Strengthening Mechanism of High Strength Titanium Alloys.
Technical rept. Dec 69-Dec 70,
NEW YORK UNIV NY ENGINEERING RESEARCH DIV
Pagination or Media Count:
The investigation to relate fracture toughness, void formation and growth and ductility to microstructural features in an alpha-beta alloy, Ti-5.25Al-5.5V-0.9Fe-0.5Cu continued. New data confirm the earlier reported relationships between fracture toughness and microstructure of both equiaxed alpha and Widmanstatten plus grain boundary in aged beta matrix morphologies. In equiaxed alpha structures, fracture toughness depends linearly upon the grain boundary area per unit volume, S sub V, and is independent of equiaxed alpha particle size or spacing. In a grain boundary alpha structure, fracture toughness depends both on S sub V and, within limits, linearly on the thickness of the grain boundary alpha. Equations relating tensile void growth rates to microstructure for both morphologies have been derived. Tensile fracture is shown to be intergranular in nature and occurs when a critical crack length-stress relationship s satisfied. The amount of ductility achievable in a specimen depends upon the rate of void growth. If the growth rate is rapid, the crack reaches a critical size for fracture at a lower applied stress and strain and hence the ductility is less. A mechanism for void growth at alpha-beta interfaces is presented which accounts for the higher frequency of voids at 30-70 degrees to the tensile axis. An explanation is offered to the apparently contradictory behavior in which grain boundary alpha improved fracture toughness but lowers tensile ductility. Author
- Properties of Metals and Alloys