Effects of the crystallographic texture on the contractile strain ratio of Ti–3Al–2.5V tubing

Abstract

The contractile strain ratio (CSR) is an important property and a quality control factor of cold-worked and stress-relieved Ti–3Al–2.5V tubing. In this work, the CSR values of three thin-walled Ti–3Al–2.5V tubing samples were obtained by uniaxial tensile tests, and the crystallographic textures of the tubing samples were characterized by orientation distribution functions (ODFs) which were determined on the basis of a series of pole figures obtained by X-ray diffraction. A quantitative method is proposed for exploring the correlation between the CSR values and the ODF data of the tubing samples, including the following steps: Firstly, taking advantage of the ODF data, the volume fraction (V%) of crystallites that lie within a certain range of Euler angles (φ1, Φ, φ2) can be calculated, and the calculation is performed on each set of Euler angles (φ1, Φ, φ2). Secondly, each V% is resolved into an effective fraction in the orientation of the ideal radial texture {0002}〈10\overline 10〉 corresponding to the Euler angles of (0, 0, 0), and the equivalent radial texture (ERT) is obtained as the sum of all such effective fractions. Thirdly, similarly to the previous step, the equivalent tangential texture (ETT) is calculated. The CSR will be related to the ratio of the ERT to the ETT, named the equivalent texture ratio (ETR). The CSR values of the tubing samples are 1.38, 1.96 and 2.19 and their ETR values are 1.33, 1.72 and 1.87, respectively. In particular, the CSR and the ETR of the tubing with a random distribution of the basal poles in the radial–tangential plane are both unity. It is found from the above data that the CSR increases approximately linearly with the ETR. Since the three-dimensional orientations of crystallites and the orientation distributions throughout the Euler space are taken into account in the calculations of the ETR, the proposed method can be used for predicting and explaining the mechanical anisotropy of Ti–3Al–2.5V tubing more accurately.