of the risk of deformation of asphalt is performed, based on the results of correlation between the behavior of the coated and his binder deducted SHRP specifications and technical advice French. These results show that the stiffness of the aged binders increases with aging temperature. Moreover, there is no risk of rutting and fatigue cracking for thermal coated projected.
基金the National High-Tech Research and Development Program of China (No. (98-A28-01-09)
文摘The influences of artificial aging on the microstructures and mechanical properties of an Al-1.01Mg-0.68Si-1.78Cu alloy were investigated. The detailed fracture surfaces, precipitates, and dislocation structures were also examined through scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that the tensile strengths exhibit two peak values and reach saturated values with increasing aging time, while the elongation decreases sharply to the minimum value and changes slightly later. The deformation and fracture behaviors are also closely related to the aging conditions.
文摘The effect of deformation and aging treatment on the electrical conductivity of Cu-Cr alloy was studied. The results show that deformation can reduce the electrical conductivity of Cu-Cr alloy, but deformation followed by optimum aging treatment can effectively improve the electrical conductivity of Cu-Cr alloy, under the condition of 0～70% deformation, and the electrical conductivity of Cu-Cr alloy by aging treatment increases and the aging time of obtaining much better electrical conductivity of Cu-Cr alloy decreases with increase in deformation quantity of Cu-Cr alloy. The best electrical conductivity of Cu-Cr alloy after deformation can be obtained by aging treatment at 500 ℃. And also the reasons for the variations of alloy's electrical conductivity and the function of adding RE were analyzed.
文摘Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitizing at 1 150℃ and water quench, deformation 10% and 30% respectively, and then thermal aging at 500℃ for different period of time. The microstructure of the specimens was analyzed in details using transmission electron microscopy （TEM）. The micro-hardness test results showed that all the hardness curves of undeformed, 10% pre-deformed and 30% pre-deformed specimens have two micro-hardness peaks with the first peak value corresponding to different thermal aging time of 1 hour, 5 hours and 10 hours, respectively. It was revealed that the hardness curves were influenced by the precipitation of Cu-rich precipitates （CRPs） and carbides, deposition of martensite and work hardening.
基金supported by key technology research and development project of Shan Xi province(20201102019)Natural science foundation of Shanxi Province(201901D111167)+1 种基金Shanxi Scholarship Council of China(2020–117)JCKY2018408B003Magnesium alloy high-performance XXX multi-directional extrusion technology and XX supporting scientific research project(xxxx-2019-021)。
文摘The extruded AZ80+0.4%Ce magnesium alloy was twisted in the temperature range of 300-380℃by using a Gleeble 3500 thermal simulation test machine with a torsion unit.The deformed cylindrical specimens were cooled at a cooling rate of 10℃/s or 0.1℃/s,respectively,and aged at 170℃.The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center(SRPC),and that the strong initial basal texture of the extruded magnesium alloy was weakened.Both continuous and discontinuous dynamic recrystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated.And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300℃.For the specimens deformed at 300℃and 340℃followed by a slow cooling rate(0.1℃/s),precipitates of various shapes(β-Mg_(17)Al_(12)),with the dominant precipitates being on the grains boundaries,appeared on the surface section.For specimen deformed at 380℃,lamellar precipitates(LPS)in the interiors of the grains were predominant.After aging,the LPS still dominated for specimens twisted at 380℃;however,the LPS gradually decreased with decreasing deformation temperatures from 380℃to 300℃.Dynamically precipitatedβ,especially those decorating the grain boundaries,changed the competition pictures for the LPS and precipitates of other shapes after aging.Interestingly,LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures.Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain,reduced precipitates size,decreased lamellar spacing as well as strain hardening.
基金Funded by the National High-tech Research&Development Program of China(No.2013AA031002)
文摘The combined effects of pre-deformation and pre-aging on the mechanical properties of AlCu-Mg alloy with Sc and Zr addition were investigated. It is revealed that the introduction of pre-deformation can enhance the peak-aging strength, as well as tensile and yield strength, effectively due to the formation of finer and more dispersive precipitation. Pre-aging process before pre-deformation can increase the elongation while maintaining higher strength with a discontinuous distribution of precipitates at grain boundary. The precipitates of bean-like Al3（Sc, Zr） particles further strengthen the alloy via pinning the dislocations which are formed during pre-deformation process and hindering the dislocation motion. Furthermore, pre-deformation and pre-aging accelerate the kinetics of precipitation due to preferential sites provided by the dislocation and the increase of GPB zones＇ size and distribution. The synergism of pre-deformation and pre-aging achieves a combination of better mechanical properties and shorter peak-aging time.
基金the research board of Ferdowsi University of Mashhad(FUM)for the financial support and the provision of research facilities used in this work through grant No.3/41681.
文摘Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes.This study aims to comprehensively investigate the strengthening of aluminium alloy 7005 through the imposition of severe plastic deformation supplemented by two different ageing treatments:pre-deformation artificial ageing or postdeformation natural ageing.For this purpose,microstructure evolutions of the alloy processed through mentioned procedures were studied using X-ray diffraction and scanning electron microscopy while the alloy strengthening was evaluated using Vickers hardness measurement.Results show that a superlative strengthening is obtained through the imposition of severe plastic deformation supplemented by post-deformation natural ageing.For instance,the yield strength of the alloy increases to more than 400 MPa,about one-third greater than the counterpart amount after the usual T6 treatment.This superlative strength mainly occurs due to refinement of grains,an increase of dislocation density and an increase of volume fraction of the precipitates that appeared during natural ageing.Considering the applied models,it is inferred that the increase of volume fraction of precipitates that appeared during natural ageing has a determinative role in the strengthening of the alloy.
基金Project supported by the National Natural Science Foundation of China (50374025)the"863"program (2003AA331110)
文摘The deformation behaviour of a casting Mg-3.6% Er magnesium alloy after T6 treatment was studied in tensile tests from room temperature to 450 ℃ under different strain rates ranging from 1.0 ×10^-4 to 6.0 × 10^-3 S^-1 Obtained local plateau in the temperature dependence of the ultimate strength （σb） and yield strength （σ0.2） under constant strain rate indicated the presence of dynamic strain ageing （DSA）. Serrated flow was observed at the temperature of 200, 250, and 300 ℃. The observed negative strain rate sensitivity suggested that the serrated flow behavior arose from DSA. The temperature and strain rate dependence of the critical strain for the onset of serrated flow was analyzed using a phenomenological DSA equation, and the apparent activation energy Q for the serrated flow was obtained by calculation.
基金financially supported by the Innovation Leading Project of Henan Province (No. 191110210400)the Key Scientific Research Projects of Colleges and Universities in Henan Province (No. 19A430012)+3 种基金the Luoyang Science and Technology Major Project (No. 1901006A)the Henan Outstanding Talents Innovation Fund (182101510003)National Key R&D Plan (No. 2016YFB0301400)National Key R&D Plan (No.2017YFB0306400)
文摘Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was investigated by Split Hopkinson Pressure Bar(SHPB)with the strain rates of 1000-25000 s^(-1),high-speed hydraulic servo material testing machine with the strain rates of 1-500 s^(-1).The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with;(111)_(Cu)//(111)_(Ag):(^(-)111)_(Cu)//(^(-)111)_(Ag):(^(-)200)_(Cu)//(^(-)200)_(Ag) and [0^(-)11]_(Cu)//[0^(-)11]_(Ag) with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.
基金Project(50571069) supported by the National Natural Science Foundation of China Project(05A061) supported by the Department of Education of Hunan Province, China
文摘Effect of large cold deformation on the age-hardening characteristics of 2024 aluminum alloys was investigated. The results reveal: 1) the aging response is accelerated after large cold deformation, and the peak strength is attained after aging for 40 min; 2) double aging peaks can be found in the age-hardening curves, and the first peak appears when aged for 40 min. The corresponding peak tensile strength (sb) and elongation are up to 580 MPa and 9.2% respectively, the second peak appears when aged for 120 min, but the peak tensile strength(520 MPa) is lower than the first one; 3) in early stage of aging (<40 min), elongation slightly increases from 8% with prolonging aging time of the alloy. Elongation markedly decreases to 2% after aging for 60 min, and shows a plateau with the prolonging of aging time on the age-elongation curve. It is indicated that the high density of dislocation introduced by large deformation accelerates the precipitation of GP zones and the aging response of the alloy. The first aging peak is due to the formation of GP zones and the deformation strengthening caused by the high density of dislocation. And the second peak present in the aging curve is attributed to the nucleation and growth of S’ phase. The offset between dislocation density decreases and precipitation S’-phase finally results in the phenomenon of double aging peaks when aged at 190 ℃. Moreover, it is suggested that the formation of PFZ and coarse equilibrium phase accompanied by the precipitation of S’ phase decrease the elongation.
基金financial support from the National Natural Science Foundation of China (Nos. 51601060, 51235010, 51671086)Natural Science Foundation of Hunan Province (No. 2018JJ3655)+5 种基金the Major Project for Defense Basic Preresearch Programthe National Key R&D Program of China (No. 2017YFB0306300)the National Key Basic Research Development Plan Funded Project of China (No. 2014CB046602)the Innovationdriven Plan in Central South University (No. 2015CX002)the Science and Technology Plan in Hunan Province (No. 2016RS2015)the Fundamental Research Funds for the Central Universities of Central South University (No. 1053320180612)
文摘The frequent occurrence of hitherto unknown phase Pre-θ′-2 and unusual 1.5 cθ′thick θ′precipitate was observed by atomic-resolution scanning transmission electron microscopy in the well-studied Al-Cu alloys. This phenomenon is associated with heterogeneous precipitate nucleation and growth on preexisting dislocations introduced by slight deformation prior to aging. In this study, the precise structure details of Pre-θ′-2 was determined by atomic scale imaging, image simulation based on image forming theories and first principle calculations. Pre-θ′-2 has a well-defined ordered structure sandwiched between two 2 aAl(~1.5 cθ′) spaced Cu layers on {200}Alplanes. The strong structural similarities between Pre-θ′-2 and 1.5 cθ′ thick θ′ in terms of interfacial structure and thickness, coupled with energetic calculations and preliminary in-situ observations, lead us to propose a new precipitation path toward key strengthening phase θ′
基金the National Key Science Foundation of China (No.40334037)the National Natural Science Foundation of China (No.40672137)
文摘By a detailed investigation of geometry and kinematics of the Shangma （商麻） fault in Dabieshan （大别山）, three different crust levels of extension movement have been recognized in sequence from the deep to the shallow：① low-angle ductile detachment shearing with top to the NW; ② low-angle normal fault with top to the NW or NWW in brittle or brittle-ductile transition domain; ③ high-angle brittle normal fault with top to the W or NWW. Two samples were chosen for zircon U-Pb age dating to constrain the activity age of the Shangma fault. A bedding intrusive granitoid pegmatite vein that is parallel to the foliation of the low-angle ductile detachment shear zone of the country rock exhibits a lotus-joint type of boudinage deformation, showing syn-tectonic emplacing at the end of the ductile deformation period and deformation in the brittle-ductile transition domain. The zircon U-Pb dating of this granitoid pegmatite vein gives an age of （125.9±4.2） Ma, which expresses the extension in the brittle-ductile transition domain of the Shangma fault. The other sample, which is collected from a granite pluton cutting the foliation of the low-angle ductile detachment shear zone, gives a zircon U-Pb age of （118.8±4.1） Ma, constraining the end of the ductile detachment shearing. Then the transformation age from ductile to brittle deformation can be constrained between 126-119 Ma. Combined with the previous researches, the formation of the Luotian （罗田） dome, which is locatedto the east of the Shangma fault, can be constrained during 150-126 Ma. This study gives a new time constraint to the evolution of the Dabie orogenic belt.
基金supported by the National Natural Science Foundation of China (Nos.50571009 and 50771019)
文摘Precipitates in the conventionally processed （solution treatment followed by aging） AZ80 alloy are coarse, cellular, and incoherent. They nucleate and grow on the basal planes of the matrix or distribute discontinuously in the alloy. Their unique morphology and undesired distribution make them ineffective for precipitation strengthening. This condition, however, can be modified by applying selected deforma-tion and heat treatment conditions. The effect of deformation and heat treatment on the morphology and distribution of precipitates has been studied. Deformation was introduced by hot extrusion, cold rolling, or equal channel angular pressing （ECAP）. The microstructures were characterized using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that cold de-formation improved precipitation more significantly than hot deformation, and twinning promoted precipitation more effectively than slip. When ECAP was applied, the Bc-route induced more precipitates than the A-route.
基金financially supported by the National Natural Science Foundation of China(No.50571035)the National High-Tech Research and Development Project (No.2006AA03Z528)
文摘The Cu-10 %Fe-1.5 %Ag in situ composite with high strength, high conductivity and low cost was prepared, and its hot deformation behavior was investi- gated by isothermal compression test with true strain of 0.69, temperature range of 750-950℃ and strain rate of 0.002-1.000 s-1. The flow stress-strain response shows the characterization of dynamic recrystallization （DRX）, and the peak stress increases gradually with deformation tem- perature decreasing and strain rate increasing. The defor- mation activation energy of the composite for DRX is calculated as 241.864 kJ.mo1-1. The constitutive relation of the composite was got by Arrhenius equation. Further- more, according to the dynamic material modeling and Kumar-Prasad＇s instability criteria, the processing map was constructed and the unsafe regions for hot deformation were analyzed. Based on the processing map and microstructural evolution, the optimal parameter range for hot deformation processing is 750-863℃ at the strain rate of 0.002-0.013 s-1.
