A new technological process of tube forming was developed, namely solution treatment → granule medium internal high pressure forming → artificial aging. During this process, the mechanical properties of AA6061 tube ...A new technological process of tube forming was developed, namely solution treatment → granule medium internal high pressure forming → artificial aging. During this process, the mechanical properties of AA6061 tube can be adjusted by heat treatment to satisfy the process requirements and the processing method can also be realized by granule medium internal high pressure forming technology with the features of convenient implementation, low requirement to equipment and flexible design in product. Results show that, at a solution temperature of 560 ℃ and time of 120 min, the elongation of AA6061 increases by 313%, but the strength and the hardness dramatically decrease. At an aging temperature of 180 ℃ and time of 360 min, the strength and hardness of AA6061 alloy are recovered to the values of the as-received alloy. The maximum expansion ratio（MER） of AA6061 tube increases by 25.5% and the material properties of formed tube reach the performances of raw material.展开更多
The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatur...The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing）, was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing） were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.展开更多
Mg-5.88 Zn-0.53 Cu-0.16 Zr(wt.%)alloy was solidified at 2-6 GPa using high-pressure solidification technology.The microstructure,strengthening mechanism and compressive properties at room temperature were studied usin...Mg-5.88 Zn-0.53 Cu-0.16 Zr(wt.%)alloy was solidified at 2-6 GPa using high-pressure solidification technology.The microstructure,strengthening mechanism and compressive properties at room temperature were studied using SEM and XRD.The results showed that the microstructure was refined and the secondary dendrite spacing changed from 35μm at atmospheric pressure to 10μm at 6 GPa gradually.Also,Mg(Zn,Cu)2 and Mg Zn Cu eutectic phases were distributed in the shape of network,while under high pressures the second phases(Mg(Zn,Cu)2 and Mg7 Zn3)were mainly granular or strip-like.The solid solubility of Zn and Cu in the matrix built up over increasing solidification pressure and reached 4.12%and 0.32%respectively at 6 GPa.The hardness value was HV 90 and the maximum compression resistance was 430 MPa.Therefore,the grain refinement strengthening,the second phase strengthening and the solid solution strengthening are the principal strengthening mechanisms.展开更多
The strength of a material is dependent on how dislocations in its crystal lattice can be easily propagated.These dislocations create stress fields within the material depending on their intrinsic character.Generally,...The strength of a material is dependent on how dislocations in its crystal lattice can be easily propagated.These dislocations create stress fields within the material depending on their intrinsic character.Generally,the following strengthening mechanisms are relevant in wrought magnesium materials tested at room temperature:fine-grain strengthening,precipitate strengthening and solid solution strengthening as well as texture strengthening.The indirect-extruded Mg-8Sn(T8)and Mg-8Sn-1Al-1Zn(TAZ811)alloys present superior tensile properties compared to the commercial AZ31 alloy extruded in the same condition.The contributions to the strengthen of Mg-Sn based alloys made by four strengthening mechanisms were calculated quantitatively based on the microstructure characteristics,physical characteristics,thermomechanical analysis and interactions of alloying elements using AZ31 alloy as benchmark.展开更多
This review summarizes the strengthening mechanisms of reduced activation ferritic/martensitic(RAFM)steels.High-angle grain boundaries,subgrain boundaries,nano-sized M_(23)C_(6),and MX carbide precipitates effectively...This review summarizes the strengthening mechanisms of reduced activation ferritic/martensitic(RAFM)steels.High-angle grain boundaries,subgrain boundaries,nano-sized M_(23)C_(6),and MX carbide precipitates effectively hinder dislocation motion and increase high-temperature strength.M23C6 carbides are easily coarsened under high temperatures,thereby weakening their ability to block dislocations.Creep properties are improved through the reduction of M23C6 carbides.Thus,the loss of strength must be compensated by other strengthening mechanisms.This review also outlines the recent progress in the development of RAFM steels.Oxide dispersion-strengthened steels prevent M23C6 precipitation by reducing C content to increase creep life and introduce a high density of nano-sized oxide precipitates to offset the reduced strength.Severe plastic deformation methods can substantially refine subgrains and MX carbides in the steel.The thermal deformation strengthening of RAFM steels mainly relies on thermo-mechanical treatment to increase the MX carbide and subgrain boundaries.This procedure increases the creep life of TMT(thermo-mechanical treatment)9Cr-1W-0.06Ta steel by~20 times compared with those of F82H and Eurofer 97 steels under 550℃/260 MPa.展开更多
Based on experimental data of positron annihilation technology, electrolyticdissolution technique, electron back-scattered pattern, etc. and by analysis the strengtheningfactors, the strengthening mechanism of ultra-t...Based on experimental data of positron annihilation technology, electrolyticdissolution technique, electron back-scattered pattern, etc. and by analysis the strengtheningfactors, the strengthening mechanism of ultra-thin hot strip of low carbon steel produced by CSP(Compact Strip Production) technique was investigated. The value of each strengthening mechanism andits contribution percentage to yield strength were achieved. The results show that refinementstrengthening is the predominant strengthening mode; precipitation strengthening and dislocationstrengthening are second to it, their contributions to yield strength are almost equal.展开更多
The hybrid addition of CNTs was used to improve both the strengths and ductility of SiCp reinforced Mg matrix composites.A novel method was developed to simultaneously disperse SiCp and CNTs in Mg melt.Firstly,new CNT...The hybrid addition of CNTs was used to improve both the strengths and ductility of SiCp reinforced Mg matrix composites.A novel method was developed to simultaneously disperse SiCp and CNTs in Mg melt.Firstly,new CNTs@SiCp hybrid reinforcements were synthesized by CVD.Thus,CNTs were well pre-dispersed on the SiCp surfaces before they were added to Mg melt.Therefore,the following semisolid stirring and ultrasonic vibration dispersed the new hybrid reinforcements well in Mg-6Zn melt.The hybrid composite exhibits some unique features in microstructures.Although the distribution of SiCp was very uniform in the Mg-6Zn matrix,most CNTs distributed along the strips in the state of micro-clusters,in which CNTs were bonded very well with Mg matrix.Most of the CNTs kept their structure integrity during fabrication process.All these factors ensure that the hybrid composite have much higher strength and elongation than the mono SiC/Mg-6Zn composites.The dominant strengthening mechanism is the load transfer effect of CNTs.Apart from grain refinement,the CNTs toughen the composites by impeding the microcrack propagation inside the material.Thus,the hybrid CNTs@SiCp successfully realizes the reinforcing advantage of“1+1>2”.展开更多
The extrusion preform of the spray-formed5A12Al alloy was hot rolled using high reduction rolling technology.By means of transmission electron microscopy(TEM),electron backscatter diffraction(EBSD)and energy dispersiv...The extrusion preform of the spray-formed5A12Al alloy was hot rolled using high reduction rolling technology.By means of transmission electron microscopy(TEM),electron backscatter diffraction(EBSD)and energy dispersive spectroscopy(EDS),the microstructure evolution was studied and the strengthening and toughening mechanism was thereby proposed.The results indicate that discontinuous and continuous dynamic recrystallization occurred during the hot rolling deformation of the spray-formed5A12Al alloy.The grain size was significantly refined and the micro-scale grains formed.Partial dynamic recrystallization leads to a significant increase of dislocation density and cellular structure.The Mg atoms were distributed in the Al matrix mainly in the presence of solid solution rather than the formation of precipitate.High solid solution of Mg atoms not only hindered the dislocation motion and increased the density of dislocation,but also exhibited a remarkable solid solution strengthening effect,which contributes to the high strength and high toughness of the as-rolled sheets.The tensile strength and elongation of spray formed5A12Al alloy at room temperature after3passes hot rolling were622MPa and20%,respectively.展开更多
The microstructure and strengthening mechanisms of as-cast Mg-6Al-6Nd alloy were studied. The results show that the addition of 6 wt.% Nd into Mg-6Al alloy leads to the precipitation of Al11Nd3 and Al2Nd phases and de...The microstructure and strengthening mechanisms of as-cast Mg-6Al-6Nd alloy were studied. The results show that the addition of 6 wt.% Nd into Mg-6Al alloy leads to the precipitation of Al11Nd3 and Al2Nd phases and decrease in the content of Al solid soluted in Mg-Al matrix. The volume fractions of Al11Nd3 and Al2Nd phases are 3.64% and 0.34%, respectively. Compared with Mg-6Al alloy, the ultimate strength, yielding strength, and elongation of Mg-6Al-6Nd alloy at room temperature and 175℃ are enhanced in some degrees. The strengthening mechanisms of Mg-6Al-6Nd alloy are mainly composed of solid solution strengthening of Al solid soluted in Mg-Al matrix and grain refmement strengthening, dispersion strengthening, and composite strengthening brought by the precipitation of Al11Nd3 phase. The composite strengthening includes the load transfer from the matrix to Al11Nd3 phase and the enhancement of dislocation density due to the geometrical mismatch and thermal mismatch between the matrix and Al11Nd3 phase.展开更多
The bobbin tool friction stir welding process was used to join 6 mm thick 5A06 aluminum alloy plates.Optical microscope was used to characterize the microstructure.The electron backscatter diffraction(EBSD)identified ...The bobbin tool friction stir welding process was used to join 6 mm thick 5A06 aluminum alloy plates.Optical microscope was used to characterize the microstructure.The electron backscatter diffraction(EBSD)identified the effect of non-homogeneous microstructure on the tensile properties.It was observed that the grain size in the top of the stir zone(SZ)is smaller than that in the centre region.The lowest ratio of recrystallization and density of the geometrically-necessary dislocations(GNDs)in the SZ was found in the middle near the thermo-mechanically affected zone(TMAZ)being 22%and 1.15×10^(−13) m^(−2),respectively.The texture strength of the heat-affected zone(HAZ)is the largest,followed by that in the SZ,with the lowest being in the TMAZ.There were additional interfaces developed which contributed to the strengthening mechanism,and their effect on tensile strength was analysed.The tensile tests identified the weakest part in the joint at the interfaces,and the specific reduction value is about 93 MPa.展开更多
The orientation relationships,carbon partitioning and strengthening mechanism of a novel ultrahigh strength steel were analyzed in depth during the complex process of heat treatment.The experimental results reveal tha...The orientation relationships,carbon partitioning and strengthening mechanism of a novel ultrahigh strength steel were analyzed in depth during the complex process of heat treatment.The experimental results reveal that the(011)α//()γ,[100]α//[011]γ orientation relationships can be drawn between martensite and retained austenite.The position and angle of martensite and retained austenite are shown more clearly from the stereographic projections.Moreover,the calculated results show that the carbon content near the austenite interface is the highest in the shorter carbon allocation time.With the further increase of time,its carbon content gradually decreases.Furthermore,a model of the relationship between yield strength and strengthening mechanism was established.It was proved that the main strengthening components contributing to the yield strength include Orowan strengthening,grain-size strengthening and dislocation hardening.The main strengthening mechanism of steel in this experiment is dislocation strengthening.展开更多
From the viewpoint of energy-saving and environment protection,it is necessary to develop Ultra Super Critical(USC) fossil-fired power plants.In order to ensure the reliable operation of power plants under high steam ...From the viewpoint of energy-saving and environment protection,it is necessary to develop Ultra Super Critical(USC) fossil-fired power plants.In order to ensure the reliable operation of power plants under high steam conditions,good mechanical properties(particularly high creep strength),corrosion resistance and fabricability are generally required for the heat resistant steels used in USC boilers.Among these heat-resistant steels,S30432 austenitic heat-resistant steels are of interest due to high creep strength,excellent oxidation and corrosion resistance at temperatures up to 650 -700℃.In this paper,the strengthening mechanism of S30432 austenitic heat-resistant steel was investigated based on the precipitation behavior of S30432 during aging and creep at 650℃.Results show that the microstructure of as-supplied S30432 steel is austenite,the main precipitation consists of only Nb(C,N).After aged for 10 000 h or crept for 10 712 h,there is a slight increase in the size of fine Nb(C,N),but the transformation from Nb(C,N) to NbCrN does not occur.Aging and creep results in the precipitation ofε-Cu and M_(23)C_6.The coarsening velocity ofε-Cu particles diminishes greatly and they are still very fine in the long-term creep range.With the increase of aging and creep time M_(23)C_6 carbides tend to coarsen gradually.The size of M_(23)C_6 is larger and the coarsening is easier in contrast toε-Cu and Nb(C,N).Nb(C,N) precipitates in the as-supplied microstructure,while aging and creep result in the precipitation ofε-Cu and M_(23)C_6.High creep rupture strength of S30432 steel is attributed to the precipitation hardening ofε-Cu,Nb(C,N) and M_(23)C_6.Extremely,ε-Cu plays an important role in improving the creep rupture strength of S30432,and at least 61%of the creep rupture strength of S30432 at 650℃results from the precipitation hardening ofε-Cu particles.展开更多
The overall promotion of all-for-one tourism requires tourists' civilized behaviors. This paper focused on tourists' environmental responsible behaviors in the context of all-for-one tourism. On the basis of c...The overall promotion of all-for-one tourism requires tourists' civilized behaviors. This paper focused on tourists' environmental responsible behaviors in the context of all-for-one tourism. On the basis of clarifying the connotation, dimension and driving factors of tourists' environmental responsible behaviors, this paper firstly analyzed the relationship between all-for-one tourism and tourists' environmental responsible behaviors, and proposed that the development of all-for-one tourism was an important path to optimize and upgrade China's tourism industry and a new concept of sustainable development of tourism industry. The emergence of all-for-one tourism has formed a new tourism trend, which will drive tourists to behave more civilly. Tourists' environmental responsible behaviors are a "subject and share" concept, and from tourists' point of view, all-for-one tourism development is the most basic requirement. Secondly, based on the theory of "value-belief-norm", this paper focused on the strengthening mechanism of "interaction effect" between all-for-one tourism and tourists' environmental responsible behaviors, and put forward the idea of "double internalization strengthening" to guide tourists' environmental responsible behaviors from being passive to active, from individuals to groups. Finally, this paper discussed the promotion of environmental responsible behaviors of tourist's specific strategies from two aspects, "external drive" and "internal drive" to enhance the level of all-for-one tourism construction and strengthen the environment responsibility of tourists. "External drives" were as follows:(1) to make a scientific development plan to implement the "host and guest sharing" mechanism;(2) to optimize the landscape, the environment, services, enhance the local attachment of visitors;(3) to improve the infrastructure system, pay attention to the details of visitors' experience;(4) to strengthen environment education and publicity, deepening the quality of tourists' civilization construction, and strengthen the environmental responsible behaviors of tourists. "Internal drives" were as follows:(1) to strengthen the sense of environmental responsibility of tourists;(2) to establish a model of environmental responsible behaviors;(3) to strengthen the supervision of environmental responsible behaviors.展开更多
In this work,selective laser melting(SLM)process is used to prepare the AlNi6TiZr alloy.By analyzing the printing quality and mechanical properties of the printed specimens with different process parameters,the SLM fo...In this work,selective laser melting(SLM)process is used to prepare the AlNi6TiZr alloy.By analyzing the printing quality and mechanical properties of the printed specimens with different process parameters,the SLM forming window of AlNi6TiZr is obtained.The relative density of the sample printed with 270 W-1100 mm/s(laser energy density:82 J/mm3)reaches 99.7%,exhibiting excellent mechanical properties(yield strength(YS):421.7 MPa;ultimate tensile strength(UTS):480.4 MPa).After an aging treatment of 325 ℃-12 h,the YS and UTS of the sample increased to 494 MPa and 550.7 MPa,respectively.Adding Ni,Ti,and Zr components promoted the generation of multi-phase precipitates in the Al alloy and improved the synergistic strengthening effect of multi-phases.The hard-shell structure(HSS)formed by the Al_(3)Ni phase at the grain boundary significantly strengthened the grain boundary strength.The precipitated Al_(3)(Ti,Zr)phases at the grain boundaries prevent grain growth and dislocation movement.The Al_(3)Ni and Al_(3)(Ti,Zr)phases have good thermal stability that can still maintain excellent enhancement effects at high temperature.AlNi6TiZr alloy has great application prospects in medium and high-temperature environments.展开更多
The objective of this study was to investigate the influence of strengthening mechanisms on the high-temperature mechanical properties of China low-activation ferrite(CLF-1)steel,which underwent thermodynamic design a...The objective of this study was to investigate the influence of strengthening mechanisms on the high-temperature mechanical properties of China low-activation ferrite(CLF-1)steel,which underwent thermodynamic design and thermo-mechanical treatment(TMT).The microstructure characterization in the normalized and tempered condition and the TMT condition was carried out using optical microscopy,X-ray diffractometer,and scanning electron microscopy with electron backscatter diffraction.High-resolution transmission electron microscopy was employed to determine the crystallographic structures of precipitated phases.The results indicated that the addition of Ti led to an increase in the allocation of C in MC phase and an enhancement in the content of MC phase.Compared to CLF-P steel in the normalized and tempered condition,a 1.5-fold increase in dislocation density and an order of magnitude improvement in MX phase density were achieved after TMT.The formation of high-density nano-scale MC phases during TMT played a significant role in precipitation strengthening due to their favorable coherent relationship with the matrix and low interfacial free energy.The excellent high-temperature mechanical properties observed in CLF-P steel after TMT can be attributed to the combined effects of precipitation strengthening,dislocation strengthening,and lath strengthening.展开更多
The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation(0-15%) were investigated,revealing the microstructure-strength relationship and the intrinsic strengthe...The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation(0-15%) were investigated,revealing the microstructure-strength relationship and the intrinsic strengthening mechanism.The results show that increasing the pre-deformation levels remarkably improves the strength of the alloy but deteriorates its ductility.Dislocations introduced by pre-deformation effectively suppress the formation of Guinier-Preston(GP) zones and provide more nucleation sites for T1 precipitates.This leads to more intensive and finer T1 precipitates in the samples with higher pre-deformation levels.Simultaneously,the enhanced precipitation of T1 precipitates and inhibited formation of GP zones cause the decreases in number and sizes of θ′ precipitates.The quantitative descriptions of the strength contributions from different strengthening mechanisms reveal that strengthening contributions from T1 and θ′ precipitates decrease with increasing pre-deformation.The reduced diameters of T1 precipitates are primarily responsible for their weakened strengthening effects.Therefore,the improved strength of the T8-aged Al-Cu-Li alloy is mainly attributed to the stronger strain hardening from the increased pre-deformation levels.展开更多
Ordered structures with functional units offer the potential for enhanced performance in metallic materials.Among these structures,gradient nanotwinned(GNT)microstructures demonstrate excellent controllability.This pa...Ordered structures with functional units offer the potential for enhanced performance in metallic materials.Among these structures,gradient nanotwinned(GNT)microstructures demonstrate excellent controllability.This paper provides a comprehensive review of the current state-of-the-art studies on GNT structures,encompassing various aspects such as design strategies,mechanical properties characterization,spatially gradient strain evolution analysis,and the significant role of geometrically necessary dislocations(GNDs).The primary objective is to systematically unravel the fundamental strengthening mechanisms by gaining an in-depth understanding of the deformation behavior of nanotwinned units.Through this work,we aim to contribute to the broader field of materials science by consolidating knowledge and providing insights for the development of novel metallic materials with enhanced properties and tailored performance characteristics.展开更多
This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium （Y） element. The addition of Y resulted in the ...This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium （Y） element. The addition of Y resulted in the formation of ternary 1 （Mg3YZn6）, W （Mg3Y2Zn3） and LPSO （Mg12YZn） phases which subse- quently reinforced alloys ZM31 ＋ 0.3Y, ZM31 ＋ 3.2Y and ZM31 ＋ 6Y, where the value denoted the amount of Y element （in wt%）. Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion （CTE）, which was derived to be 1.38 x 10^-5 K^-1 and 2.35 x 10^-5 K^-1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and crE mismatch were the predominant strengthening mechanisms in the ZM31＋0.3Y and ZM31 ＋ 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 ＋ 6Y alloy.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.展开更多
A Mg-Gd-Y-Zn-Zr magnesium alloy with different initial states was extruded under different extrusion parameters.The effect of solution treatment and extrusion parameters on the microstructure,texture and mechanical pr...A Mg-Gd-Y-Zn-Zr magnesium alloy with different initial states was extruded under different extrusion parameters.The effect of solution treatment and extrusion parameters on the microstructure,texture and mechanical properties were analyzed in detail,and the abnormal texture formation and strengthening mechanism was revealed.When extruded at low temperature and small extrusion ratio,the bimodal microstructure consisting of fine dynamically recrystallized grains and coarse deformed grains occurred both in the as-cast alloy and solution-treated alloy.When the extrusion temperature and extrusion ratio were increased,the amount and size of dynamically recrystallized grains increased and the grain size of the solution-treated alloy showed higher growth rate.Furthermore,an abnormal texture with<0001>parallel with extrusion direction developed due to the occurrence of non-basal slip and continuous dynamic recrystallization.This could be enhanced by solution treatment,high temperature,and large extrusion ratio.Both the as-cast alloy and solution-treated alloy exhibited the highest tensile strength after extrusion at 300℃with an extrusion ratio of 9.Grain refinement was the main strengthening mechanism utilized in both the as-cast alloy and the solution-treated alloy.Work hardening played an important role in the sample extruded at low temperature and small extrusion ratio,with the highest contribution of about 33 MPa after extrusion at 300℃with an extrusion ratio of 9.Texture strengthening contributed more in the sample extruded at high temperature and large extrusion ratio,but no more than 24.1 MPa.Solution strengthening was another strengthening mechanism in the extruded as-cast alloy,especially at high temperature and large extrusion ratio(no more than 9 MPa).展开更多
Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BC...Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3μm,and small amounts(<4 vol.%)of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27%and 87%at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm^(3),while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50%of the yield strength of the AlxCrNbVMo RHEAs.展开更多
基金Project(51775481)supported by the National Natural Science Foundation of ChinaProject(A2016002017)supported by the High-level Talents Program of Heibei Province,China
文摘A new technological process of tube forming was developed, namely solution treatment → granule medium internal high pressure forming → artificial aging. During this process, the mechanical properties of AA6061 tube can be adjusted by heat treatment to satisfy the process requirements and the processing method can also be realized by granule medium internal high pressure forming technology with the features of convenient implementation, low requirement to equipment and flexible design in product. Results show that, at a solution temperature of 560 ℃ and time of 120 min, the elongation of AA6061 increases by 313%, but the strength and the hardness dramatically decrease. At an aging temperature of 180 ℃ and time of 360 min, the strength and hardness of AA6061 alloy are recovered to the values of the as-received alloy. The maximum expansion ratio（MER） of AA6061 tube increases by 25.5% and the material properties of formed tube reach the performances of raw material.
基金Project(51021063)supported by the Creative Research Group of the National Natural Science Foundation of ChinaProject(50831007)supported by the National Natural Science Foundation of China+1 种基金Project(2011CB610401)supported by the National Basic Research Program of ChinaProject(12C1142)supported by the Education Department of Hunan Province,China
文摘The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing）, was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing） were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.
基金Projects(51675092,51775099)supported by the National Natural Science Foundation of ChinaProjects(E2018501030,E2018501033,E2018501032)supported by the Natural Science Foundation of Hebei Province,China.
文摘Mg-5.88 Zn-0.53 Cu-0.16 Zr(wt.%)alloy was solidified at 2-6 GPa using high-pressure solidification technology.The microstructure,strengthening mechanism and compressive properties at room temperature were studied using SEM and XRD.The results showed that the microstructure was refined and the secondary dendrite spacing changed from 35μm at atmospheric pressure to 10μm at 6 GPa gradually.Also,Mg(Zn,Cu)2 and Mg Zn Cu eutectic phases were distributed in the shape of network,while under high pressures the second phases(Mg(Zn,Cu)2 and Mg7 Zn3)were mainly granular or strip-like.The solid solubility of Zn and Cu in the matrix built up over increasing solidification pressure and reached 4.12%and 0.32%respectively at 6 GPa.The hardness value was HV 90 and the maximum compression resistance was 430 MPa.Therefore,the grain refinement strengthening,the second phase strengthening and the solid solution strengthening are the principal strengthening mechanisms.
基金This work was supported by National Natural Science Foundation of China(Grant nos.51404166 and 51201112),Shanxi Province Science Foundation for Youths(2013021013-4)Research Project Supported by Shanxi Scholarship Council of China(2014-023)+1 种基金Technological Innovation Programs of Higher Education Institutions in Shanxi(Grant nos.2014120)the Advanced Programs of Department of Human Resources and Social Security of Shanxi Province for Returned Scholars(2013068).
文摘The strength of a material is dependent on how dislocations in its crystal lattice can be easily propagated.These dislocations create stress fields within the material depending on their intrinsic character.Generally,the following strengthening mechanisms are relevant in wrought magnesium materials tested at room temperature:fine-grain strengthening,precipitate strengthening and solid solution strengthening as well as texture strengthening.The indirect-extruded Mg-8Sn(T8)and Mg-8Sn-1Al-1Zn(TAZ811)alloys present superior tensile properties compared to the commercial AZ31 alloy extruded in the same condition.The contributions to the strengthen of Mg-Sn based alloys made by four strengthening mechanisms were calculated quantitatively based on the microstructure characteristics,physical characteristics,thermomechanical analysis and interactions of alloying elements using AZ31 alloy as benchmark.
基金the National Key Research and Development Program of China(No.2016YFB 0300600)the National Natural Science Foundation of China(NSFC)(No.51922026)+1 种基金the Fundamental Research Funds for the Central Universities(Nos.N2002013,N2002005,N2007011)the 111 Project(No.B20029).
文摘This review summarizes the strengthening mechanisms of reduced activation ferritic/martensitic(RAFM)steels.High-angle grain boundaries,subgrain boundaries,nano-sized M_(23)C_(6),and MX carbide precipitates effectively hinder dislocation motion and increase high-temperature strength.M23C6 carbides are easily coarsened under high temperatures,thereby weakening their ability to block dislocations.Creep properties are improved through the reduction of M23C6 carbides.Thus,the loss of strength must be compensated by other strengthening mechanisms.This review also outlines the recent progress in the development of RAFM steels.Oxide dispersion-strengthened steels prevent M23C6 precipitation by reducing C content to increase creep life and introduce a high density of nano-sized oxide precipitates to offset the reduced strength.Severe plastic deformation methods can substantially refine subgrains and MX carbides in the steel.The thermal deformation strengthening of RAFM steels mainly relies on thermo-mechanical treatment to increase the MX carbide and subgrain boundaries.This procedure increases the creep life of TMT(thermo-mechanical treatment)9Cr-1W-0.06Ta steel by~20 times compared with those of F82H and Eurofer 97 steels under 550℃/260 MPa.
基金This work was financially supported by the state foundation for key projects: Fundamental Research on New Generation of Steels (No: G1998061500).
文摘Based on experimental data of positron annihilation technology, electrolyticdissolution technique, electron back-scattered pattern, etc. and by analysis the strengtheningfactors, the strengthening mechanism of ultra-thin hot strip of low carbon steel produced by CSP(Compact Strip Production) technique was investigated. The value of each strengthening mechanism andits contribution percentage to yield strength were achieved. The results show that refinementstrengthening is the predominant strengthening mode; precipitation strengthening and dislocationstrengthening are second to it, their contributions to yield strength are almost equal.
基金This work was supported by“National Natural Science Foundation of China”(Grant Nos.51871074,51971078 and 51671066)“The Project National United Engineering Laboratory for Advanced Bearing Tribology,Henan University of Science and Technology”(Grant No.201911).
文摘The hybrid addition of CNTs was used to improve both the strengths and ductility of SiCp reinforced Mg matrix composites.A novel method was developed to simultaneously disperse SiCp and CNTs in Mg melt.Firstly,new CNTs@SiCp hybrid reinforcements were synthesized by CVD.Thus,CNTs were well pre-dispersed on the SiCp surfaces before they were added to Mg melt.Therefore,the following semisolid stirring and ultrasonic vibration dispersed the new hybrid reinforcements well in Mg-6Zn melt.The hybrid composite exhibits some unique features in microstructures.Although the distribution of SiCp was very uniform in the Mg-6Zn matrix,most CNTs distributed along the strips in the state of micro-clusters,in which CNTs were bonded very well with Mg matrix.Most of the CNTs kept their structure integrity during fabrication process.All these factors ensure that the hybrid composite have much higher strength and elongation than the mono SiC/Mg-6Zn composites.The dominant strengthening mechanism is the load transfer effect of CNTs.Apart from grain refinement,the CNTs toughen the composites by impeding the microcrack propagation inside the material.Thus,the hybrid CNTs@SiCp successfully realizes the reinforcing advantage of“1+1>2”.
基金Project(2017JJ2073) supported by the Natural Science Foundation of Hunan Province,ChinaProject(15B063) supported by the Youth Research Foundation of Education Bureau of Hunan Province,China
文摘The extrusion preform of the spray-formed5A12Al alloy was hot rolled using high reduction rolling technology.By means of transmission electron microscopy(TEM),electron backscatter diffraction(EBSD)and energy dispersive spectroscopy(EDS),the microstructure evolution was studied and the strengthening and toughening mechanism was thereby proposed.The results indicate that discontinuous and continuous dynamic recrystallization occurred during the hot rolling deformation of the spray-formed5A12Al alloy.The grain size was significantly refined and the micro-scale grains formed.Partial dynamic recrystallization leads to a significant increase of dislocation density and cellular structure.The Mg atoms were distributed in the Al matrix mainly in the presence of solid solution rather than the formation of precipitate.High solid solution of Mg atoms not only hindered the dislocation motion and increased the density of dislocation,but also exhibited a remarkable solid solution strengthening effect,which contributes to the high strength and high toughness of the as-rolled sheets.The tensile strength and elongation of spray formed5A12Al alloy at room temperature after3passes hot rolling were622MPa and20%,respectively.
基金supported by the Major State Basic Research Development Program of China (No.2007CB613706)the Project of Key Disciplines Development "Resources, Environment and Recycling Economy" Interdisciplinary under the Jurisdiction of Beijing Municipality (No.0330005412901)the Project Sponsored by the Scientific Research Foundation for Doctoral Teachers, Beijing University of Technology (No.X0104001200905)
文摘The microstructure and strengthening mechanisms of as-cast Mg-6Al-6Nd alloy were studied. The results show that the addition of 6 wt.% Nd into Mg-6Al alloy leads to the precipitation of Al11Nd3 and Al2Nd phases and decrease in the content of Al solid soluted in Mg-Al matrix. The volume fractions of Al11Nd3 and Al2Nd phases are 3.64% and 0.34%, respectively. Compared with Mg-6Al alloy, the ultimate strength, yielding strength, and elongation of Mg-6Al-6Nd alloy at room temperature and 175℃ are enhanced in some degrees. The strengthening mechanisms of Mg-6Al-6Nd alloy are mainly composed of solid solution strengthening of Al solid soluted in Mg-Al matrix and grain refmement strengthening, dispersion strengthening, and composite strengthening brought by the precipitation of Al11Nd3 phase. The composite strengthening includes the load transfer from the matrix to Al11Nd3 phase and the enhancement of dislocation density due to the geometrical mismatch and thermal mismatch between the matrix and Al11Nd3 phase.
基金This work was financially supported by the State Key Laboratory of Solidification Processing(Northwestern Polytechnical University,China,No.2019-QZ-01)the National Natural Science Foundation of China(No.52105402)the Natural Science Foundation of Shaanxi Province(No.2021-JQ-102).
文摘The bobbin tool friction stir welding process was used to join 6 mm thick 5A06 aluminum alloy plates.Optical microscope was used to characterize the microstructure.The electron backscatter diffraction(EBSD)identified the effect of non-homogeneous microstructure on the tensile properties.It was observed that the grain size in the top of the stir zone(SZ)is smaller than that in the centre region.The lowest ratio of recrystallization and density of the geometrically-necessary dislocations(GNDs)in the SZ was found in the middle near the thermo-mechanically affected zone(TMAZ)being 22%and 1.15×10^(−13) m^(−2),respectively.The texture strength of the heat-affected zone(HAZ)is the largest,followed by that in the SZ,with the lowest being in the TMAZ.There were additional interfaces developed which contributed to the strengthening mechanism,and their effect on tensile strength was analysed.The tensile tests identified the weakest part in the joint at the interfaces,and the specific reduction value is about 93 MPa.
基金Funded by the Key Research and Development(R&D)Projects of Shanxi Province(No.201803D121028)the Research Project Supported by Shanxi Scholarship Council of China(No.2021-122)+1 种基金the Fundamental Research Program of Shanxi Province(No.20210302123014)the Shanxi Province Science Foundation for Youths(No.201901D211266)。
文摘The orientation relationships,carbon partitioning and strengthening mechanism of a novel ultrahigh strength steel were analyzed in depth during the complex process of heat treatment.The experimental results reveal that the(011)α//()γ,[100]α//[011]γ orientation relationships can be drawn between martensite and retained austenite.The position and angle of martensite and retained austenite are shown more clearly from the stereographic projections.Moreover,the calculated results show that the carbon content near the austenite interface is the highest in the shorter carbon allocation time.With the further increase of time,its carbon content gradually decreases.Furthermore,a model of the relationship between yield strength and strengthening mechanism was established.It was proved that the main strengthening components contributing to the yield strength include Orowan strengthening,grain-size strengthening and dislocation hardening.The main strengthening mechanism of steel in this experiment is dislocation strengthening.
文摘From the viewpoint of energy-saving and environment protection,it is necessary to develop Ultra Super Critical(USC) fossil-fired power plants.In order to ensure the reliable operation of power plants under high steam conditions,good mechanical properties(particularly high creep strength),corrosion resistance and fabricability are generally required for the heat resistant steels used in USC boilers.Among these heat-resistant steels,S30432 austenitic heat-resistant steels are of interest due to high creep strength,excellent oxidation and corrosion resistance at temperatures up to 650 -700℃.In this paper,the strengthening mechanism of S30432 austenitic heat-resistant steel was investigated based on the precipitation behavior of S30432 during aging and creep at 650℃.Results show that the microstructure of as-supplied S30432 steel is austenite,the main precipitation consists of only Nb(C,N).After aged for 10 000 h or crept for 10 712 h,there is a slight increase in the size of fine Nb(C,N),but the transformation from Nb(C,N) to NbCrN does not occur.Aging and creep results in the precipitation ofε-Cu and M_(23)C_6.The coarsening velocity ofε-Cu particles diminishes greatly and they are still very fine in the long-term creep range.With the increase of aging and creep time M_(23)C_6 carbides tend to coarsen gradually.The size of M_(23)C_6 is larger and the coarsening is easier in contrast toε-Cu and Nb(C,N).Nb(C,N) precipitates in the as-supplied microstructure,while aging and creep result in the precipitation ofε-Cu and M_(23)C_6.High creep rupture strength of S30432 steel is attributed to the precipitation hardening ofε-Cu,Nb(C,N) and M_(23)C_6.Extremely,ε-Cu plays an important role in improving the creep rupture strength of S30432,and at least 61%of the creep rupture strength of S30432 at 650℃results from the precipitation hardening ofε-Cu particles.
基金Sponsored by Zhejiang Provincial Philosophy and Social Science Planning Project(17NDJC218YB)Project of Hangzhou Col ege of Commerce,Zhejiang Gongshang University(2016YJ-06)+1 种基金National Natural Science Foundation of China(41661034)Public Welfare Project of International Scientific and Technology Cooperation Project of Science Technology Department of Zhejiang Province(2016C34003)
文摘The overall promotion of all-for-one tourism requires tourists' civilized behaviors. This paper focused on tourists' environmental responsible behaviors in the context of all-for-one tourism. On the basis of clarifying the connotation, dimension and driving factors of tourists' environmental responsible behaviors, this paper firstly analyzed the relationship between all-for-one tourism and tourists' environmental responsible behaviors, and proposed that the development of all-for-one tourism was an important path to optimize and upgrade China's tourism industry and a new concept of sustainable development of tourism industry. The emergence of all-for-one tourism has formed a new tourism trend, which will drive tourists to behave more civilly. Tourists' environmental responsible behaviors are a "subject and share" concept, and from tourists' point of view, all-for-one tourism development is the most basic requirement. Secondly, based on the theory of "value-belief-norm", this paper focused on the strengthening mechanism of "interaction effect" between all-for-one tourism and tourists' environmental responsible behaviors, and put forward the idea of "double internalization strengthening" to guide tourists' environmental responsible behaviors from being passive to active, from individuals to groups. Finally, this paper discussed the promotion of environmental responsible behaviors of tourist's specific strategies from two aspects, "external drive" and "internal drive" to enhance the level of all-for-one tourism construction and strengthen the environment responsibility of tourists. "External drives" were as follows:(1) to make a scientific development plan to implement the "host and guest sharing" mechanism;(2) to optimize the landscape, the environment, services, enhance the local attachment of visitors;(3) to improve the infrastructure system, pay attention to the details of visitors' experience;(4) to strengthen environment education and publicity, deepening the quality of tourists' civilization construction, and strengthen the environmental responsible behaviors of tourists. "Internal drives" were as follows:(1) to strengthen the sense of environmental responsibility of tourists;(2) to establish a model of environmental responsible behaviors;(3) to strengthen the supervision of environmental responsible behaviors.
基金Post Graduate Innovation Funding Project of Hebei Province(No.CXZZSS2023041)Hebei Natural Science Foundation of China(No.E2021203138)Special Project for Local Science and Technology Development Guided by the Central Government of Hebei Province(236Z1805G).
文摘In this work,selective laser melting(SLM)process is used to prepare the AlNi6TiZr alloy.By analyzing the printing quality and mechanical properties of the printed specimens with different process parameters,the SLM forming window of AlNi6TiZr is obtained.The relative density of the sample printed with 270 W-1100 mm/s(laser energy density:82 J/mm3)reaches 99.7%,exhibiting excellent mechanical properties(yield strength(YS):421.7 MPa;ultimate tensile strength(UTS):480.4 MPa).After an aging treatment of 325 ℃-12 h,the YS and UTS of the sample increased to 494 MPa and 550.7 MPa,respectively.Adding Ni,Ti,and Zr components promoted the generation of multi-phase precipitates in the Al alloy and improved the synergistic strengthening effect of multi-phases.The hard-shell structure(HSS)formed by the Al_(3)Ni phase at the grain boundary significantly strengthened the grain boundary strength.The precipitated Al_(3)(Ti,Zr)phases at the grain boundaries prevent grain growth and dislocation movement.The Al_(3)Ni and Al_(3)(Ti,Zr)phases have good thermal stability that can still maintain excellent enhancement effects at high temperature.AlNi6TiZr alloy has great application prospects in medium and high-temperature environments.
基金This work was supported by the State Key Laboratory of Nuclear Physics and Technology,Peking University(No.NPT2021KF-ZX).
文摘The objective of this study was to investigate the influence of strengthening mechanisms on the high-temperature mechanical properties of China low-activation ferrite(CLF-1)steel,which underwent thermodynamic design and thermo-mechanical treatment(TMT).The microstructure characterization in the normalized and tempered condition and the TMT condition was carried out using optical microscopy,X-ray diffractometer,and scanning electron microscopy with electron backscatter diffraction.High-resolution transmission electron microscopy was employed to determine the crystallographic structures of precipitated phases.The results indicated that the addition of Ti led to an increase in the allocation of C in MC phase and an enhancement in the content of MC phase.Compared to CLF-P steel in the normalized and tempered condition,a 1.5-fold increase in dislocation density and an order of magnitude improvement in MX phase density were achieved after TMT.The formation of high-density nano-scale MC phases during TMT played a significant role in precipitation strengthening due to their favorable coherent relationship with the matrix and low interfacial free energy.The excellent high-temperature mechanical properties observed in CLF-P steel after TMT can be attributed to the combined effects of precipitation strengthening,dislocation strengthening,and lath strengthening.
基金supported by the Natural Science Foundation of Hunan Province, China (No. 2023JJ30678)。
文摘The microstructure evolution and mechanical properties of a T8-aged Al-Cu-Li alloy with increased pre-deformation(0-15%) were investigated,revealing the microstructure-strength relationship and the intrinsic strengthening mechanism.The results show that increasing the pre-deformation levels remarkably improves the strength of the alloy but deteriorates its ductility.Dislocations introduced by pre-deformation effectively suppress the formation of Guinier-Preston(GP) zones and provide more nucleation sites for T1 precipitates.This leads to more intensive and finer T1 precipitates in the samples with higher pre-deformation levels.Simultaneously,the enhanced precipitation of T1 precipitates and inhibited formation of GP zones cause the decreases in number and sizes of θ′ precipitates.The quantitative descriptions of the strength contributions from different strengthening mechanisms reveal that strengthening contributions from T1 and θ′ precipitates decrease with increasing pre-deformation.The reduced diameters of T1 precipitates are primarily responsible for their weakened strengthening effects.Therefore,the improved strength of the T8-aged Al-Cu-Li alloy is mainly attributed to the stronger strain hardening from the increased pre-deformation levels.
基金support from the National Natural Science Foundation of China(Nos.51931010 and 92163202)and the Key Research Program of Frontier Science and International partnership program(No.GJHZ2029)+1 种基金Z.C.acknowledges financial support from the National Natural Science Foundation of China(No.52001312)Youth Innovation Promotion Association,Chinese Academy of Sciences(CAS).
文摘Ordered structures with functional units offer the potential for enhanced performance in metallic materials.Among these structures,gradient nanotwinned(GNT)microstructures demonstrate excellent controllability.This paper provides a comprehensive review of the current state-of-the-art studies on GNT structures,encompassing various aspects such as design strategies,mechanical properties characterization,spatially gradient strain evolution analysis,and the significant role of geometrically necessary dislocations(GNDs).The primary objective is to systematically unravel the fundamental strengthening mechanisms by gaining an in-depth understanding of the deformation behavior of nanotwinned units.Through this work,we aim to contribute to the broader field of materials science by consolidating knowledge and providing insights for the development of novel metallic materials with enhanced properties and tailored performance characteristics.
基金the Natural Sciences and Engineering Research Council of Canada (NSERC)Ontario Trillium Scholarships (OTS) program for providing financial support+8 种基金financial support by the Premier’s Research Excellence Award (PREA)Canada Foundation for Innovation (CFI)Ryerson Research Chair (RRC) programthe Ministry of Science and Technology of China (2014DFG52810)National Great Theoretic Research Project of China (2013CB632200)National Natural Science Foundation of China (Project 51474043)Ministry of Education of China (SRFDR 20130191110018)Chongqing Municipal Government(CSTC2013JCYJC60001)Chongqing Science and Technology Commission (CSTC2011gjhz50001)
文摘This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium （Y） element. The addition of Y resulted in the formation of ternary 1 （Mg3YZn6）, W （Mg3Y2Zn3） and LPSO （Mg12YZn） phases which subse- quently reinforced alloys ZM31 ＋ 0.3Y, ZM31 ＋ 3.2Y and ZM31 ＋ 6Y, where the value denoted the amount of Y element （in wt%）. Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion （CTE）, which was derived to be 1.38 x 10^-5 K^-1 and 2.35 x 10^-5 K^-1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and crE mismatch were the predominant strengthening mechanisms in the ZM31＋0.3Y and ZM31 ＋ 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 ＋ 6Y alloy.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.
基金the National Natural Science Foundation of China(Nos.51775137 and 51875127)。
文摘A Mg-Gd-Y-Zn-Zr magnesium alloy with different initial states was extruded under different extrusion parameters.The effect of solution treatment and extrusion parameters on the microstructure,texture and mechanical properties were analyzed in detail,and the abnormal texture formation and strengthening mechanism was revealed.When extruded at low temperature and small extrusion ratio,the bimodal microstructure consisting of fine dynamically recrystallized grains and coarse deformed grains occurred both in the as-cast alloy and solution-treated alloy.When the extrusion temperature and extrusion ratio were increased,the amount and size of dynamically recrystallized grains increased and the grain size of the solution-treated alloy showed higher growth rate.Furthermore,an abnormal texture with<0001>parallel with extrusion direction developed due to the occurrence of non-basal slip and continuous dynamic recrystallization.This could be enhanced by solution treatment,high temperature,and large extrusion ratio.Both the as-cast alloy and solution-treated alloy exhibited the highest tensile strength after extrusion at 300℃with an extrusion ratio of 9.Grain refinement was the main strengthening mechanism utilized in both the as-cast alloy and the solution-treated alloy.Work hardening played an important role in the sample extruded at low temperature and small extrusion ratio,with the highest contribution of about 33 MPa after extrusion at 300℃with an extrusion ratio of 9.Texture strengthening contributed more in the sample extruded at high temperature and large extrusion ratio,but no more than 24.1 MPa.Solution strengthening was another strengthening mechanism in the extruded as-cast alloy,especially at high temperature and large extrusion ratio(no more than 9 MPa).
基金the National Research Foundation(NRF)grant funded by the Ministry of Science and ICT of Korea through contracts NRF-2018K2A9A1A06069970,NRF2020R1A5A6017701the Asian Office of Aerospace Research and Development(AOARD)grant funded by the Air Force Office of Scientific Research(AFOSR)through a grant FA2386-19-1-4009。
文摘Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3μm,and small amounts(<4 vol.%)of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27%and 87%at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm^(3),while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50%of the yield strength of the AlxCrNbVMo RHEAs.
