Growth mechanism of the Nb(X)Si2 and [Nb(X)]5Si3 phases by reactive diffusion in Nb (X = Ti, Mo, or Zr)–Si systems

The effects of Mo, Ti, and Zr on the diffusion and growth of the Nb(X)Si2 and Nb(X)5Si3 phases in an Nb(X)–Si system are analyzed. The integrated diffusion coefficients are determined from diffusion couple experiments and compared with the data previously calculated in a binary Nb–Si system. The growth rates of both phases are affected by the addition of Mo and Zr, whereas the addition of Ti has no effect. The atomic mechanism of diffusion is also discussed based on the crystal structure and the possible changes in the defect concentrations due to alloying. Finally, the growth mechanism of the phases is discussed on the basis of a physico-chemical approach.