Microstructure And First-principles Study On Interface Of SiC/Al Matrix Composites

Silicon Carbide Particulate Reinforced Aluminium Matrix Composites(SiCp/Al)have shown wide application prospects in aerospace,automobile,advanced weapons,electronic packaging and other fields due to their excellent comprehensive properties such as low density,high specific stiffness,high wear resistance,low thermal expansion coefficient,high thermal conductivity,good corrosion resistance and so on.The macro-mechanical properties of the composites depend on their micro-structure and micro-deformation characteristics.As a medium between the reinforcement and matrix,the interface can effectively transfer loads from the matrix to the reinforcement.At the same time,the bonding strength is also a link between the micro-characteristics and macro-properties of the interface of composites.The interfacial bonding strength is affected by many factors,including the existence of stress,lattice matching,interfacial defects and so on.Therefore,exploring the interface bonding of composites has become an important issue to be solved urgently.It is necessary to carry out in-depth and systematic research on the interface problems with SiC/Al composites.In this study,SiCp/Al matrix reinforced composites with high performance were fabricated by powder metallurgy through high energy ball milling,unidirectional cold pressing,sintering and hot extrusion.By means of scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM),X-ray diffraction(XRD)and energy spectrum analysis,three typical interface structures between SiC and Al were found,including the clean interface,slightly reactive interface and amorphous interface.For the clean interfaces,three orientation relationships are observed,all of which are semi-coherent.The main components of the composites are 6H-SiC with hexahedral structure and Al with face-centered cube.Based on the microscopic measurement of the interface and the first principles,the interface models of SiC/Al were established.The interface structure,electronic structure and interface bonding properties of SiC/Al were studied.In the low exponential interface of Al,the interface energy of(111)surface is the lowest and the most stable.Among the clean interfaces formed by 6H-SiC/Al,6H-SiC(0001)/Al(111)and 6H-SiC(0001)/Al(001)are the two most easily formed interface configurations.The results show that the bonding strength between SiC and Al is higher than that between atomic layers in Al matrix.This makes it difficult for SiC/Al composites to fracture from the interface,and the fracture location is more likely to occur in the Al matrix near the interface.In addition,the tensile fracture location of the composites is related to the initial charge distribution near the interface,but the initial charge distribution does not completely determine the tensile fracture location.The results of several models show that when Al atoms at the interface fail to bond strongly with C or Si,the reconstruction of Al atoms near the interface may occur during the tensile process,resulting in the enhancement of tensile toughness.In order to study the electronic structure and tensile fracture properties of SiC/Al interface,the best bonding 6H-SiC(0001)/Al(111)interfaces have been specially studied.The C-terminated and Si-terminated models of 6H-SiC(0001)/Al(111)interfaces were established and compared.The results show that the weak interfacial bonding determines the basic tensile strength of the composites,but at the same time,the stronger interfacial bonding can improve the tensile properties of the composites.In the two kinds of termination,C-terminated interface has better interface combination.The interfacial bonding strength directly affects the properties of materials,and the interfacial defects will have a significant impact on the interfacial bonding.Therefore,some kinds of SiC/Al interface point defect models are constructed,and the point vacancy defects are specially studied.In SiC/Al composites,Al matrix is easy to form defects,but SiC defects are not easy.The results show that most of the interface vacancy defects weaken the bonding between the interfaces,and the weakening effect will weaken with the depth of the defects from the interface to the interior.Therefore,the vacancy defects which have a significant impact on the interface mainly exist near the interface layer.The defects weaken the interface bonding,but strengthen the tensile strength of the material.The calculation shows that when the interface bonding is weakened properly,the electrons lost by Al atoms at the interface are also reduced accordingly,which makes the atomic bonding in Al enhanced relatively.Meanwhile,the existence of interface Al defects is beneficial to the reconstruction of Al near the interface and to the enhancement of the tensile properties of the material.The results also show that the tensile properties of the composites are the best when there are C-point or Si-point vacancies in the SiC side interface layer.Although the existence of Al vacancies in the interface layer can enhance the interface bonding,Al is prone to reconstruct and the bonding energy obtained by interface Al vacancy defects is easily lost.The high strength and non-deformability of SiC make the effect of interface C or Si vacancy defects on Al remain unchanged.When their strong attraction to the interface is weakened properly,it is beneficial to the enhancement of metal bonding in the interface Al matrix and the improving of the tensile properties of the composites.