Primary slip induced band-like structures and the associated recrystallization kinetics in Ti2AlNb alloy with centimeter-grade coarse grains

Abstract

Ti₂AlNb alloy, as a highly promising superalloy in the aerospace field, is limited by inferior workability due to centimeter-grade coarse grains formed through casting. An in-depth understanding of the relationship between deformation heterogeneities and recrystallization kinetics of the matrix B2 phase is critical to refine and optimize its microstructure. Plane strain compression followed by heat treatment, microstructure characterizations, and full-field crystal plasticity simulations were conducted. The research found that uniform primary-slips existed in most regions of the alloy. These regions exhibited negligible deformation stored energy and misorientation, and therefore, recrystallization cannot occur after heating. The observed slip transfer at grain boundaries with good geometric alignment also indicates the difficulty in dislocation pileup as the potential recrystallization site. Three typical band-like structures, i.e., transition band, slip-interlacing band, and shear band, formed by intersection and localization of slips, possessed high deformation stored energy. Cell-like substructures readily developed in the first two regions with intersecting slips, rather than in the shear band with parallel slips. As a result, many subgrains and unclosed boundaries were formed in the first two types of bands within grains after heating due to the significant recovery effect. These multilevel deformation heterogeneities were found to be strongly associated with the dislocation structure of the alloy. TEM observations found the dissociation of dislocations with narrow widths, which enhances dislocation mobility. Consequently, the primary-slip characteristic can be maintained at a relatively large deformation, and slip transfer can occur at grain boundaries where a good geometric alignment exists.