Microstructural features and local properties evolution in a heavy plastic deformed Ti-29Nb-9Ta-10Zr (wt%) alloy

International audienceThe microstructure, crystallographic texture and local properties evolution were investigated during thermo-mechanical processing of Ti-29Nb-9Ta-10Zr (wt%) alloy. The Ti-29Nb-9Ta-10Zr (wt%) alloy was cold-rolled by Multi-Pass Rolling (MPR) to evaluate the influence of a high intensity plastic deformation on some microstructural features (constituent phases, constitutive phase morphology, crystallographic texture) and local mechanical properties. MPR processing led to obtaining of three structural states, corresponding to a deformation degree of 60%, 80% and 90%. The microstructural features were investigated by XRD and SEM techniques while the mechanical local properties were evaluated by nano-indentation. Investigations have shown that the initial microstructure consists in a mixture of parent equiaxed polyhedral β-Ti phase grains and sub-micron α″-Ti phase dispersed inside β-Ti grains. Further, with progress of MPR processing the broad β-Ti peaks indicates heavily distorted UFC/NC β-Ti grains; also, the large and intense α″-Ti peaks suggest the presence of NC grains and a relatively high volume fraction of α″-Ti phase in the β-Ti matrix. MPR processing leads to development of a specific crystallographic texture; the most intense fibres were: γ-fibre, with two major components: ₁11_ and ₁11_, α-fibre and ε-fibre. Also, from nano-indentation testing it was showed that local mechanical properties, such as instrumented elastic modulus (EIT), instrumented hardness (HIT) and Vickers microhardness (HV), are decreasing with progress of MPR processing due to increased α″-Ti phase fraction