Metallographic and Fractographic Observations of Hydrides during Delayed Hydride Cracking in Zr-2.5% Nb Alloy

• Published in: Materials characterization 1998, Vol.40 (1), p.15-25
• Main Authors: Jovanovic ́, M.T., Shek, G.K., Seahra, H., Eadie, R.L.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Metals. Metallurgy; Other heat and thermomechanical treatments; Physics; Treatment of materials and its effects on microstructure and properties
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/S1044-5803(97)00091-0

Potential drop measurements, optical microscopy, and scanning electron microscopy were performed to study the mechanism of delayed hydride cracking (DHC), the relation of the fracture to the hydride morphology, and the fractography of the DHC mechanism. The material used in this study was taken from modified extrusions of the material used to manufacture Zr-2.5% Nb pressure tubes. The material was electrolytically hydrided to approximately 60μg/g before testing. Cracking tests were carried out at 250°C with an applied K I of 12MPa m . The number of potential “jumps” was strongly correlated to the number of striations on the fracture surface. The results indicate that the DHC process occurs in these samples in an intermittent fashion. Brittle fracture is the operating fracture mechanism for the hydrides that cover most of the fracture surface, but there are some regions of ductile fracture both within the fracture and at the striations.