Interface Layer Structure of Solid State Bonded SiC/TiAl Joint(Materials, Metallurgy & Weldability)

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Solid state bonding of SiC to TiAl has been performed at temperatures from 1473K to 1573K. The microstructure at the SiC/TiAl interface and the growth mechanisms were analyzed by EPMA analysis and X-ray diffractometry. The interface structures were the same at all bonding temperatures. The reaction layers were divided into two parts. The first one was a Ti carbide based layer, and the other was a Ti silicide based layer. Both layers are mixed layers composed of one or two carbides and silicides including Ti_3AlC ternary compound. At the reaction layer side in TiAl, a Ti depleted zone and an Al rich TiAl layer were formed since Ti in TiAl reacted and diffused toward the SiC side. The reaction layer formed at SiC/TiAl joint was determined as, SiC/TiC/TiC+Ti_3AlC/Ti_5Si_3+TiSi_2+Ti_3AIC/TiAl (Al-rich)/TiAl The reaction layers grow in proportion to the square root of the bonding time. The growth activation energy of the carbide layer containing TiC and Ti_3AlC, the silicide layer and the total reaction layer were 398kJ/mol, 553kJ/mol and 502kJ/mol. The growth of the total reaction layer was dominated by the growth of the silicide, because the main part of thickness consisted of the silicide.
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