Correlation between acoustic emission during SCC and fractography of cracking of the Zircaloys

The fractography of all transgranular stress corrosion cracking (SCC) failures of the Zircaloys is generally similar and consists of areas of cleavage separated by regions of ductile tearing. Minor differences arise due to processes which occur after the crack front has passed (i.e., due to etching in some environments). Major differences are apparent between room temperature and high temperature [200 to 400C (392 to 752F)] fractures in the nature of the ductile process which interconnects the regions of cleavage. Two types of acoustic emission have been recorded during SCC tests: (1) A continuous swishing noise, which control experiments have shown to arise either from electrochemical noise or from dislocation generation during plastic deformation, and (2) a discontinuous, cracking noise, which may result from either brittle crack propagation, oxide film cracking, or twinning. Since •neither type of acoustic emission can be related uniquely to a single process which is occurring, its diagnostic value in the SCC of hexagonal metals is apparently limited.