| The preferred orientation of crystals, or texture, is a very important phenomenon in Ti alloys, as the hexagonal close packed (hcp) a phase is highly anisotropic, which makes the properties of the alloys extremely sensitive to the orientation distribution of this phase. Moreover, since there is an orientation relationship (OR)---the so called Burgers OR---between the low temperature alpha phase and the high temperature body centered cubic (bcc) beta phase in microstructures directly developed from the beta phase by cooling, the texture of the beta phase also becomes important. Additionally, the distribution of strains between the two phases during deformation is also dependent to an extent on the texture of these phases.; In this study, the relationship between the texture and the microstructure of both processed and alpha/beta processed Ti alloys has been examined.; In the beta-processed microstructures, the alpha phase appears in a lath morphology, in which there is generally a major growth direction, a broad face, a side face and an edge face. It has been observed that there are twelve possible variants of these alpha laths in a single prior beta grain. These comprise of six pairs, the members of which share a common {lcub}0001{rcub} plane, and are rotated from each other by about 10.5°. Although the members of these pairs have such a relatively small crystallographic misorientation between them, their growth directions exhibit a considerable difference.; Moreover, it was observed that alpha laths growing from prior beta grain boundaries sometimes shared common basal planes. In some special cases, the a laths growing into two different prior beta grains from the grain boundary between them had almost exactly the same orientation, although they had vastly different growth directions. Additionally, there were some cases in which alpha laths growing into different prior beta grains not only had the same crystallographic orientation, but also had the same growth direction.; Scanning Electron Microscopy (SEM), Orientation Imaging Microscopy (OIM), and Transmission Electron Microscopy (TEM) have been used to investigate the reasons behind these phenomena. The theories of growth directions of alpha laths forwarded by previous workers, mainly Furuhara and Aaronson, have been used along with the SEM, TEM and OIM observations to explain these apparently unexpected crystallographic and morphological conditions found in the beta processed alloys. (Abstract shortened by UMI.)... |
