Structural characterization and nanoscale strain field analysis of α/β interface layer of a near α titanium alloy

Abstract In this article, the structural and nanoscale strain field of the α/β phase interface layer in Ti80 alloy were studied by using high-resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA). The α/β interface layer was observed in forged and different annealed Ti80 alloys, which is mainly composed of lamellar face-centered cubic (FCC) phase region and α′ + β region. The FCC phases between α and β phases show a twin relationship, and the twinning plane is (1\bar{1}1) . The orientation relationship of the β phase, the α phase, and the FCC phase is (110) _β //(0001) _α // (1\bar{1}1) _FCC and [ \bar{1}11 ] _β //[ 2\bar{1}\bar{1}0 ] _α //[011] _FCC . The nanoscale strain field of FCC + α and β + α′ regions was analyzed by using the GPA technology. The FCC + α region shows more significant strain gradient than the α′ + β region, and ε _FCC > ε _α , ε _α′ > ε _β . The influence of element addition on the formation mechanism of the FCC phase was discussed. The addition of Zr promotes the formation of the FCC phase by inducing lattice distortion and reducing the stacking fault energy of the α phase. In addition, the Al element forms an obvious concentration gradient around the interface layer during the cooling process of the alloy, which provides a driving force for the formation of the FCC phase.