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Title: Phase stability and mechanical properties of C-22 alloy aged in the temperature range 590 to 760 C for 16,000 hours

Abstract

The phase stability of C-22 alloy (UNS No. N06022) was studied by aging samples at 593, 649, 704 and 760 C for 2,000 h (2.7 mo) and 16,000 h (1.8 yr). The tensile properties and the Charpy impact toughness of these samples were measured in the mill annealed condition as well as after aging. The microstructures of samples aged 16,000 hours were examined using scanning and transmission electron microscopy (SEM and TEM). Preliminary TEM results suggest that {mu} phase forms at all temperatures investigated. Discrete carbide particles in addition to a film with very uniform thickness which appears to be {mu} phase formed on grain boundaries in the sample aged at 593 C. The ordered Ni{sub 2}(Cr, Mo) phase was also seen in this sample. At the higher aging temperatures, mainly {mu} phase forms covering all the grain boundaries and also distributed throughout the bulk. Although strength increased somewhat with aging, the ductility decreased due to the formation of these grain boundary precipitates and brittle intermetallics.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (US)
Sponsoring Org.:
USDOE
OSTI Identifier:
20015847
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: 1998 Materials Research Society Fall Meeting, Boston, MA (US), 11/30/1998--12/04/1998; Other Information: Single article reprints are available from University Microfilms Inc., 300 North Zeeb Road, Ann Arbor, Michigan 48106; PBD: 1999; Related Information: In: Scientific basis for nuclear waste management XXII. Materials Research Society symposium proceedings: Volume 556, by Wronkiewicz, D.J.; Lee, J.H. [eds.], 1355 pages.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; HASTELLOYS; PHASE STUDIES; MICROSTRUCTURE; ULTIMATE STRENGTH; YIELD STRENGTH; ELONGATION; CHARPY TEST; RADIOACTIVE WASTE DISPOSAL; CONTAINERS

Citation Formats

Summers, T.S.E., Wall, M.A., Kumar, M., Matthews, S.J., and Rebak, R.B. Phase stability and mechanical properties of C-22 alloy aged in the temperature range 590 to 760 C for 16,000 hours. United States: N. p., 1999. Web.
Summers, T.S.E., Wall, M.A., Kumar, M., Matthews, S.J., & Rebak, R.B. Phase stability and mechanical properties of C-22 alloy aged in the temperature range 590 to 760 C for 16,000 hours. United States.
Summers, T.S.E., Wall, M.A., Kumar, M., Matthews, S.J., and Rebak, R.B. Thu . "Phase stability and mechanical properties of C-22 alloy aged in the temperature range 590 to 760 C for 16,000 hours". United States. doi:.
@article{osti_20015847,
title = {Phase stability and mechanical properties of C-22 alloy aged in the temperature range 590 to 760 C for 16,000 hours},
author = {Summers, T.S.E. and Wall, M.A. and Kumar, M. and Matthews, S.J. and Rebak, R.B.},
abstractNote = {The phase stability of C-22 alloy (UNS No. N06022) was studied by aging samples at 593, 649, 704 and 760 C for 2,000 h (2.7 mo) and 16,000 h (1.8 yr). The tensile properties and the Charpy impact toughness of these samples were measured in the mill annealed condition as well as after aging. The microstructures of samples aged 16,000 hours were examined using scanning and transmission electron microscopy (SEM and TEM). Preliminary TEM results suggest that {mu} phase forms at all temperatures investigated. Discrete carbide particles in addition to a film with very uniform thickness which appears to be {mu} phase formed on grain boundaries in the sample aged at 593 C. The ordered Ni{sub 2}(Cr, Mo) phase was also seen in this sample. At the higher aging temperatures, mainly {mu} phase forms covering all the grain boundaries and also distributed throughout the bulk. Although strength increased somewhat with aging, the ductility decreased due to the formation of these grain boundary precipitates and brittle intermetallics.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jul 01 00:00:00 EDT 1999},
month = {Thu Jul 01 00:00:00 EDT 1999}
}

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  • The phase stability of C-22 alloy (UNS #N06022) was studied by aging samples at 593, 649, 704 and 760°C for 2000 h (2.7 mo) and 16,000 h (1.8 yr). The tensile properties and the Charpy impact toughness of these samples were measured in the mill annealed condition as well as after aging. The microstructures of samples aged 16,000 hours were examined using scanning and transmission electron microscopy (SEM and TEM). Preliminary TEM results suggest that m phase forms at all temperatures investigated. Discrete carbide particles in addition to a film with very uniform thickness which appears to be m phasemore » formed on grain boundaries in the sample aged at 593°C. The ordered Ni 2(Cr, Mo) phase was also seen in this sample. At the higher aging temperatures, mainly m phase forms covering all the grain boundaries and also distributed throughout the bulk. Although strength increased somewhat with aging, the ductility decreased due to the formation of these grain boundary precipitates and brittle intermetallics.« less
  • Alloy 22 (UNS N06022) is a candidate material for the external wall of the high level nuclear waste containers for the potential repository site at Yucca Mountain. In the mill-annealed (MA) condition, Alloy 22 is a single face centered cubic phase. When exposed to temperatures on the order of 600 C and above for times higher than 1 h, this alloy may develop secondary phases that reduce its mechanical toughness and corrosion resistance. The objective of this work was to age Alloy 22 at temperatures between 482 C and 760 C for times between 0.25 h and 6,000 h andmore » to study the mechanical and corrosion performance of the resulting material. Aging was carried out using wrought specimens as well as gas tungsten arc welded (GTAW) specimens. Mechanical and corrosion testing was carried out using ASTM standards. Results show-that the higher the aging temperature and the longer the aging time, the lower the impact toughness of the aged material and the lower its corrosion resistance. However, extrapolating both mechanical and corrosion laboratory data predicts that Alloy 22 will remain corrosion resistant and mechanically robust for the projected lifetime of the waste container.« less
  • The phase stability of C-22 alloy (UNS No. N06022) gas tungsten arc welds was studied by aging samples at 427, 482, 538, 593, 649, 704, and 760 C for times up to 40,000 hours. The tensile properties and the Charpy impact toughness of these samples were measured in the as-welded condition as well as after aging. The corrosion resistance was measured using standard immersion tests in acidic ferric sulfate (ASTM G 28 A) and 2.5% hydrochloric acid solutions at the boiling point. The microstructures of weld samples were examined using scanning electron microscopy (SEM). One weld sample (aged 40,000 hoursmore » at 427 C) was examined using transmission electron microscopy (TEM). The structure of the unaged welds was dendritic with tetrahedrally close-packed (TCP) phase particles in the interdendritic regions. Long-range order was seen in the weld aged at 427 C for 40,000 hours and was assumed to also occur in other welds aged below approximately 600 C. At temperatures above about 600 C, TCP phase nucleation and growth of existing particles occurred. This precipitation occurred near the original particles presumably in regions of the highest molybdenum (Mo) segregation. Lower temperatures had little or no effect on the morphology of TCP phases. The C-22 weld samples were approximately 25% stronger but 30-40% less ductile than the base metal. Strengthening of the weld during aging occurred significantly only at 593 C for the aging times investigated. Because strengthening was not seen at higher temperatures, it was assumed to be due to ordering which has been seen in C-22 base metal at this temperature. A small amount of strengthening was seen at 427 C after 40,000 hours where ordering was just beginning. The Charpy impact toughness was reduced dramatically with aging. The time at which this reduction occurred decreased as aging temperature increased suggesting that the reduced ductility is due to the presence and growth of the brittle TCP phases. The corrosion rate of weld samples tested in the standard ASTM G 28 A solution and in a 2.5% HCl solution was higher than was seen with C-22 base metal. After aging, however, the corrosion rate of weld and base metal samples became comparable.« less
  • The effects of long-term aging at intermediate temperature on the mechanical properties of type 308 stainless steel weld metals have been studied. Three multipass shielded metal-arc welds with ferrite levels of 4, 8, or 12% were aged up to 50,000 h at 343{degrees}C. Tensile and Charpy V-notch specimens were used to determine the effects of aging on the mechanical properties of the weld metal. Aging had little effect on the yield strength of the weld metal, but did result in a slight increase (approximately 5%) in the ultimate tensile strength. The ferrite content had little effect on the yield strengthmore » of the materials, but the ultimate tensile strength increased slightly with higher ferrite content. In contrast to the small effect on the tensile properties, the impact properties were significantly degraded by aging. The extent of the degradation increased with increasing ferrite content and continued to increase with increasing aging time, Spinodal decomposition and the precipitation of G-phase particles in the ferrite phase are believed to be responsible for the degradation of the mechanical properties.« less