title: Transformation of BCC and B2 High Temperature Phases to HCP and Orthorhombic Structures in the Ti-Al-Nb System. Part I: Microstructural Predictions Based on a Subgroup Relation Between Phases.
abstract: Possible paths for the constant composition coherent transformation of BCC or B2 high temperature phases to low temperature HCP or Orthorhombic phases in the Ti-Al-Nb system are analyzed using a sequence of ciystallographic structural relationships developed from subgroup symmetry relations. Symmetry elements lost in each step of the sequence determine the possibilities for variants of the low symmetry phase and domains that can be present in the microstructure. The orientation of interdomain interfaces is determined by requiring the existence of a strain-free interface between the domains. Polydomain structures are also determined that minimize elastic energy. Microstructural predictions are made for comparison to experimental results given by Benderslcy and Boettinger [J. Res. Natl. Inst. Stand. Technol. 98, 585 (1993)].
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors.forename: L A
authors.initials: LA
authors.lastname: Bendersky
authors.affiliation: Dept. of Materials and Nuclear Engineering, University of Maryland, College Park, MD 20742.
authors.forename: A
authors.initials: A
authors.lastname: Roytburd
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors.forename: W J
authors.initials: WJ
authors.lastname: Boettinger
keywords: Ti-Al-Nb system; domain structure; elastic accommodation; phases; space group relations; structural relations; transformation path