Fracture micromechanisms in overaged 7000 alloy forgings

Micromechanisms controlling the fracture damage in 7000 alloy forgings are studied for T73-type heat treatments. Insight into the fracture modes are obtained by varying the microstructural attributes associated with the coarse intermetallic (IM) particles and precipitates. To identify the fracture micromechanisms, extensive fractographic analysis by scanning electron microscopy (SEM) observation of the broken plane-strain fracture-toughness test specimen surfaces are carried out. The relative fractions of the various fracture modes as a function of microstructural features are quantitatively determined. The relationships between these data and values of fracture toughness are then established. It was found that multiple-fracture micromechanisms occur and the fracture toughness degradation is consistent with a change in the dominant fracture mode governed by variations in the alloy purity. (C) 2006 Elsevier B.V. All rights reserved