Estimation of the dislocation density distribution, by microscopic and macroscopic approaches, in titanium alloys after hot-deformation in the α+β domain
Résumé
The initial microstructure to be deformed has a great influence on plastic deformation and on the storage of dislocations. In turn, microstructural evolution is tightly correlated to the structure and distribution of dislocations. The assessment of dislocation density in highly deformed materials is a challenging task. Actually, all the existing approaches only allow to obtain partial or imprecise estimates of the dislocation density distribution, and the task is even harder when dealing with dual phase materials. The aim of this work is to estimate and compare the dislocation density in Ti-6Al-4V (α + β) and Ti-10V-2Fe-3Al (metastable-β) alloys, with equiaxed and lamellar morphologies, after hot-deformation in the two-phase domain. A microscopic approach based on EBSD maps and a macroscopic one based on flow stress analysis are used. Both double-cone and cylindrical samples were hot-deformed, at 950°C and 750°C, being 50°C below the β-transus, leading to 36% and 24% α phase fraction for the Ti-6Al-4V alloy and for the Ti-10V-2Fe-3Al alloy, respectively. A detailed confrontation between the two approaches was performed, evidencing that the direct comparison of dislocation densities should not be done. Actually, the microstructure and crystallographic texture evolutions in both phases affects drastically the obtained values by each of the methods. Notably texture effects in the α phase and substructures development in the β phase must be taken into consideration to relate the results from both approaches.