TC4 titanium alloy(Ti-6Al-4V),known for its excellent specific strength,corrosion resistance,and weldability,is extensively applied in aerospace,marine engineering,and advanced manufacturing.This study focuses on the ...TC4 titanium alloy(Ti-6Al-4V),known for its excellent specific strength,corrosion resistance,and weldability,is extensively applied in aerospace,marine engineering,and advanced manufacturing.This study focuses on the microstructural uniformity and mechanical properties of TC4 ingots fabricated via the electron-beam cold hearth melting(EBCHM)process.A comprehensive analysis was performed using optical microscopy,scanning electron microscopy,electron backscatter diffraction,and energy-dispersive spectroscopy to investigate the ingot’s morphology,α-phase lamellar structure,and elemental distribution.Mechanical characterization included tensile testing,and microhardness and impact toughness assessments.Results reveal that EBCHM produces a well-defined and homogeneous microstructure,with the averageαlamellae thickness varying between 1.53 and 1.71μm and minimal fluctuations across the ingot regions,indicating high process consistency.Major alloying elements(Al and V)and impurity elements(O,N,H,C,and Fe)are evenly distributed,with no observable macrosegregation.The mechanical properties are stable and reliable,with a yield strength of 694.6-701.2 MPa,a tensile strength of 711.1-716.6 MPa,an elongation of 3.35%-3.84%,and an average impact toughness of 94.7 J/cm^(2).These results provide valuable data and technical references for the application of EBCHM in manufacturing premium-quality Ti-6Al-4V ingots.展开更多
Hypervelocity rocket sled systems are critical for testing advanced military technologies,yet track damage at speeds exceeding Mach 5 remains a significant challenge for system reliability and performance.In this stud...Hypervelocity rocket sled systems are critical for testing advanced military technologies,yet track damage at speeds exceeding Mach 5 remains a significant challenge for system reliability and performance.In this study,we investigated the hypervelocity impact response and protection for highstrength U71 Mn or bainitic steel used in rocket sled tracks.Flyer plate impact experiments using a two-stage light-gas gun were conducted to study the hypervelocity collision response,followed by the microstructural characterization via optical microscope,scanning electron microscopy equipped with electron backscatter diffraction to reveal underlying damage mechanisms.Then,the calibrated thermalmechanical coupled finite element simulations using the Johnson-Cook constitutive model and MieGrüneisen equation of state were carried out.Results indicated that bainitic steel exhibits superior impact resistance with predominantly smooth scratch-dominated damage due to its higher ductility.In contrast,U71 Mn suffered significant material spallation and crack propagation arising from brittle fracture mechanisms.Zinc-rich epoxy primer coatings effectively mitigated stress concentration and temperature rise in the substrate at impacting velocities below 2.4 km/s,so as to suppress the microstructural damage such as adiabatic shear bands and dynamic recrystallization.However,coating protection diminished at ultra-high-speed impacts due to the coating failure.Dimensional analysis established quantitative relationships of the gouge damage size to projectile mass,impact velocity,and material yield strength.This study provides in-depth insights into damage mechanisms in hypervelocity rail systems,demonstrating that bainitic steel combined with protective coatings can significantly enhance impact resistance and system reliability,offering valuable guidance for the design and optimization of hypervelocity testing platforms.展开更多
Vacancy defects,as fundamental disruptions in metallic lattices,play an important role in shaping the mechanical and electronic properties of aluminum crystals.However,the influence of vacancy position under coupled t...Vacancy defects,as fundamental disruptions in metallic lattices,play an important role in shaping the mechanical and electronic properties of aluminum crystals.However,the influence of vacancy position under coupled thermomechanical fields remains insufficiently understood.In this study,transmission and scanning electron microscopy were employed to observe dislocation structures and grain boundary heterogeneities in processed aluminum alloys,suggesting stress concentrations and microstructural inhomogeneities associated with vacancy accumulation.To complement these observations,first-principles calculations and molecular dynamics simulations were conducted for seven single-vacancy configurations in face-centered cubic aluminum.The stress response,total energy,density of states(DOS),and differential charge density were examined under varying compressive strain(ε=0–0.1)and temperature(0–600 K).The results indicate that face-centered vacancies tend to reduce mechanical strength and perturb electronic states near the Fermi level,whereas corner and edge vacancies appear to have weaker effects.Elevated temperatures may partially restore electronic uniformity through thermal excitation.Overall,these findings suggest that vacancy position exerts a critical but position-dependent influence on coupled structure-property relationships,offering theoretical insights and preliminary experimental support for defect-engineered aluminum alloy design.展开更多
Hot compression tests of an extruded Al-1.1Mn-0.3Mg-0.25RE alloy were performed on Gleeble-1500 system in the temperature range of 300-500 ℃ and strain rate range of 0.01-10 s-l. The associated microstructural evolut...Hot compression tests of an extruded Al-1.1Mn-0.3Mg-0.25RE alloy were performed on Gleeble-1500 system in the temperature range of 300-500 ℃ and strain rate range of 0.01-10 s-l. The associated microstructural evolutions were studied by observation of optical and transmission electron microscopes. The results show that the peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in the hyperbolic-sine equation with the hot deformation activation energy of 186.48 kJ/mol. The steady flow behavior results from dynamic recovery whereas flow softening is associated with dynamic recrystallization and dynamic transformation of constituent particles. The main constituent particles are enriched rare earth phases. Positive purifying effects on impurity elements of Fe and Si are shown in the Al-l.lMn-0.3Mg-0.25RE alloy, which increases the workability at high temperature. Processing map was calculated and an optimum processing was determined with deformation temperature of 440-450 ℃ and strain rate of 0.01 s-1.展开更多
The effect of laser beam welding(LBW) process on the microstructure-mechanical property relationship of a dissimilar weld between the copper(Cu) and stainless steel(SS) was investigated.Backscattered electron(BSE) bas...The effect of laser beam welding(LBW) process on the microstructure-mechanical property relationship of a dissimilar weld between the copper(Cu) and stainless steel(SS) was investigated.Backscattered electron(BSE) based scanning electron microscopy(SEM) imaging was used to characterize the highly heterogeneous microstructural features across the LBW(Cu-SS) weld.The BSE analysis thoroughly evidenced the complex microstructures produced at dissimilar weld interfaces and fusion zone along with the compositional information.Widely different grain growths from coarse columnar grains to equiaxed ultrafine grains were also evident along the Cu-weld interface.A highresolution electron backscattered diffraction(EBSD) analysis confirmed the existence of the grain refinement mechanism at the Cu-weld interface.Both tensile and impact properties of the dissimilar weld were found to be closely aligned with the property of Cu base metal.Microhardness gradients were spatially evident in the non-homogeneous material composition zones such as fusion zone and the Cu-weld interface regions.The heterogeneous nucleation spots across the weld sub-regions were clearly identified and interlinked with their microhardness measurements for a holistic understanding of structure-property relationships of the local weld sub-regions.The findings were effectively correlated to achieve an insight into the local microstructural gradients across the weld.展开更多
In this study, the microstructure and second-phase particles in yttrium （0.05 wt.%and 0.8 wt.%） bearing Fe-10Ni-7Mn steels were characterized. The results of X-ray analysis as well as scanning electron microscopy co...In this study, the microstructure and second-phase particles in yttrium （0.05 wt.%and 0.8 wt.%） bearing Fe-10Ni-7Mn steels were characterized. The results of X-ray analysis as well as scanning electron microscopy coupled with energy dispersive X-ray spectroscopy indicated the formation of （Fe, Ni, Mn）17Y2 precipitates with hexagonal structure in a Fe-10Ni-7Mn-0.8Y （wt.%） alloy. Lattice parameters of these precipitates were calculated as follows：a=0.8485 nm and c=0.8274 nm. Formation of Y2O3 sub-micron particles was also confirmed in both yttrium bearing steels via electrolytic phase extraction method. The effect of these precipitates on the prior austenite grain size was investigated. The results revealed that these precipitates had an effective role in controlling the prior austenite grain size.展开更多
In catalysis processes, activated carbon （AC） and metal oxides （MOs） are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a si...In catalysis processes, activated carbon （AC） and metal oxides （MOs） are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a single hybrid material usually entails both chemical and microstructural changes, which may largely influence the potential catalytic suitability and performance of the resulting product. Here, the prepa- ration of a wide series of AC-MO hybrid catalysts is studied. Three series of such catalysts are prepared by support first of MO （Al2O3, Fe2O3, SnO2, TiO2, WO3, and ZnO） precursors on a granular AC by wet impregnation and oven-drying at 120 ℃, and by subsequent heat treatment at 200 or 850℃ in inert atmosphere. Both the chemical composition and microstructure are mainly investigated by powder X-ray diffraction. Yield and ash content are often strongly dependent on the MO precursor and heat treatment temperature, in particular for the Sn catalysts. With the temperature rise, trends are towards the transformation of metal hydroxides into metal oxides, crystallinity improvement, and occurrence of drastic composition changes, ultimately leading to the formation of metals in elemental state and even metal carbides. Reaction paths during the preparation are explored for various hybrid catalysts and new insights into them are provided.展开更多
The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution tr...The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn.As the Zn content increases,the number density of Zn–Zr particles also increases.Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior.In the peak-aged Zn-free alloy,β′′phases are the key strengthening precipitates.When 0.5 wt%Zn is added,besidesβ′′precipitates,additional fineβ_(1)precipitates form.With the addition of 0.8 wt%Zn,the peak-aged 0.8Zn alloy is characterized by predominantly prismaticβ_(1)and scanty basal precipitate distributions.The enhanced precipitation ofβ_(1)should be primarily attributable to the presence of increased Zn–Zr dispersoids.When Zn content further increases to 1 wt%,the precipitation of basal precipitates is markedly enhanced.Basal precipitates andβ_(1)phases are the key strengthening precipitates in the peak-aged 1Zn alloy.Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt%Zn addition,whose yield strength,ultimate tensile strength and elongation are 179 MPa,301 MPa and 5.3%,respectively.展开更多
Advanced characterization techniques are utilized to investigate the effect of laser surface treatment on microstructural evolution of pure titanium（Ti）.The results show that there are three distinctly different typ...Advanced characterization techniques are utilized to investigate the effect of laser surface treatment on microstructural evolution of pure titanium（Ti）.The results show that there are three distinctly different types of microstructure from surface to substrate in Ti samples,including phase transformation and solidification microstructure in zone I（melting zone）;insufficient recrystallization grains with residual a martensitic plates in zone II（heat-affected zone,HAZ）;fully recrystallization microstructure in zone III（base metal,BM）.The hardness evolution profiles under different laser treatment parameters are similar.The highest hardness in MZ is ascribed to α plate,while the lowest hardness value in HAZ is due to the insufficiently recrystallized grains.The metallurgical process on the laser-modified Ti samples is systematically discussed in this work.展开更多
In this paper,two ways of micro structural characterization,optical microscopy(OM) and polarized light microscopy(PLM),were both employed to describe the micro structure of semisolid slurry prepared by swirling enthal...In this paper,two ways of micro structural characterization,optical microscopy(OM) and polarized light microscopy(PLM),were both employed to describe the micro structure of semisolid slurry prepared by swirling enthalpy equilibration device(SEED).The results show that PLM is more reliable and accurate than OM to describe the special morphology feature of semisolid slurry made by SEED process.Meanwhile,the effects of pouring temperature and mass of molten liquid on the primary α-Al particle size and morphology were also investigated using PLM.The quantitative metallographic results measured from PLM demonstrate that the grain size and morphology and their distribution are significantly affected by both pouring temperature and the mass of molten liquid.The grain size poured with 2.7 kg liquid decreases from 659 to186 μm,and grain morphology transforms from dendrite to globular structure with pouring temperature reducing from690 to 630℃.The decreasing pouring temperature also promotes the distribution of spherical structure on the cross section.Meanwhile,the mass of molten liquid decreasing from 2.7 to 2.3 kg can decrease the grain size by maximum of 44% at high pouring temperature.展开更多
V85Ni15(at%)alloy was proposed as a promising candidate for hydrogen separation membranes.To date,investigations of V85Ni15 alloy have concentrated on hydrogen permeation characteristics,and little work has been done ...V85Ni15(at%)alloy was proposed as a promising candidate for hydrogen separation membranes.To date,investigations of V85Ni15 alloy have concentrated on hydrogen permeation characteristics,and little work has been done on the microstructural development.In the present study,various fabrication and heat-treatment techniques were used to develop different microstructures which would then be tailored to achieve a desired candidate for acceptable mechanical stability while maintaining high hydrogen permeability.The arc-melted(AM)V85Ni15 alloy are supersaturated solid solution with dendritic segregation of Ni-solute atoms.Cold rolling(CR)followed by annealing at 1050℃and 850℃can produce a two-phase(V+σ)microstructure and a three-phase(V+σ+NiV3)microstructure,respectively.Very fine two-phase microstructure obtained at 1050℃involves a simultaneous reaction of second-phase precipitation and V-matrix recrystallization.Sigma phase is formed via primary precipitation,while NiV3 phase is formed by peritectoidal reaction.When AMCR samples were homogenized at1250℃for 2 h and sequential heat-treated at 850℃or900℃for 2 h,precipitation-strengthening microstructure is obtained:large grain structure of V-matrix with uniform distribution of second-phase particles produced by recrystallization and grain growth followed by precipitation process.展开更多
In this work, we make the best use of the vanadium element; a series of A1-V-B alloys and VB2/A390 composite alloys were fabricated. For Ak-10V-6B alloy, the grain size of VB2 can be controlled within about 1 μm and ...In this work, we make the best use of the vanadium element; a series of A1-V-B alloys and VB2/A390 composite alloys were fabricated. For Ak-10V-6B alloy, the grain size of VB2 can be controlled within about 1 μm and is distributed uniformly in the AI matrix. Further, it can be found that VB2 promises to be a useful reinforcement particle for piston alloy. The addition of VB2 can improve the mechanical properties of the A390 composite alloys significantly. The results show that with 1 % VB2 addition, A390 composite alloy exhibits the best performance. Compared with the A390 alloy, the coefficient of thermal expansion is 13.2 × 10^-6 K-1, which decreased by 12.6%; the average Brinell hardness can reach 156.5 HB, wear weight loss decreased by 28.9% and ultimate tensile strength at 25℃ （UTS25 ℃） can reach 355 MPa, which increased by 36.5%.展开更多
Aluminum alloys manufactured using traditional processes are increasingly unable to meet the high flexibility and performance requirements of modern engineering.In this study,Al-Mg-Sc-Zr alloys were manufactured via l...Aluminum alloys manufactured using traditional processes are increasingly unable to meet the high flexibility and performance requirements of modern engineering.In this study,Al-Mg-Sc-Zr alloys were manufactured via laser powder bed fusion(LPBF)to obtain high-performance aluminum alloys.To this end,process parameter optimization and heat treatment were adopted.The optimal process parameters were determined by initially analyzing the relative density and defect distribution under varying energy densities.The sample obtained under the optimal process parameters exhibited a relative density of 99.84%.Subsequently,the corresponding phase compositions,microstructures,and mechanical performance of the as-fabricated specimens were determined using the optimal process parameters before and after heat treatment.The microstructures of the samples showed typical equiaxed columnar bimodal grain structures,with Al_(3)(Sc,Zr)precipitates detected.The samples exhibited no significant anisotropy before and after heat treatment,while the grain orientation differences were dominated by high-angle grain boundaries.The mechanical properties of all the samples were characterized using tensile and hardness tests.The yield strength,ultimate tensile strength,and elongation of the sample were 475.0 MPa,508.2 MPa,and 8.3%,respectively.Overall,samples with high density,low porosity,high strength,and high plasticity were obtained by process parameter optimization and appropriate heat treatment.展开更多
Grain size and formation of the Peripheral Coarse Grain(PCG)defect influence the mechanical and crash properties of extruded profiles.Controlling microstructural evolution during the extrusion of 6XXX series aluminum ...Grain size and formation of the Peripheral Coarse Grain(PCG)defect influence the mechanical and crash properties of extruded profiles.Controlling microstructural evolution during the extrusion of 6XXX series aluminum alloys is therefore essential to ensure the performance of structural components.In this work,three profiles with the same nominal geometry were extruded with a die comprising three different bearing geometries to create different extrusion conditions.Each profile was analyzed experimentally to gather data on the microstructure and mechanical properties.Bulge testing revealed that Profile 2,with the thickest PCG layer(490-1150µm),exhibited worse mechanical performance,with a hoop strain at fracture of 0.08 and a peak load of 51.5 kN,compared to Profiles 1 and 3,which had higher hoop strains(0.13 and 0.14)and peak loads(56.1 and 57.6 kN,respectively).Finite Element Method(FEM)simulations of the extrusion process were carried out using Qform Extrusion UK with a post-processing subroutine developed and implemented to calculate additional parameters such as the stored energy,percentage dynamic recrystallization,grain size,and PCG formation based on standard output parameters from the simulation including strain,temperature and strain rate.The simulation demonstrated that the highest strain rate(40-220 s^(-1))and stored energy(150,000-440,000 J m^(-3))in Profile 2 led to the thickest PCG layer.Based on these results,the proposed predictive model was validated against experimental data,demonstrating high accuracy in predicting PCG thickness and grain size while effectively capturing the influence of process parameters on microstructural evolution.展开更多
Refractory high-entropy alloys demonstrate exceptional potential for primary loop pipe,which is mainly attributed to their excellent oxidation resistance and thermal stability under high-temperature conditions.However...Refractory high-entropy alloys demonstrate exceptional potential for primary loop pipe,which is mainly attributed to their excellent oxidation resistance and thermal stability under high-temperature conditions.However,there are limited studies on their corrosion behavior in reactor environments,and the underlying corrosion resistance mechanisms remain unclear.In this study,the corrosion behavior of equimolar ZrNbTiVHf refractory high-entropy alloy in a pressurized water reactor primary loop water was investigated.After 1500-h corrosion testing,it was found that three distinct oxide layers formed on the surface of the alloy:a corrosion particle layer,a porous deposit layer,and an internal oxidation layer.A growth model for the corrosion particles was developed.The interface effect between oxide layers was revealed by characterization and analysis.The competitive growth between the corrosion particle layer and the porous deposit layer inhibited the inward growth of the corrosion particles.The innermost amorphous oxide layer hinders the propagation of corrosion medium along grain boundaries and other defects by virtue of its disordered structure,which effectively prevents the penetration of corrosion elements.This work elucidates the corrosion resistance mechanism of refractory high-entropy alloys in reactor environments,enhances the understanding of their corrosion behavior,and contributes to the design of new primary loop pipe materials.展开更多
A martensitic initial microstructure before hot forming was prepared by direct quenching after hot rolling of the hot formed steel and the effect of such initial microstructure on mechanical properties of steel was an...A martensitic initial microstructure before hot forming was prepared by direct quenching after hot rolling of the hot formed steel and the effect of such initial microstructure on mechanical properties of steel was analyzed. The process of direct quenching after hot rolling which replaced the steps of coiling and cold rolling was termed as compact process. As the temperature before direct quenching falls within the non-recrystallization range, the deformed austenite grains exhibit flattened morphology along the hot rolling direction, and the high-density dislocations and significant strain energy in deformed austenite are inherited by directly quenched martensite. Moreover, due to promotion of austenite nucleation and subsequent recrystallization during the reverse transformation process in hot forming, both reversed austenite grains and martensite laths are significantly refined. Compared to the conventional process with an initial microstructure consisting of fully recrystallized ferrite and cementite, the compact process reduces average prior austenite grain sizes from 12.5 to 5.5 μm and martensite lath widths from 202 to 123 nm. Additionally, the compact process results in a higher density of dislocations in test steel, leading to maximum yield strength (1294 MPa) and ultimate tensile strength (2266 MPa). Compared to conventional process, this compact process significantly improves the mechanical properties of the hot formed steels while simplifying the production.展开更多
Four CrAlN coatings with various Al content were prepared by arc ion plating technology under different target currents. The effect of the Al content on the microstructure, chemical compositions, element chemical bond...Four CrAlN coatings with various Al content were prepared by arc ion plating technology under different target currents. The effect of the Al content on the microstructure, chemical compositions, element chemical bonding states and mechanical properties of the CrAlN coatings was analyzed. X-ray diffraction results show that the primary phase of the CrAlN coating is fcc-（Al, Cr）N when the Al content is about 44.02 at.%. However, when the Al content increases to about 53.34 at.%, hcp-AlN phase emerges in the coating. And the hcp-AlN phase becomes the main phase in the CrAlN coating with Al content of about 69.55 at.%. Cross-sectional images show that all the four coatings possess dense structures and the deposition rate of Al atom is higher than that of Cr atom. The hardness of the CrAlN coating with Al content about 44.02 at.% is the largest （3149.72 HV） due to the solid solution hardening effect of the Al element. When the hcp-AlN phase is generated in the CrAlN coating, the hardness declines. The tribological experiment shows that the wear resistance of the CrAlN coating decreases gradually with increasing Al content when sliding against 100Cr6 steel ball.展开更多
The hot ductility of a Fe-0.3C-9Mn-2Al medium Mn steel was investigated using a Gleeble3800 thermo-mechanical simulator.Hot tensile tests were conducted at different temperatures(600-1300℃)under a constant strain rat...The hot ductility of a Fe-0.3C-9Mn-2Al medium Mn steel was investigated using a Gleeble3800 thermo-mechanical simulator.Hot tensile tests were conducted at different temperatures(600-1300℃)under a constant strain rate of 4×10^(−3)s^(−1).The fracture behavior and mechanism of hot ductility evolution were discussed.Results showed that the hot ductility decreased as the temperature was decreased from 1000℃.The reduction of area(RA)decreased rapidly in the specimens tested below 700℃,whereas that in the specimen tested at 650℃was lower than 65%.Mixed brittle-ductile fracture feature is reflected by the coexistence of cleavage step,intergranular facet,and dimple at the surface.The fracture belonged to ductile failure in the specimens tested between 720-1000℃.Large and deep dimples could delay crack propagation.The change in average width of the dimples was in positive proportion with the change in RA.The wide austenite-ferrite intercritical temperature range was crucial for the hot ductility of medium Mn steel.The formation of ferrite film on austenite grain boundaries led to strain concentration.Yield point elongation occurred at the austenite-ferrite intercritical temperature range during the hot tensile test.展开更多
Bi has a good modification effect on the hypoeutectic Al-Si alloy, and the morphology of eutectic Si changes from coarse acicular to fine fibrous. Based on the similarity between Mg2Si and Si phases in crystalline str...Bi has a good modification effect on the hypoeutectic Al-Si alloy, and the morphology of eutectic Si changes from coarse acicular to fine fibrous. Based on the similarity between Mg2Si and Si phases in crystalline structure and crystallization process, the present study investigated the effects of different concentrations of Bi on the microstructure, tensile properties, and fracture behavior of cast Al-15wt.%Mg2Si in-situ metal matrix composite. The results show that the addition of the proper amount of Bi has a significant modification effect on both primary and eutectic Mg2Si in the Al-15wt.%Mg2Si composite. With an increase in Bi content from 0 to lwt.%, the morphology of the primary Mg2Si is changed from irregular or dendritic to polyhedral shape; and its average particle size is significantly decreased from 70 to 6 μm. Moreover, the morphology of the eutectic Mg2Si phase is altered from flake-like to very short fibrous or dot-like. When the Bi addition exceeds 4.0wt.%, the primary Mg2Si becomes coarse again. However, the eutectic Mg2Si still exhibits the modified morphology. Tensile tests reveal that the Bi addition can improve the tensile strength and ductility of the material. Compared with those of the unmodified composite, the ultimate tensile strength and percentage elongation after fracture with 1.0wt.% Bi increase 51.2% and 100%, respectively. At the same time, the Bi addition changes the fracture behavior from brittle to ductile.展开更多
As-cast Mg-6Zn-xCu-0.6Zr(x=0,0.5,1.0,wt.%)alloys were fabricated by permanent mold casting;then,the alloys were subjected to homogenization heat treatment and extrusion-shearing(ES)process.The microstructure and mecha...As-cast Mg-6Zn-xCu-0.6Zr(x=0,0.5,1.0,wt.%)alloys were fabricated by permanent mold casting;then,the alloys were subjected to homogenization heat treatment and extrusion-shearing(ES)process.The microstructure and mechanical properties of the alloys were evaluated by OM,SEM/EDS,XRD,TEM,EBSD and tensile tests.The results show that the hard MgZnCu phase in Cu-added alloy can strengthen particle-stimulated nucleation(PSN)effect and hinder the migration of dynamic recrystallization(DRX)grain boundary at an elevated temperature during ES.The ZK60+0.5Cu alloy shows an optimal tensile strength–ductility combination(UTS of 396 MPa,YS of 313 MPa,andδ=20.3%)owing to strong grain boundary strengthening and improvement of Schmid factor for{0001}■basal slip.The aggregation of microvoids around the MgZnCu phase mainly accounts for the lower tensile elongation of ZK60+1.0Cu alloy compared with ZK60 alloy.展开更多
基金funding recei-ved from the National Key R&D Program of China(No.2022YFB3705602)the Scientific Research Plan Project of Shanghai,P.R.China(No.22SQBS 00600).
文摘TC4 titanium alloy(Ti-6Al-4V),known for its excellent specific strength,corrosion resistance,and weldability,is extensively applied in aerospace,marine engineering,and advanced manufacturing.This study focuses on the microstructural uniformity and mechanical properties of TC4 ingots fabricated via the electron-beam cold hearth melting(EBCHM)process.A comprehensive analysis was performed using optical microscopy,scanning electron microscopy,electron backscatter diffraction,and energy-dispersive spectroscopy to investigate the ingot’s morphology,α-phase lamellar structure,and elemental distribution.Mechanical characterization included tensile testing,and microhardness and impact toughness assessments.Results reveal that EBCHM produces a well-defined and homogeneous microstructure,with the averageαlamellae thickness varying between 1.53 and 1.71μm and minimal fluctuations across the ingot regions,indicating high process consistency.Major alloying elements(Al and V)and impurity elements(O,N,H,C,and Fe)are evenly distributed,with no observable macrosegregation.The mechanical properties are stable and reliable,with a yield strength of 694.6-701.2 MPa,a tensile strength of 711.1-716.6 MPa,an elongation of 3.35%-3.84%,and an average impact toughness of 94.7 J/cm^(2).These results provide valuable data and technical references for the application of EBCHM in manufacturing premium-quality Ti-6Al-4V ingots.
基金financial support from the National Key Research and Development Program(Grant No.2024YFA1209801)the National Natural Science Foundation of China(Grant Nos.12302140,12325204)+4 种基金the China Postdoctoral Science Foundation(Grant No.2023M732794)the Fundamental Research Funds for the Central Universities of China(Grant No.sxzy012023213)the Scientific Research Program of Shaanxi Province(Grant No.2023JC-XJ-02)the Young Talent Support Program of Xi'an Science and Technology Association(Grant No.959202413069)Postdoctoral Fellowship Program(Grade B)of China Postdoctoral Science Foundation(Grant No.GZB20230575)。
文摘Hypervelocity rocket sled systems are critical for testing advanced military technologies,yet track damage at speeds exceeding Mach 5 remains a significant challenge for system reliability and performance.In this study,we investigated the hypervelocity impact response and protection for highstrength U71 Mn or bainitic steel used in rocket sled tracks.Flyer plate impact experiments using a two-stage light-gas gun were conducted to study the hypervelocity collision response,followed by the microstructural characterization via optical microscope,scanning electron microscopy equipped with electron backscatter diffraction to reveal underlying damage mechanisms.Then,the calibrated thermalmechanical coupled finite element simulations using the Johnson-Cook constitutive model and MieGrüneisen equation of state were carried out.Results indicated that bainitic steel exhibits superior impact resistance with predominantly smooth scratch-dominated damage due to its higher ductility.In contrast,U71 Mn suffered significant material spallation and crack propagation arising from brittle fracture mechanisms.Zinc-rich epoxy primer coatings effectively mitigated stress concentration and temperature rise in the substrate at impacting velocities below 2.4 km/s,so as to suppress the microstructural damage such as adiabatic shear bands and dynamic recrystallization.However,coating protection diminished at ultra-high-speed impacts due to the coating failure.Dimensional analysis established quantitative relationships of the gouge damage size to projectile mass,impact velocity,and material yield strength.This study provides in-depth insights into damage mechanisms in hypervelocity rail systems,demonstrating that bainitic steel combined with protective coatings can significantly enhance impact resistance and system reliability,offering valuable guidance for the design and optimization of hypervelocity testing platforms.
基金supported by the Research Project on Strengthening the Construction of an Important Ecological Security Barrier in Northern China by Higher Education Institutions in the Inner Mongolia Autonomous Region(STAQZX202313)the Inner Mongolia Autonomous Region Education Science‘14th Five-Year Plan’2024 Annual Research Project(NGJGH2024635).
文摘Vacancy defects,as fundamental disruptions in metallic lattices,play an important role in shaping the mechanical and electronic properties of aluminum crystals.However,the influence of vacancy position under coupled thermomechanical fields remains insufficiently understood.In this study,transmission and scanning electron microscopy were employed to observe dislocation structures and grain boundary heterogeneities in processed aluminum alloys,suggesting stress concentrations and microstructural inhomogeneities associated with vacancy accumulation.To complement these observations,first-principles calculations and molecular dynamics simulations were conducted for seven single-vacancy configurations in face-centered cubic aluminum.The stress response,total energy,density of states(DOS),and differential charge density were examined under varying compressive strain(ε=0–0.1)and temperature(0–600 K).The results indicate that face-centered vacancies tend to reduce mechanical strength and perturb electronic states near the Fermi level,whereas corner and edge vacancies appear to have weaker effects.Elevated temperatures may partially restore electronic uniformity through thermal excitation.Overall,these findings suggest that vacancy position exerts a critical but position-dependent influence on coupled structure-property relationships,offering theoretical insights and preliminary experimental support for defect-engineered aluminum alloy design.
基金Project(31115014)supported by the of Open Research Fund Program of State Key Laboratory of Advanced Design and Manufacture forVehicle Body(Hunan University)Project(12JJ9017)supported by the Natural Science Foundation of Hunan Province,China
文摘Hot compression tests of an extruded Al-1.1Mn-0.3Mg-0.25RE alloy were performed on Gleeble-1500 system in the temperature range of 300-500 ℃ and strain rate range of 0.01-10 s-l. The associated microstructural evolutions were studied by observation of optical and transmission electron microscopes. The results show that the peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in the hyperbolic-sine equation with the hot deformation activation energy of 186.48 kJ/mol. The steady flow behavior results from dynamic recovery whereas flow softening is associated with dynamic recrystallization and dynamic transformation of constituent particles. The main constituent particles are enriched rare earth phases. Positive purifying effects on impurity elements of Fe and Si are shown in the Al-l.lMn-0.3Mg-0.25RE alloy, which increases the workability at high temperature. Processing map was calculated and an optimum processing was determined with deformation temperature of 440-450 ℃ and strain rate of 0.01 s-1.
文摘The effect of laser beam welding(LBW) process on the microstructure-mechanical property relationship of a dissimilar weld between the copper(Cu) and stainless steel(SS) was investigated.Backscattered electron(BSE) based scanning electron microscopy(SEM) imaging was used to characterize the highly heterogeneous microstructural features across the LBW(Cu-SS) weld.The BSE analysis thoroughly evidenced the complex microstructures produced at dissimilar weld interfaces and fusion zone along with the compositional information.Widely different grain growths from coarse columnar grains to equiaxed ultrafine grains were also evident along the Cu-weld interface.A highresolution electron backscattered diffraction(EBSD) analysis confirmed the existence of the grain refinement mechanism at the Cu-weld interface.Both tensile and impact properties of the dissimilar weld were found to be closely aligned with the property of Cu base metal.Microhardness gradients were spatially evident in the non-homogeneous material composition zones such as fusion zone and the Cu-weld interface regions.The heterogeneous nucleation spots across the weld sub-regions were clearly identified and interlinked with their microhardness measurements for a holistic understanding of structure-property relationships of the local weld sub-regions.The findings were effectively correlated to achieve an insight into the local microstructural gradients across the weld.
文摘In this study, the microstructure and second-phase particles in yttrium （0.05 wt.%and 0.8 wt.%） bearing Fe-10Ni-7Mn steels were characterized. The results of X-ray analysis as well as scanning electron microscopy coupled with energy dispersive X-ray spectroscopy indicated the formation of （Fe, Ni, Mn）17Y2 precipitates with hexagonal structure in a Fe-10Ni-7Mn-0.8Y （wt.%） alloy. Lattice parameters of these precipitates were calculated as follows：a=0.8485 nm and c=0.8274 nm. Formation of Y2O3 sub-micron particles was also confirmed in both yttrium bearing steels via electrolytic phase extraction method. The effect of these precipitates on the prior austenite grain size was investigated. The results revealed that these precipitates had an effective role in controlling the prior austenite grain size.
基金Financial support by Gobierno de Extremadura and European FEDER FundsSpanish Ministerio de Educacion,Cultura y Deporte for the concession of a FPU grant(AP2010-2574)
文摘In catalysis processes, activated carbon （AC） and metal oxides （MOs） are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a single hybrid material usually entails both chemical and microstructural changes, which may largely influence the potential catalytic suitability and performance of the resulting product. Here, the prepa- ration of a wide series of AC-MO hybrid catalysts is studied. Three series of such catalysts are prepared by support first of MO （Al2O3, Fe2O3, SnO2, TiO2, WO3, and ZnO） precursors on a granular AC by wet impregnation and oven-drying at 120 ℃, and by subsequent heat treatment at 200 or 850℃ in inert atmosphere. Both the chemical composition and microstructure are mainly investigated by powder X-ray diffraction. Yield and ash content are often strongly dependent on the MO precursor and heat treatment temperature, in particular for the Sn catalysts. With the temperature rise, trends are towards the transformation of metal hydroxides into metal oxides, crystallinity improvement, and occurrence of drastic composition changes, ultimately leading to the formation of metals in elemental state and even metal carbides. Reaction paths during the preparation are explored for various hybrid catalysts and new insights into them are provided.
基金financially supported by the National Natural Science Foundation of China(Nos.U2037601,51775334 and 51821001)the National Key Research&Development Program of China(No.2016YFB0701205)+3 种基金the Joint Innovation Fund of CALT and College(No.CALT2020-TS07)the Open Fund of State Key Laboratory of Advanced Forming Technology and Equipment(No.SKL2020005)the Research Program of Joint Research Center of Advanced Spaceflight Technologies(No.USCAST2020-14)。
文摘The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn.As the Zn content increases,the number density of Zn–Zr particles also increases.Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior.In the peak-aged Zn-free alloy,β′′phases are the key strengthening precipitates.When 0.5 wt%Zn is added,besidesβ′′precipitates,additional fineβ_(1)precipitates form.With the addition of 0.8 wt%Zn,the peak-aged 0.8Zn alloy is characterized by predominantly prismaticβ_(1)and scanty basal precipitate distributions.The enhanced precipitation ofβ_(1)should be primarily attributable to the presence of increased Zn–Zr dispersoids.When Zn content further increases to 1 wt%,the precipitation of basal precipitates is markedly enhanced.Basal precipitates andβ_(1)phases are the key strengthening precipitates in the peak-aged 1Zn alloy.Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt%Zn addition,whose yield strength,ultimate tensile strength and elongation are 179 MPa,301 MPa and 5.3%,respectively.
基金supported by the National Natural Science Foundation of China (Nos. 51401039 and 51501026)the Natural Science Foundation of Chongqing (No. CSTC2014jcyj A50017)the Scientific and Technological Research Program of Chongqing Municipal Education Commission (Nos. KJ1500923 and KJ1709204)
文摘Advanced characterization techniques are utilized to investigate the effect of laser surface treatment on microstructural evolution of pure titanium（Ti）.The results show that there are three distinctly different types of microstructure from surface to substrate in Ti samples,including phase transformation and solidification microstructure in zone I（melting zone）;insufficient recrystallization grains with residual a martensitic plates in zone II（heat-affected zone,HAZ）;fully recrystallization microstructure in zone III（base metal,BM）.The hardness evolution profiles under different laser treatment parameters are similar.The highest hardness in MZ is ascribed to α plate,while the lowest hardness value in HAZ is due to the insufficiently recrystallized grains.The metallurgical process on the laser-modified Ti samples is systematically discussed in this work.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFB0301003)the Shenzhen Free Exploring Basic Research Project (No. JCYJ20170307110223452)。
文摘In this paper,two ways of micro structural characterization,optical microscopy(OM) and polarized light microscopy(PLM),were both employed to describe the micro structure of semisolid slurry prepared by swirling enthalpy equilibration device(SEED).The results show that PLM is more reliable and accurate than OM to describe the special morphology feature of semisolid slurry made by SEED process.Meanwhile,the effects of pouring temperature and mass of molten liquid on the primary α-Al particle size and morphology were also investigated using PLM.The quantitative metallographic results measured from PLM demonstrate that the grain size and morphology and their distribution are significantly affected by both pouring temperature and the mass of molten liquid.The grain size poured with 2.7 kg liquid decreases from 659 to186 μm,and grain morphology transforms from dendrite to globular structure with pouring temperature reducing from690 to 630℃.The decreasing pouring temperature also promotes the distribution of spherical structure on the cross section.Meanwhile,the mass of molten liquid decreasing from 2.7 to 2.3 kg can decrease the grain size by maximum of 44% at high pouring temperature.
基金the National Natural Science Foundation of China(Nos.51875002 and 51705038)China Postdoctoral Science Foundation(No.2019M652158)the Natural Science Foundation of Jiangsu Province of China(No.BK20150268)。
文摘V85Ni15(at%)alloy was proposed as a promising candidate for hydrogen separation membranes.To date,investigations of V85Ni15 alloy have concentrated on hydrogen permeation characteristics,and little work has been done on the microstructural development.In the present study,various fabrication and heat-treatment techniques were used to develop different microstructures which would then be tailored to achieve a desired candidate for acceptable mechanical stability while maintaining high hydrogen permeability.The arc-melted(AM)V85Ni15 alloy are supersaturated solid solution with dendritic segregation of Ni-solute atoms.Cold rolling(CR)followed by annealing at 1050℃and 850℃can produce a two-phase(V+σ)microstructure and a three-phase(V+σ+NiV3)microstructure,respectively.Very fine two-phase microstructure obtained at 1050℃involves a simultaneous reaction of second-phase precipitation and V-matrix recrystallization.Sigma phase is formed via primary precipitation,while NiV3 phase is formed by peritectoidal reaction.When AMCR samples were homogenized at1250℃for 2 h and sequential heat-treated at 850℃or900℃for 2 h,precipitation-strengthening microstructure is obtained:large grain structure of V-matrix with uniform distribution of second-phase particles produced by recrystallization and grain growth followed by precipitation process.
基金supported by the National Basic Research Program of China ("973 Program", No. 2012CB825702)the National Natural Science Foundation of China (Nos. 51001065 and 51071097)+1 种基金the Taishan Scholar Blue Industry Talents Support Program of Shandong Province (2013)Young Scholars Program of Shandong University
文摘In this work, we make the best use of the vanadium element; a series of A1-V-B alloys and VB2/A390 composite alloys were fabricated. For Ak-10V-6B alloy, the grain size of VB2 can be controlled within about 1 μm and is distributed uniformly in the AI matrix. Further, it can be found that VB2 promises to be a useful reinforcement particle for piston alloy. The addition of VB2 can improve the mechanical properties of the A390 composite alloys significantly. The results show that with 1 % VB2 addition, A390 composite alloy exhibits the best performance. Compared with the A390 alloy, the coefficient of thermal expansion is 13.2 × 10^-6 K-1, which decreased by 12.6%; the average Brinell hardness can reach 156.5 HB, wear weight loss decreased by 28.9% and ultimate tensile strength at 25℃ （UTS25 ℃） can reach 355 MPa, which increased by 36.5%.
基金supported by National Natural Science Foundation of China(Grant Nos.5233500651975073)State Key Laboratory of Mechanical Transmission for Advanced Equipment(Grant No.SKLMT-MSKFKT-202104).
文摘Aluminum alloys manufactured using traditional processes are increasingly unable to meet the high flexibility and performance requirements of modern engineering.In this study,Al-Mg-Sc-Zr alloys were manufactured via laser powder bed fusion(LPBF)to obtain high-performance aluminum alloys.To this end,process parameter optimization and heat treatment were adopted.The optimal process parameters were determined by initially analyzing the relative density and defect distribution under varying energy densities.The sample obtained under the optimal process parameters exhibited a relative density of 99.84%.Subsequently,the corresponding phase compositions,microstructures,and mechanical performance of the as-fabricated specimens were determined using the optimal process parameters before and after heat treatment.The microstructures of the samples showed typical equiaxed columnar bimodal grain structures,with Al_(3)(Sc,Zr)precipitates detected.The samples exhibited no significant anisotropy before and after heat treatment,while the grain orientation differences were dominated by high-angle grain boundaries.The mechanical properties of all the samples were characterized using tensile and hardness tests.The yield strength,ultimate tensile strength,and elongation of the sample were 475.0 MPa,508.2 MPa,and 8.3%,respectively.Overall,samples with high density,low porosity,high strength,and high plasticity were obtained by process parameter optimization and appropriate heat treatment.
基金supported by the European Union’s Horizon Europe research and innovation programme,Zero Emission electric Vehicles enabled by haRmonised circularity,under No.101138034.
文摘Grain size and formation of the Peripheral Coarse Grain(PCG)defect influence the mechanical and crash properties of extruded profiles.Controlling microstructural evolution during the extrusion of 6XXX series aluminum alloys is therefore essential to ensure the performance of structural components.In this work,three profiles with the same nominal geometry were extruded with a die comprising three different bearing geometries to create different extrusion conditions.Each profile was analyzed experimentally to gather data on the microstructure and mechanical properties.Bulge testing revealed that Profile 2,with the thickest PCG layer(490-1150µm),exhibited worse mechanical performance,with a hoop strain at fracture of 0.08 and a peak load of 51.5 kN,compared to Profiles 1 and 3,which had higher hoop strains(0.13 and 0.14)and peak loads(56.1 and 57.6 kN,respectively).Finite Element Method(FEM)simulations of the extrusion process were carried out using Qform Extrusion UK with a post-processing subroutine developed and implemented to calculate additional parameters such as the stored energy,percentage dynamic recrystallization,grain size,and PCG formation based on standard output parameters from the simulation including strain,temperature and strain rate.The simulation demonstrated that the highest strain rate(40-220 s^(-1))and stored energy(150,000-440,000 J m^(-3))in Profile 2 led to the thickest PCG layer.Based on these results,the proposed predictive model was validated against experimental data,demonstrating high accuracy in predicting PCG thickness and grain size while effectively capturing the influence of process parameters on microstructural evolution.
基金financially supported by the National Natural Science Foundation of China(Nos.12302179 and 22108316)Natural Science Foundation of Zhejiang Province(No.LY24E010001)+2 种基金Major Science and Technology Projects in Ningbo(Nos.2024Z070,2024Z158)2025 Ningbo Yongjiang Talent Programme(No.2024A-120-G)Mechanics Interdisciplinary Fund for Outstanding Young Scholars of Ningbo University(No.ZX2025000397)
文摘Refractory high-entropy alloys demonstrate exceptional potential for primary loop pipe,which is mainly attributed to their excellent oxidation resistance and thermal stability under high-temperature conditions.However,there are limited studies on their corrosion behavior in reactor environments,and the underlying corrosion resistance mechanisms remain unclear.In this study,the corrosion behavior of equimolar ZrNbTiVHf refractory high-entropy alloy in a pressurized water reactor primary loop water was investigated.After 1500-h corrosion testing,it was found that three distinct oxide layers formed on the surface of the alloy:a corrosion particle layer,a porous deposit layer,and an internal oxidation layer.A growth model for the corrosion particles was developed.The interface effect between oxide layers was revealed by characterization and analysis.The competitive growth between the corrosion particle layer and the porous deposit layer inhibited the inward growth of the corrosion particles.The innermost amorphous oxide layer hinders the propagation of corrosion medium along grain boundaries and other defects by virtue of its disordered structure,which effectively prevents the penetration of corrosion elements.This work elucidates the corrosion resistance mechanism of refractory high-entropy alloys in reactor environments,enhances the understanding of their corrosion behavior,and contributes to the design of new primary loop pipe materials.
基金financial support from the National Natural Science Foundation of China(No.52274372)the National Key Research and Development Program of China(No.2021YFB3702404).
文摘A martensitic initial microstructure before hot forming was prepared by direct quenching after hot rolling of the hot formed steel and the effect of such initial microstructure on mechanical properties of steel was analyzed. The process of direct quenching after hot rolling which replaced the steps of coiling and cold rolling was termed as compact process. As the temperature before direct quenching falls within the non-recrystallization range, the deformed austenite grains exhibit flattened morphology along the hot rolling direction, and the high-density dislocations and significant strain energy in deformed austenite are inherited by directly quenched martensite. Moreover, due to promotion of austenite nucleation and subsequent recrystallization during the reverse transformation process in hot forming, both reversed austenite grains and martensite laths are significantly refined. Compared to the conventional process with an initial microstructure consisting of fully recrystallized ferrite and cementite, the compact process reduces average prior austenite grain sizes from 12.5 to 5.5 μm and martensite lath widths from 202 to 123 nm. Additionally, the compact process results in a higher density of dislocations in test steel, leading to maximum yield strength (1294 MPa) and ultimate tensile strength (2266 MPa). Compared to conventional process, this compact process significantly improves the mechanical properties of the hot formed steels while simplifying the production.
基金supported by the National Natural Science Foundation of China (Grant Nos.51501130 and 51301181)the Tianjin Key Research Program of Application Foundation and Advanced Technology (Grant No.15JCZDJC39700)+2 种基金the Innovation Team Training Plan of Tianjin Universities and colleges (Grant No.TD12-5043)the Tianjin Science and Technology Correspondent Project (16JCTPJC49500)the Research Development Foundation of Tianjin University of Technology and Education (Grant No.KYQD14046)
文摘Four CrAlN coatings with various Al content were prepared by arc ion plating technology under different target currents. The effect of the Al content on the microstructure, chemical compositions, element chemical bonding states and mechanical properties of the CrAlN coatings was analyzed. X-ray diffraction results show that the primary phase of the CrAlN coating is fcc-（Al, Cr）N when the Al content is about 44.02 at.%. However, when the Al content increases to about 53.34 at.%, hcp-AlN phase emerges in the coating. And the hcp-AlN phase becomes the main phase in the CrAlN coating with Al content of about 69.55 at.%. Cross-sectional images show that all the four coatings possess dense structures and the deposition rate of Al atom is higher than that of Cr atom. The hardness of the CrAlN coating with Al content about 44.02 at.% is the largest （3149.72 HV） due to the solid solution hardening effect of the Al element. When the hcp-AlN phase is generated in the CrAlN coating, the hardness declines. The tribological experiment shows that the wear resistance of the CrAlN coating decreases gradually with increasing Al content when sliding against 100Cr6 steel ball.
基金the Fundamental Research Funds for the Central Universities,China(Nos.FRF-TP-18-039A1,FRF-IDRY-19-013)the China Postdoctoral Science Foundation(No.2019M650482).
文摘The hot ductility of a Fe-0.3C-9Mn-2Al medium Mn steel was investigated using a Gleeble3800 thermo-mechanical simulator.Hot tensile tests were conducted at different temperatures(600-1300℃)under a constant strain rate of 4×10^(−3)s^(−1).The fracture behavior and mechanism of hot ductility evolution were discussed.Results showed that the hot ductility decreased as the temperature was decreased from 1000℃.The reduction of area(RA)decreased rapidly in the specimens tested below 700℃,whereas that in the specimen tested at 650℃was lower than 65%.Mixed brittle-ductile fracture feature is reflected by the coexistence of cleavage step,intergranular facet,and dimple at the surface.The fracture belonged to ductile failure in the specimens tested between 720-1000℃.Large and deep dimples could delay crack propagation.The change in average width of the dimples was in positive proportion with the change in RA.The wide austenite-ferrite intercritical temperature range was crucial for the hot ductility of medium Mn steel.The formation of ferrite film on austenite grain boundaries led to strain concentration.Yield point elongation occurred at the austenite-ferrite intercritical temperature range during the hot tensile test.
基金supported by the Key Laboratory Foundation of Liaoning Provincial Committee of Education under grant Nos.20060394 and 2009S053
文摘Bi has a good modification effect on the hypoeutectic Al-Si alloy, and the morphology of eutectic Si changes from coarse acicular to fine fibrous. Based on the similarity between Mg2Si and Si phases in crystalline structure and crystallization process, the present study investigated the effects of different concentrations of Bi on the microstructure, tensile properties, and fracture behavior of cast Al-15wt.%Mg2Si in-situ metal matrix composite. The results show that the addition of the proper amount of Bi has a significant modification effect on both primary and eutectic Mg2Si in the Al-15wt.%Mg2Si composite. With an increase in Bi content from 0 to lwt.%, the morphology of the primary Mg2Si is changed from irregular or dendritic to polyhedral shape; and its average particle size is significantly decreased from 70 to 6 μm. Moreover, the morphology of the eutectic Mg2Si phase is altered from flake-like to very short fibrous or dot-like. When the Bi addition exceeds 4.0wt.%, the primary Mg2Si becomes coarse again. However, the eutectic Mg2Si still exhibits the modified morphology. Tensile tests reveal that the Bi addition can improve the tensile strength and ductility of the material. Compared with those of the unmodified composite, the ultimate tensile strength and percentage elongation after fracture with 1.0wt.% Bi increase 51.2% and 100%, respectively. At the same time, the Bi addition changes the fracture behavior from brittle to ductile.
基金Project(XLYC1807021)supported by Liaoning Revitalization Talents Program,ChinaProject(2019JH3/30100014)supported by Joint Research Fund of Lianning-Shenyang National Laboratory for Materials Science,China+2 种基金Project supported by Liaoning Bai Qian Wan Talents Program,ChinaProject(RC200414)supported by Innovation Talent Program in Sciences and Technologies for Young and Middle-aged Scientists of Shenyang City,ChinaProject(XLYC1908006)supported by High Level Innovation Team of Liaoning Province,China。
文摘As-cast Mg-6Zn-xCu-0.6Zr(x=0,0.5,1.0,wt.%)alloys were fabricated by permanent mold casting;then,the alloys were subjected to homogenization heat treatment and extrusion-shearing(ES)process.The microstructure and mechanical properties of the alloys were evaluated by OM,SEM/EDS,XRD,TEM,EBSD and tensile tests.The results show that the hard MgZnCu phase in Cu-added alloy can strengthen particle-stimulated nucleation(PSN)effect and hinder the migration of dynamic recrystallization(DRX)grain boundary at an elevated temperature during ES.The ZK60+0.5Cu alloy shows an optimal tensile strength–ductility combination(UTS of 396 MPa,YS of 313 MPa,andδ=20.3%)owing to strong grain boundary strengthening and improvement of Schmid factor for{0001}■basal slip.The aggregation of microvoids around the MgZnCu phase mainly accounts for the lower tensile elongation of ZK60+1.0Cu alloy compared with ZK60 alloy.
