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Fracture toughness as a function of test temperature was determined for a V4Cr4Ti alloy under both static and dynamic conditions using relatively small, one-third-sized, pre-cracked Charpy specimens. These data were supplemented by optical, scanning electron and confocal microscopy and fracture reconstruction methods. Specimens showed a transition to cleavage-initiated fracture at temperatures above −150°C for dynamic test conditions and below −150°C for static test conditions. However, the cleavage cracks were arrested, and final failure, if any, occurred by ductile tearing of the remaining ligament. This behavior is consistent with the relatively low strength of this alloy combined with the small dimensions of the sample, which enhanced deformation-induced changes in the geometry and decrease constraint on the crack front. Hence, it should be expected that larger specimen sizes and/or higher strengths will result in a transition from ductile to cleavage fracture at a higher temperature. |
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