| Titanium matrix composite has the characteristics of high specific strength,high specific stiffness and excellent high temperature performance,which can meet the needs of aerospace vehicles and new automotive structural parts for lightweight and high strength.However,the main problems of traditional titanium matrix composites are as follows: with the increase of reinforcement content,the strength increases greatly,while the plasticity decreases significantly,and the volume fraction of reinforcement is larger.Traditional titanium matrix composites still have poor thermoelectric properties,which make it difficult to meet the functional requirements of materials in the new aerospace field.Graphene has excellent mechanical properties,good conductivity and thermal conductivity,and is considered to be a good alternative to traditional reinforcements.In this paper,graphene reinforced titanium matrix composites were prepared by semi-solid powder metallurgy with graphene as reinforcement.In this paper,titanium matrix composites were prepared by adding multilayer graphene sheets directly and synthesizing graphene nanosheets with glucose as carbon source.The first method is to add multi-layer graphene nanosheets directly into titanium matrix by mechanical ball milling,and disperse the multi-layer graphene nanosheets(GNPs)by ball milling and stirring to form composite powder with shell micro-nanostructure.Graphene reinforced titanium matrix composite bulk materials were successfully prepared by reactive hot pressing sintering technology.The mass fractions of GNPs were 0.075wt%,0.15wt%,0.30wt% and 0.60wt% respectively.The second idea is to use glucose as carbon source,and to mix and disperse glucose and titanium powder by ball milling and stirring,and then to successfully prepare composite materials by vacuum hot pressing sintering technology.XRD,OM,SEM,TEM,Atomic Force Microscope(AFM)and Raman spectroscopy were used to analyze the phase composition,microstructures,morphology and distribution of reinforcement and the interface structure of reinforcement/matrix of titanium matrix-graphene composite powder and heat-treated bulk materials.The main results are as follows:(1)Titanium-graphene composite powders were prepared by combining mechanical high-energy and low-energy ball milling with ionic liquids as ball-milling media,and the microstructure and structure of the composite powders were characterized.The results show that the dispersion and bonding of multilayer graphene nanosheets in the matrix are stable.Ti C wrapped on the surface of pure titanium by mechanical ball milling in situ and GNPs left behind have double effects of strengthening and assisting combustion.(2)The Hot-pressing Sintering Process of titanium matrix composites was optimized by the combination of sintering double logarithm theory and experiment.The results show that the hot-pressing process for preparing titanium matrix composites is sintering temperature 1200 C,hot-pressing pressure 25 MPa and holding time 2h.(3)The mechanical and electrical properties of different GNPs were studied under sintering temperature 1200 C,hot-pressing pressure 25 MPa and holding time 2h.The results show that when the content of GNPs is less than 0.3wt%,the properties of the composites increase greatly.The interface of the composites with graphene content of0.3wt% was studied.It was found that the mechanical properties of the composites reached the best when the content of GNPs was 0.3 Wt %.Its yield strength reached 985 MPa,tensile strength reached 1120 MPa,and the extension rate was 25.3 %.To add less GNPs,the goal of increasing strength and reducing plasticity was achieved.When the content of GNPs is not more than 0.3 Wt %,the performance of the composite material has been greatly increased.The interface of 0.3-wt % composite material with graphene content was studied.There was a continuous sandwich interface structure of Ti-GNPs-Ti in the interface area of the composite material,and there was a good interface binding between the multi-layer graphene and titanium matrix.(4)Graphene nanoparticles were synthesized directly in situ by vacuum hot pressing sintering using glucose as carbon source.Compared with pure titanium samples,the plasticity of titanium matrix composites is basically unchanged.At 1200 °C sintering,the yield strength of the composite material was 688.3 MPa,which was 547.5 MPa higher than the yield strength of pure titanium,and the elongation rate was 38.2 %,which was also higher than 35.6 % of pure titanium.The structure of the interface was studied and the graphene structure and titanium matrix were found.In the composite material,many dispersed nanoscale in-situ production Ti C and GNPs were found.The Raman spectrum found that GNPs were within three levels.In this paper,it is considered that these in-situ Ti C and GNPs are coordinated,thus easing the strong plasticity of the composites.(5)Using high resolution transmission electron microscopy to study the interface of the composite material,the results show that the interface of the composite material is Ti-GNPs,Ti C-GNPs and Ti-Ti C.The interface situation in each area is not the same.The Ti-GNPs are purely mechanical and Ti C-GNPs are chemically bound.In situ Ti C shows that nanoparticles are dispersed between the matrix and GNPs,which plays a very important role in improving the performance of composite materials. |
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