Research On Process And Mechanism Of Diffusion Bonding DD3 Nickel-based Superalloy To Ti₃AlC₂ Ceramic

DD3 nickel-based superalloy is a potential candidate for the hot end of aeronautics and astronauticshas due to its excellent high temperature performance and low manufacturing cost.Ti₃AlC₂ ceramic is a novel nanolaminates,the characteristics of the structure makes the physical performance advantageous.In order to exploit the strength of the performance and broaden their application areas,it is of great significance to connect the DD3 to Ti₃AlC₂,which is also the starting point of this study.Considering the grerat difference of physical properties between DD3 and Ti₃AlC₂,we plan to join these two materials by diffusion bonding method.The DD3 and Ti₃AlC₂ were diffusion bonded using Ni interlayer,and the formation mechanism of the joint were analyzed.The diffusion behavior of elements in DD3 was analyzed using the first principles method.The formation tendency of vacancy in Ti₃AlC₂ was calculated.The influence of Ni substitution behavior on system stability was studied.The residual stress in the joint was simulated to explain the strengthening mechanism of the interlayer.The Ni/TiAl/Ti/Ni interlayer was adopted in diffusion bonding of DD3 and Ti₃AlC₂.The direct diffusion bonding of DD3 alloy to Ti₃AlC₂ ceramic was conducted and the interface morphology and formation mechanism of the joint were studied.The diffusion of Ni in DD3 alloy to Ti₃AlC₂ ceramic promoted the formation of joint.The enrichment of alloy elements adjacent to the DD3 led to a stepped transition in the interface,which could weaken the interfacial bonding of the joint,and the shear strength was only 38.6MPa.The DD3 and Ti₃AlC₂ were diffusion bonded using Ni interlayer.The formation mechanism of interface structure was analyzed.The Diffusion Zone I was formed due to the diffusion of Al and Ti from the DD3 side.When the bonding temperature was low,the Al atom and the Ti atom formed a solid solution with a gradient content.At the Ti₃AlC₂ side,Diffusion Zone II formed due to the elements interdiffusion between Ti₃AlC₂ and Ni.The ?'-Ni₃?Al,Ti?formed adjacent to Ni.On the other side,the decomposition of Ti₃AlC₂ cintributed to the formation of Al Ni2Ti+Ti C.In addition,Al Ni2Ti?111?//Ti C?111?and Al Ni2Ti[1 10]//Ti C[1 10].The effect of diffusion bonding temperature on the DD3/Ti₃AlC₂ joint was analyzed,and significant defects were occurred at a high or low temperature.Adopted with ABAQUS finite element method,the residual stress in the DD3/Ti₃AlC₂ joint was analysed and changes law without interlayer and with Ni interlayer were discussed.The diffusion behavior of elements in DD3 was analyzed,and the diffusion coefficient of elements in DD3 was calculated.The self-diffusion of Ni in DD3 follows the displacement mechanism.The vacancy formation energy is 1.644 e V,the vacancy transfer energy is 1.069 e V and the diffusion activation energy is 2.713 e V,respectively.The self-diffusion coefficient of Ni was calculated.The diffusion of Al and Ti in the ?' phase follows the five-frequency model.The diffusion activation energy of Al and Ni is 3.003 e V and 3.035 e V,respectively.The formation energy of vacancy and anti-position atomic defects were calculated simultaneously.Results have shown that the concentration of anti-position atomic defect is the highest and that of the Al vacancy is the lowest.Afterwards,the diffusion of Ni in the ?' phase is promoted due to the presence of anti-position Al atomic defect.The calculated diffusion coefficient ratio of Al and Ti in the ?' phase is 0.17 to 0.26.The lattice parameters,volume modulus,electronic structure and lattice vibration behavior of Ti₃AlC₂ ceramic have been simulated in detail using first principles method.The results of electronic structure and lattice vibration behavior showed that the excellent electrical conductivity of Ti₃AlC₂ ceramic is mainly contributed by Ti atoms.In addition,a better thermal conductivity was obseverd in the direction of c-axis.The binding energy and formation energy of the perfect unit cell of Ti₃AlC₂ and the single vacancy system at different atomic layer positions were calculated.It is found that formation energy of Al vacancy was-7.869 e V.With the lowest defect formation energies,Al vacancy was considered to be the most easily formed defect in Ti₃AlC₂ ceramic.The Ni substitutions at different atomic layer of Ti₃AlC₂ are introduced.The Ni atoms are most likely to be observed on Al sites due to the lowest defect formation energy?1.369 e V?.Besides,it was found that the substitution of Ni atom weakened the stability of the system.The diffusion bonding of DD3 alloy and Ti₃AlC₂ ceramic using Ni/TiAl interlayer was studied.The residual stress concentrates between the Ti₃AlC₂ ceramic and TiAl interlayer,which was responsible for the crack of the joint.In order to optimize the interface combination of adjacent to Ti₃AlC₂ ceramic,diffusion bonding with TiAl/Ni interlayer,TiAl/Ti/Ni interlayer and TiAl/Zr/Ni interlayer were designed,respectively.Results showed that a optimal property performance was obtained when using TiAl/Ti/Ni interlayer.Besides,the residual stress in the joint concentrated near the Ti₃AlC₂ by adding different interlayers.As a result,fracture occured at the Ti₃AlC₂ side which could affect the properties of the joint.The variations of residual stress applied with different interlayers were calculated by ABAQUS method,and the effect of interlayer on the properties of DD3/Ti₃AlC₂ joint was revealed.A good bond was obtained between the DD3 alloy and Ti₃AlC₂ ceramic using Ni/TiAl/Ti/Ni interlayer.Different interlayers as well as outer end surface of DD3 alloy were both taken into consideration?Ni/TiAl/Ti/Ni interlayer and DD3 alloy with the other outer end surfaces of {110} was adopted to diffusion bonding with Ti₃AlC₂.The maximum shear strength of the DD3/Ti₃AlC₂ joint reached 98.2MPa,which was 14% higher than that of the joint with Ni interlayer.