The effect of 0.02–0.37 strain on the precipitation law of O phase colonies in Ti2AlNb-based alloy during aging

Abstract

O phase is the main strengthening phase of the lightweight high-temperature structural material—Ti2AlNb-based alloy, its morphology, size and distribution have significant impact on the mechanical properties of the alloy. This paper obtained different deformation areas with strains within the range of 0.02–0.37 in Ti2AlNb-based alloy sample through tensile deformation and precisely characterized strain values with DIC technique. The results indicate that while the strain was larger than 0.04, O phases would precipitate at the B2 grain boundary in the form of phase colony, whereas others precipitated in B2 grains appeared as fine granule. Phase colony structure, with its size reaching to dozens of micrometers, was composed of lamellar O phase. Within the strain range of 0.08–0.24, the precipitation amount of the O phase colonies was correlated linearly with strain level. It increased with the accumulating of strain. Within the strain range of 0.24–0.37, the amount of the O phase colonies no longer increased and stabilized at 15%. The mechanism of strain promoting precipitation of O phase colonies at the B2 grain boundary is shown as follow. Deformation made B2 matrix store a lot of geometrically necessary dislocations (GND), which led atoms in deformation area arrange in disorder and thus provided sufficient nucleate sites for O phase, promoting the concentrated nucleate of the O phase in this area and formed phase colony structure. The GND density at the B2 grain boundary was noticeable higher than that inside grain, thus O phase colonies primarily formed at grain boundary.