On ordering on BCC and O-phase.

Abstract

Phase transformations involving order-disorder in BCC alloys, which were discussed with a view point of application in the late 1990s by Naka and Kahn, [97Nak] are raising again interest. Amidst the reasons, are the potential of the use of these alloys in high temperature applications, and the fact that new pathways are being found during additive manufacturing processes, like laser powder bed fusion, LPBD, which show phase transformations that instigates understanding. Alloys in the system Ti-Al-Nb have high temperature and oxidation resistance and are light what implies in a large number of applications. In this system, A2-B2 and B2 to the orthogonal O-phase transformations were pioneering studied by [94Ben] and [02Sad] in its crystallographic and thermodynamic modelling, respectively. We discuss these phases formation during LPBD additive manufacturing [23Gus] where the equilibrium condition is not present. Ref: [97Nak] S. Naka and T. Khan: J. Phase Equil., 1997, vol. 18, pp. 635–49. [94Ben] L. A. Benderskyi, A. Roytburd, and W. J. Boettinger, Acta metall. mater. Vol. 42, No. 7, pp. 2323- 2335, 1994. [02Sad] F.A Sadi and C. Servant, Materials Science and Engineering, vol 346 (1-2) 15 pp. 19-28, 2003 [23Gus] J. Gussone et al., Materials and Design, vol. 232, 112154, 2023