1990 Volume 76 Issue 6 Pages 932-939
Effect of microstructure on fracture toughness of β type Ti-15V-3Cr-3Sn-3Al alloy (Ti-15-3) was systematically examined.
At 0°C, fracture toughness (δc) is gradually decreased as strength (0.2%PS) increased. A linear relationship is obtained between fracture toughness and strength, regardless of microstructure: morphology of precipitated a phase or β grain size. Compared with (α + β) type Ti-6Al-4V alloy (Ti-6-4), Ti-15-3 has almost the same δc, in the strength range of 80 to 90 kgf/mm2 and has a higher fracture toughness above the strength of 100 kgf/mm2. The difference in fracture toughness between Ti-15-3 alloy and Ti-6-4 alloy is attributed to the difference in crack extension resistance of microcracks developed at the notch tip before unstable fracture.
At -196°C, fracture toughness is linearly decreased with increasing strength, independent of microstructure. However, the decrease in fracture toughness is rather small. Contrary to the case at 0°C, Ti-15-3 had a lower fracture toughness near the strength of 150 kgf/mm2 than that of Ti-6-4. This is because Ti-15-3 had a lower crack initiation toughness (δi) than Ti-6-4 at -196°C.
It was found that crack initiation toughness (δi) of Ti-15-3 has a close relationship with reduction of area in the round bar tensile test. And crack resistance property was greatly influenced by both strength and the size of a phase precipitated during aging.
