Coarsening behavior of lamellar orthorhombic phase and its effect on tensile properties for the Ti-22Al-25Nb alloy

This study quantitatively investigated the coarsening behavior of the lamellar O and its effect on tensile properties of the Ti-22Al-25Nb alloy. The results indicated that the growth of lamellar O was sensitive to the temperature and holding time. The alloy with different lamellar thicknesses (from 0.16 to 1.1 μm) can be obtained via varying the aging temperature and holding time. At the initial growth stage, the thickness of the lamellar O increased rapidly by diffusional process because of the high storage energy and different concentration gradients of elements in different phases (O/B2). Due to the consuming of storage energy and the decreasing of concentration gradient with the holding time, the growth rate decreased. The growth exponent and activation energy were both increased as the aging temperature and the holding time increased respectively. The room temperature (RT) and 650 °C 0.2% yield strength (YS) and elongation (EL) agree well with the Hall-Petch relationship and those can be adjusted in the range of 560-1045 MPa and 510-950 MPa for RT and 650 °C 0.2% YS respectively and 3-8% and 8-14.5% for RT and 650 °C EL via varying the thickness of lamellar O.