STP1389

    Assessments of Low Cycle Fatigue Behavior of Powder Metallurgy Alloy U720

    Published: Jan 2000


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    Abstract

    The fatigue lives of modern powder metallurgy disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary as functions of variables the different steps of materials/component processing: powder atomization, consolidation, extrusion, forging, heat treating, and machining [1–4]. It is important to understand the relationship between the statistical variations in life and these variables, as well as the change in life distribution due to changes in fatigue loading conditions. The objective of this study was to investigate these relationships in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were performed at 538°C (1000°F) at limited sets of test conditions. Analyses were performed to: (1) assess variations of microstructure, mechanical properties, and LCF failure initiation sites as functions of disk processing and loading conditions; and (2) compare mean and minimum fatigue life predictions using different approaches for modeling the data from assorted test conditions.

    Significant variations in life were observed as functions of the disk-processing variables evaluated. However, the lives of all specimens could still be combined and modeled together. The failure initiation sites for tests performed at a strain ratio Rε = εminmax of 0 were different from those in tests at a strain ratio of - 1. An approach could still be applied to account for the differences in mean and maximum stresses and strains. This allowed the data in tests of various conditions to be combined for more robust statistical estimates of mean and minimum lives.

    Keywords:

    superalloy, powder metallurgy, low cycle fatigue, inclusions, facets


    Author Information:

    Gabb, TP
    Research metallurgist, NASA Glenn Research Center, Cleveland, OH

    Bonacuse, PJ
    Research engineer, U.S. Army Research Laboratory at NASA Glenn Research Center, Cleveland, OH

    Ghosn, LJ
    Research Engineer, NASA Glenn Research CenterEveready Battery Company, Inc., ClevelandWestlake, OHOH

    Sweeney, JW
    Microscopist, Gilcrest Co., NASA Glenn Research Center, Cleveland, OH

    Chatterjee, A
    Research engineers, Allison Engine Co., Indianapolis, IN

    Green, KA
    Research engineers, Allison Engine Co., Indianapolis, IN


    Paper ID: STP14797S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP14797S


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