A fractographic study of stress corrosion cracking of Zircaloy-4 in a methanol/ HCl solution

Abstract

Stress corrosion cracking (SCC) of Zircaloy-4 in a methanol solution containing 0.4 vol% HCl has been studied at 30°C from the fractographic aspects by using the constant elongation rate and constant load methods. Scanning electron microscopic (SEM) examination of SCC fracture surfaces revealed that an intergranular fracture mode entirely appeared in the region of stress corrosion (SC) crack initiation and in the initial stage of SC crack propagation. As the SC crack propagated, a fracture mode transition occurred from the intergranular via a fluted transgranular to a quasi-cleavage type. It has also been observed that at the same crack length level the fracture mode changed from the intergranular manner at the surface region to the fluted transgranular or the quasi-cleavage manner in the inner region of the specimens. The fracture mode transitions are discussed. It is suggested that the appearances of intergranular and quasi-cleavage fracture mode in fracture surface are based upon the anodic dissolution mechanism and the change of the SCC mechanism from the anodic dissolution to the hydrogen embrittlement, respectively.