Reaction diffusion between two metals including titanium and niobium

If two metals are in contact with each other at an elevated temp. they interdiffuse. In those cases in which one or more intermetallic compds. are formed during this process it is called reaction diffusion. The intermetallic compds. may have interesting mech. and chem. properties and may be used as coatings. Formulas given by Boltzmann, Matano, Heumann, and Wagner make possible the calcn. of diffusion coeffs. from the observed concn. gradients. If the intrinsic diffusion coeffs. are not equal (which means that one of the components diffuses more rapidly than the other) a \"Kirkendall\"-effect will occur, resulting in shrinkage of one of the phases or in the formation of pores. By using a technique of diffusion couples and a modification of the calcn. method most of the layer growth characteristics have been detd. in the Ni-Al system. An interesting result is that owing to the great stability of the intermetallic phases, it depends on the nature of the diffusion couple whether Al or Ni is the moving atom. The Ti-Al, Ti-Ni, and Nb-Al systems are under investigation. Preliminary results in the Ti-Al system indicate that up to 650 Deg TiAl3 that grows. All other layers grow regularly above 700 Deg. In Ti-Ni, the TiNi layer is the thickest and regular in shape and so are layers of TiNi3 and Ti2Ni. Above 720 Deg a new layer of a solid soln. of Ni in Ti grows very rapidly. In the Nb-Al system, the first compound formed is NbAl3, which grows very slowly below 630 DegC., and only above the melting point of Al resonable layer growth occurs. A Nb2Al layer grows at 1200 DegC., according to the parabolic law. [on SciFinder (R)]