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Factors which influence directional coarsening of Gamma prime during creep in nickel-base superalloy single crystalsChanges in the morphology of the gamma prime precipitate were examined as a function of time during creep at 982 C in 001 oriented single crystals of a Ni-Al-Mo-Ta superalloy. In this alloy, which has a large negative misfit of -0.80 pct., the gamma prime particles link together during creep to form platelets, or rafts, which are aligned with their broad faces perpendicular to the applied tensile axis. The effects of initial microstructure and alloy composition of raft development and creep properties were investigated. Directional coarsening of gamma prime begins during primary creep and continues well after the onset of second state creep. The thickness of the rafts remains constant up through the onset of tertiary creep a clear indication of the stability of the finely-spaced gamma/gamma prime lamellar structure. The thickness of the rafts which formed was equal to the initial gamma prime size which was present prior to testing. The single crystals with the finest gamma prime size exhibited the longest creep lives, because the resultant rafted structure had a larger number of gamma/gamma prime interfaces per unit volume of material. Reducing the Mo content by only 0.73 wt. pct. increased the creep life by a factor of three, because the precipitation of a third phase was eliminated.
Document ID
19840009285
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Mackay, R. A. (NASA Lewis Research Center Cleveland, OH, United States)
Ebert, L. J. (Case Western Reserve Univ.)
Date Acquired
September 4, 2013
Publication Date
January 1, 1984
Subject Category
Metallic Materials
Report/Patent Number
E-1997
NAS 1.15:83595
NASA-TM-83595
Meeting Information
Meeting: Intern. Symp. on Superalloys
Location: Seven Springs, PA
Country: United States
Start Date: October 7, 1984
End Date: October 11, 1984
Sponsors: American Inst. of Mining, Metallurgical and Petroleum Engineers
Accession Number
84N17353
Funding Number(s)
PROJECT: RTOP 505-33-1A
CONTRACT_GRANT: NSG-3246
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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