Study On The Microstructure And Consolidation Behavior Of SiCp/Al Composites Prepared By Severe Plastic Deformation

As a kind of structural and functional materials, SiCp/Al composites is widely used because of its low-cost and high-performence, and it has been the focus for people. The composite material is commonly found that it has low-compactness, poor performance, high-cost and need for secondary processing and many disadvantages or limitations in traditional preparation technology. For these problems from the traditional preparation process, researchers introduce the severe plastic deformation into the preparation of composite materials in recent years, and prepare the particle reinforced metal matrix composite with a high density, high strength and toughness, excellent thermal and dimensional stability and other properties. The interface of composite materials has been the focus of research, in particular to the interfacial bonding between reinforcement and metal matrix. As we know, the solid interdfacial bonding will have a great impact on the density, microstructure and mechanical properties of metal matrix composites.Severe plastic deformation (SPD) can be consoled SiCp/Al composites in high density, especially SiC-Al interface can be produced good interfacial bonding at a lower deformation temperature. With high efficiency and low cost, the toypical SPD like high pressure torsion (HPT) and equal channel angular pressing and torsion (ECAP-T) are selected in the subject. The microstructure morphology in metal matrix and the consolidation behavior in mixed powders (the bonding behavior in SiC-Al interface) of SiCp/Al composites prepared by these two process in the same deformation temperature (250℃), the same SiC particle content (10 wt.% SiC) are studied in the subject.In this paper, firstly, the microstructure morphology in Al matrix of SiC/Al composites prepared respectively by HPT in different turns (4 and 8 turns) and ECAP-T in different passes (1,2 and 4 passes) are observed by transmission electron microscrope (TEM). It is found that, the density of lattice defects in Al matrix, like vacancy, dislocations and grain boundaries, is increasing with the increasing deformation. Secondly, the SiC-Al interface is analyzed by line scan in Energy Dispersive Spectroscopy (EDS). It is found that, the evident phenomenon of element interdiffusion exists between Al matrix and SiC reinforcement, and SiC particles breakage generates new SiC-Al interface. Using EDS point analysis, electron diddraction pattern analysis and X-ray photoelectron spectroscopy (XPS) analysis, the material composition in interfacial region is researched. And the non-neoplastic SiC-Al interface and new SiC-Al interface are observed by high-resolution TEM (HRTEM). The results show that, SPD can promote a protective interfacial reaction occurred between amorphous SiO2 layer in SiC particle surface and Al matrix, and the interfacial production is Al2O3; With the deformation increases, the degree of element interdiffusion and the interfacial reaction are increasing, the interfacial bonding is more solid; but the effect of interfacial bonding in new SiC-Al interface is bad because of its mechanical connection.In the basis of reasonable and scientific theoretical hypothesis, the thickness of SiC-Al interfacial layer with different deformation is calculated by TEM, and Al of actual average diffusion coefficient can be calculated in HPT and ECAP-T respectively. It is found that, Al of actual diffusion coefficient in HPT and ECAP-T is respectively higher 1017 and 1016 than Al of theoretical diffusion coefficient. Through kinetic analysis, the reasons for this sharp atomic diffusion are:in the process of HPT and ECAP-T, the severe shear deformation makes the temperature in SiC-Al interface higher, and results in high density of lattice defects in Al matrix, like vacancy, dislocations and grain boundaries.In this paper, the consolidation behavior in SiC-Al interface of SiCp/Al composites prepared by two typical SPD (HPT and ECAP-T) are studied from multiple angles (interfacial atomic diffusion, the interfacial layer material, the interfacial reaction type, the calculation of Al practical and theoretical diffusion coefficient). With the basis of analysis for the aluminum matrix microstructure morphology, the influence of SPD on the mechanism of the consolidation behavior of SiCp/Al composites is illustrated.