A Study of Low Young's Modulus Ti-15Ta-15Nb Alloy Using TEM Analysis

The microstructural characteristics and Young's modulus of the as-cast Ti-15Ta-15Nb alloy are reported in this study. On the basis of the examined XRD and TEM results, the microstructure of the current alloy is essentially a mixture (α + β+ α' + α″ + ω + H) phase. The new H phase has not previously been identified as a known phase in the Ti-Ta-Nb alloy system. On the basis of examination of the Kikuchi maps, the new H phase belongs to a tetragonal structural class with lattice parameters of a = b = 0.328 nm and c = 0.343 nm, denoting an optimal presentation of the atomic arrangement. The relationships of orientation between these phases would be {0001}_α//{110}_β//{1¯21¯0}_ω//{101¯}_H and (011¯0)_α//(11¯2)_β//(1¯010)_ω//(121)_H. Moreover, the Young's modulus of the as-cast Ti-15Ta-15Nb alloy is approximately E = 80.2 ± 10.66 GPa. It is implied that the Young's modulus can be decreased by the mixing of phases, especially with the presence of the H phase.