Multiscale γ variant selection in a quaternary near-γ Ti-Al alloy

Suhash Ranjan Dey (1) , Alain Hazotte (1) , Emmanuel Bouzy (1)

1 LETAM - Laboratoire d'étude des textures et application aux matériaux

Classical EBSD/SEM technique and a novel approach based on computer-aided collection and indexing of TEM Kikuchi patterns were used to study the γ variant and γ/γmisorientation distributions in lamellar grains of a near γ TiAl alloy. Coarse and fine lamellar structures obtained by continuous cooling at two different rates were investigated. The two methods were complementary and reveal the presence of one-twin-dominant zones (OTDZ) in all grains of both samples. In agreement with previous works, these OTDZ were proposed to result from a mechanism of self-accommodation through twin-variant selection at the nucleation stage. Moreover, it has been pointed out that one γ order variant often appears to be dominant in a given OTDZ. As the previous mechanism can hardly explain this experimental evidence, the presence of back-stresses due to the grain confinement is proposed as a possible explanation. The statistical analysis of γ/γ misorientation distributions, de-correlated from the effect of the non-random distribution of γ variants, reveals that γ/γ interfaces in true-twin relationship are clearly predominant in the coarse lamellar structure, but not in the fine one. This difference is discussed on the basis of different growth mechanisms recently underlined and whose respective influences depend on the transformation driving force, i.e. on the cooling rate.

Mots clés: Physical Sciences

Suhash Ranjan Dey, Alain Hazotte, Emmanuel Bouzy. Multiscale γ variant selection in a quaternary near-γ Ti-Al alloy. Philosophical Magazine, 2006, 86 (20), pp.3089-3111. ⟨10.1080/14786430600669832⟩. ⟨hal-00513687⟩