To manufacture plate by the combination of equal channel angular processing （ECAP） and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing （P-ECAP）, was studied....To manufacture plate by the combination of equal channel angular processing （ECAP） and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing （P-ECAP）, was studied. Extrusion of AL6005A plate used for the bullet train plate was investigated by finite element method. The relevant porthole dies involving ECAP technique in channels were designed. Dimensional changes in the scrap part of the extrudate obtained after extrusion from the P-ECAP die, with different channel angles, were predicted. Effects of the channel angle and extrusion speed on the maximum temperature of the workpiece and other field variables were evaluated. At the channel angle of 160° of P-ECAP dies, the extrudate exhibited the optimal performance and the least amount of extrudate scrap was obtained. The optimal extrusion speed was 3-5 mm/s. Moreover, with the increase in ram speed from 1 to 9 mm/s, the peak extrusion load increased by about 49% and the maximum temperature was increased by about 70 ℃. The effective strain exhibited ascending trend in the comer of the ECAP deformation zone. In the solder seam and the side of die bearing of extrudate, the maximum principal stresses were tensile stress.展开更多
A review on severe plastic deformation（SPD） technique of equal channel angular pressing（ECAP） process of commercially pure titanium（CP-Ti） alloys was presented with a major emphasize on the influence of ECAP par...A review on severe plastic deformation（SPD） technique of equal channel angular pressing（ECAP） process of commercially pure titanium（CP-Ti） alloys was presented with a major emphasize on the influence of ECAP parameters that include channel and curvature angles, processing route, temperature of operation, pressing speed, internal heating, number of pass through the die and back pressure. Various ECAP characteristics such as microstructure, strain inhomogeneity and mechanical properties are considered to achieve the maximum homogeneity, equilibrium grain refinement and mechanical improvement of CP-Ti. Investigations show that a pressing speed of 1-3 mm/s at 450 °C with route BC along with channel and curvature angles of 90° and 20° respectively with backpressure can lead to the most homogeneous ultrafine microstructure.展开更多
In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new ...In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.展开更多
The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. ...The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. Such band structures diminish formability and become origin of the so-called ridging. A novel processing will be shown here, which involves strain-path change by introducing one-pass ECAP prior to cold-rolling, and facilitates recrystallisation. Indeed, the recrystallisation temperature was reduced by 100℃, compared with cold-rolling alone imposing an equivalent strain. Grain- scale microshear bands introduced during one-pass ECAP perturbed the banded structures in post-ECAP cold-rolling and enhanced the recrystallisation at the final annealing.展开更多
Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is ...Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is still inhomogeneous after four passes,and two zones,namely the fine grain zone（FGZ） and the coarse grain zone（CGZ） are formed.The grain refinement occurs mainly by particle-stimulated nucleation（PSN） mechanism,which led to a more random texture after four passes of ECAP.In the ECAP-processed alloy,the strength did not increase while the ductility was enhanced dramatically compared with the as-received condition.The change of ductility of this alloy was discussed in terms of texture and second phase particles.展开更多
Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angularextrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that withincreasing semi-solid isothermal treatment te...Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angularextrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that withincreasing semi-solid isothermal treatment temperature, the a phase solid grain size of processedMg-Al-Zn alloy by ECAE increases firstly due to coarsening of a phase solid grains, then decreasesdue to melting of a phase solid grains. With the increase of extrusion passes during ECAE, the aphase solid grain size in the following semi-solid isothermal treatment decreases. The a phase solidgrain size of processed Mg-Al-Zn alloy by ECAE under route B_C is the smallest, while the a phasesolid grain size of processed material by ECAE under route A is the largest. The primary mechanismof spheroid formation depends on the melting of recrystallizing boundaries and diffusion of soluteatoms in the semi-solid state.展开更多
Equal Channel Angular Pressing(ECAP)is one of the most applicable Sever Plastic Deformation(SPD)processes which leads to strength and ductility improvement through the grain refining and development of a suitable text...Equal Channel Angular Pressing(ECAP)is one of the most applicable Sever Plastic Deformation(SPD)processes which leads to strength and ductility improvement through the grain refining and development of a suitable texture.In this study,after designing and manufacturing a suitable die,4 pass ECAP process at route C is done on strip shaped specimens of AZ31 magnesium alloy in order to achieve desirable microstructural and mechanical properties.Microstructure then got studied through the optical microscopy.Results show that mean grain size is decreased and grain size distribution got close to normal distribution state by increasing the pass number.However,the grain size is reduced by increasing of ECAP temperature.展开更多
AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temper...AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP,in placing of {1 010},planes {1 011} and {1 012} become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane(0001).展开更多
Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively r...Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.展开更多
Three high-nitrogen stainless steels with different N contents were successfully processed by equal-channel angular pressing for one pass, and their microstructures and mechanical properties were investigated. It was ...Three high-nitrogen stainless steels with different N contents were successfully processed by equal-channel angular pressing for one pass, and their microstructures and mechanical properties were investigated. It was found that the microstructure of the billet was heterogeneous across the billet thickness, resulting in the difference in the mechanical properties due to the different deformation conditions. A relatively low strength, high uniform elongation, and high work- hardening rate for the samples at the bottom of the billet was achieved in comparison with those processed at the top. Meanwhile, it was observed that the density of deformation twins increased with the content of N; accordingly, the strength and elongation of the alloys increase with the content of N, resulting in a good strength-ductility combination.展开更多
Samples of a commercial Cu-lCr-0.1Zr(mass fraction,%) alloy were subjected to equal channel angular pressing(ECAP) up to 16 passes at room temperature following route Bc.Differential scanning calorimetry(DSC) was used...Samples of a commercial Cu-lCr-0.1Zr(mass fraction,%) alloy were subjected to equal channel angular pressing(ECAP) up to 16 passes at room temperature following route Bc.Differential scanning calorimetry(DSC) was used to highlight the precipitation sequence and to calculate the stored energy,recrystallization temperature and activation energy after each ECAP pass.On another hand,electrical properties were correlated with the dislocation density.Results show that the stored energy increases upon increasing ECAP pass numbers,while the recrystallization temperature decreases significantly.展开更多
Equal-channel angular pressing(ECAP) is now recognized as an effective technique for fabricating ultrafine grained materials. The results show that prevalent macroscopic shear banding occurs in ECAP as long as the pre...Equal-channel angular pressing(ECAP) is now recognized as an effective technique for fabricating ultrafine grained materials. The results show that prevalent macroscopic shear banding occurs in ECAP as long as the pressing passes reach 2, and the severe macroscopic shear band extends from bottom to top surface and slants to the longitudinal axis of specimen at an angle of about 45°, develops at regular intervals, with a high shear strain accommodation of about 3.7 within the band. Different families of macroscopic shear bands may cut across each other, and over 60% of sample volume is occupied by macroscopic shear band when the ECAP reaches 4 passes.展开更多
The microstructure evolutions and mechanical properties of a heterogeneous Mg88Y8Zn4（in at.%） alloy during multi-pass equal channel angular pressing（ECAP） were systematically investigated in this work.The results ...The microstructure evolutions and mechanical properties of a heterogeneous Mg88Y8Zn4（in at.%） alloy during multi-pass equal channel angular pressing（ECAP） were systematically investigated in this work.The results show that four phases,i.e.α-Mg,18 R long period stacking ordered（LPSO） phase,Mg24Y5 and Y-rich phase,are present in cast alloy.During ECAP,dynamic recrystallization（DRX） occurs and the diameter of DRXedα-Mg grains decreases to 0.8 μm.Moreover,precipitation of lamellar 14 H LPSO structure is developed withinα-Mg phase.Both the refinement of α-Mg grains and precipitation of 14 H LPSO contribute to the increase in micro-hardness from 98 HV to 135 HV for α-Mg.In addition,a simplified model describing the evolution of 18 R LPSO phase is established,which illustrates that 18 R undergoes a four-step morphological evolution with increasing strains during ECAP,i.e.original lath → bent lath → cracked lath → smaller particles.Compression test results indicate that the alloy has been markedly strengthened after multi-pass ECAP,and the main reason for the significantly enhanced mechanical properties could be ascribed to the DRXed α-Mg grains,newly precipitated 14 H lamellas,18 R kinking and refined 18 R particles.展开更多
Aluminum alloy 5083(AA5083)processed by large-scale Equal-channel angular pressing(ECAP)is an excellent engineering material with great prospects for industrial applications.An accurate assessment of the underlying co...Aluminum alloy 5083(AA5083)processed by large-scale Equal-channel angular pressing(ECAP)is an excellent engineering material with great prospects for industrial applications.An accurate assessment of the underlying constitutive relationships with easily determined material constants is critical for the predictive design and informed processing of such structural materials.To develop such a design framework,uniaxial dynamic compressive tests over a wide range of temperatures(293-573 K)were carried out for an ECAP-processed AA5083 alloy.Additionally,the microstructure before and after dynamic loading was characterized by SEM and TEM.Based on the experimental results,a new dynamic constitutive model,based on thermal activation theory,was established to describe the plastic flow behavior of the AA5083 alloy that incorporates the effects of plastic strain,temperature,and strain rate.The input parameters of the new model were determined using a particle swarm optimization(PSO)method.The model predictions show excellent agreement with experimental results,which suggests that the current predictive constitutive model is highly effective in reproducing the dynamic deformation behavior of the large-scale ECAP-processed AA5083.展开更多
Among the various Severe Plastic Deformation(SPD)processes,Equal Channel Angular Pressing(ECAP)is one of the most applicable one which improves strength and ductility due to grain refinement and suitable texture devel...Among the various Severe Plastic Deformation(SPD)processes,Equal Channel Angular Pressing(ECAP)is one of the most applicable one which improves strength and ductility due to grain refinement and suitable texture development.In this study,cold rolling were carried out on the 4 pass ECAPed(in route A and C)strip shaped specimens of AZ31 magnesium alloy to investigate the ECAP effects on the roll-ability.Results showed that reduction in area which can be concerned as an index for roll-ability increased after ECAP.It was also seen that ECAP in route C enhanced roll-ability more than route A.展开更多
Al-11%Si(mass fraction)alloy was transformed into a ductile material by equal-channel angular pressing(ECAP)with a rotary die.Two mechanisms at impact test,slip deformation by dislocation motion and grain boundary sli...Al-11%Si(mass fraction)alloy was transformed into a ductile material by equal-channel angular pressing(ECAP)with a rotary die.Two mechanisms at impact test,slip deformation by dislocation motion and grain boundary sliding,were discussed.The ultrafine grains with modified grain boundaries and the high content of fine particles(<1μm)were necessary for attaining high absorbed energy.The results contradict the condition of slip deformation by dislocation motion and coincide with that of grain boundary sliding.Many fine zigzag lines like a mosaic were observed on the side surface of the tested specimens.These observed lines may show grain boundaries appeared by the sliding of grains.展开更多
A new technique to produce ultra-fine grained tubular specimen has been proposed, and the experiments have been performed using equal channel angular pressing （ECAP） with an angle of 90 between two intersecting chan...A new technique to produce ultra-fine grained tubular specimen has been proposed, and the experiments have been performed using equal channel angular pressing （ECAP） with an angle of 90 between two intersecting channels and also the use of rubber pad as a mandrel during process. Commercial purity copper tubes have been pressed up to three passes through four different fundamental routes （A, BA, Bc, and C） directions of which are identified in the text below. The influence of each route on the value, distribution, and homogeneity of hardness has been investigated by applying Vickers micro-hardness measurements at various locations of the tube＇s transverse planes. Significant enhancement of the hardness is observed after the first pass ECAP. Also, routes C and Bc show, respectively, better average hardness magnitude and hardness distribution uniformity. In addition, the results indicate that there is about 50% and 62% reduction of the grain size, compared to the annealed condition, following ECAP process of the copper tube sample after the first and the third pass via route Bc.展开更多
The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing （ECAP） up to four passes was investigated using X-ray diffxaction （XRD） analysis and transmission electron microscopy...The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing （ECAP） up to four passes was investigated using X-ray diffxaction （XRD） analysis and transmission electron microscopy （TEM）. Microhardness tests were performed to determine the associated changes in mechanical properties. An ultrafine-grained material has been obtained with a microstructure showing a mixture of highly strained crystallites. A high density of dislocations was achieved as a result of severe plastic deformation （SPD） through the die. Changes in mechanical behavior are also revealed after ECAP due to strain hardening. Thermal analysis and TEM micrographs ob- tained after annealing indicate the succession of the recovery, recrystallization, and grain growth phenomena. Moreover, the energy stored during ECAP may be related to the dislocation density introduced by SPD. We finally emphasize the role played by the precipitates in this alloy.展开更多
Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing（ECAP） have been examined after exposure to a low energy,high-flux deuterium（D） plasma at fluenc...Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing（ECAP） have been examined after exposure to a low energy,high-flux deuterium（D） plasma at fluences of 3×10^24 D/m^2 and 1×10^25 D/m^2 in a temperature range of 100 ℃-150 ℃.The methods used were scanning electron microscopy（SEM） and thermal desorption spectroscopy（TDS）.Sparse and small blisters（0.1 μm） were observed by SEM after D plasma irradiation on every irradiated surface;yet they did not exhibit significant structure or plasma fluence dependence.Larger blisters or protrusions appeared after subsequent TDS heating up to 1000 ℃.The TDS results showed a single D desorption peak at 220℃ for all samples and the D retention increased with increasing numbers of extrusion passes,i.e.,the decrease of grain sizes.The increased D retention in this low temperature range should be attributed to the faster diffusion of D along the larger volume fraction of grain boundaries introduced by ECAP.展开更多
Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain struct...Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain structure. Fe-Cr alloys were pressed at 423 K while pure copper at room temperature for 1 to 3 passes via the route Bc to compare at the equivalent homologous temperature. Microstructural evolutions were characterized by electron backscatter diffraction (EBSD) image and transmission electron microscopy (TEM). It was found that deformation structures were mostly deformation-induced subboundaries in both the materials after one pass, but the fraction of high-angle grain boundary became higher in the Fe-Cr alloys than in pure copper in subsequent passes by increasing misorientation of the boundaries. The more enhanced formation of high angle boundaries in Fe-Cr alloys was discussed in terms of the nature of crystal slip of FCC and BCC structures.展开更多
基金Project(B08040)supported by the Program of Introducing Talents of Discipline to Universities(111 Project),ChinaProject(2009ZX04005-031-11)supported by the National Science and Technology Special Program,China
文摘To manufacture plate by the combination of equal channel angular processing （ECAP） and porthole die extrusion techniques, a novel technique, namely portholes-equal channel angular processing （P-ECAP）, was studied. Extrusion of AL6005A plate used for the bullet train plate was investigated by finite element method. The relevant porthole dies involving ECAP technique in channels were designed. Dimensional changes in the scrap part of the extrudate obtained after extrusion from the P-ECAP die, with different channel angles, were predicted. Effects of the channel angle and extrusion speed on the maximum temperature of the workpiece and other field variables were evaluated. At the channel angle of 160° of P-ECAP dies, the extrudate exhibited the optimal performance and the least amount of extrudate scrap was obtained. The optimal extrusion speed was 3-5 mm/s. Moreover, with the increase in ram speed from 1 to 9 mm/s, the peak extrusion load increased by about 49% and the maximum temperature was increased by about 70 ℃. The effective strain exhibited ascending trend in the comer of the ECAP deformation zone. In the solder seam and the side of die bearing of extrudate, the maximum principal stresses were tensile stress.
基金Project(DMR-0968825)support by National Science Foundation Through Grant
文摘A review on severe plastic deformation（SPD） technique of equal channel angular pressing（ECAP） process of commercially pure titanium（CP-Ti） alloys was presented with a major emphasize on the influence of ECAP parameters that include channel and curvature angles, processing route, temperature of operation, pressing speed, internal heating, number of pass through the die and back pressure. Various ECAP characteristics such as microstructure, strain inhomogeneity and mechanical properties are considered to achieve the maximum homogeneity, equilibrium grain refinement and mechanical improvement of CP-Ti. Investigations show that a pressing speed of 1-3 mm/s at 450 °C with route BC along with channel and curvature angles of 90° and 20° respectively with backpressure can lead to the most homogeneous ultrafine microstructure.
基金Projects(50471102,50671089) supported by the National Natural Science Foundation of China
文摘In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.
文摘The extended band structures of as-cold-rolled high Cr steel sheets are recrystallisation-resistant, and tend to become aggregates of the so-called grain colonies as a partially recovered state after final annealing. Such band structures diminish formability and become origin of the so-called ridging. A novel processing will be shown here, which involves strain-path change by introducing one-pass ECAP prior to cold-rolling, and facilitates recrystallisation. Indeed, the recrystallisation temperature was reduced by 100℃, compared with cold-rolling alone imposing an equivalent strain. Grain- scale microshear bands introduced during one-pass ECAP perturbed the banded structures in post-ECAP cold-rolling and enhanced the recrystallisation at the final annealing.
文摘Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is still inhomogeneous after four passes,and two zones,namely the fine grain zone（FGZ） and the coarse grain zone（CGZ） are formed.The grain refinement occurs mainly by particle-stimulated nucleation（PSN） mechanism,which led to a more random texture after four passes of ECAP.In the ECAP-processed alloy,the strength did not increase while the ductility was enhanced dramatically compared with the as-received condition.The change of ductility of this alloy was discussed in terms of texture and second phase particles.
基金Projects(50475029,50605015) supported by the National Natural Science Foundation of China
文摘Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angularextrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that withincreasing semi-solid isothermal treatment temperature, the a phase solid grain size of processedMg-Al-Zn alloy by ECAE increases firstly due to coarsening of a phase solid grains, then decreasesdue to melting of a phase solid grains. With the increase of extrusion passes during ECAE, the aphase solid grain size in the following semi-solid isothermal treatment decreases. The a phase solidgrain size of processed Mg-Al-Zn alloy by ECAE under route B_C is the smallest, while the a phasesolid grain size of processed material by ECAE under route A is the largest. The primary mechanismof spheroid formation depends on the melting of recrystallizing boundaries and diffusion of soluteatoms in the semi-solid state.
文摘Equal Channel Angular Pressing(ECAP)is one of the most applicable Sever Plastic Deformation(SPD)processes which leads to strength and ductility improvement through the grain refining and development of a suitable texture.In this study,after designing and manufacturing a suitable die,4 pass ECAP process at route C is done on strip shaped specimens of AZ31 magnesium alloy in order to achieve desirable microstructural and mechanical properties.Microstructure then got studied through the optical microscopy.Results show that mean grain size is decreased and grain size distribution got close to normal distribution state by increasing the pass number.However,the grain size is reduced by increasing of ECAP temperature.
基金Project(08JK240) supported by the Special Program of Education Bureau of Shaanxi Province, ChinaProject(SLGQD0751) supported by the Scientific Research Startup Program for Introduced Talents of Shaanxi University of Technology, China
文摘AZ31 Mg alloy bar was subjected to 8-pass equal-channel angular pressing(ECAP) at 623 K. Microstructure evolution was observed by optical microscopy(OM) on cross section and X-ray diffraction analysis. The room temperature mechanical properties of the ECAP processed specimens were also investigated. A fine-grained structure with an average sub-grain size of 9 μm is obtained after 7 ECAP passes. XRD analysis indicates that after ECAP,in placing of {1 010},planes {1 011} and {1 012} become the dominant directions that are favourable for grain refinement. ECAP processed AZ31 Mg alloy exhibits significant improvement in elongation but decrease in strength. The elongation of the specimen increases continuously up to 2 passes and then remains stable at further passes. This improvement can be related to the evolution of crystallographic texture and the scattered orientation of the basal plane(0001).
基金Project(12JJ2028)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(201308430093)supported by the China Scholarship CouncilProjects(201012200006,2013zzts185,2012zzts066)supported by the Freedom Explore Program of Central South University,China
文摘Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.
基金The National Natural Science Foundation of China(NSFC)under Grant Nos.5130117951331007+1 种基金31370976financially supported this work
文摘Three high-nitrogen stainless steels with different N contents were successfully processed by equal-channel angular pressing for one pass, and their microstructures and mechanical properties were investigated. It was found that the microstructure of the billet was heterogeneous across the billet thickness, resulting in the difference in the mechanical properties due to the different deformation conditions. A relatively low strength, high uniform elongation, and high work- hardening rate for the samples at the bottom of the billet was achieved in comparison with those processed at the top. Meanwhile, it was observed that the density of deformation twins increased with the content of N; accordingly, the strength and elongation of the alloys increase with the content of N, resulting in a good strength-ductility combination.
文摘Samples of a commercial Cu-lCr-0.1Zr(mass fraction,%) alloy were subjected to equal channel angular pressing(ECAP) up to 16 passes at room temperature following route Bc.Differential scanning calorimetry(DSC) was used to highlight the precipitation sequence and to calculate the stored energy,recrystallization temperature and activation energy after each ECAP pass.On another hand,electrical properties were correlated with the dislocation density.Results show that the stored energy increases upon increasing ECAP pass numbers,while the recrystallization temperature decreases significantly.
文摘Equal-channel angular pressing(ECAP) is now recognized as an effective technique for fabricating ultrafine grained materials. The results show that prevalent macroscopic shear banding occurs in ECAP as long as the pressing passes reach 2, and the severe macroscopic shear band extends from bottom to top surface and slants to the longitudinal axis of specimen at an angle of about 45°, develops at regular intervals, with a high shear strain accommodation of about 3.7 within the band. Different families of macroscopic shear bands may cut across each other, and over 60% of sample volume is occupied by macroscopic shear band when the ECAP reaches 4 passes.
基金the financial support from the Natural Science Foundation of Jiangsu Province(No.BK20160869)the Nantong Science and Technology Project(No.GY12015009)+1 种基金the Fundamental Research Funds for the Central Universities(No.2015B01314)the National Natural Science Foundation of China(No.51501039)
文摘The microstructure evolutions and mechanical properties of a heterogeneous Mg88Y8Zn4（in at.%） alloy during multi-pass equal channel angular pressing（ECAP） were systematically investigated in this work.The results show that four phases,i.e.α-Mg,18 R long period stacking ordered（LPSO） phase,Mg24Y5 and Y-rich phase,are present in cast alloy.During ECAP,dynamic recrystallization（DRX） occurs and the diameter of DRXedα-Mg grains decreases to 0.8 μm.Moreover,precipitation of lamellar 14 H LPSO structure is developed withinα-Mg phase.Both the refinement of α-Mg grains and precipitation of 14 H LPSO contribute to the increase in micro-hardness from 98 HV to 135 HV for α-Mg.In addition,a simplified model describing the evolution of 18 R LPSO phase is established,which illustrates that 18 R undergoes a four-step morphological evolution with increasing strains during ECAP,i.e.original lath → bent lath → cracked lath → smaller particles.Compression test results indicate that the alloy has been markedly strengthened after multi-pass ECAP,and the main reason for the significantly enhanced mechanical properties could be ascribed to the DRXed α-Mg grains,newly precipitated 14 H lamellas,18 R kinking and refined 18 R particles.
文摘Aluminum alloy 5083(AA5083)processed by large-scale Equal-channel angular pressing(ECAP)is an excellent engineering material with great prospects for industrial applications.An accurate assessment of the underlying constitutive relationships with easily determined material constants is critical for the predictive design and informed processing of such structural materials.To develop such a design framework,uniaxial dynamic compressive tests over a wide range of temperatures(293-573 K)were carried out for an ECAP-processed AA5083 alloy.Additionally,the microstructure before and after dynamic loading was characterized by SEM and TEM.Based on the experimental results,a new dynamic constitutive model,based on thermal activation theory,was established to describe the plastic flow behavior of the AA5083 alloy that incorporates the effects of plastic strain,temperature,and strain rate.The input parameters of the new model were determined using a particle swarm optimization(PSO)method.The model predictions show excellent agreement with experimental results,which suggests that the current predictive constitutive model is highly effective in reproducing the dynamic deformation behavior of the large-scale ECAP-processed AA5083.
文摘Among the various Severe Plastic Deformation(SPD)processes,Equal Channel Angular Pressing(ECAP)is one of the most applicable one which improves strength and ductility due to grain refinement and suitable texture development.In this study,cold rolling were carried out on the 4 pass ECAPed(in route A and C)strip shaped specimens of AZ31 magnesium alloy to investigate the ECAP effects on the roll-ability.Results showed that reduction in area which can be concerned as an index for roll-ability increased after ECAP.It was also seen that ECAP in route C enhanced roll-ability more than route A.
文摘Al-11%Si(mass fraction)alloy was transformed into a ductile material by equal-channel angular pressing(ECAP)with a rotary die.Two mechanisms at impact test,slip deformation by dislocation motion and grain boundary sliding,were discussed.The ultrafine grains with modified grain boundaries and the high content of fine particles(<1μm)were necessary for attaining high absorbed energy.The results contradict the condition of slip deformation by dislocation motion and coincide with that of grain boundary sliding.Many fine zigzag lines like a mosaic were observed on the side surface of the tested specimens.These observed lines may show grain boundaries appeared by the sliding of grains.
文摘A new technique to produce ultra-fine grained tubular specimen has been proposed, and the experiments have been performed using equal channel angular pressing （ECAP） with an angle of 90 between two intersecting channels and also the use of rubber pad as a mandrel during process. Commercial purity copper tubes have been pressed up to three passes through four different fundamental routes （A, BA, Bc, and C） directions of which are identified in the text below. The influence of each route on the value, distribution, and homogeneity of hardness has been investigated by applying Vickers micro-hardness measurements at various locations of the tube＇s transverse planes. Significant enhancement of the hardness is observed after the first pass ECAP. Also, routes C and Bc show, respectively, better average hardness magnitude and hardness distribution uniformity. In addition, the results indicate that there is about 50% and 62% reduction of the grain size, compared to the annealed condition, following ECAP process of the copper tube sample after the first and the third pass via route Bc.
文摘The microstructural evolution of a recycled aluminum alloy after equal channel angular pressing （ECAP） up to four passes was investigated using X-ray diffxaction （XRD） analysis and transmission electron microscopy （TEM）. Microhardness tests were performed to determine the associated changes in mechanical properties. An ultrafine-grained material has been obtained with a microstructure showing a mixture of highly strained crystallites. A high density of dislocations was achieved as a result of severe plastic deformation （SPD） through the die. Changes in mechanical behavior are also revealed after ECAP due to strain hardening. Thermal analysis and TEM micrographs ob- tained after annealing indicate the succession of the recovery, recrystallization, and grain growth phenomena. Moreover, the energy stored during ECAP may be related to the dislocation density introduced by SPD. We finally emphasize the role played by the precipitates in this alloy.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2013GB105001,2013GB105002,2015GB109001)National Natural Science Foundation of China(Nos.11305213,11405201)+1 种基金Technological Development Grant of Hefei Science Center of CAS(No.2014TDG-HSC003)China National Funds for Distinguished Young Scientists(No.51325103)
文摘Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing（ECAP） have been examined after exposure to a low energy,high-flux deuterium（D） plasma at fluences of 3×10^24 D/m^2 and 1×10^25 D/m^2 in a temperature range of 100 ℃-150 ℃.The methods used were scanning electron microscopy（SEM） and thermal desorption spectroscopy（TDS）.Sparse and small blisters（0.1 μm） were observed by SEM after D plasma irradiation on every irradiated surface;yet they did not exhibit significant structure or plasma fluence dependence.Larger blisters or protrusions appeared after subsequent TDS heating up to 1000 ℃.The TDS results showed a single D desorption peak at 220℃ for all samples and the D retention increased with increasing numbers of extrusion passes,i.e.,the decrease of grain sizes.The increased D retention in this low temperature range should be attributed to the faster diffusion of D along the larger volume fraction of grain boundaries introduced by ECAP.
文摘Microstructural development of ultra low C, N, Fe-Cr alloy and pure copper processed by equal-channel angular pressing (ECAP) have been examined focusing on the initial stage of the formation of ultrafine grain structure. Fe-Cr alloys were pressed at 423 K while pure copper at room temperature for 1 to 3 passes via the route Bc to compare at the equivalent homologous temperature. Microstructural evolutions were characterized by electron backscatter diffraction (EBSD) image and transmission electron microscopy (TEM). It was found that deformation structures were mostly deformation-induced subboundaries in both the materials after one pass, but the fraction of high-angle grain boundary became higher in the Fe-Cr alloys than in pure copper in subsequent passes by increasing misorientation of the boundaries. The more enhanced formation of high angle boundaries in Fe-Cr alloys was discussed in terms of the nature of crystal slip of FCC and BCC structures.
