Study On Continuous Carbon Fibres Reinforced Aluminum Matrix Composites Subjected To Interfacial Modification

Owing to their excellent properties,such as low density,high elastic modulus and strength,excellent dimensional stability,and low thermal expansion coefficient,continuous fiber-reinforced aluminum matrix composites（CFR AMCs）have great potential for application in the manufacturing of high-performance equipment,such as airplane tails and marine oil storage tanks;in many applications,these composites have the potential to be used as alternatives to various titanium alloys.Compared wit h ceramic fibers and high-strength metal wires,carbon fibers（CF）represent a superior reinforcement for use in CFRAMCs for structural applications owing to their excellent properties,such as excellent high-temperature strength and stability and low density.Due to their low manufacturing cost and excellent mechanical properties,basalt fibers（BF）,which are used in the reinforcement of Al matrix composites,are useful in the manufacturing and promotion of low-cost,high-performance CFRAMCs.Harmful interfacial reactions between the reinforcement and matrix as well as mismatches in the bonding state between these two elements often limit the extent of the strengthening effect of the reinforcements,which is the primary reason why the measured strength of composites is significantly lower than their theoretical strength.At present,interfacial modification is the most effective method for improving the physical and chemical compatibility between the reinforcement and the matrix at the interface between the two components.However,there are few works reporting the comparisons between the effectiveness of different coatings and depth optimization of the mechanical properties of CFRAMCs.In this study,BFs and CFs were used as reinforcement fibers,and an Al–Zn–Mg–Cu alloy was used as the matrix material;Ni–Co–P and SiC coatings were used to modify the fibers in the reinforced Al matrix composites;these composites were fabricated using vacuum hot-pressed sintered techniques.The microstructures of the co mposites were then characterized via scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffractometry（XRD）,and other techniques.The mechanical properties of the different composites were evaluated using a universal testin g machine.The structure–performance relationship between the coatings and mechanical properties and the effect of the type of coating used on the failure mechanism of composites were investigated;with the optimal interface modification,the hybrid reinfo rcing effects of particles and fibers were studied;this study may act as a reference for designing and manufacturing Al matrix composites that are both lightweight and strong.The primary findings and innovations demonstrated in this study are as follows:（1）Ni–Co–P coatings containing 20-wt%Co,70-wt%Ni,and 10-wt%P were prepared via electroless plating;CF/Al and（CF/Al（Ni–Co–P））were fabricated via a vacuum hot pressing sintering process at 580°C for 10 min.Generation of Al ₄C₃ was inhibited,and a multilayer interface phase was formed due to the presence of the Ni–Co–P coatings;CF/Al（Ni–Co–P）composites were found to have the highest tensile strength（690 MPa）,which was two times greater than that of the matrix alloy;the failure mode of the CF/Al（Ni–Co–P）composites was found to be accumulative fracture failure,fiber fracture,and fiber pullout.（2）Ni–Co–P coatings with a thickness of 0.4μm were obtained on the surface of BFs via electroless plating,and BF/Al composites with BF contents of 10,20,30,and40 vol%were fabricated using a low-temperature and high-pressure sintering process.the results show that the tensile strength of BF（Ni-Co-P）/Al is up to 360MPa and is superior to BF/Al and Al matrix,which is caused by several reasons:（1）the interface reaction between the BF and matrix was inhibited by Ni–Co–P;（2）Crack deflection occurs at the interface between BF and Ni-Co-P coatings,which induces that the failure mode changed from brittle fracture in BF/Al to accumulative fracture failure in BF（Ni–Co–P）/Al.（3）SiC coatings on the surface of the CFs were obtained via a polymer impregnation and pyrolysis process,and the SiC-coated CF-reinforced Al matrix composites（CF（SiC）/Al）and uncoated CF-reinforced Al matrix composites（CF/Al）were fabricated through the vacuum hot pressing sintering process at 580°C and 30MPa.The tensile strength of the SiC-coated CFs was up to 2800MPa,and the m-shape parameter value showed a small increase.The Mg element enrichment zone around the CF and harmful interface reactions were inhibited by the presence of SiC,and the obtained tensile strength of 590 MPa for the CF（SiC）/Al composites was superior to that of the matrix alloy and CF/Al composites;fiber pullout,fiber fracture,and crack deflection of microcracks were the primary failure mode in the case of the CF（SiC）/Al composites.（4）Fe Co Ni Cr Al high entropy alloy particles（HEA _p）and Ni–Co–P-coated CFs were selected for use as discontinuous reinforcements;HEAp-reinforced Al matrix composites（HEA_p/Al）and HEAp-and Ni–Co–P-coated CF-reinforced Al matrix composites（HEA_p-CF（Ni–Co–P）/Al）were fabricated via the vacuum hot pressing sintering process.A large quantity of dislocations was formed around the HEA _p due to a mismatch in the thermal expansion coefficient of the reinforcement and the matrix,and the HEA_p/Al composites with 10 vol%of HEA_p had the best mechanical properties.HEA_p-CF/Al（Ni–Co–P）with 10-vol%HEA_p and 30-vol%CF was found to have the highest tensile strength（705 MPa）,bending strength（620 MPa）,and fracture toughness(84 MPa·m^1/2),which are superior to reinforced composites that use a single reinforcement material;this improvement is induced by the synergistic strengthening effect of HEA_p and Ni–Co–P-coated CFs.In this study,we focused on the effect of interfacial structure on the mechanical properties of composites,and the effects of interface modification were as follows:（1）the harmful interfacial reaction that occurs between the reinforcement and matrix,structural damage,and associated performance degradation of the fibers with a composite can be inhibited using a coating layer.（2）The metallurgical bonding between the interface phase and the matrix can be beneficial for load transfer within a composite structure,and the nonmetallurgical bonding between the interface phase and the reinforcement can help suppress the diffusion of cracks within the reinforcement material.（3）mechanical properties of BF（Ni-Co-P）/Al composites are inferior to CF（Ni-Co-P）/Al composites,which is caused by difference of mechanical properties of fibres and interfacial microstructure,this indicates that BF/Al composites have research value and engineering significance.