STRENGTHENING AND TOUGHENING OF TITANIUM-ALLOYS

This paper will summarize the strengthening and toughening behaviors of alpha + beta and beta-alloys at room temperature. In addition, some considerations on the strengthening capacity and some relationships between microstructures and mechanical properties will be presented. The strength of alpha + beta-alloys can be improved by increasing the volume fraction of the beta-phase and using an ultra refinement of an equiaxed alpha-structure. On the other hand, the toughness can be improved by adjusting an acicular alpha-structure. The strength of beta-alloys can be increased by the homogeneous and fine precipitation of the alpha-phase and by the beta-grain refinement. The toughness of beta-alloys is usually superior to that of alpha + beta-alloys at given strength levels. This is mainly due to the disappearance of the coarse primary alpha-phase in beta-alloys. Increases in the strength of smooth, notched and precracked specimens are limited by ductility, notched tensile strength and fracture toughness, respectively. As a result, there is a critical value for strengthening for each specimen. Finally, some guidelines for microstructural modification for optimization of the strength-ductility and strength-toughness balance will be presented.