TS-100 High-Cycle Fatigue Failure Modelling and the Endurance Prediction of Ni-Base Superalloy Protective Coatings(Session D-5 Maintenance and Control 2)

概要

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The effect of protective coating on the high-cycle fatigue strength of Ni-base superalloy, IN738LC, is first modeled from the viewpoint of fracture mechanics, summarizing the previous works by the authors in which the influences of the coating material, test temperature, thickness of coating film, long term thermal aging and multi-layers coatings have been studied. The effect was condensed into the following roles, depending on the relative and absolute mechanical properties of the coating film and the substrate: a role as fatigue crack initiator, a role to make geometric change of fatigue crack, and a role to induce stress concentration. A new semi-empirical method to predict the fatigue endurance of the coated material is proposed, by applying the concept of latent, or fictitious crack, which has been originally introduced by Haddad et al. to explain the crack length dependence in the fatigue crack threshold in monolithic materials. In the proposed method the coating film and the incidental diffusion zone are treated as a part of latent crack which interacts with the substrate, depending on the mechanical properties. The method is developed so that it can be applied not only to single layer coatings but also to multi-layers coatings. It is shown that the proposed method gives good estimation corresponding well with the experimental results.
社団法人日本ガスタービン学会の論文
1999-11-14