C/C Composite Material And C_f/SiC Composite Material Diffusion Bonding Technology And Mechanism Research

As two kinds of important high temperature structural materials,though carbon-carbon(C/C)composites and carbon fiber reinforced silicon carbide(Cf/SiC)composites have homologous advantages of low density,high ratio strength,high temperature resistance and ablation resistance,they also have their own outstanding properties.In addition,these two materials,with high productioncost,long productioncycle and poor machinability,are difficult to be manufactured into large scaleandcomplex structural parts.Therefore,If C/C composites and Cf/SiC composites can be joined to form suitable composite components,the advantages of these two materials can be effectively combined andthe scope of their application can be further extended.In this paper,C/C composites and Cf/SiC composites were joinedby transient liquid phase(TLP)diffusion bonding using Ti/Ni/Ti composite foil as interlayer and hot pressure diffusion bonding technology using Ti-Si-C mixed powder as interlayer,respectively.The as-prepared joints were characterized and analyzed by scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),X-ray diffraction(XRD),universal testing machine and other testing techniques.The formation process of the joints obtained by two different bonding methods was explored.The main research contents and results are as follows:The typical interface structure of C/C-Cf/SiC composite joint obtained by TLP diffusion bonding using Ti/Ni/Ti composite foil as the interlayer can be formed as following:C/C composite/TiC layer/residual Ti layer/Ti-Ni compound/TiC layer/Cf/SiC composite.With the increase of bonding temperature and the prolongation of holding time,the room temperature shear strength of the joints first increases and then decreases.The maximum average room temperature shear strength of the joints is46.5MPa under the process parameters of 1010℃,30 min and 5 MPa.The fracture of the joint mainly occurs near the TiC region formed by the reaction between the C/C composite and the intelayer.In order to improve the working temperature of the joint,Ti-Si-C mixed powder was used as the interlayer to successfully join the C/C composites and Cf/SiC composites by hot press diffusion bonding.The typical interface structure of C/C-Cf/SiC composite jointcan be formed as following:C/C composite/TiC-SiC-Ti3SiC2 mixed layer/Cf/SiC composite.The maximum room temperature shear strength of C/C-Cf/SiC composite joints was 11.1 MPa,which was obtained under the process parameters of 1550℃,60 min and 30MPa.The high brittleness,low strength and poor toughness of the ceramic interlayer are main reasons for the lower strength of the powder interlayer joint.The Si powder in the interlayer could melt rapidly and flow out of the interlayer,resulting in the decrease of joint strength and the increase of joint brittleness.The fracture of the joint mainly occurs near the area of titanium carbide or silicon carbide.The joiningprocess of the joint can be proposed by analyzing the element distribution and phase composition of the joint.A concept formation model of C/C-Cf/SiC composite joint is presented by TLP diffusion bonding.The formationprocess of the joint is divided into four steps:the surface contact stage of the joint;the diffusion andinitial reaction in joint;the formation stage of joint interface;the homogenization of joint composition and complete forming of reaction phase.Simlarly,the hot-pressure diffusion bonding process of C/C-Cf/SiC composite joints is divided into three stages:the physical contact stage;the reaction and diffusion stage;the joint complete forming stage.