Dwell Notch Low-cycle Fatigue Performance of Powder Metal Alloy 10

Abstract

Alloy 10 is a third generation powder metal nickelbased superalloy developed by Honeywell for higher temperature turbine and compressor disk applications. Turbine disk blade attachments experience concentrated stresses at elevated temperatures for extended periods of time. Therefore, the notch dwell fatigue capability of an alloy is critical in determining the durability of a turbine disk. A dwell notch lowcycle fatigue (LCF) program was conducted to assess the high temperature capability of Alloy 10 under different geometric stress concentration conditions. The initial intent was not to significantly revise or develop new life prediction methods, but to determine practical operating conditions and temperature limits that minimize the detrimental effects of sustained peak loading. The test program consisted of uniaxially loaded flat double edge notch specimens with geometric stress concentration factors (Kt) of 2 and 3 evaluated under various sustained peak loading conditions. The Kt 2 and 3 specimens were selected to represent the range of stress gradients for turbine disk blade attachment locations. The test temperatures ranged from 650⁰C to 704⁰C with a typical peak tensile hold time of 90 seconds. Conventional non-dwell notch fatigue and creep rupture tests were also conducted to determine baseline properties.An elastic/plastic finite element model with additional creep visco-plasticity was also developed to better understand the potential mechanisms that influence fatigue crack initiation. The empirical and analytical results indicate that stress gradient, creep-induced stress relaxation, cyclic stress state, and environmental factors such as oxidation-assisted crack closure contribute to the elevated temperature dwell fatigue performance of Alloy 10.