Influence of a pre-deformation on the growth of titanium multicrystals

Abstract

In the present study, we have developed a new elaboration process which facilitates the growth of titanium single crystals by combining plastic strain and thermal cycling around the transition temperature. It consists in introducing a small plastic deformation into annealed specimens (like in the critical strain hardening method) before carrying out annealing cycles of only a few days under high vacuum. This method has been applied to titanium of commercial purity (CP-Ti). At the end of each cycle, samples are examined in SEM / EBSD for the characterization of grain sizes and shapes, crystallographic orientations and crystalline quality.Our first results demonstrate that we can obtain grains bigger than one square centimetre (thickness 2mm) after a preliminary plastic deformation of 3% followed by two 2 pairs of annealing cycles (total time: 96 hours). This enhanced growth is thought to be due to the combination of two driving forces associated (i) to the energy stored within the grains during plastic strain and (ii) to the phase transformation, which acts alone in the transus cycling process. These single crystals are intended to be used to study their mechanical behaviour with the small tensile machines developed to perform in situ mechanical tests into microscopes (SEM, AFM) or diffractometers.