Diffusion structures and diffusion paths in ternary systems - Selected unusual observations

Selected diffusion studies are presented to bring out some of the unusual diffusion structures and diffusion paths observed for single phase and multiphase diffusion couples in ternary systems. The studies include diffusion couples assembled with refractory metals, such as Mo, W, Re, in contact with MoSi2 at selected temperatures between 900 degrees and 1700 degrees C as well as couples investigated in the Fe-Ni-Al system at 1000 degrees C with beta(B-2) Single phase alloys and two-phase alloys containing beta(B-2) and gamma(fcc)phases. The development of nonplanar morphologies is illustrated for both binary and ternary silicide layers. Examples of uphill diffusion and zero-flux plane development without the formation of a relative extremum in concentration profiles are presented for Mo in ternary (Mo,W)(5)Si-3 and (Re,Mo)Si diffusion layers and are described in terms of relative magnitudes of main and cross ternary interdiffusion coefficients. New observations of a double serpentine path for a beta(B-2)single phase couple and demixing of (beta+gamma)two-phase layers in a multiphase couple in the Fe-Ni-Al system are also presented. The diffusion paths and structures are discussed in the light of ternary interdiffusion coefficients and diffusional interactions among the components.