1990 Volume 76 Issue 4 Pages 606-613
Effect of microstructure on fracture toughness of a near α Ti-8Al-1Mo-1V alloy was systematically examined.
At 0°C, β-processed specimens with acicular microstructure had higher fracture toughness at a given strength than those with equiaxed microstructure, because the former had a greater crack extension resistance than the latter. The embrittling phase, α2 phase, which precipitated during furnace cooling after annealed at 650950°C, reduced fracture toughness by more than 20 percent although that increased tensile strength. Precipitation of α2 phase had a great influence on crack initiation and reduced CTOD value at crack initiation, δi, by 50 percent.
At-196°C, the specimens with acicular microstructure had higher fracture toughness than those with equiaxed microstructure similar to those tested at 0°C. The latter had lower fracture toughness than that of Ti-6Al-4V with equiaxed microstructure at a given strength, because the crack initiation of Ti-8Al-1Mo-1V were lower than that of Ti-6Al-4V.
It is concluded that the relationship between microstructure and crack initiation or crack extension resistance properties of microcracks preceding unstable fracture accounted for the changes in fracture toughness of Ti-8Al-Mo-1V.