Diffusion and reactions at the interface of an SCS-6/Ti-22Al-23Nb composite

Specimens of an SCS-6/Ti-22Al-23Nb composite in the as-fabricated and heat treated conditions were prepared for reaction zone characterization using, mainly, transmission electron microscopy. Three layers were identified in the zone; the resulting phases were based upon, (Ti,Nb)C, (Ti,Nb)5(Si,Al)3, and (Ti,Nb)3(Si,Al). No significant growth was observed for the inner or intermediate layers. After the longest treatment time at the highest temperature a new phase layer appeared and grew at the expense of its neighbor. This is believed to be due to the fact that while there was no difficulty in obtaining the elements Ti, Nb and Al from the matrix for this outer layer, substantial amounts of Si could reach this layer only after diffusion through the highly non-stoichiometric inner and intermediate layers. No simple relationship between the thickness of reaction zone and the time could be confirmed. Thermodynamic analysis was made on the possible appearance of the reaction layers in a multi-component diffusion couple