Interfacial Reactions And Properties In SiC_f/C/Ti17 Composites Effected By Texture Of Carbon Coatings

Continuous SiC fiber reinforced Ti matrix composite?SiC_f/Ti?was known as a desirable structural material of light-weight and high temperature resistant.And because of its high specific strength and stiffness,excellent creep and fatigue resistance properties,SiC_f/Ti has been considered to be the most promising candidate material for the next generation of high thrust ratio aeroengine in aerospace.However,due to the high chemical activity between SiC fiber and Ti matrix,violent interfacial chemical reactions were unavoidable during the manufacture and service process under high temperature of SiC_f/Ti,which would decrease its strength dramatically.So far the most common method to retard this problem was depositing C coating onto the surface of SiC fiber,the mechanism of interfacial reaction dominated by the microstructure of C coating has not been clear yet.In this work,two kinds of turbostratic carbon coatings with different texture were deposited on SiC fibers using single filament chemical vapor deposition by changing substrate temperature:920 and 1000?,labeled as C₉₂₀ and C₁₀₀₀,respectively,followed by coating Ti17 matrix,and then SiC_f/C₉₂₀/Ti17 and SiC_f/C₁₀₀₀/Ti17 composites were fabricated by hot isostatic pressing?HIP?.C₁₀₀₀possessed much stronger texture than C₉₂₀,evidenced by combined tests of X-ray photoelectron spectrum,Raman spectroscopy and transmission electron microscope?TEM?.Interfacial reactions of SiC_f/C₉₂₀/Ti17 and SiC_f/C₁₀₀₀/Ti17 composites were found to depend strongly on texture of turbostratic carbon coatings after HIP,revealing that C₁₀₀₀ with stronger texture could hinder the outward diffusion of C and inward diffusion of matrix elements more efficiently than C₉₂₀,which was elucidated by the results of scanning electron microscope,TEM and energy dispersive spectroscopy.Interdiffusion between C coating and Ti17 matrix resulted in the formation of C gradient distribution in interfacial reaction layer for both composites,in which the interfacial zone of fiber and matrix could be described as turbostratic C||amorphous C||fine-grained TiC||transition TiC||coarse-grained TiC,however,each sub-layer thickness was determined by the texture of C coating.Based on these results,the model of interfacial reactions dominated by texture of C coatings was proposed firstly.Then mechanical tests were carried out on these composites to discuss the affect of the texture of C coatings.Fiber push-out test has been used to characterize the interfacial strength,observing the interfacial strength of SiC_f/C₉₂₀/Ti17 with medium textured C₉₂₀ was stronger than SiC_f/C₁₀₀₀/Ti17.And the longitudinal tensile test showed that though both of the composites possessed fracture morphology with fiber pulled out,tensile strength of SiC_f/C₉₂₀/Ti17 was higher than SiC_f/C₁₀₀₀/Ti17.Also,thermal stability of the interfaces and the mechanism of the evolution of interfacial zones dominated by the high textured C₁₀₀₀000 has been investigated through thermally exposing SiC_f/C₁₀₀₀/Ti17 for 450?/600 h,800?/600 h and 1100?/2 h,respectively.