Mitigating time-dependent crack growth in Ni-base superalloy components. (January 2016)

• Record Type: Journal Article
• Authors: Chan, Kwai S.; Enright, Michael P.; Moody, Jonathan; Fitch, Simeon H.K.
• Is Part Of: International journal of fatigue. Volume 82:Part 2(2016)
• Page Start: 332
• Page End: 341
• Publication Date: 2016-01
• Subjects: Time-dependent crack growth -- Dwell fatigue -- Small-scale creep -- Life-prediction -- Risk mitigation; Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2015.03.020
• Languages: English
• ISSNs: 0142-1123

Abstract

Highlights: Develop a methodology to treat cycle- and time-dependent crack growth. Model the effects of tertiary γ ′ and grain size on time-dependent crack growth. Treat small-scale creep, oxidation, and stress relaxation at the crack tip. Reduce the risk of fracture of a gas turbine disk via microstructural control. Large grain size and tertiary γ ′ size at the rim extend disk life and reduce risk. Abstract: Advanced Ni-based gas turbine disks are expected to operate at higher service temperatures in aggressive environments for longer time durations. Exposures of Ni-base alloys to these aggressive environments can lead to cycle-dependent and time-dependent crack growth in superalloy components for advanced turbopropulsion systems. In this article, the effects of tertiary γ ′ on the crack-tip stress relaxation process, oxide fracture and time-dependent crack growth kinetics are treated in a micromechanical model which is then incorporated into the DARWIN® probabilistic life-prediction code. Using the enhanced risk analysis tool and material constants calibrated to powder-metallurgy (PM) disk alloy ME3, the effects of grain size and tertiary γ ′ size on combined time-dependent and cycle-dependent crack growth in a PM Ni-alloy disk is demonstrated for a generic rotor design and a realistic mission profile using DARWIN. The results of this investigation are utilized to assess the effects of controlling grain size and γ ′ size on the risk of disk fracture and to identify possible means for mitigating time-dependent crack growth (TDCG) in hot-section components.