Prepare SiCp(in Situ CNT) Reinforced Aluminum Matrix Composites And Study On Its Properties

Micro-sized particle reinforced aluminum matrix composites?SiCp/Al?,which have high specific strength?high specific modulus and the integration of structural and functional characteristics,have a great potential application in the fields of aerospace,weapon equipment and transportation and so on.For the pursuit of better performance of SiCp/Al composites,increasing the content of SiCp can further enhance the strength and modulus,but a sharp decline in plastic toughness is occurring at the same time.With the discovery of ultra-high performance reinforcement such as carbon nanotubes?CNT?,it is theoretically possible to obtain CNT reinforced aluminum matrix composites with better properties.However,uniformed dispersion of CNT in composites is very difficult due to its nano-sized effect.SiCp?CNT?were prepared by in-situ growth of CNT on the surface of micro-sized SiCp,and then mixed with Al matrix.CNT not only achieve homogeneous dispersion in Al matrix with the help of SiCp,but also act as synergetic reinforcements,which provides a new idea for the design particle reinforced aluminum matrix composites.Based on the above idea,we fabricated hybrid reinforced aluminum matrix composites with in-situ growth of CNT on the surface of SiCp.At first,SiCp?CNT?hybrid reinforcements were prepared by chemical vapor deposition?CVD?.Then,SiCp?CNT?/Al composites were fabricated by powder mixing,hot pressing and hot extruding.The effect of CVD parameters on the morphology and structure of the SiCp?CNT?hybrid reinforcements and its influence on the properties of SiCp?CNT?/Al composite were systematically studied.In order to further improve the mechanical properties of composites,SiCp?CNT?/6061Al composites were prepared by using 6061Al powders as matrix.The effects of particle size ratio about reinforcement and matrix on the properties of the composites were investigated,and the influence of SiCp?CNT?hybrid reinforcement on the interfacial properties of the composites were calculated and characterized.In addition,for acquiring composites with excellent damping properties and good mechanical properties simultaneously,the damping capacity of SiCp?CNT?/6061Al composites were also analyzed.The major results are listed as follows:1.Nano-sized Ni catalyst particles were coated on the surface of SiCp by deposition and precipitation method firstly.And then,SiCp?CNT?hybrid reinforcements were prepared by catalytic pyrolysis of CH₄ gas using CVD.Effects of reduction temperature,catalyst content,reaction temperature,reaction time and reaction gas ratio on the morphology and structure of SiCp?CNT?were systematically studied.The results show that the deposition and precipitation method is suitable for the preparation of nanoparticles on the surface of micro-sized particles.The Ni particles obtained on the surface of SiCp are spherical and the particle size is between 10³0nm at 400?reduction of 2h,which satisfies the requirement of synthesized CNT.The CNT synthesized at the Ni content less than 10%,the ratio of V_Ar:V_CH4:V_H2 of 6:1:1,catalytic temperature of 700?and catalytic time of 30 min,has high purity and suitable size.Moreover,SiCp?CNT?hybrid reinforcements with controlled content and morphology can be obtained by controlling these parameters,which lays a foundation for subsequent preparation of hybrid composites.2.With SiCp?7?m?as carrier,SiCp?CNT?were prepared and mixed with pure Al powder?10?m?as raw material,then SiCp?CNT?/Al composite was fabricated by hot pressing and hot extruding.Effects of parameters about powder mixing,hot pressing and hot extruding on the properties of the composites were systematically studied.The results show that the SiCp?CNT?/Al composite fabricated at rotating speed of 200r/min,mixing time of 60min,hot pressing temperature of 400?and extrusion ratio of 22.5,extrusion rate of 2mm/s and extrusion temperature of 600?has compact microstructure and reinforcements are homogeneous distribution.SiCp?CNT?/Al composite reinforced with SiCp?CNT?and SiCp/CNT/Al composite reinforced with SiCp and CNT at the same time were prepared.Compared with SiCp/CNT/Al composite,SiCp?CNT?/Al composite not only have further improvement in strength and modulus,but also have better ductility,which indicated that SiCp and CNTplay a synergistic enhancement effect.3.Effects of different contents of SiCp and CNT on the morphology of hybrid reinforcement and the microstructure and properties of SiCp?CNT?/Al composite were investigated by adjusting the content of CNT in SiCp?CNT?.The results show that SiCp?CNT?hybrid reinforcement has a good hybrid structure when the content of CNT in SiCp?CNT?is 6wt.%,and it can be well distributed in the composites having a good interface with the matrix.Compared with Al matrix,the SiCp?CNT?/Al composite fabricated with 16wt.%SiCp and 1wt.%CNT exhibited the best enhancing effects in tensile properties,such as elastic modulus,yield strength and tensile strength were 96 GPa,120MPa and 201MPa,increasing by 35%,52%and 74%,respectively,4.SiCp?CNT?/6061Al composite was fabricated by using 6061Al as matrix to further improve the properties of composite and meet the practical requirements.Effects of the size of SiCp on the morphology of SiCp?CNT?hybrid reinforcement and the tensile properties of SiCp?CNT?/6061Al composite were investigated by using SiCp?2.5?m,7?m,13?m?.The effect of SiCp?CNT?on the interfacial properties is compared with that of single SiCp enhancement by theoretical calculation and nanoindentation experiment.The results show that 13?m and 7?m sized SiCp?CNT?can be mixed uniformly with 18?m sized 6061 Al powder,which has a good enhancement effect in the composites.The mechanical properties of 7?m sized SiCp?CNT?reinforced 6061Al composites exhibited the best enhancing effects in modulus and tensile strength of 97GPa and 428MPa,respectively,and the plasticity of the composites was also improved by 10%compared with single SiCp reinforced composite.In the SiCp?CNT?/6061Al composite,CNT is mainly distributed at the interface between the SiCp and the matrix,which leads to the increase of the size of dislocation hardening zone and the enhancement of dislocation strengthening and strain hardening.Therefore,the modulus and strength of composite were further enhanced.The presence of CNT also enhances the interfacial adhesion between SiCp and 6061Al matrix,delaying the interfacial cracking and hindering the process of crack propagation.Therefore,SiCp?CNT?hybrid reinforcement can improve the plasticity of SiCp reinforced composites.5.The damping capacity of matrix and composites at different temperatures and different frequencies was studied by using multifunctional internal friction equipment.The results show that SiCp?CNT?/6061Al composite exhibits the best damping capacity at room temperature because CNT have good intrinsic damping.With the increase of temperature,the damping capacity of SiCp?CNT?/6061Al composite increases more significantly due to the introduction of a large number of interfaces with the addition of the reinforcement.And with the increase of frequency,the material damping capacity is better.In this paper,based on the idea of in-situ micro/nano hybrid enhancement,the fabrication process and the mechanism of synergistic enhancement of SiCp?CNT?reinforced aluminum matrix composites were proposed and studied in detail.The fabricated SiCp?CNT?reinforced aluminum matrix composites not only have better mechanical properties than SiCp/Al composites,but also have better damping properties.In order to further improve the strength and plasticity of particle reinforced aluminum matrix composites,in-situ micro/nano hybrid reinforcement provides a very good solution,and has a broad application prospects.