Competing Modes for Crack Initiation from Non-metallic Inclusions and Intrinsic Microstructural Features During Fatigue
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Competing Modes for Crack Initiation from Nonmetallic Inclusions and Intrinsic Microstructural Features During Fatigue in a Polycrystalline NickelBased Superalloy JEAN-CHARLES STINVILLE, ETIENNE MARTIN, MALLIKARJUN KARADGE, SHAK ISMONOV, MONICA SOARE, TIM HANLON, SAIRAM SUNDARAM, MCLEAN P. ECHLIN, PATRICK G. CALLAHAN, WILLIAM C. LENTHE, JIASHI MIAO, ANDREW E. WESSMAN, REBECCA FINLAY, ADRIAN LOGHIN, JUDSON MARTE, and TRESA M. POLLOCK Cyclic fatigue experiments in the high and very high cycle fatigue regimes have been performed on a Rene´ 88DT polycrystalline nickel-based superalloy. The microstructural configurations that favor early strain localization and fatigue crack initiation at high temperature from 400 °C to 650 °C have been investigated. Competing failure modes are observed in the high to the very high cycle fatigue regime. Fatigue cracks initiate from non-metallic inclusions and from intrinsic internal microstructural features. Interestingly, as stresses are reduced into the very high cycle regime, there is a transition to initiation only at crystallographic facets. At higher stress in the high cycle fatigue regime, a significant fraction of specimens initiate cracks at non-metallic inclusions. This transition is analyzed with regard to microstructural features that favor strain localization and accumulate damage early during cycling. https://doi.org/10.1007/s11661-018-4780-3 Ó The Minerals, Metals & Materials Society and ASM International 2018
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INTRODUCTION
FATIGUE is an important life limiting property for turbine engine disk components. The highly engineered polycrystalline superalloy materials used in these applications possess intrinsic and extrinsic microstructural features that strongly influence fatigue crack initiation.[1,2] The process of crack initiation and early crack propagation consumes a large part of the total fatigue life in polycrystalline superalloys,[3] motivating the study of the microstructural features and corresponding grain
JEAN-CHARLES STINVILLE, MCLEAN P. ECHLIN, PATRICK G. CALLAHAN, WILLIAM C. LENTHE, and TRESA M. POLLOCK are with the Materials Department, University of California Santa Barbara, Santa Barbara, CA 93106-5050. Contact e-mail: [email protected] ETIENNE MARTIN, MALLIKARJUN KARADGE, SHAK ISMONOV, MONICA SOARE, TIM HANLON, SAIRAM SUNDARAM, ADRIAN LOGHIN, and JUDSON MARTE are with General Electric Global Research, Niskayuna, NY 12309. ANDREW E. WESSMAN and REBECCA FINLAY are with General Electric Aviation, Cincinnati, OH 45215. JIASHI MIAO is with the Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109. Manuscript submitted March 29, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
neighborhoods that are life limiting. One concern is the introduction of non-metallic inclusions that are inherent to powder metallurgy processing. The presence of inclusions often leads to competing failure modes and a wide variability in fatigue durability.[2,4] To develop predictive models for cyclic loading, the relationship bet
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