Carbonated recycled powder as cementitious auxiliary material can reduce carbon emissions and realize high-quality recycling of recycled concrete.In this paper,microscopic property of recycled powder with three carbon...Carbonated recycled powder as cementitious auxiliary material can reduce carbon emissions and realize high-quality recycling of recycled concrete.In this paper,microscopic property of recycled powder with three carbonation methods was tested through XRD and SEM,the mechanical property and microstructure of recycled powder mortar with three replacement rates were studied by ISO method and SEM,and the strengthening mechanism was analyzed.The results showed that the mechanical property of recycled powder mortar decreased with the increasing of replacement rate.It is suggested that the replacement rate of recycled powder should not exceed 20%.The strength index and activity index of carbonated recycled powder mortar were improved,in which the flexural strength was increased by 27.85%and compressive strength was increased by 20%at the maximum.Recycled powder can be quickly and completely carbonated,and the improvement effect of CH pre-soaking carbonation was the best.The activity index of carbonated recycled powder can meet the requirements of Grade II technical standard for recycled powder.Microscopic results revealed the activation mechanism of carbonated recycled powder such as surplus calcium source effect,alkaline polycondensation effect and carbonation enhancement effect.展开更多
In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HE...In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can effectively inhibit the interfacial diffusion between Al and Mg,which is conducive to the formation of solid solution,especially when the thickness of HEA is 800 nm.With the increase of casting temperature from 720 ℃ to 730 ℃,740℃,and 750 ℃,α-Al(Mg),α-Al(Mg)+Al3Mg2,Al3Mg2+Al12Mg17,and Al12Mg17+δ-Mg are formed at the interface of Ti/Mg bimetal,respectively.When the thickness of the HEA layer is 800 nm and the pouring temperature is 720 ℃,the bonding strength of the Ti/Mg bimetal can reach the maximum of 93.6 MPa.展开更多
Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c...Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c. HEAs is generally low, significantly limiting their practical applications. Recently, the alloying of W has been evidenced to be able to remarkably improve the mechanical properties of f.c.c. HEAs and is becoming a hot topic in the community of HEAs. To date, when W is introduced, multiple strengthening mechanisms, including solid-solution strengthening, precipitation strengthening (μphase,σphase, and b.c.c. phase), and grain-refinement strengthening, have been discovered to be activated or enhanced. Apart from mechanical properties, the addition of W improves corrosion resistance as W helps to form a dense WO_(3) film on the alloy surface. Until now, despite the extensive studies in the literature, there is no available review paper focusing on the W doping of the f.c.c. HEAs. In that context, the effects of W doping on f.c.c. HEAs were reviewed in this work from three aspects, i.e., microstructure,mechanical property, and corrosion resistance. We expect this work can advance the application of the W alloying strategy in the f.c.c. HEAs.展开更多
Thermal stabilities of microstructure and mechanical property have been investigated on super- alloy U72OLi, which is of great interest of application for jet engine and land-based turbine disc. The results showed tha...Thermal stabilities of microstructure and mechanical property have been investigated on super- alloy U72OLi, which is of great interest of application for jet engine and land-based turbine disc. The results showed that, the primary and secondary γ’?particles maintain good thermal stability at 650 and 7000C with aging time up to 3000 h, while the tertiary γ’?is apparently dependent on aging temperature and time. The tertiary γ’?particles undergo a procedure of coarsening, dissolution and eventually complete disappearance with the increasing of aging time and temper- ature. They exhibit unusual high sensibility upon aging temperature, which is attributed to the lattice misfit between the γ’?precipitates and the matrix in the alloy. The grain boundary phase M23C6 remains stable without forming of sigma phase even with aging time up to 3000 h at 700℃. Microhardness decreases apparently with increasing aging time and aging temperature. Theoretical analysis based on dislocation mechanism indicates that the change of microhardness should be attributed to the evolution of the tertiary γ’?during aging.展开更多
The effects of addition of La on the microstructure of as-cast ADC12 A1-Alloy were investigated by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy disperse ...The effects of addition of La on the microstructure of as-cast ADC12 A1-Alloy were investigated by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy disperse spectroscopy (EDS). The experimental results showed that the a-A1 and eutectic Si crystals were modified with the addition of 0.3 wt% La. The eutectic Si crystals showed a granular distribution. At the same time, the alloy possessed the best mechanical property. When more than 0.3 wt% La was added to ADC12 aluminum alloy, the microstructure of as-cast alloy was coarsening gradually with the increase of the content of La and the mechanical property decreased. The effect of rare earth La which was added in ADC 12 A1-Alloy for up to 0.9 wt% had been investigated in this study. The dendrites ofADC12 Al-alloy was refined obviously and the morphology of Si crystals showed a particle structure when the addition of La reached 0,3 wt%. Besides, the acicular La-rich intermetallics in the alloy deteriorated the mechanical property of alloy: To avoid this unwanted phase, the amount of added rare earth La must be less than 0.6 wt%.展开更多
The solid sintering behavior and mechanical properties of Fe Ni powders prepared by mechanical alloying of elemental powders and hot pressing sintering in vacuum atmospheres were investigated. It was observed that th...The solid sintering behavior and mechanical properties of Fe Ni powders prepared by mechanical alloying of elemental powders and hot pressing sintering in vacuum atmospheres were investigated. It was observed that the microstructure of the powder particles evolves in three stages. The alloy powder with average grain size of 20-30 nm was obtained. The sinter densification depends crucially on the particle rearrangement and the large amount of internal strain introduced during milling. The theoretical density of over 95 % was obtained after hot pressing sintering at 800 ℃ for 30 min with pressure of 50 MPa. No significant grain growth was observed during sintering. And also relatively high hardness was obtained.展开更多
The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, elec...The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, electron backscatter diffraction(EBSD) and uniaxial tensile test. The Mg-Y alloys exhibited a weakened basal texture before the ECAP, and the texture was further weakened with the max basal poles dispersed along ~45° between the extrusion direction and the transverse direction after the ECAP. The Mg-5 Y alloys always exhibited a finer grain size comparing to that of Mg-1 Y for the same ECAP process. With a proper ECAP process, both the strength and elongation of Mg-5 Y alloy could be improved simultaneously after the ECAP, i.e., the yield strength(273.9 ± 1.2 MPa), ultimate strength(306.4 ± 3.0 MPa),and elongation(23.9 ± 1.0%) were increased by 10%, 6%, and 72%, respectively, comparing to that before the ECAP. This was considered to be arose from the combined effects of grain refinement, significant improved microstructure homogeneity and solid solution hardening.In addition, it was found that Mg-Y alloy with better comprehensive properties could be obtained by the decreasing-temperature ECAP processes. The yield strength-grain size relationship could be well described by the Hall-Petch relation for all the ECAPed Mg-Y alloys,which was consistent with that the texture changes did not significantly affect the average Schmid factors of basal, prismatic and pyramidal slips for both Mg-Y alloys.展开更多
The effects of trace yttrium(Y)element on the microstructure,mechanical properties,and corrosion resistance of Mg-2Zn-0.1Mn-0.3Ca-xY(x=0,0.1,0.2,0.3)biological magnesium alloys are investigated.Results show that grain...The effects of trace yttrium(Y)element on the microstructure,mechanical properties,and corrosion resistance of Mg-2Zn-0.1Mn-0.3Ca-xY(x=0,0.1,0.2,0.3)biological magnesium alloys are investigated.Results show that grain size decreases from 310 to 144µm when Y content increases from 0wt%to 0.3wt%.At the same time,volume fraction of the second phase increases from 0.4%to 6.0%,yield strength of the alloy continues to increase,and ultimate tensile strength and elongation decrease initially and then increase.When the Y content increases to 0.3wt%,Mg_(3)Zn_(6)Y phase begins to precipitate in the alloy;thus,the alloy exhibits the most excellent mechanical property.At this time,its ultimate tensile strength,yield strength,and elongation are 119 MPa,69 MPa,and 9.1%,respectively.In addition,when the Y content is 0.3wt%,the alloy shows the best corrosion resistance in the simulated body fluid(SBF).This investigation has revealed that the improvement of mechanical properties and corrosion resistance is mainly attributed to the grain refinement and the precipitated Mg_(3)Zn_(6)Y phase.展开更多
Microstructures and phase compositions of as-cast and extruded ZK60-xBi(x=0-1.64)alloys were investigated.Meanwhile,the tensile mechanical property and hardness were tested.With increasing the Bi content,the as-cast m...Microstructures and phase compositions of as-cast and extruded ZK60-xBi(x=0-1.64)alloys were investigated.Meanwhile,the tensile mechanical property and hardness were tested.With increasing the Bi content,the as-cast microstructure is first refined obviously,and then becomes coarse slightly.New small block compound which is rich in Zr,Zn,Bi and poor in Mg increases gradually,and MgZn_(2) phase decreases gradually.The second phase mainly precipitates along the grain boundary.The as-cast tensile mechanical property is first enhanced obviously,where the tensile strengthσb,yield strengthσ0.2 and elongationδcan reach 265 MPa,151 MPa and 13.5%for ZK60-0.23Bi alloy,respectively,then remains the high value for ZK60-(0.37-1.09)Bi alloys,and finally decreases obviously for ZK60-1.64Bi alloy.After hot extrusion,the obvious dynamic recrystallization occurs.Broken block compound distributes along the extrusion direction by zonal shape.The average grain size can reach only 4-6μm.The extruded tensile mechanical property is enhanced significantly,where σ_(b),σ_(0.2) and δ are at the range of 345-360 MPa,285-300 MPa and 15.5-19.5%,respectively.Extruded tensile fracture exhibits a typical character of ductile fracture.展开更多
An experiment was carried out on the friction stir welding of MB3 magnesium alloy to determine welding parameters for obtaining an excellent weld appearance without void, cracking, or distortion. Frictional heat and p...An experiment was carried out on the friction stir welding of MB3 magnesium alloy to determine welding parameters for obtaining an excellent weld appearance without void, cracking, or distortion. Frictional heat and plastic flow created fine and equiaxed grains in the weld nugget, and the elongated and recovered grains in the thermomechanically affected zone (TMAZ). The grains in the heat affected zone (HAZ) grow slightly. The me- chanical property results show that maximum joint tensile strength can reach 97. 2% of the parent material, which is stronger than that of fusion joints; and the failure almost occurs in the heat affected zone.展开更多
The microstructure evolution of as-cast,as-extruded and peak-aged Mg-12Gd-2Er-1Zn-0.6Zr alloys were investigated by Optical Microscope(OM),X-ray Diffraction(XRD),Scanning Electron Microscope(SEM)and Transmission Elect...The microstructure evolution of as-cast,as-extruded and peak-aged Mg-12Gd-2Er-1Zn-0.6Zr alloys were investigated by Optical Microscope(OM),X-ray Diffraction(XRD),Scanning Electron Microscope(SEM)and Transmission Electron Microscope(TEM).The mechanical performance was also tested by tensile test at room temperature in the present study.The results indicated that the lamellar 14H-LPSO structure formed during the solid solution process at 793 K for 24 h,and also existed after hot extrusion process.The dynamic recrystallization(DRX)occurred during hot extrusion.The DRXed fine grain size was∼5μm.Meanwhile,some un-DRXed grains contained LPSO structure had a roughly orientation along the extrusion direction.The tensile test result showed that the as-extruded alloy had a better elongation of 14%due to fine DRXed grain and fiber-like un-DRXed with LPSO structure attributed to the high elongation.Because of the precipitation of theβ′-phase,the ultimate tensile strength(UTS)and yield tensile strength(YTS)increased up to 415 MPa(UTS)and 374 MPa(YTS),respectively.展开更多
Hot spinning of tubular workpiece of TA15 alloy was conducted on a CNC spinning machine, and the microstructure evolution during hot spinning and annealing was observed and mechanical properties of spun tubes were tes...Hot spinning of tubular workpiece of TA15 alloy was conducted on a CNC spinning machine, and the microstructure evolution during hot spinning and annealing was observed and mechanical properties of spun tubes were tested. The results show that with the increase of spinning pass, the fiber microstructure comes into being gradually in axial direction and the circumferential microstructure also stretches obviously along circumferential direction. At the same time, the tensile strength increases and elongation decreases not only in axial direction but also in circumferential direction. When the reduction ratio of wall thickness rises close to or over 40%, tensile strength increases and elongation decreases more rapidly, which means that tubular workpiece of titanium alloy can be strengthened bi-directionally by power spinning. The ductility of spun workpiece of TA15 alloy could be improved by annealing at the temperature no higher than recrystallization temperature with slight decrease of tensile strength.展开更多
The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline ...The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel.The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated.Consequently,the impact toughness of the steel is increased by more than one time,compared with no addition of RE-modifier.展开更多
Hot plastic deformation was conducted using a new solid die on a Mg-Mn-Ce magnesium alloy. The results of microstructural examination through OM and TEM show that the grain size is greatly refined from 45 μm to 1.1 ...Hot plastic deformation was conducted using a new solid die on a Mg-Mn-Ce magnesium alloy. The results of microstructural examination through OM and TEM show that the grain size is greatly refined from 45 μm to 1.1 μm with uniform distribution due to the occurrence of dynamic recrystallization. The grain refinement and high angle grain boundary formation improve the mechanical properties through tensile testing with the strain rate of 1.0×10?4 s?1 at room temperature and Vickers microhardness testing. The maximum values of tensile strength, elongation and Vickers microhardness are increased to 256.37 MPa, 17.69% and HV57.60, which are 21.36%, 133.80% and 20.50% more than those of the as-received Mg-Mn-Ce magnesium alloy, respectively. The SEM morphologies of tensile fractured surface indicate that the density and size of ductile dimples rise with accumulative strain increasing. The mechanism of microstructural evolution and the relationship between microstructure and mechanical property of Mg-Mn-Ce magnesium alloy processed by this solid die were also analyzed.展开更多
Pre-heat treatment is a vital step before cold ring rolling and it has significant effect on the microstructure and mechanical properties of rolled rings.The 100Cr6 steel rings were subjected to pre-heat treatment and...Pre-heat treatment is a vital step before cold ring rolling and it has significant effect on the microstructure and mechanical properties of rolled rings.The 100Cr6 steel rings were subjected to pre-heat treatment and subsequent cold rolling process.Scanning electron microscopy and tensile tests were applied to investigate microstructure characteristic and mechanical property variations of 100Cr6 steel rings undergoing different pre-heat treatings.The results indicate that the average diameter of carbide particles,the tensile strength and hardness increase,while the elongation decreases with the decrease of cooling rate.The cooling rate has minor effect on the yield strength of sample.After cold ring rolling,the ferrite matrix shows a clear direction along the rolling direction.The distribution of cementite is more homogeneous and the cementite particles are finer.Meanwhile,the hardness of the rolled ring is higher than that before rolling.展开更多
The formation process, microstructure and mechanical properties of transient liquid phase (TLP) bonded aluminium based metal matrix composite (MMC) joint with copper interlayer were investigated. The formation process...The formation process, microstructure and mechanical properties of transient liquid phase (TLP) bonded aluminium based metal matrix composite (MMC) joint with copper interlayer were investigated. The formation process of the TLP joint comprises a number of stages: plastic deformation and solid diffusion (stage 1), dissolution of interlayer and base metal (stage 2), isothermal solidification (stage 3) and homogenization (stage 4). The microstructure of the joint depends on the joint formation process (distinct stages). The plastic deformation and solid diffusion in stage 1 favoure the intimate contact at interfaces and liquid layer formation. The microstructure of joint consists of aluminium solid solution, alumina particle, Al 2Cu and MgAl 2O 4 compounds in stage 2. The most pronounced feature of joint microstructure in stage 3 is the alumina particle segregation in the center of the joint. The increase of joint shear strength with increasing bonding temperature is mainly attributed to improving the fluidity and wettability of liquid phase and decreasing the amount of Al 2Cu brittle phase in the joint. The principal reason of higher bonding temperature (>600 ℃) resulting in lowering obviously the joint shear strength is the widening of alumina particle segregation region that acts as a preferential site for failure. The increase of joint shear strength with increasing holding time is mainly associated with decreasing the amount of Al 2Cu brittle phase and promoting homogenization of joint.展开更多
In the present work, N 2, N 2+H 2, Ar and Ar+H 2, were used as the sintering atmosphere of Metal Injection Molded 316L stainless steel respectively. The influences of the sintering atmospheres on C, O, N contents of t...In the present work, N 2, N 2+H 2, Ar and Ar+H 2, were used as the sintering atmosphere of Metal Injection Molded 316L stainless steel respectively. The influences of the sintering atmospheres on C, O, N contents of the sintered specimens, sintered density, grain morphology and mechanical properties were investigated. The results show that C, O, N contents of the sintered specimens can be controlled in permitted low values. The ultimate tensile strength and elongation of the specimen sintered in N 2+H 2 atmosphere are 765 MPa and 32% respectively. Using Ar and Ar+H 2 as the sintering atmosphere, the density of the sintered specimens is 98% of the theoretical density; the pores are uniformly distributed as small spherical shape and the grain size is about 50 μm. The mechanical properties of the specimen, i.e. ultimate tensile strength 630 MPa, yield strength 280 MPa, elongation 52%, HRB 71, are much better than those of the American Metal Powder Industries Federation(MPIF) 35 Standard after being sintered in Ar+H 2.展开更多
The mechanical behavior and microstructural evolution of an Fe-30Mn-3Al-3Si twinninginduced plasticity(TWIP)steel processed using warm forging was investigated.It is found that steel processed via warm forging improve...The mechanical behavior and microstructural evolution of an Fe-30Mn-3Al-3Si twinninginduced plasticity(TWIP)steel processed using warm forging was investigated.It is found that steel processed via warm forging improves comprehensive mechanical properties compared to the TWIP steel processed via cold rolling,with a high tensile strength(R_(m))of 793 MPa,a yield strength(R_(P))of 682 MPa,an extremely large R_(P)/R_(m)ratio as high as 0.86 as well as an excellent elongation rate of 46.8%.The microstructure observation demonstrates that steel processed by warm forging consists of large and elongated grains together with fine,equiaxed grains.Complicated micro-defect configurations were also observed within the steel,including dense dislocation networks and a few coarse deformation twins.As the plastic deformation proceeds,the densities of dislocations and deformation twins significantly increase.Moreover,a great number of slip lines could be observed in the elongated grains.These findings reveal that a much more dramatic interaction between microstructural defect and dislocations glide takes place in the forging sample,wherein the fine and equiaxed grains propagated dislocations more rapidly,together with initial defect configurations,are responsible for enhanced strength properties.Meanwhile,larger,elongated grains with more prevalently activated deformation twins result in high plasticity.展开更多
Surrounding rocks of underground engineering are subjected to long-term seepage pressure,which can deteriorate the mechanical properties and cause serious disasters.In order to understand the impact of seepage pressur...Surrounding rocks of underground engineering are subjected to long-term seepage pressure,which can deteriorate the mechanical properties and cause serious disasters.In order to understand the impact of seepage pressure on the mechanical property of sandstone,uniaxial compression tests,P-wave velocity measurements,and nuclear magnetic resonance(NMR)tests were conducted on saturated sandstone samples with varied seepage pressures(i.e.0 MPa,3 MPa,4 MPa,5 MPa,6 MPa,7 MPa).The results demonstrate that the mechanical parameters(uniaxial compressive strength,peak strain,elastic modulus,and brittleness index),total energy,elastic strain energy,as well as elastic strain energy ratio,decrease with increasing seepage pressure,while the dissipation energy and dissipation energy ratio increase.Moreover,as seepage pressure increases,the micro-pores gradually transform into meso-pores and macro-pores.This increases the cumulative porosity of sandstone and decreases P-wave velocity.The numerical results indicate that as seepage pressure rises,the number of tensile cracks increases progressively,the angle range of microcracks is basically from 50-120to 80-100,and as a result,the failure mode transforms to the tensile-shear mixed failure mode.Finally,the effects of seepage pressure on mechanical properties were discussed.The results show that decrease in the effective stress and cohesion under the action of seepage pressure could lead to deterioration of strength behaviors of sandstone.展开更多
In this study, the in-situ synthesized ZrB_(2) nanoparticles and rare earth Sc were introduced to enhance the strength and ductility of 7N01 aluminum alloy, via the generation of high-melting and uniform nanodispersoi...In this study, the in-situ synthesized ZrB_(2) nanoparticles and rare earth Sc were introduced to enhance the strength and ductility of 7N01 aluminum alloy, via the generation of high-melting and uniform nanodispersoids. The microstructure and mechanical property evolution of the prepared composites and the interaction between ZrB_(2) and Sc were studied in detail. The microstructure investigation shows that the introduction of rare earth scandium(Sc) can promote the distribution of ZrB_(2) nanoparticles, by improving their wettability to the Al melt. Meanwhile, the addition of rare earth Sc also modifies the coarse Al Zn Mg Mn Fe precipitated phases, refines the matrix grains and generates high-melting Al_3(Sc,Zr)/Al_3Sc nanodispersoids. Tensile tests of the composites show that with the combinatorial introduction of ZrB_(2) and Sc, the strength and ductility of the composites are improved simultaneously compared with the corresponding 7N01 alloy, ZrB_(2) /7N01 composite and Sc/7N01 alloy. And the optimum contents of ZrB_(2) and Sc are 3 wt% and 0.2 wt% in this study. The yield strength, ultimate strength and elongation of(3 wt% ZrB_(2) +0.2 wt% Sc)/7N01 composite are 477 MPa, 506 MPa and 9.8%, increased about 18.1%, 12.2%and 38% compared to 7N01 alloy. Furthermore, the cooperation strengthening mechanisms of ZrB_(2) and Sc are also discussed.展开更多
基金Funded by Joint Funds of the National Natural Science Foundation of China(No.U1904188)Jiangxi Provincial Department of Education Science and Technology Project(Nos.GJJ171079,GJJ181023 and GJJ181022)。
文摘Carbonated recycled powder as cementitious auxiliary material can reduce carbon emissions and realize high-quality recycling of recycled concrete.In this paper,microscopic property of recycled powder with three carbonation methods was tested through XRD and SEM,the mechanical property and microstructure of recycled powder mortar with three replacement rates were studied by ISO method and SEM,and the strengthening mechanism was analyzed.The results showed that the mechanical property of recycled powder mortar decreased with the increasing of replacement rate.It is suggested that the replacement rate of recycled powder should not exceed 20%.The strength index and activity index of carbonated recycled powder mortar were improved,in which the flexural strength was increased by 27.85%and compressive strength was increased by 20%at the maximum.Recycled powder can be quickly and completely carbonated,and the improvement effect of CH pre-soaking carbonation was the best.The activity index of carbonated recycled powder can meet the requirements of Grade II technical standard for recycled powder.Microscopic results revealed the activation mechanism of carbonated recycled powder such as surplus calcium source effect,alkaline polycondensation effect and carbonation enhancement effect.
基金financial supports from the National Natural Science Foundation of China (No. 51875062)China Postdoctoral Science Foundation (No. 2021M700567)。
文摘In this study,HEA/AI composite interlayer was used to fabricate Ti/Mg bimetal composites by solidliquid compound casting process.The Al layer was prepared on the surface of TC4 alloy by hot dipping,and the FeCoNiCr HEA layer was prepared by magnetron sputtering onto the Al layer.The influence of the HEA layer thickness and pouring temperature on interface evolution was investigated based on SEM observation and thermodynamic analysis.Results indicate that the sluggish diffusion effect of HEA can effectively inhibit the interfacial diffusion between Al and Mg,which is conducive to the formation of solid solution,especially when the thickness of HEA is 800 nm.With the increase of casting temperature from 720 ℃ to 730 ℃,740℃,and 750 ℃,α-Al(Mg),α-Al(Mg)+Al3Mg2,Al3Mg2+Al12Mg17,and Al12Mg17+δ-Mg are formed at the interface of Ti/Mg bimetal,respectively.When the thickness of the HEA layer is 800 nm and the pouring temperature is 720 ℃,the bonding strength of the Ti/Mg bimetal can reach the maximum of 93.6 MPa.
基金financially supported by the National Key R&D Program of China (No.2021YFA1200203)the National Natural Science Foundation of China (Nos.51922026 and 51975111)+1 种基金the Fundamental Research Funds for the Central Universities (No.N2202015,N2002005,and N2105001)the 111 Project of China (No.BP0719037 and B20029)。
文摘Face-centered cubic (f.c.c.) high entropy alloys (HEAs) are attracting more and more attention owing to their excellent strength and ductility synergy, irradiation resistance, etc. However, the yield strength of f.c.c. HEAs is generally low, significantly limiting their practical applications. Recently, the alloying of W has been evidenced to be able to remarkably improve the mechanical properties of f.c.c. HEAs and is becoming a hot topic in the community of HEAs. To date, when W is introduced, multiple strengthening mechanisms, including solid-solution strengthening, precipitation strengthening (μphase,σphase, and b.c.c. phase), and grain-refinement strengthening, have been discovered to be activated or enhanced. Apart from mechanical properties, the addition of W improves corrosion resistance as W helps to form a dense WO_(3) film on the alloy surface. Until now, despite the extensive studies in the literature, there is no available review paper focusing on the W doping of the f.c.c. HEAs. In that context, the effects of W doping on f.c.c. HEAs were reviewed in this work from three aspects, i.e., microstructure,mechanical property, and corrosion resistance. We expect this work can advance the application of the W alloying strategy in the f.c.c. HEAs.
文摘Thermal stabilities of microstructure and mechanical property have been investigated on super- alloy U72OLi, which is of great interest of application for jet engine and land-based turbine disc. The results showed that, the primary and secondary γ’?particles maintain good thermal stability at 650 and 7000C with aging time up to 3000 h, while the tertiary γ’?is apparently dependent on aging temperature and time. The tertiary γ’?particles undergo a procedure of coarsening, dissolution and eventually complete disappearance with the increasing of aging time and temper- ature. They exhibit unusual high sensibility upon aging temperature, which is attributed to the lattice misfit between the γ’?precipitates and the matrix in the alloy. The grain boundary phase M23C6 remains stable without forming of sigma phase even with aging time up to 3000 h at 700℃. Microhardness decreases apparently with increasing aging time and aging temperature. Theoretical analysis based on dislocation mechanism indicates that the change of microhardness should be attributed to the evolution of the tertiary γ’?during aging.
基金Supported by the National Natural Science Foundation of China(No.51165032)the Innovative Group of Science and Technology of College of Jiangxi Province(No.00008713)
文摘The effects of addition of La on the microstructure of as-cast ADC12 A1-Alloy were investigated by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy disperse spectroscopy (EDS). The experimental results showed that the a-A1 and eutectic Si crystals were modified with the addition of 0.3 wt% La. The eutectic Si crystals showed a granular distribution. At the same time, the alloy possessed the best mechanical property. When more than 0.3 wt% La was added to ADC12 aluminum alloy, the microstructure of as-cast alloy was coarsening gradually with the increase of the content of La and the mechanical property decreased. The effect of rare earth La which was added in ADC 12 A1-Alloy for up to 0.9 wt% had been investigated in this study. The dendrites ofADC12 Al-alloy was refined obviously and the morphology of Si crystals showed a particle structure when the addition of La reached 0,3 wt%. Besides, the acicular La-rich intermetallics in the alloy deteriorated the mechanical property of alloy: To avoid this unwanted phase, the amount of added rare earth La must be less than 0.6 wt%.
文摘The solid sintering behavior and mechanical properties of Fe Ni powders prepared by mechanical alloying of elemental powders and hot pressing sintering in vacuum atmospheres were investigated. It was observed that the microstructure of the powder particles evolves in three stages. The alloy powder with average grain size of 20-30 nm was obtained. The sinter densification depends crucially on the particle rearrangement and the large amount of internal strain introduced during milling. The theoretical density of over 95 % was obtained after hot pressing sintering at 800 ℃ for 30 min with pressure of 50 MPa. No significant grain growth was observed during sintering. And also relatively high hardness was obtained.
基金supported by the National Natural Science Foundation of China(Nos.51401172 and 51601003)Sichuan Science and Technology Program(2019YJ0238)+1 种基金Fundamental Research Funds for the Central Universities(2682020ZT114)open funding of International Joint Laboratory for Light Alloys(MOE),Chongqing University。
文摘The microstructure, texture and mechanical property evolution of the extruded Mg-x Y(x = 1, 5 wt.%) alloys during equal channel angular pressing(ECAP) were systematically investigated using an optical microscope, electron backscatter diffraction(EBSD) and uniaxial tensile test. The Mg-Y alloys exhibited a weakened basal texture before the ECAP, and the texture was further weakened with the max basal poles dispersed along ~45° between the extrusion direction and the transverse direction after the ECAP. The Mg-5 Y alloys always exhibited a finer grain size comparing to that of Mg-1 Y for the same ECAP process. With a proper ECAP process, both the strength and elongation of Mg-5 Y alloy could be improved simultaneously after the ECAP, i.e., the yield strength(273.9 ± 1.2 MPa), ultimate strength(306.4 ± 3.0 MPa),and elongation(23.9 ± 1.0%) were increased by 10%, 6%, and 72%, respectively, comparing to that before the ECAP. This was considered to be arose from the combined effects of grain refinement, significant improved microstructure homogeneity and solid solution hardening.In addition, it was found that Mg-Y alloy with better comprehensive properties could be obtained by the decreasing-temperature ECAP processes. The yield strength-grain size relationship could be well described by the Hall-Petch relation for all the ECAPed Mg-Y alloys,which was consistent with that the texture changes did not significantly affect the average Schmid factors of basal, prismatic and pyramidal slips for both Mg-Y alloys.
基金financially supported by the National Natural Science Foundation of China(Nos.52005034 and 52027805)the China Postdoctoral Science Foundation Funded Project(No.2021M691860)+2 种基金the Beijing Postdoctoral Research Foundation(No.2021-ZZ-073)the Zhuhai Industry-University-Research Cooperation Project(No.ZH22017001200176PWC)the Tai’an City Science and Technology Innovation Major Project(No.2021ZDZX011)。
文摘The effects of trace yttrium(Y)element on the microstructure,mechanical properties,and corrosion resistance of Mg-2Zn-0.1Mn-0.3Ca-xY(x=0,0.1,0.2,0.3)biological magnesium alloys are investigated.Results show that grain size decreases from 310 to 144µm when Y content increases from 0wt%to 0.3wt%.At the same time,volume fraction of the second phase increases from 0.4%to 6.0%,yield strength of the alloy continues to increase,and ultimate tensile strength and elongation decrease initially and then increase.When the Y content increases to 0.3wt%,Mg_(3)Zn_(6)Y phase begins to precipitate in the alloy;thus,the alloy exhibits the most excellent mechanical property.At this time,its ultimate tensile strength,yield strength,and elongation are 119 MPa,69 MPa,and 9.1%,respectively.In addition,when the Y content is 0.3wt%,the alloy shows the best corrosion resistance in the simulated body fluid(SBF).This investigation has revealed that the improvement of mechanical properties and corrosion resistance is mainly attributed to the grain refinement and the precipitated Mg_(3)Zn_(6)Y phase.
基金The authors would like to acknowledge theMajor Science and Technology Project of Guangdong Province,China(Grant No.2010A090200078 and 2011A080403008)for financial supports。
文摘Microstructures and phase compositions of as-cast and extruded ZK60-xBi(x=0-1.64)alloys were investigated.Meanwhile,the tensile mechanical property and hardness were tested.With increasing the Bi content,the as-cast microstructure is first refined obviously,and then becomes coarse slightly.New small block compound which is rich in Zr,Zn,Bi and poor in Mg increases gradually,and MgZn_(2) phase decreases gradually.The second phase mainly precipitates along the grain boundary.The as-cast tensile mechanical property is first enhanced obviously,where the tensile strengthσb,yield strengthσ0.2 and elongationδcan reach 265 MPa,151 MPa and 13.5%for ZK60-0.23Bi alloy,respectively,then remains the high value for ZK60-(0.37-1.09)Bi alloys,and finally decreases obviously for ZK60-1.64Bi alloy.After hot extrusion,the obvious dynamic recrystallization occurs.Broken block compound distributes along the extrusion direction by zonal shape.The average grain size can reach only 4-6μm.The extruded tensile mechanical property is enhanced significantly,where σ_(b),σ_(0.2) and δ are at the range of 345-360 MPa,285-300 MPa and 15.5-19.5%,respectively.Extruded tensile fracture exhibits a typical character of ductile fracture.
文摘An experiment was carried out on the friction stir welding of MB3 magnesium alloy to determine welding parameters for obtaining an excellent weld appearance without void, cracking, or distortion. Frictional heat and plastic flow created fine and equiaxed grains in the weld nugget, and the elongated and recovered grains in the thermomechanically affected zone (TMAZ). The grains in the heat affected zone (HAZ) grow slightly. The me- chanical property results show that maximum joint tensile strength can reach 97. 2% of the parent material, which is stronger than that of fusion joints; and the failure almost occurs in the heat affected zone.
基金This projects was supported by Projects(2142005)supported by Beijing Natural Science FoundationProjects(KM201310005001)supported by Beijing Municipal Commission of Education.
文摘The microstructure evolution of as-cast,as-extruded and peak-aged Mg-12Gd-2Er-1Zn-0.6Zr alloys were investigated by Optical Microscope(OM),X-ray Diffraction(XRD),Scanning Electron Microscope(SEM)and Transmission Electron Microscope(TEM).The mechanical performance was also tested by tensile test at room temperature in the present study.The results indicated that the lamellar 14H-LPSO structure formed during the solid solution process at 793 K for 24 h,and also existed after hot extrusion process.The dynamic recrystallization(DRX)occurred during hot extrusion.The DRXed fine grain size was∼5μm.Meanwhile,some un-DRXed grains contained LPSO structure had a roughly orientation along the extrusion direction.The tensile test result showed that the as-extruded alloy had a better elongation of 14%due to fine DRXed grain and fiber-like un-DRXed with LPSO structure attributed to the high elongation.Because of the precipitation of theβ′-phase,the ultimate tensile strength(UTS)and yield tensile strength(YTS)increased up to 415 MPa(UTS)and 374 MPa(YTS),respectively.
文摘Hot spinning of tubular workpiece of TA15 alloy was conducted on a CNC spinning machine, and the microstructure evolution during hot spinning and annealing was observed and mechanical properties of spun tubes were tested. The results show that with the increase of spinning pass, the fiber microstructure comes into being gradually in axial direction and the circumferential microstructure also stretches obviously along circumferential direction. At the same time, the tensile strength increases and elongation decreases not only in axial direction but also in circumferential direction. When the reduction ratio of wall thickness rises close to or over 40%, tensile strength increases and elongation decreases more rapidly, which means that tubular workpiece of titanium alloy can be strengthened bi-directionally by power spinning. The ductility of spun workpiece of TA15 alloy could be improved by annealing at the temperature no higher than recrystallization temperature with slight decrease of tensile strength.
文摘The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel.The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated.Consequently,the impact toughness of the steel is increased by more than one time,compared with no addition of RE-modifier.
基金Project(2005B10301020) supported by the Science and Technology Development Program of Guangdong Province, China
文摘Hot plastic deformation was conducted using a new solid die on a Mg-Mn-Ce magnesium alloy. The results of microstructural examination through OM and TEM show that the grain size is greatly refined from 45 μm to 1.1 μm with uniform distribution due to the occurrence of dynamic recrystallization. The grain refinement and high angle grain boundary formation improve the mechanical properties through tensile testing with the strain rate of 1.0×10?4 s?1 at room temperature and Vickers microhardness testing. The maximum values of tensile strength, elongation and Vickers microhardness are increased to 256.37 MPa, 17.69% and HV57.60, which are 21.36%, 133.80% and 20.50% more than those of the as-received Mg-Mn-Ce magnesium alloy, respectively. The SEM morphologies of tensile fractured surface indicate that the density and size of ductile dimples rise with accumulative strain increasing. The mechanism of microstructural evolution and the relationship between microstructure and mechanical property of Mg-Mn-Ce magnesium alloy processed by this solid die were also analyzed.
基金Project(2011CB706605)supported by the National Basic Research Program of ChinaProject(2011CDA12)supported by the Innovative Research Groups of the Natural Science Foundation of Hubei Province,ChinaProjects(2012-Ia-017,2013-IV-014)supported by the Fundamental Research Funds for the Central Universities,China
文摘Pre-heat treatment is a vital step before cold ring rolling and it has significant effect on the microstructure and mechanical properties of rolled rings.The 100Cr6 steel rings were subjected to pre-heat treatment and subsequent cold rolling process.Scanning electron microscopy and tensile tests were applied to investigate microstructure characteristic and mechanical property variations of 100Cr6 steel rings undergoing different pre-heat treatings.The results indicate that the average diameter of carbide particles,the tensile strength and hardness increase,while the elongation decreases with the decrease of cooling rate.The cooling rate has minor effect on the yield strength of sample.After cold ring rolling,the ferrite matrix shows a clear direction along the rolling direction.The distribution of cementite is more homogeneous and the cementite particles are finer.Meanwhile,the hardness of the rolled ring is higher than that before rolling.
文摘The formation process, microstructure and mechanical properties of transient liquid phase (TLP) bonded aluminium based metal matrix composite (MMC) joint with copper interlayer were investigated. The formation process of the TLP joint comprises a number of stages: plastic deformation and solid diffusion (stage 1), dissolution of interlayer and base metal (stage 2), isothermal solidification (stage 3) and homogenization (stage 4). The microstructure of the joint depends on the joint formation process (distinct stages). The plastic deformation and solid diffusion in stage 1 favoure the intimate contact at interfaces and liquid layer formation. The microstructure of joint consists of aluminium solid solution, alumina particle, Al 2Cu and MgAl 2O 4 compounds in stage 2. The most pronounced feature of joint microstructure in stage 3 is the alumina particle segregation in the center of the joint. The increase of joint shear strength with increasing bonding temperature is mainly attributed to improving the fluidity and wettability of liquid phase and decreasing the amount of Al 2Cu brittle phase in the joint. The principal reason of higher bonding temperature (>600 ℃) resulting in lowering obviously the joint shear strength is the widening of alumina particle segregation region that acts as a preferential site for failure. The increase of joint shear strength with increasing holding time is mainly associated with decreasing the amount of Al 2Cu brittle phase and promoting homogenization of joint.
文摘In the present work, N 2, N 2+H 2, Ar and Ar+H 2, were used as the sintering atmosphere of Metal Injection Molded 316L stainless steel respectively. The influences of the sintering atmospheres on C, O, N contents of the sintered specimens, sintered density, grain morphology and mechanical properties were investigated. The results show that C, O, N contents of the sintered specimens can be controlled in permitted low values. The ultimate tensile strength and elongation of the specimen sintered in N 2+H 2 atmosphere are 765 MPa and 32% respectively. Using Ar and Ar+H 2 as the sintering atmosphere, the density of the sintered specimens is 98% of the theoretical density; the pores are uniformly distributed as small spherical shape and the grain size is about 50 μm. The mechanical properties of the specimen, i.e. ultimate tensile strength 630 MPa, yield strength 280 MPa, elongation 52%, HRB 71, are much better than those of the American Metal Powder Industries Federation(MPIF) 35 Standard after being sintered in Ar+H 2.
基金Funded by the National Natural Science Foundation of China(Nos.51701206 and 51671187)the Shanxi Natural Science Foundation(No.2019JQ-833)+2 种基金the Anhui Natural Science Foundation(1808085QE166)the Special Scientific Research Project of Shanxi Education Committee(No.19JQ0974)the Doctoral Research Initiation Project of Yan’an University(No.YDBD2018-21)。
文摘The mechanical behavior and microstructural evolution of an Fe-30Mn-3Al-3Si twinninginduced plasticity(TWIP)steel processed using warm forging was investigated.It is found that steel processed via warm forging improves comprehensive mechanical properties compared to the TWIP steel processed via cold rolling,with a high tensile strength(R_(m))of 793 MPa,a yield strength(R_(P))of 682 MPa,an extremely large R_(P)/R_(m)ratio as high as 0.86 as well as an excellent elongation rate of 46.8%.The microstructure observation demonstrates that steel processed by warm forging consists of large and elongated grains together with fine,equiaxed grains.Complicated micro-defect configurations were also observed within the steel,including dense dislocation networks and a few coarse deformation twins.As the plastic deformation proceeds,the densities of dislocations and deformation twins significantly increase.Moreover,a great number of slip lines could be observed in the elongated grains.These findings reveal that a much more dramatic interaction between microstructural defect and dislocations glide takes place in the forging sample,wherein the fine and equiaxed grains propagated dislocations more rapidly,together with initial defect configurations,are responsible for enhanced strength properties.Meanwhile,larger,elongated grains with more prevalently activated deformation twins result in high plasticity.
基金supported by the National Natural Science Foundation of China(Grant Nos.U22A20234 and 42277170)Hubei Province Key Research and Development Project(Grant No.2023BCB121).
文摘Surrounding rocks of underground engineering are subjected to long-term seepage pressure,which can deteriorate the mechanical properties and cause serious disasters.In order to understand the impact of seepage pressure on the mechanical property of sandstone,uniaxial compression tests,P-wave velocity measurements,and nuclear magnetic resonance(NMR)tests were conducted on saturated sandstone samples with varied seepage pressures(i.e.0 MPa,3 MPa,4 MPa,5 MPa,6 MPa,7 MPa).The results demonstrate that the mechanical parameters(uniaxial compressive strength,peak strain,elastic modulus,and brittleness index),total energy,elastic strain energy,as well as elastic strain energy ratio,decrease with increasing seepage pressure,while the dissipation energy and dissipation energy ratio increase.Moreover,as seepage pressure increases,the micro-pores gradually transform into meso-pores and macro-pores.This increases the cumulative porosity of sandstone and decreases P-wave velocity.The numerical results indicate that as seepage pressure rises,the number of tensile cracks increases progressively,the angle range of microcracks is basically from 50-120to 80-100,and as a result,the failure mode transforms to the tensile-shear mixed failure mode.Finally,the effects of seepage pressure on mechanical properties were discussed.The results show that decrease in the effective stress and cohesion under the action of seepage pressure could lead to deterioration of strength behaviors of sandstone.
基金Project supported by the National Natural Science Foundation of China(U20A20274,52071158,51701085,U1664254)the Six Talents Peak Project of Jiangsu Province(2018-XCL-202)+1 种基金the Open Funds of SKLMMC of SJTU(MMC-KF18-16)the Jiangsu Province Key Laboratory of High-end Structural Materials(HSM1803,1902)。
文摘In this study, the in-situ synthesized ZrB_(2) nanoparticles and rare earth Sc were introduced to enhance the strength and ductility of 7N01 aluminum alloy, via the generation of high-melting and uniform nanodispersoids. The microstructure and mechanical property evolution of the prepared composites and the interaction between ZrB_(2) and Sc were studied in detail. The microstructure investigation shows that the introduction of rare earth scandium(Sc) can promote the distribution of ZrB_(2) nanoparticles, by improving their wettability to the Al melt. Meanwhile, the addition of rare earth Sc also modifies the coarse Al Zn Mg Mn Fe precipitated phases, refines the matrix grains and generates high-melting Al_3(Sc,Zr)/Al_3Sc nanodispersoids. Tensile tests of the composites show that with the combinatorial introduction of ZrB_(2) and Sc, the strength and ductility of the composites are improved simultaneously compared with the corresponding 7N01 alloy, ZrB_(2) /7N01 composite and Sc/7N01 alloy. And the optimum contents of ZrB_(2) and Sc are 3 wt% and 0.2 wt% in this study. The yield strength, ultimate strength and elongation of(3 wt% ZrB_(2) +0.2 wt% Sc)/7N01 composite are 477 MPa, 506 MPa and 9.8%, increased about 18.1%, 12.2%and 38% compared to 7N01 alloy. Furthermore, the cooperation strengthening mechanisms of ZrB_(2) and Sc are also discussed.