Ti-6 Al-4 V合金の破壊靱性に及ぼす微視組織および不純物の影響

抄録

The influence of hot working and heat treatment conditions, impurity elements and test temperature on the fracture toughness of Ti-6Al-4V alloy was systematically examined. The fracture mechanism of this alloy was also discussed on the result of the detail observation of cracking behavior at the notch-tip of COD test specimens unloaded prior to the maximum load.
At 0°C, microstructure has a more influence on the strength-toughness relationship than impurity content. The βtreated specimens with acicular microstructure show a better strength-toughness combination than α+β treated specimenes with equiaxed microstructure at any strength level.
At -196°C, the impurity content has a great influence on the strength-toughness relationship and specimens with low impurity contents, ELI, have a better strength-toughness combination than those with standard impurity contents, regardless of their strength.
These tendencies in the strength-toughness relationship are proved to be closely related with both the occurrence of microcracks and their length at the notch-tip of the specimens before the final unstable fracture. It is found that a specimen shows higher fracture toughness, when microcraks are developed at the notch-tip through void coalescence below the maximum load and their propagation is hindered or distorted by lath-colony boundaries, grain boundaries or phase boundaries.