Crack initiation sensitivity of wrought direct aged alloy 718 in the very high cycle fatigue regime: the role of non-metallic inclusions

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:678

Article

Texier, Damien^1,2,3  Cormier, Jonathan¹  Villechaise, Patrick¹  Stinville, Jean-Charles²  Torbet, Chris J.²  Pierret, Stephane⁴  Pollock, Tresa M.² 

[1] ISAE ENSMA, UPR CNRS 3346, Inst Pprime, Teleport 2,1 Ave Clement Ader,BP 40109, F-86961 Futuroscope, France

[2] Univ Calif Santa Barbara, Dept Mat, Santa Barbara, CA 93106 USA

[3] Ecole Technol Super, Dept Mech Engn, 1100 Rue Notre Dame Ouest, Montreal, PQ H3C 1K3, Canada

[4] Safran Aircraft Engines, Site Villaroche, F-77550 Rond Point Rene Ravaud, Moissy Cramayel, France

关键词: Very high cycle fatigue;    Superalloy;    Inconel 718;    Carbide;    Nitride;    EBSD;   

DOI  :  10.1016/j.msea.2016.09.098

来源: Elsevier

【 摘 要 】

Fatigue crack initiation in the direct aged version of the nickel-based superalloy Inconel 718 has been investigated at room temperature in the low stress/very high cycle regime via ultrasonic fatigue testing. Three different microstructures have been examined at the same strain amplitude in order to understand the influence of non-metallic inclusions (NMIs), i.e. carbides, carbonitrides and nitrides, and Sigma 3 twin boundary density on lifetime and failure mode. A slight refinement in grain structure and a higher Sigma 3 twin boundary density is associated with substantial reductions in lifetime. Decreasing Sigma 3 twin boundary density for fine grain microstructures results in a change in crack initiation mechanism from strain localization within grains at the high end of the grain size distribution to cracking of NMIs. To study the early stages of crack initiation and growth, specimens with pre-cracked NMIs were also tested in order to examine the role of the surrounding grain structure. Pre-cracked NMIs mainly result in macroscopic failure initiation at NMIs independent of the wrought microstructure. However, pre-loading specimens within the plastic domain highlighted the competition in crack initiation mode between cracked-NMIs and favorably oriented twin boundaries. Crack arrest from most of the pre-cracked NMIs demonstrates that surrounding grain structure (grain orientation, local plasticity and roughness in the vicinity of crack tip due to pre-straining) play a key role in the fatigue life of components stressed in the nominal elastic regime.

【 授权许可】

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