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

In this article, the structural and nanoscale strain field of the alpha/beta phase interface layer in Ti80 alloy were studied by using high-resolution transmission elec-tron microscopy (HRTEM) and geometric phase analysis (GPA). The alpha/beta interface layer was observed in forged and different annealed Ti80 alloys, which is mainly composed of lamellar face-centered cubic (FCC) phase region and alpha' + beta region. The FCC phases between alpha and beta phases show a twin relationship, and the twinning plane is ( 11 over line 1). The orientation relationship of the beta phase, the alpha phase, and the FCC phase is (110)(beta)//(0001)(alpha)//(11 over line 1)FCC and [1 over line 11](beta)// [21 over line 1 over line 0](alpha)//[011](FCC). The nanoscale strain field of FCC + alpha and beta + alpha' regions was analyzed by using the GPA tech-nology. The FCC + alpha region shows more significant strain gradient than the alpha' + beta region, and epsilon FCC > epsilon(alpha), epsilon(alpha') > epsilon(beta). The influence of element addition on the formation mechanism the FCC phase was discussed. The addition of Zr pro-motes the formation of the FCC phase by inducing lattice distortion and reducing the stacking fault energy of the alpha phase. In addition, the Al element forms an obvious con-centration gradient around the interface layer during the cooling process of the alloy, which provides a driving force for the formation of the FCC phase.