The functionally graded materials(FGMs)are obtained by various processes.Although a few FGMs are obtained naturally,such as oyster,pearl,and bamboo,additive manufacturing(AM),known as 3D printing,is a net-shaped manuf...The functionally graded materials(FGMs)are obtained by various processes.Although a few FGMs are obtained naturally,such as oyster,pearl,and bamboo,additive manufacturing(AM),known as 3D printing,is a net-shaped manufacturing process employed to manufacture complex 3D objects without tools,molds,assembly,and joining.Currently,commercial AM techniques mostly use homogeneous composition with simplified geometric descriptions,employing a single material across the entire component to achieve functional graded additive manufacturing(FGAM),in contrast to multi-material FGAM with heterogeneous structures.FGMs are widely used in various fields due to their mechanical property advantages.Because FGM plays a significant role in the industrial production,the characteristics and mechanical behaviour of FGMs prepared by AM were reviewed.In this review,the research on FGMs and AM over the past 30 years was reviewed,suggesting that future researchers should focus on the application of artificial intelligence and machine learning technologies in industry to optimize the process parameters of different gradient systems.展开更多
Fatigue failure continues to be a significant challenge in designing structural and mechanical components subjected to repeated and complex loading.While earlier studies mainly examined material properties and how str...Fatigue failure continues to be a significant challenge in designing structural and mechanical components subjected to repeated and complex loading.While earlier studies mainly examined material properties and how stress affects lifespan,this review offers the first comprehensive,multiscale comparison of strategies that optimize geometry to improve fatigue performance.This includes everything from microscopic features like the shape of graphite nodules to large-scale design elements such as fillets,notches,and overall structural layouts.We analyze and combine various methods,including topology and shape optimization,the ability of additive manufacturing to finetune internal geometries,and reliability-based design approaches.A key new contribution is our proposal of a standard way to evaluate geometry-focused fatigue design,allowing for consistent comparison and encouraging validation across different fields.Furthermore,we highlight important areas for future research,such as incorporating manufacturing flaws,using multiscale models,and integrating machine learning techniques.This work is the first to provide a broad geometric viewpoint in fatigue engineering,laying the groundwork for future design methods that are driven by data and centered on reliability.展开更多
Different proportions of commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy （HEA） powder were ball-milled （BM） for different time. The powder was consolidated by hot extrusion method. The mic...Different proportions of commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy （HEA） powder were ball-milled （BM） for different time. The powder was consolidated by hot extrusion method. The microstructures of the milled powder and bulk alloy were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Mechanical properties of the extruded alloy were examined by mechanical testing machine. The results show that after BM, the particle size and microstructures of the mixed alloy powder change obviously. After 48 h BM, the average size of mixed powder is about 30 nm, and then after hot extrusion, the average size of grains reaches about 70 rim. The compressive strength of the extruded alloy reaches 710 MPa under certain conditions of milling time and composition. As a result of the identification of the nano-/micro-strueture-property relationship of the samples, such high strength is attributed mainly to the nanocrystalline grains of a（Al） and nanoscaled FeNiCrCoAl3 particles, and the fine secondary phase of Al2Cu and Fe-rich phases.展开更多
Al86Ni7Y4.5Co1La1.5 （mole fraction, %） alloy powder was produced by argon gas atomization process. After high-energy ball milling, the powder was consolidated by vacuum hot press sintering and spark plasma sintering...Al86Ni7Y4.5Co1La1.5 （mole fraction, %） alloy powder was produced by argon gas atomization process. After high-energy ball milling, the powder was consolidated by vacuum hot press sintering and spark plasma sintering （SPS） under different process conditions. The microstructure and morphology of the powder and consolidated bulk sample were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. It is shown that amorphous phase appears when ball milling time is more than 100 h, and the bulk sample consolidated by SPS can maintain amorphous/ nanocrystalline microstructure but has lower relative density. A compressive strength of 650 MPa of Al86Ni7Y4.5Co1La1.5 nanostructured samples is achieved by vacuum hot extrusion （VHE）.展开更多
Carbon nanotubes （CNTs） reinforced aluminum matrix composites were fabricated by mechanical milling followed by hot extrusion. The commercial Al-2024 alloy with 1% CNTs was milled under various ball milling conditio...Carbon nanotubes （CNTs） reinforced aluminum matrix composites were fabricated by mechanical milling followed by hot extrusion. The commercial Al-2024 alloy with 1% CNTs was milled under various ball milling conditions. Microstructure evolution and mechanical properties of the milled powder and consolidated bulk materials were examined by X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM） and mechanical test. The effect of CNTs concentration and milling time on the microstructure of the CNTs/Al-2024 composites was studied. Based on the structural observation, the formation behavior of nanostructure in ball milled powder was discussed. The results show that the increment in the milling time and ration speed, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MM. The finest particle size was obtained after 15 h of milling. Moreover, the composite had an increase in tensile strength due to the small amount of CNTs addition.展开更多
Equal channel angular pressing(ECAP)is one of the most effective processes to produce ultra-fine grain(UFG)and nanocrystalline(NC)materials.Because the commercially pure titanium exhibits excellent biocompatibility pr...Equal channel angular pressing(ECAP)is one of the most effective processes to produce ultra-fine grain(UFG)and nanocrystalline(NC)materials.Because the commercially pure titanium exhibits excellent biocompatibility properties,it has a significant potential to be utilized as an implant material.The low static and dynamic strengths of the pure titanium are one of the weaknesses of this material.This defect can be removed by applying the ECAP process on the pure titanium.In this work,the commercially pure titanium Grade2(CP-Ti of Grade2)was pressed at room temperature by the ECAP process via a channel angle of135°for3passes.The microstructural analysis and mechanical tests such as tensile test,hardness test,three-point bending test and Charpy impact test were all carried out on the ECAPed CP-Ti through3passes.The microstructural evolution reveals that by applying the ECAP process,coarse grain(CG)structure develops to UFG/NC structure.Moreover,the results of the mechanical tests show that the process significantly increases the yield and ultimate tensile strengths,bending strength,hardness and fracture toughness of the commercially pure titanium so that it can be used as a replacement for metallic alloys used as biomaterials.展开更多
Laser cladding is a promising photon-based surface engineering technique broadly utilized for fabricating harder and wear resistant composite coatings. In spite of excellent properties, the practical applications of l...Laser cladding is a promising photon-based surface engineering technique broadly utilized for fabricating harder and wear resistant composite coatings. In spite of excellent properties, the practical applications of laser claddings are relatively restricted when compared with well-established coating techniques because of their inherent defects identified as cracks, pores and inclusions. Substantial evidence suggests that the incorporation of an appropriate amount of rare earth in laser claddings can remarkably prevent these defects. Additionally, the presence of rare earth in laser claddings can notably enhance tribo-mechanical properties such as surface hardness, modulus of elasticity, fracture toughness, friction coefficient and wear rate. In this literature review, the effect of rare earth in reducing dilution and cracks susceptibility of laser claddings in addition to microstructural refinement attained was examined. Mechanical and tribological properties of these claddings along with their underlying mechanism were discussed in detail. Finally, this article summarizes current applications of laser claddings based on rare earth and was concluded with future research directions.展开更多
The influences of the dissimilarity in the roll speeds on the microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling(CCCR) process were investiga...The influences of the dissimilarity in the roll speeds on the microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling(CCCR) process were investigated. Several experiments were conducted with three different upper/lower roll rotational speed ratios(ω/ω0, ω is the upper roll rotational speed and ω0 is the lower roll rotational speed), namely 1:1, 1:1.2 and 1:1.4. It was found that the greatest dissimilarity in the roll speed(ω/ω0=1:1.4) improved the yield strength and ultimate tensile strength of 7075 Al plate in the rolling direction by 41.5% and 21.9%, respectively. Moreover, at a roll speed ratio of ω/ω0=1:1.4, the average grain size was decreased by 36% whereas the mean hardness of the transverse cross-section of the finally rolled plate was increased by about 9.2%. Texture studies also revealed that the more the difference in the roll speeds was, the greater the isotropy and the hardness of the final product were. Nevertheless, conducting CCCR operation with different roll speeds resulted in about 6% reduction in the elongation of the deformed plate.展开更多
This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg2Si–2Cu in situ composite treated with different Bi contents. The desired modification of prim...This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg2Si–2Cu in situ composite treated with different Bi contents. The desired modification of primary Mg2 Si particles was achieved with the addition of 0.4 wt% Bi. Increasing Bi beyond 0.4 wt%resulted in a loss of modification, possibly due to the formation of Al8 MgB iS i4 compound before the precipitation of the primary Mg2 Si. Additionally, the structure of the pseudo-eutectic Mg2 Si was transformed from plate to fibrous, which was consistent with decrease of growth temperature extracted from the cooling curve thermal analysis. Addition of Bi had an effect on the morphology of Al5 Fe Si（β）, Al2Cu（θ） and Al5Cu2Mg8Si6（Q） intermetallic compounds. The tensile strength, elongation percentage, impact toughness, and hardness increased by 6%, 13%, 75%, and 23%, respectively, due to modification of both the primary and eutectic Mg2 Si crystals. The tensile and impact fracture surfaces showed fewer decohered particles in the Bi-treated composite. The enhancement in wear resistance of the Bi-treated composite could be attributed to solid lubricant function of insoluble soft Bi phase and modification effects on Mg2 Si particles.展开更多
The microstructure evolution, mechanical and corrosion properties of Al-11Si-2Cu-0.8Zn die cast alloy treated with Bi, Sb and Sr additions were investigated. The results of mechanical testing showed that all additions...The microstructure evolution, mechanical and corrosion properties of Al-11Si-2Cu-0.8Zn die cast alloy treated with Bi, Sb and Sr additions were investigated. The results of mechanical testing showed that all additions increased impact toughness, ultimate tensile strength, and elongation of the alloy as a result of change in eutectic Si morphology. The analysis of fracture surfaces revealed that with addition of Sr and to lesser extent Bi and Sb, the alloy exhibited a predominantly ductile fracture rather than quasi-cleavage brittle fracture. Moreover, with the additions of Sr, Bi and Sb, the quality index increased to 164.7 MPa, 156.3 MPa and 152.6 MPa respectively from 102 MPa for the base alloy. Polarization corrosion tests conducted in sodium chloride solution showed that the corrosion potential shifted to more negative values with additions of Sb, Bi and Sr, respectively. Corrosion immersion tests also revealed that the element additions have a detrimental effect on the corrosion rate of alloys, due to the increase of boundaries between the Al and eutectic Si phases.展开更多
Dual equal channel lateral extrusion (DECLE), as a severe plastic deformation (SPD) process, was employed forimproving the mechanical properties of AA5083 aluminum alloy. Several experiments were conducted to study th...Dual equal channel lateral extrusion (DECLE), as a severe plastic deformation (SPD) process, was employed forimproving the mechanical properties of AA5083 aluminum alloy. Several experiments were conducted to study the influences of theroute type, namely A and B, and pass number on mechanical properties of the material. The process was conducted up to 6 passeswith decreasing process temperature, specifically from 573 to 473 K. Supplementary experiments involving metallography, hardnessand tensile tests were carried out in order to evaluate the effects of the process variables. The hardness measurements exhibitedreasonably uniform distributions within the product with a maximum increase of 64% via a 6-pass operation. The yield and ultimatestrengths also amended 107% and 46%, respectively. These significant improvements were attributed to the severe shear deformationof grains and decreasing pass temperature, which intensified the grain refinement. TEM images showed an average grain sizereduction from 100 μm for the annealed billet to 200 nm after 6 passes of DECLE. Finally, the experimental findings for routes A andB were compared and discussed and some important conclusions were drawn.展开更多
The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the microgroove surface.There is a reduction in cutting and thrust forces with the application of ink during microc...The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the microgroove surface.There is a reduction in cutting and thrust forces with the application of ink during microcutting.Moreover,the microhardness of the ink-affected microgroove is lower than that of the ink-free microgroove.Numerous substructured grains exist in the ink-affected microgroove zone whilst deformed grains dominate in the ink-free microgroove zone produced by microcutting.Furthermore,the mechanochemical effect can facilitate the nucleation of precipitates in the microgroove zone and induce the formation of subgrains with multiple orientations.According to the analysis and calculation,the main texture components of the ink-affected sample are Goss{110}<001>and R{124}<211>,and that of the ink-free sample are Brass{110}<112>,Copper{112}<111>and S{123}<634>.Besides,a clear difference of slip systems is found between the ink-free and ink-affected microgrooves,and the results show that R texture is easier to form on the ink-affected microgroove.展开更多
The influence of thermo-mechanical processing (TMP) on the microstructure and the electrochemical behavior of new metastableβ alloy Ti?20.6Nb?13.6Zr?0.5V (TNZV) was investigated. The TMP included hot working in below...The influence of thermo-mechanical processing (TMP) on the microstructure and the electrochemical behavior of new metastableβ alloy Ti?20.6Nb?13.6Zr?0.5V (TNZV) was investigated. The TMP included hot working in belowβ transus, solution heat treatments at the same temperature and different cooling rates in addition to aging. Depending upon the TMP conditions, a wide range of microstructures with varying spatial distributions and morphologies of equiaxed/elongatedα andβ phases were attained, allowing for a wide range of electrochemical properties to be achieved. The corrosion behavior of the studied alloy was evaluated in a Ringer’s solution at 37 °C via open circuit potential?time and potentiodynamic polarization measurements.展开更多
Over the past decade,the interest in aluminum composites reinforced with carbon nanotubes has grown significantly.Studies have been carried out to overcome problems with uniform dispersion,interfacial bonding,void for...Over the past decade,the interest in aluminum composites reinforced with carbon nanotubes has grown significantly.Studies have been carried out to overcome problems with uniform dispersion,interfacial bonding,void formation and carbide formation of the composites.In the present work,multi-wall carbon nanotubes(MWCNTs) aluminum composites were produced.High-energy ball milling with the aim at developing well-dispersed MWCNTs Al composites was followed by cold compaction,sintering,and hot extrusion at 500 ℃.Different amounts of stearic acid as processing control agent(PCA) is used in order to minimize cold welding of the Al particles,and to produce finer particles.Differential scanning calorimetry(DSC),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray diffraction(XRD) were employed to analyze the MWCNTs,the aluminum powder,and the composites’ microstructural behavior.The hardness and tensile properties of the composites are also evaluated.The results showed 500% increase in yield stress after the addition of 1 wt% MWCNTs in Al-MWCNTs based composite.The ball-milling time of 4 h is found to be sufficient as excessive milling time destroys a vast number of MWCNTs.展开更多
The use of a constrained groove pressing(CGP) method to plastically deform AA6063 aluminum alloy led to the improved surface properties. It was found that hardness magnitude is dramatically improved and its uniformity...The use of a constrained groove pressing(CGP) method to plastically deform AA6063 aluminum alloy led to the improved surface properties. It was found that hardness magnitude is dramatically improved and its uniformity is considerably decreased after the first pass, while subsequent passes result in better hardness behavior for the processed material. Also, the elongated grains formed in the first pass of the CGP are gradually converted to the equiaxed counterparts by adding pass numbers. Eventually, higher corrosion resistance of the sample by imposing the CGP process is related to the quick formation of passivation film and the change in the morphology of the second phase and precipitates which hinder their electrochemical reactions and decrease the potential localized attack sites.展开更多
Zr was added to Ti−Nb−Fe alloys to develop low elastic modulus and high strengthβ-Ti alloys for biomedical applications.Ingots of Ti−12Nb−2Fe−(2,4,6,8,10)Zr(at.%)were prepared by arc melting and then subjected to hom...Zr was added to Ti−Nb−Fe alloys to develop low elastic modulus and high strengthβ-Ti alloys for biomedical applications.Ingots of Ti−12Nb−2Fe−(2,4,6,8,10)Zr(at.%)were prepared by arc melting and then subjected to homogenization,cold rolling,and solution treatments.The phases and microstructures of the alloys were analyzed by optical microscopy,X-ray diffraction,and transmission electron microscopy.The mechanical properties were measured by tensile tests.The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys;thus,all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa,respectively.Zr plays a weak role in the deformation mechanism.Further,twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity.Ti−12Nb−2Fe−(8,10)Zr alloys with metastableβphases show low elastic modulus,high tensile strength,and good plasticity and are suitable candidate materials for biomedical implants.展开更多
Herein,a strong extensional and shearing field was introduced to construct highly oriented hybrid networks of silicon carbide(SiC)-packed boron nitride(BN)platelets to fabricate high-performance wearresistant PA6 comp...Herein,a strong extensional and shearing field was introduced to construct highly oriented hybrid networks of silicon carbide(SiC)-packed boron nitride(BN)platelets to fabricate high-performance wearresistant PA6 composites.Results show that in-plane and through-plane thermal conductivity(TC)of the prepared PA6 composites with a total filler loading of 20 wt.%reached 1.31 and 0.35 W/(m K),352%and 25%higher than those of pure PA6,respectively.It is attributed to the highly oriented hybrid network that facilitates the formation of efficient thermal conductivity pathways.Temperature monitoring results during friction confirm that high TC favors the friction heat dissipation performance.Meanwhile,the yield strength of PA6 composites increased by 39.1%and they still have excellent ductility with an elongation at break of 207.1%.Finally,the wear rate of PA6 composites decreased sharply by 92.5%.This method can be used to manufacture advanced linear bearing and guideway parts,etc。展开更多
Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materi...Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materials are focused on. Diffusion coefficient decreases with increase of the number of shells in CNF-MF. The structure of CNF-MFs with crystalline alignment is totally stabilized with twist which is an accumulation of torsion angles at Glycosidic bonds between monomers inside CNFs. Unique fiber drawing simulation, where a single CNF fiber is taken out of CNF-MF structure, is first conducted. The CNF fiber which is drawn out stretches up to relatively large strain, with linear increase of tensile stress. The computation results show that, the larger the number of shell structure of CNF-MF is, the larger the stretch and the stress of drawn fibers are.展开更多
When an unruptured aneurysm is found, deciding whether to operate or follow up is one of the most important issues. There are guidelines for making the best final decision on treatment, taking into account the effecti...When an unruptured aneurysm is found, deciding whether to operate or follow up is one of the most important issues. There are guidelines for making the best final decision on treatment, taking into account the effectiveness of diagnostic and therapeutic devices and the risk-benefit ratio of patients, caregivers, and healthcare professionals. The guidelines evidence-based of large clinical data for this purpose are presented by national medical societies. As one of the rupture risk indicators, there is the hazard risk ratio derived by the UCAS Japan research group based on the statistical method of 6697 aneurysms in 5720 patients with cerebral aneurysms of 3 mm or more. Therefore, we investigated the biomechanical significance of this hazard risk ratio using a spherical aneurysm model. It was revealed that 1) the reason why the frequency of aneurysm rupture is relatively high up to about 10 mm, 2) the UCAS hazard risk ratio corresponds to stress of the aneurysm wall, and the true stress can be calculated by multiplying the patient’s blood pressure, and 3) the factors that cause the daughter’s sac (irregular protrusion of the aneurysm wall). In addition, our two methods for measuring the strength of the blood vessel wall of an individual patient were described.展开更多
In current research,the interactive effects of different parameters such as melt overheating temperature,the location of gating system and incorporation of the grain refiner in bar and micro-powder form on the mechani...In current research,the interactive effects of different parameters such as melt overheating temperature,the location of gating system and incorporation of the grain refiner in bar and micro-powder form on the mechanical and structural characteristics of commercially pure aluminium are examined.Results show that increasing the melt temperature as well as employing a gating system with higher heat transfer rate increases the ultimate tensile strength(UTS)of the pure aluminium by 7%.Also,the introduction of 2wt%Al–5Ti–1B grain refiner in bar form into the overheated melt enhances the UTS values by two times,while incorporating 2wt%Al–5Ti–1B grain refiner in micro-powder form leads to achieving 32%higher UTS compared to the samples with grain refiner in the bar form due to the elimination of Al3Ti brittle phase,as confirmed by XRD patterns and SEM fracture surface images.展开更多
文摘The functionally graded materials(FGMs)are obtained by various processes.Although a few FGMs are obtained naturally,such as oyster,pearl,and bamboo,additive manufacturing(AM),known as 3D printing,is a net-shaped manufacturing process employed to manufacture complex 3D objects without tools,molds,assembly,and joining.Currently,commercial AM techniques mostly use homogeneous composition with simplified geometric descriptions,employing a single material across the entire component to achieve functional graded additive manufacturing(FGAM),in contrast to multi-material FGAM with heterogeneous structures.FGMs are widely used in various fields due to their mechanical property advantages.Because FGM plays a significant role in the industrial production,the characteristics and mechanical behaviour of FGMs prepared by AM were reviewed.In this review,the research on FGMs and AM over the past 30 years was reviewed,suggesting that future researchers should focus on the application of artificial intelligence and machine learning technologies in industry to optimize the process parameters of different gradient systems.
文摘Fatigue failure continues to be a significant challenge in designing structural and mechanical components subjected to repeated and complex loading.While earlier studies mainly examined material properties and how stress affects lifespan,this review offers the first comprehensive,multiscale comparison of strategies that optimize geometry to improve fatigue performance.This includes everything from microscopic features like the shape of graphite nodules to large-scale design elements such as fillets,notches,and overall structural layouts.We analyze and combine various methods,including topology and shape optimization,the ability of additive manufacturing to finetune internal geometries,and reliability-based design approaches.A key new contribution is our proposal of a standard way to evaluate geometry-focused fatigue design,allowing for consistent comparison and encouraging validation across different fields.Furthermore,we highlight important areas for future research,such as incorporating manufacturing flaws,using multiscale models,and integrating machine learning techniques.This work is the first to provide a broad geometric viewpoint in fatigue engineering,laying the groundwork for future design methods that are driven by data and centered on reliability.
基金Project(2012CB619503)supported by the Nation Basic Research Program of ChinaProject(2013AA031001)supported by the National High Technology Research and Development Program of ChinaProject(2012DFA50630)supported by the International Science&Technology Cooperation Program of China
文摘Different proportions of commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy （HEA） powder were ball-milled （BM） for different time. The powder was consolidated by hot extrusion method. The microstructures of the milled powder and bulk alloy were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Mechanical properties of the extruded alloy were examined by mechanical testing machine. The results show that after BM, the particle size and microstructures of the mixed alloy powder change obviously. After 48 h BM, the average size of mixed powder is about 30 nm, and then after hot extrusion, the average size of grains reaches about 70 rim. The compressive strength of the extruded alloy reaches 710 MPa under certain conditions of milling time and composition. As a result of the identification of the nano-/micro-strueture-property relationship of the samples, such high strength is attributed mainly to the nanocrystalline grains of a（Al） and nanoscaled FeNiCrCoAl3 particles, and the fine secondary phase of Al2Cu and Fe-rich phases.
基金Project(2012CB619503)supported by the National Basic Research Program of ChinaProject(2013AA031001)supported by the National High Technology Research and Development Program of ChinaProject(2012DFA50630)supported by the International Science&Technology Cooperation Program of China
文摘Al86Ni7Y4.5Co1La1.5 （mole fraction, %） alloy powder was produced by argon gas atomization process. After high-energy ball milling, the powder was consolidated by vacuum hot press sintering and spark plasma sintering （SPS） under different process conditions. The microstructure and morphology of the powder and consolidated bulk sample were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. It is shown that amorphous phase appears when ball milling time is more than 100 h, and the bulk sample consolidated by SPS can maintain amorphous/ nanocrystalline microstructure but has lower relative density. A compressive strength of 650 MPa of Al86Ni7Y4.5Co1La1.5 nanostructured samples is achieved by vacuum hot extrusion （VHE）.
基金Project(2012CB619503)supported by the National Basic Research Program of ChinaProject(2013AA031001)supported by the National High-tech Research and Development Program of ChinaProject(2012DFA50630)supported by the International Science&Technology Cooperation Program of China
文摘Carbon nanotubes （CNTs） reinforced aluminum matrix composites were fabricated by mechanical milling followed by hot extrusion. The commercial Al-2024 alloy with 1% CNTs was milled under various ball milling conditions. Microstructure evolution and mechanical properties of the milled powder and consolidated bulk materials were examined by X-ray diffraction （XRD）, field emission scanning electron microscopy （FESEM） and mechanical test. The effect of CNTs concentration and milling time on the microstructure of the CNTs/Al-2024 composites was studied. Based on the structural observation, the formation behavior of nanostructure in ball milled powder was discussed. The results show that the increment in the milling time and ration speed, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MM. The finest particle size was obtained after 15 h of milling. Moreover, the composite had an increase in tensile strength due to the small amount of CNTs addition.
文摘Equal channel angular pressing(ECAP)is one of the most effective processes to produce ultra-fine grain(UFG)and nanocrystalline(NC)materials.Because the commercially pure titanium exhibits excellent biocompatibility properties,it has a significant potential to be utilized as an implant material.The low static and dynamic strengths of the pure titanium are one of the weaknesses of this material.This defect can be removed by applying the ECAP process on the pure titanium.In this work,the commercially pure titanium Grade2(CP-Ti of Grade2)was pressed at room temperature by the ECAP process via a channel angle of135°for3passes.The microstructural analysis and mechanical tests such as tensile test,hardness test,three-point bending test and Charpy impact test were all carried out on the ECAPed CP-Ti through3passes.The microstructural evolution reveals that by applying the ECAP process,coarse grain(CG)structure develops to UFG/NC structure.Moreover,the results of the mechanical tests show that the process significantly increases the yield and ultimate tensile strengths,bending strength,hardness and fracture toughness of the commercially pure titanium so that it can be used as a replacement for metallic alloys used as biomaterials.
基金Project supported by the University of Malaya Research Grant(UMRG,RP013A-13AET)University of Malaya Research Grant(UMRG,RP035A-15AET)
文摘Laser cladding is a promising photon-based surface engineering technique broadly utilized for fabricating harder and wear resistant composite coatings. In spite of excellent properties, the practical applications of laser claddings are relatively restricted when compared with well-established coating techniques because of their inherent defects identified as cracks, pores and inclusions. Substantial evidence suggests that the incorporation of an appropriate amount of rare earth in laser claddings can remarkably prevent these defects. Additionally, the presence of rare earth in laser claddings can notably enhance tribo-mechanical properties such as surface hardness, modulus of elasticity, fracture toughness, friction coefficient and wear rate. In this literature review, the effect of rare earth in reducing dilution and cracks susceptibility of laser claddings in addition to microstructural refinement attained was examined. Mechanical and tribological properties of these claddings along with their underlying mechanism were discussed in detail. Finally, this article summarizes current applications of laser claddings based on rare earth and was concluded with future research directions.
文摘The influences of the dissimilarity in the roll speeds on the microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling(CCCR) process were investigated. Several experiments were conducted with three different upper/lower roll rotational speed ratios(ω/ω0, ω is the upper roll rotational speed and ω0 is the lower roll rotational speed), namely 1:1, 1:1.2 and 1:1.4. It was found that the greatest dissimilarity in the roll speed(ω/ω0=1:1.4) improved the yield strength and ultimate tensile strength of 7075 Al plate in the rolling direction by 41.5% and 21.9%, respectively. Moreover, at a roll speed ratio of ω/ω0=1:1.4, the average grain size was decreased by 36% whereas the mean hardness of the transverse cross-section of the finally rolled plate was increased by about 9.2%. Texture studies also revealed that the more the difference in the roll speeds was, the greater the isotropy and the hardness of the final product were. Nevertheless, conducting CCCR operation with different roll speeds resulted in about 6% reduction in the elongation of the deformed plate.
文摘This work investigated the microstructure evolution, tensile, impact, hardness, and sliding wear properties of an Al–20Mg2Si–2Cu in situ composite treated with different Bi contents. The desired modification of primary Mg2 Si particles was achieved with the addition of 0.4 wt% Bi. Increasing Bi beyond 0.4 wt%resulted in a loss of modification, possibly due to the formation of Al8 MgB iS i4 compound before the precipitation of the primary Mg2 Si. Additionally, the structure of the pseudo-eutectic Mg2 Si was transformed from plate to fibrous, which was consistent with decrease of growth temperature extracted from the cooling curve thermal analysis. Addition of Bi had an effect on the morphology of Al5 Fe Si（β）, Al2Cu（θ） and Al5Cu2Mg8Si6（Q） intermetallic compounds. The tensile strength, elongation percentage, impact toughness, and hardness increased by 6%, 13%, 75%, and 23%, respectively, due to modification of both the primary and eutectic Mg2 Si crystals. The tensile and impact fracture surfaces showed fewer decohered particles in the Bi-treated composite. The enhancement in wear resistance of the Bi-treated composite could be attributed to solid lubricant function of insoluble soft Bi phase and modification effects on Mg2 Si particles.
文摘The microstructure evolution, mechanical and corrosion properties of Al-11Si-2Cu-0.8Zn die cast alloy treated with Bi, Sb and Sr additions were investigated. The results of mechanical testing showed that all additions increased impact toughness, ultimate tensile strength, and elongation of the alloy as a result of change in eutectic Si morphology. The analysis of fracture surfaces revealed that with addition of Sr and to lesser extent Bi and Sb, the alloy exhibited a predominantly ductile fracture rather than quasi-cleavage brittle fracture. Moreover, with the additions of Sr, Bi and Sb, the quality index increased to 164.7 MPa, 156.3 MPa and 152.6 MPa respectively from 102 MPa for the base alloy. Polarization corrosion tests conducted in sodium chloride solution showed that the corrosion potential shifted to more negative values with additions of Sb, Bi and Sr, respectively. Corrosion immersion tests also revealed that the element additions have a detrimental effect on the corrosion rate of alloys, due to the increase of boundaries between the Al and eutectic Si phases.
基金partially supported by the Iran National Science Foundation(INSF) with grant number 92014140
文摘Dual equal channel lateral extrusion (DECLE), as a severe plastic deformation (SPD) process, was employed forimproving the mechanical properties of AA5083 aluminum alloy. Several experiments were conducted to study the influences of theroute type, namely A and B, and pass number on mechanical properties of the material. The process was conducted up to 6 passeswith decreasing process temperature, specifically from 573 to 473 K. Supplementary experiments involving metallography, hardnessand tensile tests were carried out in order to evaluate the effects of the process variables. The hardness measurements exhibitedreasonably uniform distributions within the product with a maximum increase of 64% via a 6-pass operation. The yield and ultimatestrengths also amended 107% and 46%, respectively. These significant improvements were attributed to the severe shear deformationof grains and decreasing pass temperature, which intensified the grain refinement. TEM images showed an average grain sizereduction from 100 μm for the annealed billet to 200 nm after 6 passes of DECLE. Finally, the experimental findings for routes A andB were compared and discussed and some important conclusions were drawn.
基金the Singapore Ministry of Education Academic Research Fund(R265-000-686-114 and MOE2018-T2-1-140)。
文摘The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the microgroove surface.There is a reduction in cutting and thrust forces with the application of ink during microcutting.Moreover,the microhardness of the ink-affected microgroove is lower than that of the ink-free microgroove.Numerous substructured grains exist in the ink-affected microgroove zone whilst deformed grains dominate in the ink-free microgroove zone produced by microcutting.Furthermore,the mechanochemical effect can facilitate the nucleation of precipitates in the microgroove zone and induce the formation of subgrains with multiple orientations.According to the analysis and calculation,the main texture components of the ink-affected sample are Goss{110}<001>and R{124}<211>,and that of the ink-free sample are Brass{110}<112>,Copper{112}<111>and S{123}<634>.Besides,a clear difference of slip systems is found between the ink-free and ink-affected microgrooves,and the results show that R texture is easier to form on the ink-affected microgroove.
基金the financial assistance provided by Ministry of High Education and Scientific Research, the Government of Iraq
文摘The influence of thermo-mechanical processing (TMP) on the microstructure and the electrochemical behavior of new metastableβ alloy Ti?20.6Nb?13.6Zr?0.5V (TNZV) was investigated. The TMP included hot working in belowβ transus, solution heat treatments at the same temperature and different cooling rates in addition to aging. Depending upon the TMP conditions, a wide range of microstructures with varying spatial distributions and morphologies of equiaxed/elongatedα andβ phases were attained, allowing for a wide range of electrochemical properties to be achieved. The corrosion behavior of the studied alloy was evaluated in a Ringer’s solution at 37 °C via open circuit potential?time and potentiodynamic polarization measurements.
文摘Over the past decade,the interest in aluminum composites reinforced with carbon nanotubes has grown significantly.Studies have been carried out to overcome problems with uniform dispersion,interfacial bonding,void formation and carbide formation of the composites.In the present work,multi-wall carbon nanotubes(MWCNTs) aluminum composites were produced.High-energy ball milling with the aim at developing well-dispersed MWCNTs Al composites was followed by cold compaction,sintering,and hot extrusion at 500 ℃.Different amounts of stearic acid as processing control agent(PCA) is used in order to minimize cold welding of the Al particles,and to produce finer particles.Differential scanning calorimetry(DSC),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray diffraction(XRD) were employed to analyze the MWCNTs,the aluminum powder,and the composites’ microstructural behavior.The hardness and tensile properties of the composites are also evaluated.The results showed 500% increase in yield stress after the addition of 1 wt% MWCNTs in Al-MWCNTs based composite.The ball-milling time of 4 h is found to be sufficient as excessive milling time destroys a vast number of MWCNTs.
基金funded by“Quality Engineering Project of Anhui Province of China in 2016”entitled mold design and manufacturing experimental training center(2016sxzx050)。
文摘The use of a constrained groove pressing(CGP) method to plastically deform AA6063 aluminum alloy led to the improved surface properties. It was found that hardness magnitude is dramatically improved and its uniformity is considerably decreased after the first pass, while subsequent passes result in better hardness behavior for the processed material. Also, the elongated grains formed in the first pass of the CGP are gradually converted to the equiaxed counterparts by adding pass numbers. Eventually, higher corrosion resistance of the sample by imposing the CGP process is related to the quick formation of passivation film and the change in the morphology of the second phase and precipitates which hinder their electrochemical reactions and decrease the potential localized attack sites.
基金the Natural Science Foundation of Shanghai,China(No.15ZR1428400)Shanghai Engineering Research Center of High-Performance Medical Device Materials,China(No.20DZ2255500)the Project of Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development,Tohoku University,sponsored by Ministry,Education,Culture,Sports,Science and Technology,Japan,and the Grant-in Aid for Scientific Research(C)(No.20K05139)from JSPS(Japan Society for the Promotion of Science),Tokyo,Japan.
文摘Zr was added to Ti−Nb−Fe alloys to develop low elastic modulus and high strengthβ-Ti alloys for biomedical applications.Ingots of Ti−12Nb−2Fe−(2,4,6,8,10)Zr(at.%)were prepared by arc melting and then subjected to homogenization,cold rolling,and solution treatments.The phases and microstructures of the alloys were analyzed by optical microscopy,X-ray diffraction,and transmission electron microscopy.The mechanical properties were measured by tensile tests.The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys;thus,all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa,respectively.Zr plays a weak role in the deformation mechanism.Further,twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity.Ti−12Nb−2Fe−(8,10)Zr alloys with metastableβphases show low elastic modulus,high tensile strength,and good plasticity and are suitable candidate materials for biomedical implants.
基金supported by the National Natural Science Foundation of China(No.51790501)the Sichuan Science and Technology Program(No.2022YFH0090)the Fundamental Research Funds for the Central Universities.
文摘Herein,a strong extensional and shearing field was introduced to construct highly oriented hybrid networks of silicon carbide(SiC)-packed boron nitride(BN)platelets to fabricate high-performance wearresistant PA6 composites.Results show that in-plane and through-plane thermal conductivity(TC)of the prepared PA6 composites with a total filler loading of 20 wt.%reached 1.31 and 0.35 W/(m K),352%and 25%higher than those of pure PA6,respectively.It is attributed to the highly oriented hybrid network that facilitates the formation of efficient thermal conductivity pathways.Temperature monitoring results during friction confirm that high TC favors the friction heat dissipation performance.Meanwhile,the yield strength of PA6 composites increased by 39.1%and they still have excellent ductility with an elongation at break of 207.1%.Finally,the wear rate of PA6 composites decreased sharply by 92.5%.This method can be used to manufacture advanced linear bearing and guideway parts,etc。
文摘Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materials are focused on. Diffusion coefficient decreases with increase of the number of shells in CNF-MF. The structure of CNF-MFs with crystalline alignment is totally stabilized with twist which is an accumulation of torsion angles at Glycosidic bonds between monomers inside CNFs. Unique fiber drawing simulation, where a single CNF fiber is taken out of CNF-MF structure, is first conducted. The CNF fiber which is drawn out stretches up to relatively large strain, with linear increase of tensile stress. The computation results show that, the larger the number of shell structure of CNF-MF is, the larger the stretch and the stress of drawn fibers are.
文摘When an unruptured aneurysm is found, deciding whether to operate or follow up is one of the most important issues. There are guidelines for making the best final decision on treatment, taking into account the effectiveness of diagnostic and therapeutic devices and the risk-benefit ratio of patients, caregivers, and healthcare professionals. The guidelines evidence-based of large clinical data for this purpose are presented by national medical societies. As one of the rupture risk indicators, there is the hazard risk ratio derived by the UCAS Japan research group based on the statistical method of 6697 aneurysms in 5720 patients with cerebral aneurysms of 3 mm or more. Therefore, we investigated the biomechanical significance of this hazard risk ratio using a spherical aneurysm model. It was revealed that 1) the reason why the frequency of aneurysm rupture is relatively high up to about 10 mm, 2) the UCAS hazard risk ratio corresponds to stress of the aneurysm wall, and the true stress can be calculated by multiplying the patient’s blood pressure, and 3) the factors that cause the daughter’s sac (irregular protrusion of the aneurysm wall). In addition, our two methods for measuring the strength of the blood vessel wall of an individual patient were described.
文摘In current research,the interactive effects of different parameters such as melt overheating temperature,the location of gating system and incorporation of the grain refiner in bar and micro-powder form on the mechanical and structural characteristics of commercially pure aluminium are examined.Results show that increasing the melt temperature as well as employing a gating system with higher heat transfer rate increases the ultimate tensile strength(UTS)of the pure aluminium by 7%.Also,the introduction of 2wt%Al–5Ti–1B grain refiner in bar form into the overheated melt enhances the UTS values by two times,while incorporating 2wt%Al–5Ti–1B grain refiner in micro-powder form leads to achieving 32%higher UTS compared to the samples with grain refiner in the bar form due to the elimination of Al3Ti brittle phase,as confirmed by XRD patterns and SEM fracture surface images.
