Creep, fatigue, and environmental response of Alloy 800H tested at 900 degrees C
Leet, David Michael
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https://hdl.handle.net/2142/22214
Description
Title
Creep, fatigue, and environmental response of Alloy 800H tested at 900 degrees C
Author(s)
Leet, David Michael
Issue Date
1990
Doctoral Committee Chair(s)
Stubbins, James F.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Nuclear
Engineering, Metallurgy
Engineering, Materials Science
Language
eng
Abstract
Creep and creep rupture studies have been carried out at 900$\sp\circ$C in lab air and in vacuum on Alloy 800H. Three different notch acuities were chosen so that the effect of stress intensity on the rupture lifetimes could be examined. The effect of oxidation on the creep rupture lifetimes has also been examined using reduced section modelling and vacuum testing of pre-oxidized specimens. Tests in oxidizing environments were found to have similar, but somewhat shorter failure lives compared to vacuum exposure. This effect is accentuated in the low stress notched specimen tests where the stress concentration and oxidation can act together most effectively to reduce failure life.
A direct current potential drop technique was utilized to monitor in situ creep strain. A high speed data acquisition system was employed to collect and transform the direct current potential drop data. This methodology was found to provide accurate measurements of creep strain even in notched specimens.
A finite difference method was developed to perform second derivative analysis of the creep curves. This technique showed that it is possible to quantitatively identify the end points of the various creep stages as well as to identify crack initiation and crack advance events.
High resolution electron metallography was performed on the creep and creep rupture specimens, and a finite element analysis of smooth and notched specimens was used, in conjunction with this microstructural data, to aid in the interpretation of the smooth and notched specimen failures.
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