Microstructure and mechanical properties evolution of Ti-13Nb-13Zr alloy processed by ECAP-Conform and rotary swaging

The evolution of the microstructure and properties of Ti-13 Nb-13Zr alloy was investigated for the materials states ranging from the solution treated (ST) state over the continuous equal channel angular pressing (ECAPConform) state to the states of the materials processed by combination of ECAP-Conform with rotary swaging (RS) multilevel deformation. In order to investigate microstructure features and mechanical properties for all considered material states, SEM, TEM, XRD and tensile and hardness tests were employed. The two-dimensional mismatch between alpha ', beta, and alpha phases was calculated to evaluate the effect of the precipitation of the second phase. The results indicate that the microstructure of Ti-13 Nb-13Zr alloy transformed into majority of alpha ' martensite and a small percentage of residual metastable beta m phase after ST. The grains were significantly refined, and a small part of alpha phase was precipitated during ECAP-Conform. As a result of ECAP-Conform + RS, the average grain size was refined from 34 mu m after ST to 152 nm. The vast majority of the unstable phase was retained. Due to the ECAP-Conform + RS, the tensile strength increased to 1167.7 MPa while the elongation was 8.6%. The two-dimensional mismatch between alpha ', alpha, and beta phases was 22.1%, which belongs to a semi-coherent relationship. The excellent mechanical properties were mainly attributed to the strengthening by alpha phase precipitation, dislocation strengthening, and grain refinement.