In order to improve the hardness and tribological performance of Ti6Al4V alloy,NiCoCrAlY-B_(4)C composite coatings with B_(4)C of 5%,10%and 15%(mass fraction)were fabricated on its surface by laser cladding(LC).The mo...In order to improve the hardness and tribological performance of Ti6Al4V alloy,NiCoCrAlY-B_(4)C composite coatings with B_(4)C of 5%,10%and 15%(mass fraction)were fabricated on its surface by laser cladding(LC).The morphologies,chemical compositions and phases of obtained coatings were analyzed using scanning electronic microscope(SEM),energy dispersive spectrometer(EDS),and X-ray diffraction(XRD),respectively.The effects of B_(4)C mass fraction on the coefficient of friction(COF)and wear rate of NiCoCrAlY-B_(4)C coatings were investigated using a ball-on-disc wear tester.The results show that the NiCoCrAlY-B_(4)C coatings with different B_(4)C mass fractions are mainly composed of NiTi,NiTi_(2),α-Ti,CoO,AlB_(2),TiC,TiB and TiB_(2)phases.The COFs and wear rates of NiCoCrAlY-B_(4)C coatings decrease with the increase of B_(4)C content,which are contributed to the improvement of coating hardness by the B_(4)C addition.The wear mechanisms of NiCoCrAlY-B_(4)C coatings are changed from adhesive wear and oxidation wear to fatigue wear with the increase of B_(4)C content.展开更多
B4C/6061Al composites reinforced with nano-to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering(SPS)and hot extrusion and rolling(HER),followed by T6 treat...B4C/6061Al composites reinforced with nano-to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering(SPS)and hot extrusion and rolling(HER),followed by T6 treatment.The microstructural evolution and mechanical properties were investigated.Results showed that the status of B4C particles changed from a network after SPS to a dispersion distribution after HER.The substructured grains reached 66.5%owing to the pinning effect of nano-sized B4C,and the grain size was refined from 3.12μm to 1.56μm after HER.After T6 treatment,dispersed Mg_(2)Si precipitated phases formed,and the grain size increased to 1.87μm.Fine recrystallized grains around micro-sized B4C were smaller than those in the areas with uniform distribution of nano-sized B4C and Mg_(2)Si.The stress distributions of as-rolled and heated composites were similar,considering that the T6 heat treatment was only effective in eliminating the first internal stress.The Vickers,microhardness,and tensile strength of as-SPSed composites were greatly improved from HV 55.45,0.86 GPa,and 180 MPa to HV 77.51,1.08 GPa,and 310 MPa,respectively.Despite the precipitation strengthening,the corresponding values of as-heated composites decreased to HV 70.82,0.85 GPa,and 230 MPa owing to grain coarsening.展开更多
Nb and Ti-13 Nb powders were used for improving the surface of Ti6Al4 V alloy.The deposition of the powders was carried out at various laser powers.The scanning electron microscopy（SEM）-EDS and optical microscopy we...Nb and Ti-13 Nb powders were used for improving the surface of Ti6Al4 V alloy.The deposition of the powders was carried out at various laser powers.The scanning electron microscopy（SEM）-EDS and optical microscopy were used for characterization.X-ray diffractometer（XRD） was used for analyzing the elemental composition and phase constituents.The hardness,wear and corrosion properties were achieved.The corrosion and the wear behaviours of the deposited layers were studied in a Hanks solution（simulated body fluid,SBF）.The microstructures of Nb coatings reveal the presence of orthorhombic,dendritic α″ and metastable β-Nb phases which produce uneven hardness with an average of HV 364.For Ti-13 Nb coatings,martensitic α′ and metastable β-Nb phases with an average hardness of HV 423 were observed.The resistance of wear on dry sliding of Ti-13 Nb coating is attributed to the increase in hardness.Experimental results indicate that deposition of Nb and Ti-13 Nb on Ti6Al4 V grossly reduces the mass fractions of Al and V in all coatings.In SBF,Nb reinforcement produces the best coating that reveals the best wear and corrosion resistances as compared with the substrate.Hence,this coating will perform best for orthopaedic implant material enhancement.展开更多
Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) ...Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.展开更多
The composition and structure of Ti 6Al 4V alloy plasma based ion implanted with nitrogen was investigated.The nitrogen depth distribution shows more antiballistic with distribution peak heightened with increased i...The composition and structure of Ti 6Al 4V alloy plasma based ion implanted with nitrogen was investigated.The nitrogen depth distribution shows more antiballistic with distribution peak heightened with increased implantation time(dose),and more like a parabola at the low implantation pulse voltage.When implantation pulse voltage is increased,the implantation depth increased with the nitrogen distribution peak being deepened,widened and lowered somewhat.TiN,TiN+Ti 2N,or Ti 2N second phases were formed in the implanted layer.The relative percentage of nitrogen content in the form of TiN increases when going deeper into the implanted(TiN formed) layer.The increase of implantation pulse width and/or time is favourable for the formation of TiN rather than Ti 2N.It is unfavourable for formation of any nitrides when implantation pulse voltage is decreased to 30kV or less.Tiny crystalline particles (made mainly of Ti 2N and a smaller percentage of TiO 2 phases) of regular shapes such as triangle and tetragon, etc .(about 20 nm) are found distrbuted dispersively in the near surface region of samples implanted at the high implantation pulse voltage (75kV).展开更多
A combinatorial approach was applied to investigating the influence of Fe content on the microstructures and properties of Ti6Al4V alloy.A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Fe alloys and anne...A combinatorial approach was applied to investigating the influence of Fe content on the microstructures and properties of Ti6Al4V alloy.A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Fe alloys and annealed at 1000°C for 600 h to obtain a wide range of compositions.By combining electron probe micro-analysis(EPMA),scanning electron microscopy(SEM)and nanoindentation,the relationships between composition and microstructure as well as hardness were determined.It is found that after aging the Ti6Al4V5Fe sample contains reasonable(about 55%)volume fraction of fineαphase and shows the peak hardness among the Ti6Al4VxFe alloys.Therefore,it is a promising candidate for the development of titanium alloys.HAADF-STEM and XRD reveal that after quenching from the singleβphase field,the metastableα''lamellae form in the Ti6Al4V5Fe alloy,and on subsequent isothermal aging,theα''lamellae become coarse and act as precursors/preferential nucleation sites for the stableαphase.展开更多
Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of...Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of the ingots. Furthermore, the optimal speed of the heating and the liquid stirring could overcome particle settlement caused by the density difference between the matrix and the particles. Ti6Al4V particles distributed uniformly in the composites with different particle contents. The average grain size decreased with the increase in the particle contents. The Ti6A14V particles bonded pretty well with the alloy matrix. In addition, there were some interfacial reactions in the composites. There were rod-like A13Ti phases at the interface. The precipitates extended from the particle surface to the matrix, and they might improve the interfacial bonding strength. The ultimate tensile strength, yield strength and elastic modulus were enhanced as the particle contents increased, and the elongation was much better than that of the same matrix material reinforced with SiC particles. Thus, the novel composites exhibit better comprehensive mechanical properties.展开更多
A good joint of Ti Bw/Ti6Al4V composites and Inconel 718 alloys was obtained by Gas Tungsten Arc Welding(GTAW) heat transmission. The interfacial reaction mechanism of joint was investigated and analyzed in details. O...A good joint of Ti Bw/Ti6Al4V composites and Inconel 718 alloys was obtained by Gas Tungsten Arc Welding(GTAW) heat transmission. The interfacial reaction mechanism of joint was investigated and analyzed in details. Owing to the heat input applied on the surface of Ti Bw/Ti6Al4V composites, a solid-state reaction layer appeared at the interface of Ti Bw/Ti6Al4 V composites to Inconel 718 alloys. The thickness of the reaction layer was obviously increased with increasing heat input.Developing of reaction layer mainly depended on the diffusion of elements of Ti and Ni through the interface during welding to form solid solutions and intermetallic compounds(IMCs). The reaction layer can be divided into Ti-rich zone(layer 2) and Nirich zone(layer 1). In Ni-rich zone, relatively coarse dendrites were the predominant, however, more brittle IMCs like Ti2Ni were found in the Ti-rich zone. Micro hardness of reaction layer was much higher than that of base metal. While a slight decrease of hardness was found between Ti-rich zone and Ni-rich zone due to the formation of TiNi.展开更多
In the present study, a series of in situ TiB/Ti6Al4V composites were fabricated using selective laser melting. The formability, microstructure evolution and mechanical properties of the as-built samples added with di...In the present study, a series of in situ TiB/Ti6Al4V composites were fabricated using selective laser melting. The formability, microstructure evolution and mechanical properties of the as-built samples added with different contents of TiB2 were studied. It is found that the densification level is related to both the content of TiB2 and laser energy density. The added TiB2 reinforcement particle can spontaneously react with titanium and then form the TiB phase. The needle-like TiB phase tends to transform into dot-like particles with the decrease in energy density. Additionally, with the increase in TiB2 content, the TiB phase is coarsened due to the increased nucleation rate and more reactions. The grain morphology is found to largely depend on the translational speed of solid–fluid interface determined by the temperature gradient and cooling rate. Also, the microhardness of the as-built TiB/Ti6Al4V composites is obviously improved. More interestingly, as the energy density increases, the microhardness of the as-built TiB/Ti6Al4V composites firstly increases and then decreases due to the synergy of grain size and different morphologies and distribution of TiB phases. The wear resistance of TiB/Ti6Al4V composites is far superior to that of Ti6Al4V alloy owing to the increased microhardness resulted from the uniform distribution of the hard TiB phase in the matrix.展开更多
A B_(4)C@amorphous carbon(APC)/Al matrix composite was fabricated by using hydrothermal carbonized deposition on chips(HTCDC)process and solid-state synthesis process.The microstructure and mechanical properties of th...A B_(4)C@amorphous carbon(APC)/Al matrix composite was fabricated by using hydrothermal carbonized deposition on chips(HTCDC)process and solid-state synthesis process.The microstructure and mechanical properties of the B_(4)C@APC/Al matrix composite were investigated.After HTCDC process,nano-B_(4)C particles(50 nm)and micron-sized B_(4)C@APC core-shell spheres with a diameter of 2μm were found in the composites.The microhardness of the micron-sized B_(4)C@APC spheres is 1.66 GPa,which is greater than that of theα-Al matrix(1.06 GPa).Dislocation accumulation is observed around the micron-sized B_(4)C@APC spheres,indicating that the micron-sized B_(4)C@APC spheres have a strengthening effect on theα-Al matrix.Due to the formation of micron-sized B_(4)C@APC spheres,the reinforcement of nano-B_(4)C particles into the composites is transformed from single-sized particle enhancement to bimodal-sized particle enhancement.The strengthening mechanism for B_(4)C@APC/Al matrix composites with bimodalsized particles of nano-B_(4)C and micron-sized B_(4)C@APC spheres were analyzed,which includes thermal mismatch strengthening generated by the mismatch of coefficient of thermal expansion(CTE)between micron-sized B_(4)C@APC core-shell spheres andα-Al matrix,Orowan strengthening produced by nano-B_(4)C particles,Hall-Petch strengthening and load transfer strengthening produced by the bimodal-sized enhancement from nano and microspheres.A relationship model between the yield strength(YS)increment and the conversion rate(x)of micron-sized B_(4)C@APC core-shell spheres was estimated.展开更多
文摘In order to improve the hardness and tribological performance of Ti6Al4V alloy,NiCoCrAlY-B_(4)C composite coatings with B_(4)C of 5%,10%and 15%(mass fraction)were fabricated on its surface by laser cladding(LC).The morphologies,chemical compositions and phases of obtained coatings were analyzed using scanning electronic microscope(SEM),energy dispersive spectrometer(EDS),and X-ray diffraction(XRD),respectively.The effects of B_(4)C mass fraction on the coefficient of friction(COF)and wear rate of NiCoCrAlY-B_(4)C coatings were investigated using a ball-on-disc wear tester.The results show that the NiCoCrAlY-B_(4)C coatings with different B_(4)C mass fractions are mainly composed of NiTi,NiTi_(2),α-Ti,CoO,AlB_(2),TiC,TiB and TiB_(2)phases.The COFs and wear rates of NiCoCrAlY-B_(4)C coatings decrease with the increase of B_(4)C content,which are contributed to the improvement of coating hardness by the B_(4)C addition.The wear mechanisms of NiCoCrAlY-B_(4)C coatings are changed from adhesive wear and oxidation wear to fatigue wear with the increase of B_(4)C content.
基金Projects(51775366,51805358)supported by the National Natural Science Foundation of ChinaProject(20130321024)supported by the Key Science and Technology Program of Shanxi Province,China。
文摘B4C/6061Al composites reinforced with nano-to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering(SPS)and hot extrusion and rolling(HER),followed by T6 treatment.The microstructural evolution and mechanical properties were investigated.Results showed that the status of B4C particles changed from a network after SPS to a dispersion distribution after HER.The substructured grains reached 66.5%owing to the pinning effect of nano-sized B4C,and the grain size was refined from 3.12μm to 1.56μm after HER.After T6 treatment,dispersed Mg_(2)Si precipitated phases formed,and the grain size increased to 1.87μm.Fine recrystallized grains around micro-sized B4C were smaller than those in the areas with uniform distribution of nano-sized B4C and Mg_(2)Si.The stress distributions of as-rolled and heated composites were similar,considering that the T6 heat treatment was only effective in eliminating the first internal stress.The Vickers,microhardness,and tensile strength of as-SPSed composites were greatly improved from HV 55.45,0.86 GPa,and 180 MPa to HV 77.51,1.08 GPa,and 310 MPa,respectively.Despite the precipitation strengthening,the corresponding values of as-heated composites decreased to HV 70.82,0.85 GPa,and 230 MPa owing to grain coarsening.
基金financially supported by the National Research Foundation of South AfricaThe National Laser Centre,CSIR,Pretoria,South Africa,is appreciated for laser facilitythe support from Tshwane University of Technology,South Africa
文摘Nb and Ti-13 Nb powders were used for improving the surface of Ti6Al4 V alloy.The deposition of the powders was carried out at various laser powers.The scanning electron microscopy（SEM）-EDS and optical microscopy were used for characterization.X-ray diffractometer（XRD） was used for analyzing the elemental composition and phase constituents.The hardness,wear and corrosion properties were achieved.The corrosion and the wear behaviours of the deposited layers were studied in a Hanks solution（simulated body fluid,SBF）.The microstructures of Nb coatings reveal the presence of orthorhombic,dendritic α″ and metastable β-Nb phases which produce uneven hardness with an average of HV 364.For Ti-13 Nb coatings,martensitic α′ and metastable β-Nb phases with an average hardness of HV 423 were observed.The resistance of wear on dry sliding of Ti-13 Nb coating is attributed to the increase in hardness.Experimental results indicate that deposition of Nb and Ti-13 Nb on Ti6Al4 V grossly reduces the mass fractions of Al and V in all coatings.In SBF,Nb reinforcement produces the best coating that reveals the best wear and corrosion resistances as compared with the substrate.Hence,this coating will perform best for orthopaedic implant material enhancement.
基金the National Natural Science Foundation of China(Nos.52174372,51974224)the Natural Science Foundation of Shaanxi Province,China(No.2020JM-047)the Fundamental Research Funds for Central Universities,China(No.xtr0118008)for their support。
基金Project(51271012)supported by the National Natural Science Foundation of China
文摘Anodized composite films containing Si C nanoparticles were synthesized on Ti6Al4 V alloy by anodic oxidation procedure in C4O6H4Na2 electrolyte. Scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) were employed to characterize the morphology and composition of the films fabricated in the electrolytes with and without addition of Si C nanoparticles. Results show that Si C particles can be successfully incorporated into the oxide film during the anodizing process and preferentially concentrate within internal cavities and micro-cracks. The ball-on-disk sliding tests indicate that Si C-containing oxide films register much lower wear rate than the oxide films without Si C under dry sliding condition. Si C particles are likely to melt and then are oxidized by frictional heat during sliding tests. Potentiodynamic polarization behavior reveals that the anodized alloy with Si C nanoparticles results in a reduction in passive current density to about 1.54×10-8 A/cm2, which is more than two times lower than that of the Ti O2 film(3.73×10-8 A/cm2). The synthesized composite film has good anti-wear and anti-corrosion properties and the growth mechanism of nanocomposite film is also discussed.
文摘The composition and structure of Ti 6Al 4V alloy plasma based ion implanted with nitrogen was investigated.The nitrogen depth distribution shows more antiballistic with distribution peak heightened with increased implantation time(dose),and more like a parabola at the low implantation pulse voltage.When implantation pulse voltage is increased,the implantation depth increased with the nitrogen distribution peak being deepened,widened and lowered somewhat.TiN,TiN+Ti 2N,or Ti 2N second phases were formed in the implanted layer.The relative percentage of nitrogen content in the form of TiN increases when going deeper into the implanted(TiN formed) layer.The increase of implantation pulse width and/or time is favourable for the formation of TiN rather than Ti 2N.It is unfavourable for formation of any nitrides when implantation pulse voltage is decreased to 30kV or less.Tiny crystalline particles (made mainly of Ti 2N and a smaller percentage of TiO 2 phases) of regular shapes such as triangle and tetragon, etc .(about 20 nm) are found distrbuted dispersively in the near surface region of samples implanted at the high implantation pulse voltage (75kV).
基金Project(2014CB644000)supported by the National Basic Research Program of ChinaProject(2016YFB0701301)supported by the National Key Technology R&D Program of China+1 种基金Projects(51371200,51671218)supported by the National Natural Science Foundation of ChinaProject supported by State Key Laboratory of Powder Metallurgy,Central South University,China
文摘A combinatorial approach was applied to investigating the influence of Fe content on the microstructures and properties of Ti6Al4V alloy.A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Fe alloys and annealed at 1000°C for 600 h to obtain a wide range of compositions.By combining electron probe micro-analysis(EPMA),scanning electron microscopy(SEM)and nanoindentation,the relationships between composition and microstructure as well as hardness were determined.It is found that after aging the Ti6Al4V5Fe sample contains reasonable(about 55%)volume fraction of fineαphase and shows the peak hardness among the Ti6Al4VxFe alloys.Therefore,it is a promising candidate for the development of titanium alloys.HAADF-STEM and XRD reveal that after quenching from the singleβphase field,the metastableα''lamellae form in the Ti6Al4V5Fe alloy,and on subsequent isothermal aging,theα''lamellae become coarse and act as precursors/preferential nucleation sites for the stableαphase.
基金supported by the National Natural Science Foundation of China (Grant No. 51471059)the China Postdoctoral Science Foundation (Grant No. 2014T70328)
文摘Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of the ingots. Furthermore, the optimal speed of the heating and the liquid stirring could overcome particle settlement caused by the density difference between the matrix and the particles. Ti6Al4V particles distributed uniformly in the composites with different particle contents. The average grain size decreased with the increase in the particle contents. The Ti6A14V particles bonded pretty well with the alloy matrix. In addition, there were some interfacial reactions in the composites. There were rod-like A13Ti phases at the interface. The precipitates extended from the particle surface to the matrix, and they might improve the interfacial bonding strength. The ultimate tensile strength, yield strength and elastic modulus were enhanced as the particle contents increased, and the elongation was much better than that of the same matrix material reinforced with SiC particles. Thus, the novel composites exhibit better comprehensive mechanical properties.
基金supported by the National Key R&D Program of China(Grant No.2017YFB0703100)the National Natural Science Foundation of China(Grant Nos.51822103,51801206,and 51731009)the Fundamental Research Funds for the Central Universities(Grant No.HIT.BRETIV.201902)
文摘A good joint of Ti Bw/Ti6Al4V composites and Inconel 718 alloys was obtained by Gas Tungsten Arc Welding(GTAW) heat transmission. The interfacial reaction mechanism of joint was investigated and analyzed in details. Owing to the heat input applied on the surface of Ti Bw/Ti6Al4V composites, a solid-state reaction layer appeared at the interface of Ti Bw/Ti6Al4 V composites to Inconel 718 alloys. The thickness of the reaction layer was obviously increased with increasing heat input.Developing of reaction layer mainly depended on the diffusion of elements of Ti and Ni through the interface during welding to form solid solutions and intermetallic compounds(IMCs). The reaction layer can be divided into Ti-rich zone(layer 2) and Nirich zone(layer 1). In Ni-rich zone, relatively coarse dendrites were the predominant, however, more brittle IMCs like Ti2Ni were found in the Ti-rich zone. Micro hardness of reaction layer was much higher than that of base metal. While a slight decrease of hardness was found between Ti-rich zone and Ni-rich zone due to the formation of TiNi.
基金the Civil Aerospace Pre-research Project:research on additive manufacturing of core components in the liquid rocket enginethe Fundamental Research Funds for the Central Universities(Nos.2019kfyXMPY005 and 2019kfyXKJC042)。
文摘In the present study, a series of in situ TiB/Ti6Al4V composites were fabricated using selective laser melting. The formability, microstructure evolution and mechanical properties of the as-built samples added with different contents of TiB2 were studied. It is found that the densification level is related to both the content of TiB2 and laser energy density. The added TiB2 reinforcement particle can spontaneously react with titanium and then form the TiB phase. The needle-like TiB phase tends to transform into dot-like particles with the decrease in energy density. Additionally, with the increase in TiB2 content, the TiB phase is coarsened due to the increased nucleation rate and more reactions. The grain morphology is found to largely depend on the translational speed of solid–fluid interface determined by the temperature gradient and cooling rate. Also, the microhardness of the as-built TiB/Ti6Al4V composites is obviously improved. More interestingly, as the energy density increases, the microhardness of the as-built TiB/Ti6Al4V composites firstly increases and then decreases due to the synergy of grain size and different morphologies and distribution of TiB phases. The wear resistance of TiB/Ti6Al4V composites is far superior to that of Ti6Al4V alloy owing to the increased microhardness resulted from the uniform distribution of the hard TiB phase in the matrix.
基金financially supported by the National Natural Science Foundation of China(No.51704087)the Natural Science Foundation of Heilongjiang Province(No.LH2020E083)。
文摘A B_(4)C@amorphous carbon(APC)/Al matrix composite was fabricated by using hydrothermal carbonized deposition on chips(HTCDC)process and solid-state synthesis process.The microstructure and mechanical properties of the B_(4)C@APC/Al matrix composite were investigated.After HTCDC process,nano-B_(4)C particles(50 nm)and micron-sized B_(4)C@APC core-shell spheres with a diameter of 2μm were found in the composites.The microhardness of the micron-sized B_(4)C@APC spheres is 1.66 GPa,which is greater than that of theα-Al matrix(1.06 GPa).Dislocation accumulation is observed around the micron-sized B_(4)C@APC spheres,indicating that the micron-sized B_(4)C@APC spheres have a strengthening effect on theα-Al matrix.Due to the formation of micron-sized B_(4)C@APC spheres,the reinforcement of nano-B_(4)C particles into the composites is transformed from single-sized particle enhancement to bimodal-sized particle enhancement.The strengthening mechanism for B_(4)C@APC/Al matrix composites with bimodalsized particles of nano-B_(4)C and micron-sized B_(4)C@APC spheres were analyzed,which includes thermal mismatch strengthening generated by the mismatch of coefficient of thermal expansion(CTE)between micron-sized B_(4)C@APC core-shell spheres andα-Al matrix,Orowan strengthening produced by nano-B_(4)C particles,Hall-Petch strengthening and load transfer strengthening produced by the bimodal-sized enhancement from nano and microspheres.A relationship model between the yield strength(YS)increment and the conversion rate(x)of micron-sized B_(4)C@APC core-shell spheres was estimated.
