| 其他摘要 | Joining is a critical enabling technology, essential to widespread use of ceramics in many applications. Specifically, it allows manufacture of large, complex, multifunctional assemblies through the controlled integrations of smaller, simple, and more easily manufacture parts. Recently, the nanolaminate ternary ceramics Mn+1AXn have attracted extensive attention due to their combination of the excellent properties of metals and ceramics. Such unique properties make it possible to use them in structural components for high-temperature applications. However, up to now, its applications are limited because of the difficulty of the synthesis of bulk Mn+1AXn phase with big dimensions. Therefore, studies on joining of Mn+1AXn phase are significant for promoting their applications.
In the present work, we studied the bonding processes of Ti3SiC2/Ni, Ti3SiC2/ Al/Ti3SiC2, Ti3AlC2/Si/Ti3AlC2, and Ti3SiC2/Ti3AlC2. The following conclusions were drawn:
(1) Ti3SiC2 and Ni were successfully bonded to each other. During diffusion bonding, the interfacial reactions happened, and the total diffusion path of the joining is determined to be Ni/Ni31Si12+Ni16Ti6Si7+TiCx/Ti3SiC2+Ti2Ni+TiCx/Ti3SiC2. The growth of the reaction layer follows parabolic law, and the temperature dependence of the reaction constant, k, can be expressed as k = 1.68×10-4 exp(-118±12 kJ/RT) m/s1/2. The diffusion of nickel through the reaction zone toward Ti3SiC2 is the main controlling step in the bonding process. The joint obtained under the condition at 1000 oC for 10 min under 20 MPa has maximum shear strength of 121±7 MPa, which is close to the shear strength of Ti3SiC2.
(2) Joining of Ti3SiC2 ceramic via Al interlayer through transient liquid phase bonding method is studied. It has been shown that this method is effective for the production of strong joints. The mechanism of bonding is attributed to aluminum diffusing into the Ti3SiC2. Ti3Si(Al)C2 solid solution formed at the interface during bonding process. The formation of Ti3Si(Al)C2 solid solution causes the joint to possess high strength, owing to the similar mechanical properties and TEC value of Ti3Si(Al)C2 solid solution to Ti3SiC2 substrate. At 1000 oC, the flexural strength of the joint was still as high as 226±30 MPa, about 74% of that of Ti3SiC2 substrate.
(3) Strong joints of Ti3AlC2 ceramic can be achieved through diffusion bonding via Si interlayer. Ti3Al(Si)C2 solid solution formed at the interface during bonding process. The mechanism of bonding is attributed to the inward diffusion of Si. The room temperature flexural strength of the joint is 285±11 MPa, which is about 80% of that of the Ti3AlC2 substrate; and retain this strength up to 1000 oC. The distributions of residual stress in Ti3AlC2/Si/Ti3AlC2 joint were simulated by FEM calculation. The results show that the maximum tensile residual stress situated in the small area adjacent to interface of Ti3Al(Si)C2 solid solution, which would decrease the strength of the joint.
(4) Ti3SiC2 and Ti3AlC2 were successfully bonded to each other under bonding conditions of 1100 – 1300 oC. The mechanism of bonding is attributed to silicon diffusing inward the Ti3AlC2 and to aluminum diffusing inward the Ti3SiC2 simultaneously. During bonding, Ti3Al(Si)C2 and Ti3Al(Si)C2 solid solution formed at the interface, and a little of Ti5Si3 was produced adjacent to Ti3AlC2.
The diffusion coefficients of Si and Al in Ti3SiC2 and Ti3AlC2 were calculated at the temperature range of 1100-1300 oC, respectively. The activation energies of Si and Al were also obtained. These results could be used to explain the diffusion behavior of elements quantitatively during the oxidation and surface treatment processes of Mn+1AXn phase. |
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