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
http://dx.doi.org/10.4322/tmm.2014.019
Tecnol. Metal. Mater. Min., vol.11, n2, p.125-130, 2014
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 imprescindÃvel 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 cÃclico 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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