M. G. Glavicic, Rolls-Royce Corporation, Indianapolis, IN; J. Calcaterra, S. L. Semiatin, Air Force Research Laboratory, Wright-Patterson AFB, OH
Crystallographic texture in titanium alloys plays a key role in the design and service life of aerospace components. The texture of the hexagonal-closed-packed (hcp) alpha-phase forming during decomposition of the high-temperature, body-centered-cubic (bcc) beta phase typically follows a Burgers-type orientation relationship in which there are twelve distinct possible variants that can form from a single orientation of a prior beta-phase grain; i.e., the alpha orientation is related to one of six {110} planes, each of which contains two <111> directions. In addition, the transformation texture thus formed can vary widely depending upon the initial texture of the beta phase and the local stress and strain fields present during the phase transformation that occurs during cooling. To provide insight into the factors which control which variants are selected during phase transformation, high-temperature torsion experiments were performed on Ti-6Al-4V specimens preheated in the beta phase field and then allowed to cool into the two-phase (alpha-beta) field with and without an externally applied load. EBSD measurements of the colony-alpha microstructure thus formed, a computational technique to determine the parent beta-phase texture from these measurements, and an analysis of the stresses and strains fields present during the torsional loading were then used to provide insight into the variant selection process.
Summary: Crystallographic texture in titanium alloys plays a key role in the design and service life of aerospace components. The texture of the hexagonal-closed-packed (hcp) alpha-phase forming during decomposition of the high-temperature, body-centered-cubic (bcc) beta phase typically follows a Burgers-type orientation relationship, in which there are twelve distinct possible variants that can form from a single orientation of a prior beta-phase grain; i.e., the alpha orientation is related to one of six {110} planes, each of which contains two <111> directions. In addition, the transformation texture thus formed can vary widely depending upon the initial texture of the beta phase and the local stress and strain fields present during the phase transformation that occurs during cooling. To provide insight into the factors which control which variants are selected during phase transformation, high-temperature torsion experiments were performed on Ti-6Al-4V specimens preheated in the beta phase field and then allowed to cool into the two-phase (alpha-beta) field with and without an externally applied load. EBSD measurements of the colony-alpha microstructure thus formed, a computational technique to determine the parent beta-phase texture from these measurements, and an analysis of the stresses and strains fields present during the torsional loading were then used to provide insight into the variant selection process.
