C/C Composite Material And Ti₂AINb Alloy Transient Liquid Phase (TLP) Diffusion Bonding Process And Mechanism Research

C/C composites are often used as high-temperature structural parts in aerospace and other fields due to their light weight,high temperature strength,thermal shock resistance and ablation resistance.Ti2AlNb alloys can be used as thermal structure material for aircraft engine weight reduction and have received a great deal of attention.If the two materials can be bonded together and practical application,it will be able to play a large degree of the respective characteristics of the two materials and have great significance to expand the application of the two materials.In this paper,Ti-Ni-Nb interlayer were chosen to bonding C/C composites and Ti2AlNb alloys by transient liquid phase(TLP)diffusion bonding.In order to improve the performance of bonding joint,the C/C composites was performed by magnetron sputtering Cr coating and chemical vapor deposition SiC coating.The modified C/C composites were also be bonded with Ti2AlNb alloy.The bonding joints were analysed by scanning electron microscope(SEM),energy disperse spectroscopy(EDS),X-ray diffractometer(XRD),universal testing machine,etc.The micro structure and properties of the joints before and after surface modification of C/C composites were studied.The typical interface structure of C/C composite/Ti2AlNb alloy TLP diffusion bonding joints using Ti/Ni/Nb multilayer foils as interlayer were C/C composite/TiC layer/Ti-Ni compound+Ni-Nb compound/residual Nb layer/Ti-Al-Nb solid solution layer/Ti2AlNb base metal.The shear strength of the joints increased with the increase of temperature and then decreased,the maximum room temperature shear strength 8.41 MPa was achieved when the bonding temperature was 1040℃.The fracture of the joint mainly occured at the interface of C/C composite and TiC layer due to the difference of thermal expansion coefficient of C/C composite and Ti2AlNb alloy.In order to achieve better C/C composite/Ti2AlNb alloy joints,The modified C/C composites surface by the means of magnetron sputtering Cr coating and chemical vapor deposition SiC coating were studied.The results shown that,while the sputtering time reached to 60min,C/C composites surface was metalized apparently and it can be used to bonding with Ti2AlNb alloy.It can be seen that the interface of joint was loose and the mechanical properties of the joints made by magnetron sputtering Cr coating C/C composites was increased first and then decreased with the temperature increasing and the highest shear strength achieved to 2.23MPa when the bonding temperature was 1040℃.The fracture of joint mainly occured at the interface of Cr coating where Cr3C2 and TiC phase were detected.The morphology of chemical vapor deposition SiC coating C/C composites surface was whisker shape and the surface composition mainly was β-SiC,the preferred growth orientation surface was(111)crystal face of β-SiC.The typical interface structure of chemical vapor deposition SiC coating C/C composite/Ti2AlNb alloy joints were C/C composite/SiC coating+TiC layer/Ti-Ni compound+Ti-Ni-Nb solid solution/residual Nb layer/Ti-Al-Nb solid solution layer/Ti2AlNb alloy.The maximum shear strength was also achieved at 1040℃ and the value was 32.06MPa,the main phase at the fracture surface was SiC and a small quantity of TiC.SiC coating can effectively relieve the internal stress caused by the thermal expansion coefficient difference of C/C composites and metals.It can also form a better bonding layer with C/C composites.So the interface microstructure and the mechanical properties of chemical vapor deposition SiC coating C/C composites/Ti2AlNb joints were all enhanced apparently compared with the without modified C/C composites and modified by surface magnetron sputtering Cr coating.