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High temperature coarsening of Cr2Nb precipitates in Cu-8 Cr-4 Nb alloyA new high-temperature-strength, high-conductivity Cu-Cr-Nb alloy with a CrNb ratio of 2:1 was developed to achieve improved performance and durability. The Cu-8 Cr4 Nb alloy studied has demonstrated remarkable thermal and microstructural stability after long exposures at temperatures up to 0.98 T(sub m). This stability was mainly attributed to the slow coarsening kinetics of the Cr2Nb precipitates present in the alloy. At all temperatures, the microstructure consists of a bimodal and sometimes trimodal distribution of strengthening Cr2Nb precipitates, depending on precipitation condition, i.e. from liquid or solid solution, and cooling rates. These precipitates remain in the same size range, i.e. large precipitates of approximately I pm, and small precipitates less dm 300 nm, and effectively pin the grain boundaries thus retaining a fine grain size of 2.7 micro-m after 100 h at 1323 K. (A relatively small number of Cr-rich and Nb-rich particles were also present.) This grain boundary pinning and sluggish coarsening of Cr2Nb particles explain the retention of good mechanical properties after prolonged holding at very high temperatures, e.g., 75% of the original hardness after aging for 100 h at 1273 K. Application of LSW-based coarsening models indicated that the coarsening kinetics of the large precipitates are most likely governed by grain boundary diffsion and, to a lesser extent, volume diffusion mechanisms.
Document ID
19960028089
Acquisition Source
Legacy CDMS
Document Type
Thesis/Dissertation
Authors
Anderson, Kenneth Reed
(California Univ. Davis, CA United States)
Date Acquired
September 6, 2013
Publication Date
June 1, 1996
Subject Category
Metallic Materials
Report/Patent Number
NASA-CR-198492
E-10293
NAS 1.26:198492
Accession Number
96N29180
Funding Number(s)
PROJECT: RTOP 446-03-02
CONTRACT_GRANT: NASA Order C--77166-B
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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