Study On Mechanical Properties Of SiC_f/Ti₂AlNb Composites

Continuous SiC fiber reinforced titanium matrix composites have high specific modulus,high specific strength,good fatigue resistance and corrosion resistance along the fiber axis.Compared with traditional titanium alloys,TMCs components have a wide application prospect in the aviation field.Ti₂AlNb alloy is a kind of O-phase alloy which can be used for a long time at the highest 750℃.With continuous SiC fiber as the reinforcement and Ti₂AlNb alloy as the matrix,the prepared composite material is expected to become one of the required materials in aero-engine,and be applied to the structure of integral blade ring and fan blade.In this paper,SiC_f/Ti₂AlNb composite was prepared by magnetron sputtering precursor wire method and hot isostatic pressing process.The preparation of SiC_f/Ti₂AlNb composite,fiber/matrix interface element distribution,different fiber volume fraction chambers,high temperature tensile properties,different sample section diameter chambers,high temperature tensile properties,A comprehensive study on the tensile properties of different test temperature chambers and high temperature and their effects on the tensile fracture mechanism of chambers and high temperature was conducted.The main research conclusions are as follows:（1）Scanning electron microscopy（SEM）,electron probe（EPMA）and other instruments were used to analyze and characterize the microstructure and fiber/matrix interface of SiC_f/Ti₂AlNb composites.The results show that the fibers of SiC_f/Ti₂AlNb composites are arranged in a hexagonal uniform manner after hot isostatic pressing.The SiC fiber is tightly bound to the C layer,and the C layer is tightly bound to the reaction layer.The Si element in SiC_f/Ti₂AlNb composite is distributed in SiC fiber,C coating and reaction layer.C element is distributed in C coating,SiC fiber and reaction layer.Ti element is distributed inα₂ phase of matrix.Nb elements are mainly concentrated in the B2 phase of the matrix.Al element is distributed in theα₂ phase of the matrix.（2）The tensile properties of SiC_f/Ti₂AlNb composites with different fiber volume fractions are excellent at room temperature and high temperature,and the fibers show high strength.At room temperature,the reaction layer preferentially generates cracks,and the load continues to increase.The cracks in the reaction layer propagate into the matrix and expand to some extent in the matrix.Subsequently,the weak fiber breaks and the fractured fiber and matrix break to form a fracture surface.The load increases again,resulting in the intersection of multiple crack surfaces,which leads to the fracture of the composite material and the formation of macroscopic fracture.The tensile fracture mechanism at room temperature is as follows:reaction layer fracture,C layer/reaction layer interface debonding,fiber primary fracture,fiber secondary fracture,matrix fracture and fiber bridging.The high temperature performance of SiC_f/Ti₂AlNb composite decreases to a certain degree,and its fracture morphology and fracture mechanism are different from that at room temperature.The high temperature fracture mechanism includes:reaction layer multiple fracture,fiber multiple fracture,W core"pulling out",fiber pulling out,C layer/reaction layer interface debonding and matrix fracture.（3）The tensile properties of SiC_f/Ti₂AlNb composites with different section diameters in chambers and at high temperatures are evenly distributed,and the variation range of the properties in chambers and at high temperatures is small,indicating that the diameter of the sample has little influence on the tensile properties.The fracture mechanism of SiC_f/Ti₂AlNb composites with different section diameters in chamber and at high temperature does not change much,indicating that section diameters of samples have little effect on the fracture mechanism.（4）The properties of SiC_f/Ti₂AlNb composites were tested at different temperatures（room temperature,350℃,550℃and 750℃）.It was found that the tensile strength of SiC_f/Ti₂AlNb composites increased with the increase of temperature,but decreased at 750℃.The elastic modulus of SiC_f/Ti₂AlNb composites gradually decreased with the increase of temperature.（5）There are some differences in the fracture mechanism of SiC_f/Ti₂AlNb composites at different temperatures.With the gradual increase of temperature,the brittle properties of matrix and envelope gradually change from brittle fracture to ductile fracture.At room temperature,brittle fracture occurs in matrix,and brittle（mostly）and ductile（local）fracture occurs in envelope.At 350℃and 550℃,a mixed fracture mode of brittleness+toughness occurred in the matrix and envelope.At 750℃,ductile fracture occurs in the matrix and sheath.