The results of investigations of structure and physical properties of submicrocrystalline (SMC) metals are presented. The SMC structure was formed by severe plastic deformation.The structure was investi- gated by...The results of investigations of structure and physical properties of submicrocrystalline (SMC) metals are presented. The SMC structure was formed by severe plastic deformation.The structure was investi- gated by calorimetric and mossbauer measurements and TEW stuidies. The behavior of physical proper- ties of SMC metals were analysed taking into account spectific features of their structure.展开更多
Hardness of the TiB2/7075 composite increased with increasing deformation temperature In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about I μm in length) and small MgZn2 phases (abou...Hardness of the TiB2/7075 composite increased with increasing deformation temperature In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about I μm in length) and small MgZn2 phases (about 100 nm in size) were precipitated nearby the grain boundaries where the TiB2 particles exist. After deformation at 3000 C, some of the large pre- cipitates and all the small precipitates in these area dissolved into the matrix, meanwhile, fine precipitates were formed in grains. After deformation at 450℃, all the precipitates in the an- nealed composite dissolved into the matrix, and new phases were precipitated in grains. The dissolution of the large fiber-like precipitate makes the saturation level of the matrix increased and leads to an increased solution hardening and natural aging, which contribute much to the hardening effect.展开更多
Characterizing material 3D deformation and damage is a key challenge in mechanical research. Digital volume correlation (DVC), as a tool for quantifying the internal mechanical response, can comprehensively study th...Characterizing material 3D deformation and damage is a key challenge in mechanical research. Digital volume correlation (DVC), as a tool for quantifying the internal mechanical response, can comprehensively study the extraction of key failure parameters. This review summarizes the recent progresses in the study of the internal movement of granular materials, inhomogeneous deformation of composite materials, and stress intensity factor around a crack front in static and fatigue states using DVC. To elaborate on the technique's potential, we discussed the accuracy and efficiency of the algorithm and the acquisition of real microstructure data within the material under a complex environment.展开更多
The main goal of this study is to investigate the microstructure and electrical properties of Al–Zr–La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator...The main goal of this study is to investigate the microstructure and electrical properties of Al–Zr–La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator was used to carry out multi-pass hot compression tests. For five-pass hot compression deformation, the last-pass deformation temperatures were 240, 260, 300, 340, 380, and 420°C, respectively, where the first-pass deformation temperature was 460°C. The experimental results indicated that increasing the hot compression deformation temperature with each pass resulted in improved electrical conductivity of the alloy. Consequently, the flow stress was reduced after deformation of the samples subjected to the same number of passes. In addition, the dislocation density gradually decreased and the grain size increased after hot compression deformation. Furthermore, the dynamic recrystallization behavior was effectively suppressed during the hot compression process because spherical Al;Zr precipitates pinned the dislocation movement effectively and prevented grain boundary sliding.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
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
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
In this paper we examine the effect on the determination of boundary length per unit area of the stepped nature of boundaries in orientation maps derived from electron back-scatter diffraction data.A correction factor...In this paper we examine the effect on the determination of boundary length per unit area of the stepped nature of boundaries in orientation maps derived from electron back-scatter diffraction data.A correction factor is derived for isotropic microstructures.Two measures based on length per unit area for the determination of the cross-link boundary spacing in high strain deformation microstructures are then compared.A geometric method based on subtraction of the contribution to the length per area of the lamellar boundaries gives the best results,though in some cases a method based on boundary misorientation angles may be preferred.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
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 c...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 in δ-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 the δ-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 by δ-ferrite.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
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
The high-temperature deformation behavior of a beta Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy was investigated by a Gleeble-1500 D thermal simulator. The height reduction was 50%, corresponding to a true strain of 0.693. Th...The high-temperature deformation behavior of a beta Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy was investigated by a Gleeble-1500 D thermal simulator. The height reduction was 50%, corresponding to a true strain of 0.693. The strain rate ranging from 0.01 to 10.00 s^-1 and the deformation temperature ranging from 800 to 950 ℃ were considered.The flow stress and the apparent activation energy for deformation, along with the constitutive equation, were used to analyze the behavior of the Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy. The processing map was established. The effect of strain rate on the microstructure at 850 ℃ was evaluated.The flow stress-strain curves indicated that the peak flow stresses increased along with an increase in the strain rate and decreased as the deformation temperature increased.Based on the true stress-true strain curves, the constitutive equation was established and followed as the ε= 6.58×10-(10)[sinh(0.0113σ)]-(3.44)exp(-245481.3/RT). The processing map exhibited the "unsafe" region at the strain rate of10 s^-1 and the temperature of 850 ℃,and the rest region was "safe". The deformation microstructure demonstrated that both dynamic recovery(DRV) and dynamic recrystallization(DRX) existed during deformation. At the lower strain rate of 0.01 s^-1, the main deformation mechanism was the DRV, and the DRX was the dominant deformation mechanism at the higher strain rate of 1.00 s^-1.展开更多
Temperature rise is a significant factor influencing microstructure during(α+β) deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to...Temperature rise is a significant factor influencing microstructure during(α+β) deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to deformation heat.The experiment was carried out in(α+β) phase field at typical temperature rise rates.The microstructures of the alloy under different temperature rise rates were observed by scanning electron microscopy(SEM).It is found that the dissolution rate of primary equiaxed a phase increases with the increase in both temperature and temperature rise rate.In the same temperature range,the higher the temperature rise rate is,the larger the final content and grain size of primary equiaxed a phase are due to less dissolution time.To quantitatively depict the evolution behavior of primary equiaxed a phase under any temperature rise rates,the dissolution kinetics of primary equiaxed a phase were well described by a diffusion model.The model predictions,including content and grain size of primary equiaxed a phase,are in good agreement with experimental observations.The work provides an important basis for the prediction and control of microstructure during hot working of titanium alloy.展开更多
The static recrystallization behavior of 25CrMo4 mirror plate steel has been determined by hot compression testing on a Gleeble 1500 thermal mechanical simulation tester. Compression tests were performed using double ...The static recrystallization behavior of 25CrMo4 mirror plate steel has been determined by hot compression testing on a Gleeble 1500 thermal mechanical simulation tester. Compression tests were performed using double hit schedules at temperatures of 950-- 1 150 ~C, strain rates of 0.01--0.5 s-1 , and recrystallization time of 1--100 s. Results show that the kinetics of static recrystallization and the microstructural evolution were greatly influenced by the deformation parameters (deformation temperature, strain rate and pre strain) and the initial austenite grain size. Based on the experimental results, the kinetics model of static recrystallization has been generated and the comparison between the experimental results and the predicted results has been carried out. It is shown that the predicted results were in good agreement with the experimental results.展开更多
The(submicron+micron) bimodal size Si Cp-reinforced Mg matrix composite was compressed at the temperature of 270–420 °C and strain rate of 0.001–1 s^-1. Then, dynamic recrystallization(DRX) behavior of the...The(submicron+micron) bimodal size Si Cp-reinforced Mg matrix composite was compressed at the temperature of 270–420 °C and strain rate of 0.001–1 s^-1. Then, dynamic recrystallization(DRX) behavior of the composite was investigated by thermodynamic method and verified by microstructure analysis. Results illustrated that the composite possess the lower critical strain and higher DRX ratio as compared to monolithic Mg alloys during hot deformation process. The predicted DRX ratio increased with the proceeding of compression, which was well consistent with the experimental value. Results from thermodynamic calculation suggested that the occurrence of DRX could be promoted by Si Cp, which would be further proved by microstructure analysis. Formation of particle deformation zone around micron Si Cp played a significant role in promoting DRX nucleation. Nevertheless, the distribution of submicron Si Cp was increasingly uniform with the proceeding of compression, which could fully restrain grain growth. Therefore, the corporate effects of micron and submicron Si Cp on DRX contributed to the improvement of DRXed ratio and the refinement of grain size for the composite during compression process.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
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
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
文摘The results of investigations of structure and physical properties of submicrocrystalline (SMC) metals are presented. The SMC structure was formed by severe plastic deformation.The structure was investi- gated by calorimetric and mossbauer measurements and TEW stuidies. The behavior of physical proper- ties of SMC metals were analysed taking into account spectific features of their structure.
基金This work was supported by Alexander von Humboldt Foundation of Germany and the National Natural Science Foundation of China under the grant number of
文摘Hardness of the TiB2/7075 composite increased with increasing deformation temperature In the annealed TiB2/7075 composite, a great amount of fiber-like MgZn2 phases (about I μm in length) and small MgZn2 phases (about 100 nm in size) were precipitated nearby the grain boundaries where the TiB2 particles exist. After deformation at 3000 C, some of the large pre- cipitates and all the small precipitates in these area dissolved into the matrix, meanwhile, fine precipitates were formed in grains. After deformation at 450℃, all the precipitates in the an- nealed composite dissolved into the matrix, and new phases were precipitated in grains. The dissolution of the large fiber-like precipitate makes the saturation level of the matrix increased and leads to an increased solution hardening and natural aging, which contribute much to the hardening effect.
基金supported by the National Natural Science Foundation of China (11722221, 11272305, and 11472265)the National Key Research and Development Program of China (2017YFA0403800 and 2017YFB0702000)the Anhui Provincial Natural Science Foundation (1508085MA17)
文摘Characterizing material 3D deformation and damage is a key challenge in mechanical research. Digital volume correlation (DVC), as a tool for quantifying the internal mechanical response, can comprehensively study the extraction of key failure parameters. This review summarizes the recent progresses in the study of the internal movement of granular materials, inhomogeneous deformation of composite materials, and stress intensity factor around a crack front in static and fatigue states using DVC. To elaborate on the technique's potential, we discussed the accuracy and efficiency of the algorithm and the acquisition of real microstructure data within the material under a complex environment.
基金Sichuan Provincial Development and Reform Commission for funding this work by Panxi Strategic Resources Innovation Development Fund (2015)the department of Science and Technology of Sichuan Province (2015GZ0052)
文摘The main goal of this study is to investigate the microstructure and electrical properties of Al–Zr–La alloys under different hot compression deformation temperatures. In particular, a Gleeble 3500 thermal simulator was used to carry out multi-pass hot compression tests. For five-pass hot compression deformation, the last-pass deformation temperatures were 240, 260, 300, 340, 380, and 420°C, respectively, where the first-pass deformation temperature was 460°C. The experimental results indicated that increasing the hot compression deformation temperature with each pass resulted in improved electrical conductivity of the alloy. Consequently, the flow stress was reduced after deformation of the samples subjected to the same number of passes. In addition, the dislocation density gradually decreased and the grain size increased after hot compression deformation. Furthermore, the dynamic recrystallization behavior was effectively suppressed during the hot compression process because spherical Al;Zr precipitates pinned the dislocation movement effectively and prevented grain boundary sliding.
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.
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Supported by the National Natural Science Foundation of China(No.50371041 and No.50571049)
文摘In this paper we examine the effect on the determination of boundary length per unit area of the stepped nature of boundaries in orientation maps derived from electron back-scatter diffraction data.A correction factor is derived for isotropic microstructures.Two measures based on length per unit area for the determination of the cross-link boundary spacing in high strain deformation microstructures are then compared.A geometric method based on subtraction of the contribution to the length per area of the lamellar boundaries gives the best results,though in some cases a method based on boundary misorientation angles may be preferred.
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 in δ-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 the δ-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 by δ-ferrite.
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.
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 (No.51401027)the China Postdoctoral Science Foundation Funded Project (No.2016M591040)
文摘The high-temperature deformation behavior of a beta Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy was investigated by a Gleeble-1500 D thermal simulator. The height reduction was 50%, corresponding to a true strain of 0.693. The strain rate ranging from 0.01 to 10.00 s^-1 and the deformation temperature ranging from 800 to 950 ℃ were considered.The flow stress and the apparent activation energy for deformation, along with the constitutive equation, were used to analyze the behavior of the Ti-3.0 Al-3.5 Cr-2.0 Fe-0.1 B alloy. The processing map was established. The effect of strain rate on the microstructure at 850 ℃ was evaluated.The flow stress-strain curves indicated that the peak flow stresses increased along with an increase in the strain rate and decreased as the deformation temperature increased.Based on the true stress-true strain curves, the constitutive equation was established and followed as the ε= 6.58×10-(10)[sinh(0.0113σ)]-(3.44)exp(-245481.3/RT). The processing map exhibited the "unsafe" region at the strain rate of10 s^-1 and the temperature of 850 ℃,and the rest region was "safe". The deformation microstructure demonstrated that both dynamic recovery(DRV) and dynamic recrystallization(DRX) existed during deformation. At the lower strain rate of 0.01 s^-1, the main deformation mechanism was the DRV, and the DRX was the dominant deformation mechanism at the higher strain rate of 1.00 s^-1.
基金financially supported by the National Natural Science Foundation of China (Nos.51175427 and 51205317)the Open Fund of State Key Laboratory of Materials Processing and Die & Mould Technology of China (No.P2014-005)+1 种基金the Marie Curie International Research Staff Exchange Scheme within the 7th EC Framework Programme (FP7) (No.318968)the Programme of Introducing Talents of Discipline to Universities (No.B08040)
文摘Temperature rise is a significant factor influencing microstructure during(α+β) deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to deformation heat.The experiment was carried out in(α+β) phase field at typical temperature rise rates.The microstructures of the alloy under different temperature rise rates were observed by scanning electron microscopy(SEM).It is found that the dissolution rate of primary equiaxed a phase increases with the increase in both temperature and temperature rise rate.In the same temperature range,the higher the temperature rise rate is,the larger the final content and grain size of primary equiaxed a phase are due to less dissolution time.To quantitatively depict the evolution behavior of primary equiaxed a phase under any temperature rise rates,the dissolution kinetics of primary equiaxed a phase were well described by a diffusion model.The model predictions,including content and grain size of primary equiaxed a phase,are in good agreement with experimental observations.The work provides an important basis for the prediction and control of microstructure during hot working of titanium alloy.
基金sponsored by National Basic Research Program of China (2011CB012903)
文摘The static recrystallization behavior of 25CrMo4 mirror plate steel has been determined by hot compression testing on a Gleeble 1500 thermal mechanical simulation tester. Compression tests were performed using double hit schedules at temperatures of 950-- 1 150 ~C, strain rates of 0.01--0.5 s-1 , and recrystallization time of 1--100 s. Results show that the kinetics of static recrystallization and the microstructural evolution were greatly influenced by the deformation parameters (deformation temperature, strain rate and pre strain) and the initial austenite grain size. Based on the experimental results, the kinetics model of static recrystallization has been generated and the comparison between the experimental results and the predicted results has been carried out. It is shown that the predicted results were in good agreement with the experimental results.
基金supported by the National Natural Science Foundation of China (Nos. 51201112, 51274149 and 51474152)the Natural Science Foundation of Shanxi (No. 2013021013-3)the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20121402120004)
文摘The(submicron+micron) bimodal size Si Cp-reinforced Mg matrix composite was compressed at the temperature of 270–420 °C and strain rate of 0.001–1 s^-1. Then, dynamic recrystallization(DRX) behavior of the composite was investigated by thermodynamic method and verified by microstructure analysis. Results illustrated that the composite possess the lower critical strain and higher DRX ratio as compared to monolithic Mg alloys during hot deformation process. The predicted DRX ratio increased with the proceeding of compression, which was well consistent with the experimental value. Results from thermodynamic calculation suggested that the occurrence of DRX could be promoted by Si Cp, which would be further proved by microstructure analysis. Formation of particle deformation zone around micron Si Cp played a significant role in promoting DRX nucleation. Nevertheless, the distribution of submicron Si Cp was increasingly uniform with the proceeding of compression, which could fully restrain grain growth. Therefore, the corporate effects of micron and submicron Si Cp on DRX contributed to the improvement of DRXed ratio and the refinement of grain size for the composite during compression process.
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 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.