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Processing, physical metallurgy and creep of NiAl + Ta and NiAl + Nb alloysPowder processed NiAl + Ta alloys containing 1, 2, and 4.5 at percent tantalum and NiAl + Nb alloys containing 1 and 2 at percent niobium were developed for improved creep properties. In addition, a cast alloy with 5 at percent tantalum was also studied. Hot extrusion parameters for processing alloys with 1 and 2 at percent of tantalum or niobium were designed. The NiAl + 4.5 at percent Ta alloy could be vacuum hot pressed successfully, even though it could not be extruded. All the phases in the multiphase alloys were identified and the phase transformations studied. The Ni2AlTa in NiAl + 4.5 at percent Ta alloy transforms into a liquid phase above 1700 K. Solutionizing and annealing below this temperature gives rise to a uniform distribution of fine second phase precipitates. Compressive creep properties were evaluated at 1300 K using constant load and constant velocity tests. In the higher strain rate region single phase NiAl + 1 at percent Ta and NiAl + 1 at percent Nb alloys exhibit a stress exponent of 5 characteristic of climb controlled dislocation creep. In slower strain rate regime diffusional creep becomes important. The two phase alloys containing 2 to 5 at percent Ta and 2 at percent Nb show considerable improvement over binary NiAl and single phase alloys. Loose dislocation networks and tangles stabilized by the precipitates were found in the as crept microstructure. The cast alloy which has larger grains and a distribution of fine precipitates shows the maximum improvement over binary NiAl.
Document ID
19880011911
Acquisition Source
Legacy CDMS
Document Type
Thesis/Dissertation
Authors
Pathare, Viren M.
(Case Western Reserve Univ. Cleveland, OH, United States)
Date Acquired
September 5, 2013
Publication Date
April 1, 1988
Subject Category
Metallic Materials
Report/Patent Number
NAS 1.26:182113
NASA-CR-182113
Accession Number
88N21295
Funding Number(s)
CONTRACT_GRANT: NAG3-387
PROJECT: RTOP 535-07-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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