Change in Al concentration profile related to the D0₁₉→L1₀ structural change in Ti-Al alloys

The change in the Al concentration profile together with the structural change from hexagonal close packed (hcp) to D0₁₉+L1₀ lamellar structures is described. The chemical compositions of both the B₁₉ and the lattice-destructed (LD) regions as well as that of the D0₁₉ matrix, all of which appear during the structural change in a Ti-40 at.% Al alloy, were measured by analytical electron microscopy. The role of the B₁₉ metastable state in the formation of the LD state and the Al concentration profile for the stability of the LD state are discussed.