In-situ Synthesis Of Carbon Nanophases In Aluminum Matrix And Mechanical Properties Of Their Composites

Aluminum matrix composites have been widely used in the fields of aerospace,and transportation due to its high specific strength,specific modulus,and excellent electrical and thermal conductivity properties.Carbon nanotubes(CNT)and graphene(GN),as two of typical carbon naonophases(CNP),are ideal reinforcements for aluminum matrix composites owning to its excellent mechanical and physical properties.However,the problems of agglomeration,formation of brittle compounds and weak interfacial bonding hinder the development of the composites by traditional ex-situ methods,which is detrimental to fulfill the performance of CNP.Therefore,it is a great challenge to achieve favorable dispersion and interfacial bonding of CNP in aluminium matrix by exploring new preparation methods in order to obtain high performance of aluminium matrix composites.In this paper,one-dimensional CNT and two-dimensional carbon nanosheets(CNS)as a reinforcement for aluminum matrix composites were respectively in-situ synthesized by chemical vapor deposition combined with powder metallurgy method.Basing on this,three-dimensional network-like graphene nanosheets(GNS)modified by metal or ceramic nanoparticles(NP)as reinforcements for aluminium matrix composites(NP@GNS/Al)were prepared.The microstructure,mechanical properties,interfacial bonding and strengthening mechanism of CNP reinforced aluminium composites were discussed.The main contents and results are shown as follows:(1)CNT was in-situ synthesized on aluminium powder by using Ni as catalyst,acetylene as carbon source via chemical vapor deposition method.CNT/Al composites were prepared by powder metallurgy route.The effects of catalyst content and temperature on the morphology of CNT,and the microstructure and mechanical properties of CNT/Al composites were studied.It was found that CNT was synthesized on aluminium powder by using 1wt.%Ni as catalyst at 600°C with uniform dispersion,well crystallinity and high purity.Tensile strength of the composites increases first and then decreases with the increase content of CNT.When 1.5 vol%-CNT was added,the tensile strength was 191 MPa,?75%strengthening efficiency compared to that of pure aluminum.(2)CNS was in-situ synthesized on aluminium powder by using sucrose as carbon source via high temperature pyrolysis.Then CNS/Al composites were prepared by powder metallurgy method.The effects of temperature and time on the morphology of CNS,and the microstructure and mechanical properties of CNS/Al composites were studied.It was found that a high graphitized CNS was synthesized on aluminium powder at 600°C keeping for 60 min.The compressive strength and tensile strength of the composites increase first and then decrease with the increase of CNS content.When 1.5 vol%-CNS was added,the compressive yield strength of the composites was 150 MPa,nearly 1.5 times higher than that of pure aluminium.It was also higher than that of CNT with the same volume fraction.In addition,Al₄C₃was formed on Al-C interface during annealing.The output of Al₄C₃ increases with the increase of annealing temperature and time.When the annealing temperature is600°C with a heating time of 30 min,the tensile strength of the composite is 245MPa,?93%strengthening efficiency compared to that of pure aluminium.(3)Three-dimensional network-like graphene nanosheets(GNS)modified by Ni,Cu and Al₂O₃ nanoparticles(NP)as reinforcements for aluminium matrix composites(NP@GNS/Al)were prepared respectively.The effects of catalyst content,carbon source content,and temperature on the morphology of NP@GNS,and the microstructure and mechanical properties of NP@GNS/Al composites were studied.It was found that Ni@GNS and Cu@GNS can be synthesized on aluminium powder at 600°C by using Ni and Cu as catalysts,epoxy resin and methane as carbon sources,respectively.Al₂O₃@GNS can be synthesized by a Na Cl template associated with Al₂O₃ catalyzed solid carbon source strategy at 700°C,which has stable structure and crystallization.The addition of NP could improve the wettability of Al-C interface,increasing the interfacial bonding and enhancing the mechanical properties of the composites significantly.The tensile strength of the composites containing 1.0 vol%-Ni@GNS,1.5 vol%-Cu@GNS and 1.0 vol%-Al₂O₃@GNS were 266 MPa,315 MPa and 359 MPa,respectively.(4)The effects of CNP and NP-modified CNP on the interfacial structure and mechanical properties of the composites that fabricated by chemical vapor deposition-powder metallurgy method were studied combining the experimental results and first-principles study.It was found that the formation of Al₄C₃ and the additon of Ni,Cu and Al₂O₃ on Al-C interface can increase the adhesion work of the interface,increasing the interfacial bonding and improving the properties of the composites.The main strengthening mechanism of CNT/Al and CNS/Al composites are the load transfer,dislocation strengthening with some contributions of grain refinement that caused by CNP and Al₄C₃,while the strengthening mechanism of NP@GNS/Al composites are not only the load transfer and dislocation strengthening that caused by GNS,but also benefits from the synergistic strengthening of NP and GNS.