title: Analytical electron microscopy of a crack tip extracted from a stressed Alloy 800 sample exposed to an acid sulfate environment.
abstract: Alloy 800 (Fe-21Cr-33Ni) has been found susceptible to cracking in acid sulfate environments, but the mechanism is not well understood. Alloy 800 C-ring samples were exposed to an acid sulfate environment at 315°C and cracks were found with depths in excess of 300μm after 60h. Preparation of a TEM sample containing crack tips is challenging, but the ability to perform high-resolution microscopy at the crack tip would lend insight to the mechanism of acid sulfate stress corrosion cracking (AcSCC). The lift-out technique combined with a focused ion beam sample preparation was used to extract a crack tip along the cross-section of an acid sulfate crack in an Alloy 800 C-ring. TEM elemental analysis was done using EDS and EELS which identified a duplex oxide within the crack; an inner oxide consisting of a thin 3-4nm Cr-rich oxide and an outer oxide enriched in Fe and Cr. Preliminary conclusions and hypotheses resulted with respect to the mechanism of AcSCC in Alloy 800.
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada. Electronic address: suraj.persaud@mail.utoronto.ca.
authors.forename: S Y
authors.initials: SY
authors.lastname: Persaud
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada.
authors.forename: A G
authors.initials: AG
authors.lastname: Carcea
authors.affiliation: Department of Materials Science and Engineering, and Canadian Centre for Electron Microscopy, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4M1, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Huang
authors.affiliation: Department of Materials Science and Engineering, and Canadian Centre for Electron Microscopy, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4M1, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Korinek
authors.affiliation: Department of Materials Science and Engineering, and Canadian Centre for Electron Microscopy, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4M1, Canada.
authors.forename: G A
authors.initials: GA
authors.lastname: Botton
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 3E5, Canada. Electronic address: roger.newman@utoronto.ca.
authors.forename: R C
authors.initials: RC
authors.lastname: Newman
keywords: Acid sulfate; Alloy 800; Crack tip; FIB; SCC; TEM