Phase precipitation behavior of a quenched β-solidifying TiAl alloy with a fully-B2 microstructure during annealing at 800°C

In this work, a fully-B2 microstructure was obtained in a Ti-40Al-8Nb (at. %) alloy by water-quenching from the single beta phase region, and the decomposition behavior of the fully-B2 microstructure during annealing at 800 degrees C was investigated. Results showed that the fully-B2 microstructure was thermodynamically unstable and numerous lath-liked alpha(2) phases precipitated from the B2 matrix following the Burgers orientation relationships after annealing for 3 min. With the increase of isothermal holding time, these lath-liked alpha(2) phases transformed into ultra-thin (alpha(2)+gamma) lamellar structures with a lamellar spacing of 4 nm. Due to the perpendicular decomposition of the alpha(2) lamellar and coarsening of the gamma lamellar, omega(0) and gamma phases formed in the lamellar structures. Besides, the decomposition of the B2 phase directly into fine gamma and omega(0) particles was also observed and the orientation relationships among these three phases were (1-10)(B2)(1-1-1)ii//(11-20)(omega 0) and [111](B2)//[01-1](gamma)//[0001]omega(0). After tempering for 3000 min, the growth of the gamma and omega(0) phases occurred, leading to a omega(0)-gamma+B2 microstructure with phase size of 300 -500 nm. (C) 2019 Elsevier B.V. All rights reserved.