Plastic behaviour and cristallographic texture of alpha titanium alloys for heat resistant applications [Anisotropia ed orientamento cristallografico preferenziale di leghe di titanio alfa per impieghi a caldo]

As known, metallic materials presenting HCP crystallographic structure show a marked anisotropic behavior during plastic deformation, especially deep drawing. This attitude is due to the intrinsic asymmetry of hexagonal crystal lattice and is also depending on the c/a ratio of the cell itself. In addition to this aspect, also the tendency of materials such as titanium, magnesium and zirconium, to give rise to a preferential crystallographic orientation (texture) during the rolling phases needs to be taken into account. The most important aspects which contribute to texture formation are: nature and quantity of the alloying elements, reduction ratio during rolling, and heat treatments made on the alloys. Subject of present study are two alpha titanium alloys, specifically developed for heat resistant applications. Despite being quite similar in terms of chemical composition, oxidation resistance and field of application, these two alloys exhibit dissimilar plastic deformation mechanisms. The feature which makes the use of these materials very demanding on an industrial scale is the modification of their plastics properties, in particular plastic strain ratio (R-value), during the deformation progress. On the aforementioned alpha titanium alloys, a complete microstructural and mechanical characterization has been performed analyzing the material according to different orientation, whit the main purpose of identifying the trend of R-value toward strain. In addition to that, a study of the original texture of the two alloys has been made using different measuring methods (X-Ray diffraction, Electron Back-Scattering Diffraction). The purpose of this activity is finding a correlation between the macroscopic behavior of the alloys during deformation and their crystallographic orientation on microstructural scale, for better understanding the specific role played by the individual sliding systems and their spatial orientation on the plastic properties of the materials.