Diffusion in B2 NiAl and FeAl Intermetallics and Their Alloys

Both FeAl and NiAl with B2 crystal structure are envisaged for their usage in high temperature applications and hence, availability of diffusion data in these intermetallics is crucial in designing their alloys and processes as well as deciding their in-service performance. A comprehensive overview of diffusion data available in B2 FeAl and NiAl and their alloys is provided in this article. Nearest neighbor vacancy jumps in B2 intermetallic lead to a local disorder in the lattice and hence it is not necessarily the unit step of diffusion in these structures. Several mechanisms of diffusion proposed in the literature are discussed including nearest neighbor jumps, next nearest neighbor jumps, six-jump vacancy cycle, triple defect and antisite bridge. Relevance of these mechanisms in FeAl and NiAl is discussed. An overview is given on the self-and solute diffusion and interdiffusion data available in both binary FeAl and NiAl. Due to wide solubility range of both FeAl and NiAl as well as their alloying requirements for improved properties, it becomes pertinent to study the multicomponent diffusion in the alloys based on these B2 itnermetallics. Hence, in the latter part of the article, various methods used for determining multicomponent diffusion data are reviewed. A detail overview is also provided on the diffusion studies available in literature on ternary alloys based on FeAl and NiAl with an emphasis on highlighting the diffusional interactions observed in these systems.