It was pointed out that, during diffusion-bonding, an Fe-Si solid solution formed via the interaction of Fe with Si3N or SiC. At temperatures above 1373K, the solid solution extended to beyond 25at%Si on the Fe-rich side. Previous studies of interdiffusion had revealed that interdiffusion depended strongly upon composition; thus reflecting the complex structure (ordering) of the solid solution. The interdiffusion coefficient (figures 10 and 11) exhibited a distinct maximum at the stoichiometric composition, Fe3Si, which corresponded to the highest degree of order in the D03 structure. This was a surprising observation which could not be explained by the presence of thermal vacancies alone.

Interdiffusion in Ordered and Disordered Fe(Si) Solid Solution. E.Heikinheimo, A.A.Kodentsov, F.J.J.Van Loo: Scripta Materialia, 1998, 38[8], 1229-35

Figure 10

Diffusivity of Si in Fe-Si Alloys at 1373K

Figure 11

Diffusivity of Si in Fe-Si Alloys

(a: 12%Si, b: 5%Si)