Effect of Creep-Exposure on Mechanical Properties of Rene' 41. Part I.

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Report Number: ASD TR 61-73
Author(s): Gluck, Jeremy V., Freeman, James W.
Corporate Author(s): University of Michigan
Laboratory: Directorate of Materials and Processes
Date of Publication: 1961-08
Pages: 79
Contract: AF 33(616)-6462
DoD Project: 7381
DoD Task: 73810
Identifier: AD0271480

An investigation of the influence of creep-exposure on the mechanical properties at room temperature of Rene' 41 alloy is in progress. The objec­tives are to delineate the conditions causing changes in these properties and to develop general principles for predicting the influence of creep on such properties of nickel-base superalloys. The results obtained to date for exposures at 1200 ° to 1800 ° F and for 10 to 200 hours show that thermally-­induced structural changes reduce room temperature strength and ductility when the exposure temperatures are 1500° F or higher. Limited data indicate that surface reactions also reduce properties with the temperature range of the effect extending to lower temperatures than 1500 ° F. Creep accelerated the structural changes to some extent. In addition, it raised yield strength by a Bauschinger effect. Strain hardening, possibly in combination with strain-induced precipitation hardening raised tensile strength for exposure below 1500° F. In addition, ductility was reduced more in the presence of creep than by thermally-induced structural changes. Creep strains approaching the ultimate ductility of the alloy at 1200 ° and 1300 °F induced deep cracking which reduced properties. This type of an effect was not found at higher temperatures. The loss in strength from thermally-induced structural changes appeared to be due to overaging of the gamma prime precipitate. The loss in ductility was associated with agglomeration of carbides and gamma prime in the grain boundaries. The surface effects were associated with surface intergranular oxidation and/or cracking plus depletion of alloying elements. The role of creep remains to be further clarified and more study of the surface reactions is required before general principles can be established for the influence of creep on ordinary temperature mechanical properties.

Provenance: Lockheed Martin Missiles & Fire Control

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