Microstructural study: an aid to determination of failure mechanism in nickel base superalloy blades

Sujata, M and Madan, M and Raghavendra, K and Venkataswamy, MA and Bhaumik, SK (2010) Microstructural study: an aid to determination of failure mechanism in nickel base superalloy blades. Transactions of the Indian Institute of Metals, 63 (2-3). pp. 681-685. ISSN 0019-493X

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Cast nickel base superalloys are extensively used for high temperature gas turbine blade applications. The elevated temperature properties in these alloys are optimized through engineered microstructure, which is a combination of (a) γ-solid solution of Ni with elements such as W,Mo, Cr, Ta, Re etc, (b) γ′ precipitates, and (c) dispersed carbides. Over the years, the demand for high engine efficiency has resulted in the development of new generation superalloys with improved elevated temperature properties, especially creep resistance. These superalloys are highly alloyed with solid-solution strengthening elements and hence, impose greater technological challenges in fabrication. Due to high alloy contents, these alloys are prone to formation of detrimental phases such as the topologically close packed (TCP) phases. These phases may appear in the microstructure during the blade fabrication stages or precipitate out during exposure to high temperature and stress. In addition, the γ′ precipitates can change in morphology, shape and size during applications resulting in deterioration in high temperature mechanical properties, in general. These unfavorable microstructural changes often lead to premature failure in gas turbine engines. While analyzing these failures, the microstructural study provides important information in identifying whether the blades had faulty microstructure to start with or the abnormalities observed have resulted during exposure to service conditions. This in turn can be related to engine operating conditions. In the present paper, this has been demonstrated through analysis of two service failure cases wherein the high pressure turbine blades had failed in flight leading to aircraft accidents.

Item Type: Article
Additional Information: Copyright for this article belongs to M/s. Indian Institute of Metals
Uncontrolled Keywords: Turbine blades;Superalloy;Microstructure;TCP phases;Rafting
Subjects: AERONAUTICS > Aeronautics (General)
Depositing User: Ms. Alphones Mary
Date Deposited: 12 Mar 2012 06:16
Last Modified: 12 Mar 2012 06:16
URI: http://nal-ir.nal.res.in/id/eprint/10376

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