Study On The Interface And Mechanical Properties Of SiC_f/Ti₂AlNb Composites

Continuous SiC fiber-reinforced Ti matrix composites are a new generation of ideal high temperature structural materials,which have high specific modulus,high specific strength,excellent corrosion resistance and fatigue performance,and have a broad application prospect in the field of aero engines.Ti₂AlNb alloy is a kind of O phase alloy which can be used in the range of 600℃～750℃.SiC_f/Ti₂AlNb composites are expected to be a candidate material for structural components such as drive shaft,integral blade ring and fan blade of aeroengine.In this paper,SiC_f/Ti₂AlNb composites were prepared by magnetron sputtering precursor wire method in combination with hot isostatic pressing process.The interfacial reaction,thermal stability,tens ile properties,fatigue properties and damage mechanism of SiC_f/Ti₂AlNb composites have been studied in this paper.The main research results are as follows:（1）In the process of hot isostatic pressing of SiC_f/Ti₂AlNb composites,the element diffusion formed Ti C reaction layer at the interface.The thermal exposure experiments were carried out at 650℃,700℃,750℃and 800℃for25h,100h,200h and 300h,respectively.The results show that the Ti C reaction layer was form by element diffus ion at the interfacial reaction layer during the hot isostatic pressing process,and the thickness of Ti C reaction layer increases with the increase of thermal exposure temperature and the time of experiment,and the Ti Si₂ and Nb Si₂ phases are formed by element diffusion near the interfacial reaction layer.The activation energy of interface of SiC _f/Ti₂AlNb composite is 24.27k J/mol,and this suggests that the interfacial reaction layer can maintain long-lasting stability at 700℃and below.（2）The tensile properties and fracture mechanism of SiC_f/Ti₂AlNb composite at room temperature and 750℃were studied.The results show that the tensile properties of SiC_f/Ti₂AlNb composite performed excellent at both temperatures,and the fiber gave a good reinforcement effect.During the tensile test at room temperature,cracks initiated in the matrix at first.With the increase of load,the crack length and number of matrix increase.The fracture surface is formed by the matrix and fiber fracture at the same time,and the internal damage of the composite material gradually aggravated,and the intersection of multiple sections leads to the instantaneous fracture of the composite material.The tensile fracture mechanisms at room temperature include:C coating layer/interfacial layer cracking,fiber primary fracture and fiber secondary fracture,matrix multiple fracture,fiber pull-out and fiber bridging.There are significant differences in fracture morphology and fracture mechanism between high temperature tensile fracture and room temperature.The fracture mechanism of high temperature tensile fracture includes multiple fracture of interfacial reaction layer,multiple fracture of fiber,fiber pull-out,W-core"pull-out",fiber/matrix interface debonding and matrix fracture.（3）The fatigue behavior and fracture mechanism of SiC_f/Ti₂AlNb composite at room temperature and 750℃under different cyclic load were studied.The results show that the fatigue life of SiC_f/Ti₂AlNb composite at room temperature and high temperature decreases with the increase of cyclic load.The fatigue crack initiation sites of SiC_f/Ti₂AlNb composite are mainly the surface crack initiation,the fiber crack initiation,the matrix crack initiation,and the fiber and matrix interface crack initiation.When the fatigueσ_max≥1300MPa at room temperature,the fatigue failure of composite is dominated by fiber fracture.At medium cyclic load（1000-1200MPa）,the failure of composite was dominated by fiber fracture and matrix fracture.Whenσ_max is below 900MPa,the fatigue failure of composite was mainly controlled by fiber bridging mechanism.The main failure mechanism of high temperature fatigue was fiber accumulation damage and fracture.