An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The ...An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200–1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between recrystallization and transformation. The microstructural evolution of severely deformed low-carbon steel after ultra-rapid annealing is investigated based on the proposed regimes. Regarding the intensity and start temperature of the interaction, different microstructures consisting of ferrite and pearlite/martensite are formed. It is found that when the interaction is strong, the microstructure is refined because of the high kinetics of transformation and recrystallization. Moreover, strain shifts an interaction zone to a relatively higher heating rate. Therefore, severely deformed steel should be heated at relatively higher heating rates for it to undergo a strong interaction.展开更多
The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature. Suspend-dense structure and Skeleton-dense structure were selected to i...The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature. Suspend-dense structure and Skeleton-dense structure were selected to investigate the deformation of pavement at meso-scale. The internal microstructures of typical asphalt concretes, AC, SUP and SMA, were scanned by X-ray CT device, and microstructural changes before and after high-temperature damage were researched by digital image processing. Adaptive threshold segmentation algorithm（ATSA） based on image radius was developed and utilized to obtain the binary images of aggregates, air-voids and asphalt mastic. Then the shape and distribution of air-voids and aggregates were analyzed. The results show that the ATSA can distinguish the target and background effectively. Gradation and coarse aggregate size of asphalt mixtures have an obvious influence on the distribution of air-voids. The movements of aggregate particles are complex and aggregates with elliptic sharp show great rotation. The effect of gradation on microstructure during high-temperature damage promotes the research about the failure mechanism of asphalt concrete pavement.展开更多
Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and sc...Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.展开更多
Two actual rocks drilled from a typical ultra-deep hydrocarbon reservoir in the Tarim Basin are selected to conduct in-situ stress-loading micro-focus CT scanning experiments.The gray images of rock microstructure at ...Two actual rocks drilled from a typical ultra-deep hydrocarbon reservoir in the Tarim Basin are selected to conduct in-situ stress-loading micro-focus CT scanning experiments.The gray images of rock microstructure at different stress loading stages are obtained.The U-Net fully convolutional neural network is utilized to achieve fine semantic segmentation of rock skeleton,pore space,and microfractures based on CT slice images of deep rocks.The three-dimensional digital rock models of deformed multiscale fractured-porous media at different stress loading stages are thereafter reconstructed,and the equivalent fracture-pore network models are finally extracted to explore the underlying mechanisms of gas-water two-phase flow at the pore-scale.Results indicate that,in the process of insitu stress loading,both the deep rocks have experienced three stages:linear elastic deformation,nonlinear plastic deformation,and shear failure.The micro-mechanical behavior greatly affects the dynamic deformation of rock microstructure and gas-water two-phase flow.In the linear elastic deformation stage,with the increase in in-situ stress,both the deep rocks are gradually compacted,leading to decreases in average pore radius,pore throat ratio,tortuosity,and water-phase relative permeability,while the coordination number nearly remains unchanged.In the plastic deformation stage,the synergistic influence of rock compaction and existence of micro-fractures typically exert a great effect on pore-throat topological properties and gas-water relative permeability.In the shear failure stage,due to the generation and propagation of micro-fractures inside the deep rock,the topological connectivity becomes better,fluid flow paths increase,and flow conductivity is promoted,thus leading to sharp increases in average pore radius and coordination number,rapid decreases in pore throat ratio and tortuosity,as well as remarkable improvement in relative permeability of gas phase and waterphase.展开更多
The recently established theory has built clear connections between hardness and toughness and electron structure involving both valence electron concentration(VEC)and core electron count(CEC)in transition metal nitri...The recently established theory has built clear connections between hardness and toughness and electron structure involving both valence electron concentration(VEC)and core electron count(CEC)in transition metal nitride(TMN)ceramics.However,the underlying deformation mechanisms remain unclear.Herein,we conduct in-depth analysis on microstructure evolution during deformation of the high VEC-CEC solution TiMoN coatings having desired combination of high hardness and toughness.The effects of solid solution,preferred orientation linked with symbiotic compressive stress,grain size and dislocations are systematically discussed.We discover that numerous dislocations have been implanted into the nanocrystals of the TiMoN coating during the high-ionization arc deposition.Using two-beam bright-field imaging,we count the dislocation density and confirm occurrence of dislocation multiplication to form effective plastic deformation,which contributes to significant strain hardening,comparable to solid solution hardening,fine-grain hardening and compressive stress hardening.The improved dislocation activities also play a crucial role in enhancing the toughness by providing extra energy dissipation paths.This work gains new insights into the origins of mechanical properties of ceramic coatings and possibility to tune them via defects.展开更多
The effects of austenite grain size on the deformed microstructure and mechanical properties of an Fe-20Mn-6Al-0.6C-0.15Si(wt.%)low-density steel were investigated.The microstructure of the experimental steel after so...The effects of austenite grain size on the deformed microstructure and mechanical properties of an Fe-20Mn-6Al-0.6C-0.15Si(wt.%)low-density steel were investigated.The microstructure of the experimental steel after solution treatment was single austenitic phase.The austenite grain size increased with solution temperature and time.A model was established to show the relationship between temperature,time and austenite grain size for the experimental steel.In addition,as the solution temperature increased,the strength decreased,while the elongation first increased and then decreased.This decrease in elongation after solution treatment at 1100℃ for 90 min is contributed to the over-coarse austenite grains.However,after solution treatment at 900℃ for 90 min,the strength-elongation product reached the highest value of 44.4 GPa%.As the austenite grain size increased,the intensity of<111>//tensile direction fiber decreased.This was accompanied by a decrease in dislocation density,resulting in a lower fraction of low-angle grain boundaries and a lower work hardening rate.Therefore,the austenite grain size has a critical influence on the mechanical properties of the low-density steels.Coarser grains lead to a lower yield strength due to the Hall-Petch effect and a lower tensile strength because of lower dislocation strengthening.展开更多
Dynamic recrystallization (DRX) behavior in β phase region for the burn resistant titanium alloy Ti?25V?15Cr?0.2Si was investigated with a compression test in the temperature range of 950?1100 °C and the strain ...Dynamic recrystallization (DRX) behavior in β phase region for the burn resistant titanium alloy Ti?25V?15Cr?0.2Si was investigated with a compression test in the temperature range of 950?1100 °C and the strain rate of 0.001?1 s?1. The results show that deformation mechanism of this alloy in hot deformation is dominated by DRX, and new grains of DRX are evolved by bulging nucleation mechanism as a predominant mechanism. DRX occurs more easily with the decrease of strain rate and the increase of deformation temperature. Grain refinement is achieved due to DRX during the hot deformation at strain rate range of 0.01?0.1 s?1 and temperature range of 950?1050 °C. DRX grain coarsening is observed for the alloy deformed at the higher temperatures of 1100 °C and the lower strain rates of 0.001 s?1. Finally, in order to determine the recrystallized fraction and DRX grain size under different deformation conditions, the prediction models of recrystallization kinetics and recrystallized grain sizes were established.展开更多
Microstructural evolution of a refractory tantalum-tungsten alloy(Ta-4%W)after cold rolling from small to large von-Mises strains(0.12-2.7)was quantitatively studied using transmission electron microscopy.Grain subdiv...Microstructural evolution of a refractory tantalum-tungsten alloy(Ta-4%W)after cold rolling from small to large von-Mises strains(0.12-2.7)was quantitatively studied using transmission electron microscopy.Grain subdivision was observed to take place at two levels.Geometrically necessary boundaries nearly paralleling to slip planes enclosed volumes further divided by diffuse cells and by remnants of Taylor lattices.With increasing strain,the diffuse cells evolved into clear incidental dislocation boundaries enclosing cells,while the Taylor lattices disappeared.Grain subdivision was thus intermediate between those observed in cell forming and in non-cell forming alloys.Meanwhile,the average misorientation angle across all boundaries increased while the average boundary spacing decreased.Distributions of the microstructural parameters at each strain level were found to exhibit universal scaling laws.The microstructural evolution was found closely linking to the observed high strength and strain hardening of this alloy.Based on measured microstructural parameters,the flow stress was calculated utilizing linearly addition of the strengthening by solutes,incidental dislocation boundaries(Taylor strengthening)and geometrically necessary boundaries(Hall-Petch equation).The relative contribution of each strength mechanism evolved with increasing strain and with microstructural evolution:solutes and friction stress dominated at small strains while boundaries dominated at larger strains.Calculated strengths were in close agreement with experimental tension tests and demonstrated an unexpectedly high and continuous parabolic hardening without transition across this large strain range.展开更多
This study examined the mechanical properties, springback behavior from three-point bending loading–unloading tests and biocompatibility from human osteoblast cell adhesion and proliferation experiments in Ti-15Mo al...This study examined the mechanical properties, springback behavior from three-point bending loading–unloading tests and biocompatibility from human osteoblast cell adhesion and proliferation experiments in Ti-15Mo alloy with different microstructures. The springback ratio increased after the appearance of deformation microstructures including {332} < 113 > twins and dislocations, due to the increased bending strength and unchanged Young’s modulus. By contrast, the change in springback ratio was dependent on the competing effect of the simultaneous increase in bending strength and Young’s modulus after phase transformation, namely, the isothermal ω-phase formation. Good cell adhesion and proliferation were observed on the alloy surface, and they were not significantly affected by the deformation twins, dislocations and isothermal ω-phase.The diversity of deformation and phase transformation microstructures made it possible to control the springback behavior effectively while keeping the biocompatibility of the alloy as an implant rod used for spinal fixation devices.展开更多
The austenitic heat resistant-steels have been considered as important candidate materials for advanced supercritical boilers, nuclear reactors, super heaters and chemical reactors, due to their favorable combination ...The austenitic heat resistant-steels have been considered as important candidate materials for advanced supercritical boilers, nuclear reactors, super heaters and chemical reactors, due to their favorable combination of high strength, corrosion resistance, perfect mechanical properties, workability and low cost.Since the precipitation behavior of the steels during long-term service at elevated temperature would lead to the deterioration of mechanical properties, it is essential to clarify the evolution of secondary phases in the microstructure of the steels. Here, a summary of recent progress in the precipitation behavior and the coarsening mechanism of various precipitates during aging in austenitic steels is made. Various secondary phases are formed under service conditions, like MX carbonitrides, M_（23）C_6 carbides, Z phase, sigma phase and Laves phase. It is found that the coarsening rate of M_（23）C_6 carbides is much higher than that of MX carbonitrides. In order to understand the thermal deformation mechanism, a constitutive equation can be established, and thus obtained processing maps are beneficial to optimizing thermal processing parameters, leading to improved thermal processing properties of steels.展开更多
Stress-rupture properties of a Ni-base Re-containing single-crystal superalloy with three orientations have been tested under 900℃/445 MPa.An obvious anisotropy of stress-rupture property is attributed to orientation...Stress-rupture properties of a Ni-base Re-containing single-crystal superalloy with three orientations have been tested under 900℃/445 MPa.An obvious anisotropy of stress-rupture property is attributed to orientation reliant deformation microstructure.The good strength in[001]orientation is attributed to the rapid multiplication of dislocations active in horizontal channels and laterγ'cutting via dislocations pair coupled with anti-phase boundary.The microtwin formation largely limits the strength and plasticity as a result of the continuous shearing acrossγ/γ'microstructure by{111}112 slip activated in[011]orientation.The property in[111]orientation results mainly from the lateral cross-slip movements of the screw dislocations within connected matrix channels as well as the precipitate shearing by coplanar dislocations.Microcracks all initially originate from the interdendritic micropores in three orientations.The critical temperature of stress-rupture anisotropy could be increased by a high level of refractory solutes especially Re.展开更多
Recrystallization of cold-rolled discontinuous, precipitation microstructurewhich has fine laminar structure in an Al-40 percent Zn (atom fraction) binary alloy is investigatedby optical microscopy, SEM and TEM. It is...Recrystallization of cold-rolled discontinuous, precipitation microstructurewhich has fine laminar structure in an Al-40 percent Zn (atom fraction) binary alloy is investigatedby optical microscopy, SEM and TEM. It is found that there are two kinds of recrystallizationmechanisms: continuous coarsening (CC) and discontinuous coarsening (DC). The latter can be dividedinto coarsening mainly driven by stored deformation energy at colony boundaries and slip bands andthe one mainly driven by boundary energy in the area with little deformation. It is shown that theaddition of Cu can retard the nucleation of coarsening cells and their growth. X-Ray diffractionanalysis indicated the metastable phase CuZn_4 transformed into equilibrium phase A;_4Cu_3Zn duringthe heating process.展开更多
Microstructural evolution and mechanical properties of cryogenic rolled Fe-36Ni steel were investigated. The annealed Fe-36Ni steel was rolled at cryogenic temperature（ 123-173 K） with 20%- 90% rolling reduction in ...Microstructural evolution and mechanical properties of cryogenic rolled Fe-36Ni steel were investigated. The annealed Fe-36Ni steel was rolled at cryogenic temperature（ 123-173 K） with 20%- 90% rolling reduction in thickness.The deformation process was accompanied by twinning at cryogenic temperature,and the mean thickness of deformation twins was about 200 nm with 20% rolling reduction. When the rolling reduction was above 40%,twinning was suppressed due to the stress concentration in the tested steel. Deformation microstructure of Fe-36Ni steel consisted of both twin boundaries and dislocations by cryogenic rolling（ CR）,while it only contained dislocations after rolling at room temperature（ RT）. The tensile strength of Fe-36Ni steel was improved to 930 MPa after 90% reduction at cryogenic temperature,while the tensile strength after 90% reduction at RT was only 760 MPa. More dislocations could be produced as the nucleation sites of recrystallization during CR process.展开更多
Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable st...Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results onfcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo- mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.展开更多
The evolution of the microstructure and texture in copper has been studied during repetitive extrusionupsetting（REU） to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It i...The evolution of the microstructure and texture in copper has been studied during repetitive extrusionupsetting（REU） to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It is found that the texture is significantly altered by each deformation pass. A duplex 001 ＋ 111 fiber texture with an increased 111 component is observed after each extrusion pass,whereas the 110 fiber component dominates the texture after each upsetting pass. During REU, the microstructure is refined by deformation-induced boundaries. The average cell size after a total strain of 4.7 is measured to be ~0.3 μm. This refined microstructure is unstable at room temperature as is evident from the presence of a small number of recrystallized grains in the deformed matrix. Pronounced recrystallization took place during annealing at 200？C for 1 h with recrystallized grains developing predominantly in high misorientation regions. At 350？C the microstructure is fully recrystallized with an average grain size of only 2.3 μm and a very weak crystallographic texture. This REU-processed and subsequently annealed material is considered to be potentially suitable for using as a material for sputtering targets.展开更多
The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electro...The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe_2（W,Mo）Laves phase has formed during creep with 200 MPa applied stress at 883 Kfor 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.展开更多
This work investigated the effect of pre-strain and microstructures and their interactions on hydrogen trapping behaviors in case of 1-GPa high-strength martensitic steel Fe-0.05C-0.30Si-1.10Mn-3.50Ni-0.53Cr-0.50Mo-0....This work investigated the effect of pre-strain and microstructures and their interactions on hydrogen trapping behaviors in case of 1-GPa high-strength martensitic steel Fe-0.05C-0.30Si-1.10Mn-3.50Ni-0.53Cr-0.50Mo-0.03 V(wt%).We found that the trapped reversible and trapped irreversible hydrogen contents increased significantly after applying a pre-strain of 5%,with an increase in the trapped reversible hydrogen content from 0.6 ppm in the original sample to 2.1 ppm.The hydrogen desorption activation energy also showed a slight increase.The microstructural evolution revealed that the concomitant dislocation cell-twin duplex microstructure with high-density tangled dislocations after pre-strain substantially increased the trapped reversible hydrogen contents.Additionally,the tangled dislocations pinned by the nanoprecipitates acted as deep irreversible hydrogen traps,increasing the trapped hydrogen at high temperatures after applying 5%pre-strain.These findings provide an expanded understanding of the hydrogen trapping behaviors of pre-strained microstructures.展开更多
The proton-irradiated 308L stainless steel weld metal was strained by using constant extension rate tensile testing in simulated PWR primary water,and its deformation microstructures and irradiation assisted stress co...The proton-irradiated 308L stainless steel weld metal was strained by using constant extension rate tensile testing in simulated PWR primary water,and its deformation microstructures and irradiation assisted stress corrosion cracking(IASCC)behavior were investigated.The results suggest that the irradiation significantly increases the SCC susceptibility of 308L weld metal and causes various deformation microstructures including lathy faulted planes,dislocation channels and deformation twins in austenite and atomic plane rotation inδ-ferrite.The propagation of intergranular IASCC cracks is closely related to the location of the crack tip.For the crack tip in the specimen matrix interior,localized deformation is likely the key factor responsible for the crack growth.For the crack tip close to the specimen surface,however,localized corrosion along the grain boundary rather than the localized deformation appears to dominate the crack propagation.Unlike the intergranular cracks,the IASCC cracks along theδ-ferrite/austenite phase boundary can initiate either by crack initiation at the phase boundary or by crack propagation from the grain boundary.In both cases,the cracked phase boundaries contain a large number of carbides and are severely corroded,but no deformation microstructures are observed,which implies that the localized corrosion may play an important role in the IASCC along the phase boundary.In addition,δ-ferrite can retard the IASCC crack propagation along the grain boundary,which is probably related to the reduction of localized deformation byδ-ferrite.展开更多
High temperature stress rupture anisotropies of a second generation Ni-base single crystal（SC） superalloy specimens with [001], [011] and [111] orientations under 900 ℃/445 MPa and 1100 ℃/100 MPa have been investi...High temperature stress rupture anisotropies of a second generation Ni-base single crystal（SC） superalloy specimens with [001], [011] and [111] orientations under 900 ℃/445 MPa and 1100 ℃/100 MPa have been investigated in the present study, with attentions to the evolution of γ/γ′ microstructure observed by scanning electron microscopy and the dislocation configuration characterized by transmission electron microscopy in each oriented specimen. At 1100 ℃/100 MPa as well as 900 ℃/445 MPa, the single crystal superalloy exhibits obvious stress rupture anisotropic behavior. The [001] oriented specimen has the longest rupture lifetime at 900 ℃/445 MPa, and the [111] oriented sample shows the best rupture strength at 1100 ℃/100 MPa. While the [011] oriented specimen presents the worst rupture lifetime at each testing condition, its stress rupture property at 1100 ℃/100 MPa is clearly improved, compared with900 ℃/445 MPa. The evident stress rupture anisotropy at 900 ℃/445 MPa is mainly attributed to the distinctive movement way of dislocations in each oriented sample. Whereas, at 1100 ℃/100 MPa, together with the individual dislocation configuration, the evolution of γ/γ′ microstructure in each orientation also plays a key role in the apparent stress rupture anisotropy.展开更多
Results of an experimental and modelling study of forming processes in the AA2099 Al–Cu–Li alloy, for a wide range of temperatures, strains and strain rates, are presented. The analyses are based on tensile testing ...Results of an experimental and modelling study of forming processes in the AA2099 Al–Cu–Li alloy, for a wide range of temperatures, strains and strain rates, are presented. The analyses are based on tensile testing at 20 °C at a strain rate of 0.02 s-1and uniaxial compression testing in the temperature range 400–550 °C at strain rates ranging from0.001 to 100 s-1, for constant values of true strain of 0.5 and 0.9. The stability of plastic deformation and its relationship with a sensitivity of stress to strain rate are considered. The power dissipation efficiency coefficient, g（%）, and the flow instability parameter, n B 0, were determined. The complex processing maps for hot working were determined and quantified, including process frames for basic forging processes： conventional forging and for near-superplastic and isothermal conditions. A significant aspect is the convergence of power dissipation when passing through the 500 °C peak.Deformation, temperature and strain-rate-dependent microstructures at 500 °C for strain rates of 0.1, 1, 10 and 100 s-1are described and analysed for the conventional die forging process frame, corresponding to 465–523 °C and strain rates of50–100 s-1.展开更多
基金the research board of the Sharif University of Technology for financial support and the provision of the research facilities used in this work
文摘An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200–1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between recrystallization and transformation. The microstructural evolution of severely deformed low-carbon steel after ultra-rapid annealing is investigated based on the proposed regimes. Regarding the intensity and start temperature of the interaction, different microstructures consisting of ferrite and pearlite/martensite are formed. It is found that when the interaction is strong, the microstructure is refined because of the high kinetics of transformation and recrystallization. Moreover, strain shifts an interaction zone to a relatively higher heating rate. Therefore, severely deformed steel should be heated at relatively higher heating rates for it to undergo a strong interaction.
基金Funded by National Natural Science Foundation of China(No.51178114)the Fundamental Research Funds for the Central Universities(No.CXLX12_0117)the Scientific Research Foundation of Graduate School of Southeast University(No.YBJJ1318)
文摘The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature. Suspend-dense structure and Skeleton-dense structure were selected to investigate the deformation of pavement at meso-scale. The internal microstructures of typical asphalt concretes, AC, SUP and SMA, were scanned by X-ray CT device, and microstructural changes before and after high-temperature damage were researched by digital image processing. Adaptive threshold segmentation algorithm（ATSA） based on image radius was developed and utilized to obtain the binary images of aggregates, air-voids and asphalt mastic. Then the shape and distribution of air-voids and aggregates were analyzed. The results show that the ATSA can distinguish the target and background effectively. Gradation and coarse aggregate size of asphalt mixtures have an obvious influence on the distribution of air-voids. The movements of aggregate particles are complex and aggregates with elliptic sharp show great rotation. The effect of gradation on microstructure during high-temperature damage promotes the research about the failure mechanism of asphalt concrete pavement.
基金financial support from the National Natural Science Foundation of China (No. 51675143)
文摘Magnesium（Mg） alloy AZ31 was produced by continuous variable cross-section direct extrusion（CVCDE）to study its deformation behavior. Metallographic microscopy（OM）, transmission electron microscopy（TEM）, and scanning electron microscopy（SEM） were used to observe the variations in microstructure and fracture morphology of Mg alloy AZ31 as a function of processing methods. The results reveal that grains of Mg alloy AZ31 were refined and their microstructure was homogenized by CVCDE. The recrystallization in Mg alloy AZ31 produced by CVCDE with 2 interim dies was more complete than that produced by conventional extrusion（CE） and CVCDE with 1 interim die, and the grains were finer and more uniform.Plasticity of the AZ31 alloy was improved. Fracture mode was evolved from a combination of ductility and brittleness to a sole ductile form. In summary, a CVCDE mold structure with 2 interim dies can improve microstructure, plasticity, and toughness of Mg alloy AZ31.
基金supported by the National Natural Science Foundation of China(No.52174043)the Beijing Natural Science Foundation(No.3242019)+1 种基金the CNPC Innovation Foundation(No.2022DQ02-0208)the State Key Laboratory of Deep Oil and Gas(No.SKLD0G2024-KFZD-06).
文摘Two actual rocks drilled from a typical ultra-deep hydrocarbon reservoir in the Tarim Basin are selected to conduct in-situ stress-loading micro-focus CT scanning experiments.The gray images of rock microstructure at different stress loading stages are obtained.The U-Net fully convolutional neural network is utilized to achieve fine semantic segmentation of rock skeleton,pore space,and microfractures based on CT slice images of deep rocks.The three-dimensional digital rock models of deformed multiscale fractured-porous media at different stress loading stages are thereafter reconstructed,and the equivalent fracture-pore network models are finally extracted to explore the underlying mechanisms of gas-water two-phase flow at the pore-scale.Results indicate that,in the process of insitu stress loading,both the deep rocks have experienced three stages:linear elastic deformation,nonlinear plastic deformation,and shear failure.The micro-mechanical behavior greatly affects the dynamic deformation of rock microstructure and gas-water two-phase flow.In the linear elastic deformation stage,with the increase in in-situ stress,both the deep rocks are gradually compacted,leading to decreases in average pore radius,pore throat ratio,tortuosity,and water-phase relative permeability,while the coordination number nearly remains unchanged.In the plastic deformation stage,the synergistic influence of rock compaction and existence of micro-fractures typically exert a great effect on pore-throat topological properties and gas-water relative permeability.In the shear failure stage,due to the generation and propagation of micro-fractures inside the deep rock,the topological connectivity becomes better,fluid flow paths increase,and flow conductivity is promoted,thus leading to sharp increases in average pore radius and coordination number,rapid decreases in pore throat ratio and tortuosity,as well as remarkable improvement in relative permeability of gas phase and waterphase.
基金supported by the Distinguished Young Scholars of China(No.52025014)Natural Science Foundation of Zhejiang Province(No.LQ23E010002)Innovation 2025 Major Project of Ningbo(Nos.2022Z011 and 2023Z022).
文摘The recently established theory has built clear connections between hardness and toughness and electron structure involving both valence electron concentration(VEC)and core electron count(CEC)in transition metal nitride(TMN)ceramics.However,the underlying deformation mechanisms remain unclear.Herein,we conduct in-depth analysis on microstructure evolution during deformation of the high VEC-CEC solution TiMoN coatings having desired combination of high hardness and toughness.The effects of solid solution,preferred orientation linked with symbiotic compressive stress,grain size and dislocations are systematically discussed.We discover that numerous dislocations have been implanted into the nanocrystals of the TiMoN coating during the high-ionization arc deposition.Using two-beam bright-field imaging,we count the dislocation density and confirm occurrence of dislocation multiplication to form effective plastic deformation,which contributes to significant strain hardening,comparable to solid solution hardening,fine-grain hardening and compressive stress hardening.The improved dislocation activities also play a crucial role in enhancing the toughness by providing extra energy dissipation paths.This work gains new insights into the origins of mechanical properties of ceramic coatings and possibility to tune them via defects.
基金supports from National Natural Science Foundation of China(No.U20A20270)China Postdoctoral Science Foundation(No.2022M722486).
文摘The effects of austenite grain size on the deformed microstructure and mechanical properties of an Fe-20Mn-6Al-0.6C-0.15Si(wt.%)low-density steel were investigated.The microstructure of the experimental steel after solution treatment was single austenitic phase.The austenite grain size increased with solution temperature and time.A model was established to show the relationship between temperature,time and austenite grain size for the experimental steel.In addition,as the solution temperature increased,the strength decreased,while the elongation first increased and then decreased.This decrease in elongation after solution treatment at 1100℃ for 90 min is contributed to the over-coarse austenite grains.However,after solution treatment at 900℃ for 90 min,the strength-elongation product reached the highest value of 44.4 GPa%.As the austenite grain size increased,the intensity of<111>//tensile direction fiber decreased.This was accompanied by a decrease in dislocation density,resulting in a lower fraction of low-angle grain boundaries and a lower work hardening rate.Therefore,the austenite grain size has a critical influence on the mechanical properties of the low-density steels.Coarser grains lead to a lower yield strength due to the Hall-Petch effect and a lower tensile strength because of lower dislocation strengthening.
基金Projects(51261020,51164030)supported by the National Natural Science Foundation of ChinaProject(GF201401007)supported by the Open Fund of National Defense Key Disciplines Laboratory of Light Alloy Processing Science and Technology,China
文摘Dynamic recrystallization (DRX) behavior in β phase region for the burn resistant titanium alloy Ti?25V?15Cr?0.2Si was investigated with a compression test in the temperature range of 950?1100 °C and the strain rate of 0.001?1 s?1. The results show that deformation mechanism of this alloy in hot deformation is dominated by DRX, and new grains of DRX are evolved by bulging nucleation mechanism as a predominant mechanism. DRX occurs more easily with the decrease of strain rate and the increase of deformation temperature. Grain refinement is achieved due to DRX during the hot deformation at strain rate range of 0.01?0.1 s?1 and temperature range of 950?1050 °C. DRX grain coarsening is observed for the alloy deformed at the higher temperatures of 1100 °C and the lower strain rates of 0.001 s?1. Finally, in order to determine the recrystallized fraction and DRX grain size under different deformation conditions, the prediction models of recrystallization kinetics and recrystallized grain sizes were established.
基金financially supported by the National Natural Science Foundation of China(Nos.52071038,51421001)support from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme(ERC Advanced grant M4D/grant agreement number 788567)for part of the workthe support of the“111 Project”(B16007)by the Ministry of Education and the State Administration of Foreign Experts Affairs of China。
文摘Microstructural evolution of a refractory tantalum-tungsten alloy(Ta-4%W)after cold rolling from small to large von-Mises strains(0.12-2.7)was quantitatively studied using transmission electron microscopy.Grain subdivision was observed to take place at two levels.Geometrically necessary boundaries nearly paralleling to slip planes enclosed volumes further divided by diffuse cells and by remnants of Taylor lattices.With increasing strain,the diffuse cells evolved into clear incidental dislocation boundaries enclosing cells,while the Taylor lattices disappeared.Grain subdivision was thus intermediate between those observed in cell forming and in non-cell forming alloys.Meanwhile,the average misorientation angle across all boundaries increased while the average boundary spacing decreased.Distributions of the microstructural parameters at each strain level were found to exhibit universal scaling laws.The microstructural evolution was found closely linking to the observed high strength and strain hardening of this alloy.Based on measured microstructural parameters,the flow stress was calculated utilizing linearly addition of the strengthening by solutes,incidental dislocation boundaries(Taylor strengthening)and geometrically necessary boundaries(Hall-Petch equation).The relative contribution of each strength mechanism evolved with increasing strain and with microstructural evolution:solutes and friction stress dominated at small strains while boundaries dominated at larger strains.Calculated strengths were in close agreement with experimental tension tests and demonstrated an unexpectedly high and continuous parabolic hardening without transition across this large strain range.
基金supported by the National Natural Science Foundation of China(No.52071051)。
文摘This study examined the mechanical properties, springback behavior from three-point bending loading–unloading tests and biocompatibility from human osteoblast cell adhesion and proliferation experiments in Ti-15Mo alloy with different microstructures. The springback ratio increased after the appearance of deformation microstructures including {332} < 113 > twins and dislocations, due to the increased bending strength and unchanged Young’s modulus. By contrast, the change in springback ratio was dependent on the competing effect of the simultaneous increase in bending strength and Young’s modulus after phase transformation, namely, the isothermal ω-phase formation. Good cell adhesion and proliferation were observed on the alloy surface, and they were not significantly affected by the deformation twins, dislocations and isothermal ω-phase.The diversity of deformation and phase transformation microstructures made it possible to control the springback behavior effectively while keeping the biocompatibility of the alloy as an implant rod used for spinal fixation devices.
基金the China National Funds for Distinguished Young Scientists(Grant No.51325401)the National Natural Science Foundation of China(Grant No.51474156 and U1660201)the National High Technology Research and Development Program of China(Grant No.2015AA042504)for grant and financial support
文摘The austenitic heat resistant-steels have been considered as important candidate materials for advanced supercritical boilers, nuclear reactors, super heaters and chemical reactors, due to their favorable combination of high strength, corrosion resistance, perfect mechanical properties, workability and low cost.Since the precipitation behavior of the steels during long-term service at elevated temperature would lead to the deterioration of mechanical properties, it is essential to clarify the evolution of secondary phases in the microstructure of the steels. Here, a summary of recent progress in the precipitation behavior and the coarsening mechanism of various precipitates during aging in austenitic steels is made. Various secondary phases are formed under service conditions, like MX carbonitrides, M_（23）C_6 carbides, Z phase, sigma phase and Laves phase. It is found that the coarsening rate of M_（23）C_6 carbides is much higher than that of MX carbonitrides. In order to understand the thermal deformation mechanism, a constitutive equation can be established, and thus obtained processing maps are beneficial to optimizing thermal processing parameters, leading to improved thermal processing properties of steels.
基金financially supported by the National Key R&D Program of China(No.2017YFA0700704)the National Natural Science Foundation of China(No.51871221)the National Science and Technology Major Project(No.2017-VI-0002-0072)。
文摘Stress-rupture properties of a Ni-base Re-containing single-crystal superalloy with three orientations have been tested under 900℃/445 MPa.An obvious anisotropy of stress-rupture property is attributed to orientation reliant deformation microstructure.The good strength in[001]orientation is attributed to the rapid multiplication of dislocations active in horizontal channels and laterγ'cutting via dislocations pair coupled with anti-phase boundary.The microtwin formation largely limits the strength and plasticity as a result of the continuous shearing acrossγ/γ'microstructure by{111}112 slip activated in[011]orientation.The property in[111]orientation results mainly from the lateral cross-slip movements of the screw dislocations within connected matrix channels as well as the precipitate shearing by coplanar dislocations.Microcracks all initially originate from the interdendritic micropores in three orientations.The critical temperature of stress-rupture anisotropy could be increased by a high level of refractory solutes especially Re.
文摘Recrystallization of cold-rolled discontinuous, precipitation microstructurewhich has fine laminar structure in an Al-40 percent Zn (atom fraction) binary alloy is investigatedby optical microscopy, SEM and TEM. It is found that there are two kinds of recrystallizationmechanisms: continuous coarsening (CC) and discontinuous coarsening (DC). The latter can be dividedinto coarsening mainly driven by stored deformation energy at colony boundaries and slip bands andthe one mainly driven by boundary energy in the area with little deformation. It is shown that theaddition of Cu can retard the nucleation of coarsening cells and their growth. X-Ray diffractionanalysis indicated the metastable phase CuZn_4 transformed into equilibrium phase A;_4Cu_3Zn duringthe heating process.
基金Item Sponsored by Research Fund for the Central Universities of China(N130607002)National Natural Science Foundation of China(51174057,51274062)Research Fund for the Doctoral Program of Higher Education of China(20130042110040)
文摘Microstructural evolution and mechanical properties of cryogenic rolled Fe-36Ni steel were investigated. The annealed Fe-36Ni steel was rolled at cryogenic temperature（ 123-173 K） with 20%- 90% rolling reduction in thickness.The deformation process was accompanied by twinning at cryogenic temperature,and the mean thickness of deformation twins was about 200 nm with 20% rolling reduction. When the rolling reduction was above 40%,twinning was suppressed due to the stress concentration in the tested steel. Deformation microstructure of Fe-36Ni steel consisted of both twin boundaries and dislocations by cryogenic rolling（ CR）,while it only contained dislocations after rolling at room temperature（ RT）. The tensile strength of Fe-36Ni steel was improved to 930 MPa after 90% reduction at cryogenic temperature,while the tensile strength after 90% reduction at RT was only 760 MPa. More dislocations could be produced as the nucleation sites of recrystallization during CR process.
基金financially supported by the National Natural Science Foundation of China (Nos. 51501069, 51671093 and 51625402)Partial financial support came from the Science and Technology Development Program of Jilin Province (Nos. 20160519002JH and 20170520124JH)+1 种基金the Chang Bai Mountain Scholars Program (2013014)the talented youth lift project of Jilin province
文摘Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results onfcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo- mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.
基金supported by the Chongqing Research Program of Basic Research and Frontier Technology (No. cstc2015jcyj BX0115)support of the “111” Project (B16007) by the Ministry of Education and the State Administration of Foreign Experts Affairs of Chinathe National Natural Science Foundation of China (Nos. 51471039, 51421001)
文摘The evolution of the microstructure and texture in copper has been studied during repetitive extrusionupsetting（REU） to a total von Mises strain of 4.7 and during subsequent annealing at different temperatures. It is found that the texture is significantly altered by each deformation pass. A duplex 001 ＋ 111 fiber texture with an increased 111 component is observed after each extrusion pass,whereas the 110 fiber component dominates the texture after each upsetting pass. During REU, the microstructure is refined by deformation-induced boundaries. The average cell size after a total strain of 4.7 is measured to be ~0.3 μm. This refined microstructure is unstable at room temperature as is evident from the presence of a small number of recrystallized grains in the deformed matrix. Pronounced recrystallization took place during annealing at 200？C for 1 h with recrystallized grains developing predominantly in high misorientation regions. At 350？C the microstructure is fully recrystallized with an average grain size of only 2.3 μm and a very weak crystallographic texture. This REU-processed and subsequently annealed material is considered to be potentially suitable for using as a material for sputtering targets.
基金Item Sponsored by National Natural Science Foundation of China(51201061,51475315)China Postdoctoral Science Foundation(2015M571804)Natural Science Foundation of Jiangsu Province of China(BK20150329)
文摘The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe_2（W,Mo）Laves phase has formed during creep with 200 MPa applied stress at 883 Kfor 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.
基金The authors acknowledge the financial support received from the National Natural Science Foundation of China(Nos.52201060,51922002,and 52001182)the China Postdoctoral Science Foundation(Nos.BX20220035 and 2022M710347)the Science Center for Gas Turbine Project(No.P2022-B-IV-008-001).
文摘This work investigated the effect of pre-strain and microstructures and their interactions on hydrogen trapping behaviors in case of 1-GPa high-strength martensitic steel Fe-0.05C-0.30Si-1.10Mn-3.50Ni-0.53Cr-0.50Mo-0.03 V(wt%).We found that the trapped reversible and trapped irreversible hydrogen contents increased significantly after applying a pre-strain of 5%,with an increase in the trapped reversible hydrogen content from 0.6 ppm in the original sample to 2.1 ppm.The hydrogen desorption activation energy also showed a slight increase.The microstructural evolution revealed that the concomitant dislocation cell-twin duplex microstructure with high-density tangled dislocations after pre-strain substantially increased the trapped reversible hydrogen contents.Additionally,the tangled dislocations pinned by the nanoprecipitates acted as deep irreversible hydrogen traps,increasing the trapped hydrogen at high temperatures after applying 5%pre-strain.These findings provide an expanded understanding of the hydrogen trapping behaviors of pre-strained microstructures.
基金financially supported by the Jiangsu Natural Science Foundation(No.BK20191178)the National Natural Science Foundation of China(No.52071018)the China Postdoctoral Science Foundation(No.2021M692018)。
文摘The proton-irradiated 308L stainless steel weld metal was strained by using constant extension rate tensile testing in simulated PWR primary water,and its deformation microstructures and irradiation assisted stress corrosion cracking(IASCC)behavior were investigated.The results suggest that the irradiation significantly increases the SCC susceptibility of 308L weld metal and causes various deformation microstructures including lathy faulted planes,dislocation channels and deformation twins in austenite and atomic plane rotation inδ-ferrite.The propagation of intergranular IASCC cracks is closely related to the location of the crack tip.For the crack tip in the specimen matrix interior,localized deformation is likely the key factor responsible for the crack growth.For the crack tip close to the specimen surface,however,localized corrosion along the grain boundary rather than the localized deformation appears to dominate the crack propagation.Unlike the intergranular cracks,the IASCC cracks along theδ-ferrite/austenite phase boundary can initiate either by crack initiation at the phase boundary or by crack propagation from the grain boundary.In both cases,the cracked phase boundaries contain a large number of carbides and are severely corroded,but no deformation microstructures are observed,which implies that the localized corrosion may play an important role in the IASCC along the phase boundary.In addition,δ-ferrite can retard the IASCC crack propagation along the grain boundary,which is probably related to the reduction of localized deformation byδ-ferrite.
基金supported by the National High Technology Research and Development Program of China (“863 Program”,No. 20102014AA041701)the National Natural Science Foundation of China (No. 51331005) and (No. 51401210)
文摘High temperature stress rupture anisotropies of a second generation Ni-base single crystal（SC） superalloy specimens with [001], [011] and [111] orientations under 900 ℃/445 MPa and 1100 ℃/100 MPa have been investigated in the present study, with attentions to the evolution of γ/γ′ microstructure observed by scanning electron microscopy and the dislocation configuration characterized by transmission electron microscopy in each oriented specimen. At 1100 ℃/100 MPa as well as 900 ℃/445 MPa, the single crystal superalloy exhibits obvious stress rupture anisotropic behavior. The [001] oriented specimen has the longest rupture lifetime at 900 ℃/445 MPa, and the [111] oriented sample shows the best rupture strength at 1100 ℃/100 MPa. While the [011] oriented specimen presents the worst rupture lifetime at each testing condition, its stress rupture property at 1100 ℃/100 MPa is clearly improved, compared with900 ℃/445 MPa. The evident stress rupture anisotropy at 900 ℃/445 MPa is mainly attributed to the distinctive movement way of dislocations in each oriented sample. Whereas, at 1100 ℃/100 MPa, together with the individual dislocation configuration, the evolution of γ/γ′ microstructure in each orientation also plays a key role in the apparent stress rupture anisotropy.
基金financed by the Ministry of Science and Higher Education (AGH-UST statutory research project No. 11.11.110.292)
文摘Results of an experimental and modelling study of forming processes in the AA2099 Al–Cu–Li alloy, for a wide range of temperatures, strains and strain rates, are presented. The analyses are based on tensile testing at 20 °C at a strain rate of 0.02 s-1and uniaxial compression testing in the temperature range 400–550 °C at strain rates ranging from0.001 to 100 s-1, for constant values of true strain of 0.5 and 0.9. The stability of plastic deformation and its relationship with a sensitivity of stress to strain rate are considered. The power dissipation efficiency coefficient, g（%）, and the flow instability parameter, n B 0, were determined. The complex processing maps for hot working were determined and quantified, including process frames for basic forging processes： conventional forging and for near-superplastic and isothermal conditions. A significant aspect is the convergence of power dissipation when passing through the 500 °C peak.Deformation, temperature and strain-rate-dependent microstructures at 500 °C for strain rates of 0.1, 1, 10 and 100 s-1are described and analysed for the conventional die forging process frame, corresponding to 465–523 °C and strain rates of50–100 s-1.
