Microstructure and mechanical properties of a commercially pure Ti processed by warm equal channel angular pressing

A commercially pure (CP) Titanium alloy classified as Grade 1, was processed by Equal Channel Angular Pressing (ECAP) up to 4 passes in the temperature range of 450–150°C. The resulting microstructures were observed by Electron Back-Scattered Diffraction, revealing a bimodal grain size distribution consisting of small recrystallized grains of submicrometer size, with an average value of 0.3µm, and elongated bands of 1.4µm with different degree of substructure. Additionally the fraction of restored and deformed grains were evaluated as a function of processing temperature following an internal grain misorientation criterion, leading to an overall fraction of recrystallized grains between 40% and 20% in samples ECAPed at 450 and 150°C, respectively. The strengthening contributions of the grain size, equivalent oxygen content (Oeq) and Low Angle Grain Boundaries (LAGBs) to the yield stress were identified by the Hall Petch and Taylor equations. The strengthening coefficient k of the Hall–Petch relation was approximately 5MPamm−1/2, with an increment of 0.44MPamm−1/2 per 0.1 Oeq.-%, while the LAGB strengthening contribution was responsible approximately by half of the experimental yield stress values measured.