Study On The Connection Behavior Of C_f/LAS Ceramic Matrix Composite With Ti60 Alloy

Cf/LAS composites have excellent properties such as high strength,high stiffness,low density and good wear resistance,and because of its ultra-low or even negative thermal expansion coefficient,it can be well applied in the field of precision aviation.Ti60 alloy is a kind of near-α type high-temperature titanium alloy made by increasing the content of Si element on the basis of IMl834 alloy and adding Ta element.It has many advantages such as high use temperature,low density,high strength,good thermal strength and thermal stability.In order to jointly exert the advantages of both Cf/LAS composites and Ti60 alloys,it is important to achieve a reliable connection between the Cf/LAS composites and Ti60 alloys.This paper first uses Ti Zr Ni Cu traditional brazing alloy to braze the Cf/LAS composites to the Ti60 alloy.Determine the optimum brazing temperature within a certain range,and based on the optimum temperature,determine the optimum holding time within a certain temperature range.The microstructure of the typical brazed joint(980°C/20min)is Ti60 alloy/Ti(s,s)+(Ti,Zr)2(Ni,Cu)+Ti(s,s)+(Ti C + Zr C + Ti2 O +Zr Si2 + Ti5Si3)/Cf/LAS composites.After changing the process parameters,the microstructure of the brazed joint will change accordingly.As the brazing temperature increases or the holding time lengthens,the area occupied by the brazing seam region I and III gradually decreases,and the area occupied by the region II gradually increases,which the Ti(s,s)reaction layer Gradually thickening,and the thickness of the discontinuous reaction layer produced by the reaction of the matrix and reinforcement in the Cf/LAS composite in region III with the brazing alloy increases significantly.The shear performance of a typical brazed joint is 47.27 MPa.Within a certain range,changing the brazing temperature or holding time will degrade the mechanical properties of the brazed joint.When changing the brazing temperature or holding time,the fracture position of the brazed joint also changes.In order to relieve some of the residual stress of the brazed joint and improve its performance,the Ti Zr Ni Cu+Cf composite brazing material was used to vacuum braze the Cf/LAS composite and the Ti60 alloy.Based on the above identified optimum brazing temperature and brazing holding time,the effects of Cf content in the composite solder on the microstructure,mechanical properties and fracture paths of the Cf/LAS composite/Ti Zr Ni Cu+Cf/Ti60 alloy brazed joints were investigated.Under the brazing parameters of 980°C/20 min,the Cf/LAS ceramic matrix composites and Ti60 alloy were brazed with Ti Zr Ni Cu+0.3wt%Cf composite brazing alloy.The typical interface structure obtained was: Ti60 alloy/Ti(s,s)+(Ti,Zr)2(Ni,Cu)+ Cf + Ti C + Zr C + Ti(s,s)+(Ti C + Zr C + Ti2 O + Zr Si2 + Ti5Si3)/Cf/LAS/composites.With the increase of the mass fraction of the reinforcing phase Cf in the composite brazing alloy,the microstructure of the braze joint interface changes,the eutecticstructure in the area I of the brazing seam is gradually refined,and the distribution gradually disperses;the Ti(s,s)reaction layer in the area II is thinned and scattered.the thickness of the discontinuous reaction layer formed on the Cf/LAS composite side gradually becomes thinner.The shear strength of the connector increases first and then decreases with the increase of the Cf content in the composite solder.When the Cf content is 0.3wt%,the shear strength is the largest,about 73.50 MPa.At the same time,the fracture path of the brazed joint also changes as the Cf content in the composite brazing alloy increases.In order to guide the practical application through theory,the brazing joint mechanism of Ti60 alloy and Cf/LAS composites was studied.Through comparative experiments,it was found that the Ti element dissolved in the Ti60 alloy and the perpendicular orientation of the carbon fiber to the joint surface in the Cf/LAS composite determined the interface structure of the brazed joint to be well formed and significantly affect the mechanical properties of the joint.The formation mechanism of brazed joints in the brazing process when using conventional Ti Zr Ni Cu and Ti Zr Ni Cu+Cf composite brazing alloys for Ti60 and Cf/LAS composites were analyzed.The influence of the amount of carbon fiber in the composite solder on the morphology and mechanical properties of the brazing joint was studied.