Phase transformation mechanisms involved in two-phase TiAl-based alloys. I. Lamellar structure formation

• Published in: Acta materialia Vol. 44; no. 1; pp. 343 - 352
• Main Authors: Naka, S, Denquin, A
• Format: Journal Article
• Language: English
• Published: 01.01.1996
• ISSN: 1359-6454
• DOI: 10.1016/1359-6454(95)00167-4

The present paper deals with the mechanism operating in one of the three major transformation modes appearing in two-phase TiAl-based alloys: the formation of the so-called gamma / alpha sub 2 lamellar structure. This microstructure, the most typical of the alloys of this category, results from precipitation of gamma (L1 sub 0 ) lamellae in the alpha (A3) or alpha sub 2 (DO sub 19 ) matrix. This reaction is achieved through (i) pre-nucleation stage corresponding to the formation of a local fcc type stacking sequence by the movement of Shockley partials; and (ii) nucleation and growth stages involving both ordering and ledge movement. The presence of numerous order domain boundaries in a given gamma lamellar precipitate is explained by the encounter of separately nucleated order domains.