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The Effect of Boron on the Low Cycle Fatigue Behavior of Disk Alloy KM4The durability of powder metallurgy nickel base superalloys employed as compressor and turbine disks is often limited by low cycle fatigue (LCF) crack initiation and crack growth from highly stressed surface locations (corners, holes, etc.). Crack growth induced by dwells at high stresses during aerospace engine operation can be particularly severe. Supersolvus solution heat treatments can be used to produce coarse grain sizes approaching ASTM 6 for improved resistance to dwell fatigue crack growth. However, the coarse grain sizes reduce yield strength, which can lower LCF initiation life. These high temperature heat treatments also can encourage pores to form. In the advanced General Electric disk superalloy KM4, such pores can initiate fatigue cracks that limit LCF initiation life. Hot isostatic pressing (HIP) during the supersolvus solution heat treatment has been shown to improve LCF initiation life in KM4, as the HIP pressure minimizes formation of the pores. Reduction of boron levels in KM4 has also been shown to increase LCF initiation life after a conventional supersolvus heat treatment, again possibly due to effects on the formation tendencies of these pores. However, the effects of reduced boron levels on microstructure, pore characteristics, and LCF failure modes in KM4 still need to be fully quantified. The objective of this study was to determine the effect of boron level on the microstructure, porosity, LCF behavior, and failure modes of supersolvus heat treated KM4.
Document ID
20000120366
Acquisition Source
Glenn Research Center
Document Type
Technical Memorandum (TM)
Authors
Gabb, Timothy (NASA Glenn Research Center Cleveland, OH United States)
Gayda, John (NASA Glenn Research Center Cleveland, OH United States)
Sweeney, Joseph (Gilcrest Electric Brook Park, OH United States)
Date Acquired
September 7, 2013
Publication Date
September 1, 2000
Subject Category
Metals And Metallic Materials
Report/Patent Number
NAS 1.15:210458
NASA/TM-2000-210458
E-12454
Funding Number(s)
PROJECT: RTOP 714-04-10
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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