Tecnologia em Metalurgia, Materiais e Mineração
https://tecnologiammm.com.br/article/doi/10.4322/tmm.2014.019
Tecnologia em Metalurgia, Materiais e Mineração
Artigo Original

FADIGA ISOTÉRMICA E TERMOMECÂNICA DE UMA SUPERLIGA À BASE DE NIQUEL

ISOTHERMAL AND THERMOMECHANICAL FATIGUE OF A NICKEL-BASE SUPERALLOY

Engler-Pinto Junior, Carlos Carvalho; Spinelli, Dirceu

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Resumo

Os gradientes térmicos originados durante regimes transientes em operações de liga/desliga produzem complexos carregamentos mecânicos e térmicos de fadiga, que limitam a vida de palhetas de turbina e de outros componentes de motores que operam a altas temperaturas. Assim, torna-se imprescindível uma avaliação mais criteriosa e confiável da fadiga não isotérmica. Este trabalho investiga o comportamento em fadiga isotérmica de baixo ciclo (FBC) e fadiga termomecânica (FTM) de uma superliga à base de Ni, CM 247LC-DS, extensivamente utilizada a altas temperaturas. Os ensaios mecânicos foram realizados em temperaturas entre 600°C e 1.000°C. O comportamento mecânico da liga foi fortemente afetado no intervalo 800°C-1.000°C e o comportamento tensão-deformação cíclico observado para todo o intervalo de temperatura obedeceu à equação de Ramberg-Osgood. Um modelo simplificado de tensão-deformação não isotérmico, baseado no conceito de plasticidade linear foi proposto e descreveu o comportamento de fadiga termomecânica observado, tanto para ciclos em fase, como para fora de fase.

Palavras-chave

Superliga, Fadiga isotérmica, Fadiga termomecânica

Abstract

Thermal gradients arising during transient regimes of start-up and shutdown operations produce a complex thermal and mechanical fatigue loading which limits the life of turbine blades and other engine components operating at high temperatures. More accurate and reliable assessment under non-isothermal fatigue becomes therefore mandatory. This paper investigates the nickel base superalloy CM 247LC-DS under isothermal low cycle fatigue (LCF) and thermomechanical fatigue (TMF). Test temperatures range from 600°C to 1,000°C. The behavior of the alloy is strongly affected by the temperature variation, especially in the 800°C-1,000°C range. The Ramberg-Osgood equation fits very well the observed isothermal behavior for the whole temperature range. The simplified non-isothermal stress-strain model based on linear plasticity proposed to represent the thermo-mechanical fatigue behavior was able to reproduce the observed behavior for both in-phase and out-of-phase TMF cycling.

Keywords

Superalloy, Isothermal fatigue, Thermomechanical fatigue

Referências



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2. Harris K, Erickson GL, Schwer RE. Development of CMSX series of single-crystals alloys for advanced technology turbine components. In: American Institute of Mining, Metallurgical, and Petroleum Engineers. Proceedings of the TMS-AIME Fall Meeting; 1982; St. Louis, USA. Warrendale: TMS; 1982.

3. Date CG. TMF design considerations in turbine airfoil of advanced turbine engines. In: American Society of Mechanical Engineers. Proceedings of the Symposium, 112th ASME Winter Annual Meeting; 1-6 Dec. 1991; Atlanta, USA. Nova Iorque: ASME; 1991. p.59-64.

4. Erickson GL, Harris K. DS and SX for industrial turbines. In: Coutsouradis D., et al., editors. Materials for advanced power engineering, Part II. Amsterdam: Kluwer Academic Publishers; 1994. p.1055-74.

5. American Society for Testing Materials. ASTM E606-04: Standard practice for strain-controlled fatigue testing. West Conshohocken: ASTM; 2004. http://dx.doi.org/10.1520/E0606-04.

6. American Society for Testing Materials. ASTM E2368-04: Standard practice for strain controlled thermomechanical fatigue testing. West Conshohocken: ASTM; 2004. http://dx.doi.org/10.1520/E2368-04.

7. Engler-Pinto CC Jr, Spinelli D. Cyclic behavior of the CM247LC-DS superalloy at high temperatures. In: Institut für Prozess-und Werkstofftechnik. Proceedings of Conferences on Applied Mechanics, Materials Science and Joining and Processes – CAMP; 3-4 Apr. 2002; Paderborn, Germany. Paderborn: Institut für Prozess-und Werkstofftechnik,Universität Paderborn; 2002. p. 2-13.
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