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High temperature oxidation of 304L stainless steel and its effects on glass-to-metal joining

Proceedings of the 3rd International Brazing and Soldering Conference

Susan, D.F.; Van Den Avyle, James A.; Monroe, Saundra L.; Sorensen, Neil R.; McKenzie, Bonnie B.; Michael, Joseph R.; Christensen, J.E.; Walker, Charles A.

An oxidation treatment, often termed "pre-oxidation", is performed on austenitic stainless steel prior to glass/metal joining to produce hermetic seals. The resulting thin oxide acts as a transitional layer and a source of Cr and other elements which diffuse into the glass during the subsequent bonding process. Pre-oxidation is performed in a low pO 2 atmosphere to avoid iron oxide formation and the final oxide is composed of Cr 2O 3, MnCr 2O 4 spinel, and SiO 2. Significant heat-to-heat variations in the oxidation behavior of 304L stainless steel have been observed, which result in inconsistent glass/metal seal behavior. The objectives of this work were to characterize the oxidation kinetics, the oxide morphology and composition, and the stainless steel attributes that lead to robust glass/metal seals. The oxidation kinetics were determined by thermogravimetric (TG) analysis and the oxide layers were characterized using metallography, SEM, focused ion beam (FIB) analysis, and image analysis. The results show that poor sealing behavior is associated with slower oxidation kinetics and a more continuous layer of SiO 2 at the metal/oxide interface. In addition, the effects of 304L heat composition on oxidation behavior will be discussed. Copyright © 2006 ASM International®.

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The effects of 304L stainless steel pre-oxidation on bonding to alkali barium silicate glass

Ceramic Engineering and Science Proceedings

Susan, D.F.; Van Den Avyle, James A.; Monroe, Saundra L.; Sorensen, Neil R.; McKenzie, Bonnie B.; Michael, Joseph R.; Christensen, J.E.; Walker, Charles A.

An oxidation treatment, often termed "pre-oxidation", is performed on austenitic stainless steel prior to joining to alkali barium silicate glass to produce hermetic seals. The resulting thin oxide acts as a transitional layer and a source of Cr and other elements which diffuse into the glass during the subsequent bonding process. Pre-oxidation is performed in a low pO2 atmosphere to avoid iron oxide formation and the final oxide is composed of Cr2O3, MnCr2O4 spinel, and SiO2. Significant heat-to-heat variations in the oxidation behavior of 304L stainless steel have been observed, which result in inconsistent glass-to-metal (GTM) seal behavior. The objectives of this work were to characterize the stainless steel pre-oxidized layer and the glass/oxide/304L interface region after glass sealing. The 304L oxidation kinetics were determined by thermogravimetric (TG) analysis and the glass/metal seals characteristics were studied using sessile drop tests, in which wetting angles were measured and glass adhesion was analyzed. The pre-oxidized layers and glass/metal interface regions were characterized using metallography, focused ion beam (FIB) sectioning, scanning and transmission electron microscopy, and electron probe microanalysis (EPMA). The results show that poor glass sealing behavior is associated with a more continuous layer of SiO 2 at the metal/oxide interface.

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Failure analysis of rutile sleeves in MC3080 lightning arrestor connectors

Watson, Chad S.; Kilgo, Alice C.; Ernest, Terry L.; Monroe, Saundra L.; Tuttle, Bruce T.; Olson, Walter R.

The purpose of this SAND Report is to document efforts in the extraction and failure analyses of sleeve-style Lightning Arrestor Connectors (LACs). Several MC3080 and MC3079 LACs were recovered from the field and tested as part of the Enhanced Surveillance Campaign. A portion of these LACs failed retesting. Terry Ernest (01733), the LAC Component Engineer, provided eleven MC3080 LACs for evaluation where four of the LACs failed IR/DCW and one failed FRB requirements. The extraction of rutile sleeves from failed LACs was required to determine the source of failure. Rutile sleeves associated with connector function failures were examined for cracks, debris as well as any other anomalies which could have caused the LAC to not function properly. Sleeves that failed FRB or that experienced high FRB exhibited high symmetry, smooth surface, long-flow amicon, and slightly over-sized inside diameter. LACs that failed DCW or IR requirements had rutile sleeves that exhibited breakdown tracks.

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6 Results
6 Results