STRENGTHENING OF TI-15V-3CR-3SN-3AL BY THERMOMECHANICAL TREATMENTS

Mechanical properties of beta titanium alloys strongly depend on the precipitation behavior of alpha, which is controlled by thermo-mechanical treatments. To obtain high strength beta titanium alloys, uniform distribution of fine alpha precipitates is required, and various thermo-mechanical treatments have been developed for this purpose. This paper discusses strengthening by fine alpha precipitation using a thermo-mechanical process which combinates cold rolling and un-recrystallized heat treatments. High tensile strength of over 1 700 MPa can be attained by the thermo-mechanical process combining over-aging, cold rolling and aging for 86.4 ks at 723 K. Higher strength can be attained after aging by alpha-beta solution treatment than by beta solution treatment because fine alpha particles precipitate in the aging after the former treatment. It seems that un-recrystallized beta matrix supplies the effective nucleation sites of alpha particles. Ultra high tensile strength of 1 940 MPa can be attained through aging after repeated applications of the cold rolling and recovering process. The microstructure after 723 K aging displayed uniform distribution with very fine alpha precipitates 2-5 nm in thickness.