Fatigue oxidation interaction in in 100 superalloy
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I.
INTRODUCTION
HIGHtemperature low cycle fatigue is one of the major problems for turbine components in jet engines. Service conditions of blades and guide vanes are in fact very complex and include temperature changes and exposures to aggressive environment. In engineering practice the crack initiation resistance of components is generally estimated from simple isothermal low cycle fatigue tests which are carried out in laboratory air. Coffin has produced considerable evidence that in superalloys oxidation is a major damaging cause in high temperature low cycle fatigue, till The detrimental influence of oxidation was further evidenced by Woodford. [5] Frequencymodified parametric equations were proposed by Coffin 111 and then by Antolovich and co-workers I6] to account for fatigue life through intergranular oxidation. A model of high temperature fatigue damage has to account properly for the influence of oxidation on crack initiation and crack propagation mechanisms. One of the key problems in setting up such a model is to assess whether there is an interaction between oxidation kinetics and cyclic straining. Ward and co-workers in a low carbon steel r71 and. Bucklow and Skelton in a Cr-Mo-V steel tSj have shown the strong influence of cyclic stresses on oxidation kinetics. Low cycle fatigue at high temperature was found to strongly enhance oxidation kinetics in a cast cobalt based superalloy MAR-M509.19'1~ A simple model based on oxidation *MAR-M is a trademark of Martin Marietta Company.
kinetics which was measured from quantitative metallography on longitudinal sections was proposed to account for crack propagation in air. t9j This crack propagation model was found to be able to predict fatigue life under saw-tooth cycling, r9J compressive or tensile strain hold cycles, 111'121as well as under thermal fatigue, c1~'121 *IN is a trademark of the INCO family of companies. M. REGER, formerly with the Centre des Mat6riaux, Ecole des Mines de Paris, is with the D6partment Etudes des Mat6riaux, EDF les Renardi~res, BP 1, 77250 Moret-sur-Loing, France. L. REMY is with the Centre des Mat6riaux, Ecole des Mines de Paris, UA CNRS 866, BP 87, 91003 Evry Cedex, France. Manuscript submitted July l, 1987.
METALLURGICAL TRANSACTIONS A
The present study addresses the influence of low cycle fatigue stressing on the oxidation of uncoated IN 100 at 1000 ~ This superalloy is used as a blade or a guide vane material in jet engines. The low cycle fatigue behavior of this alloy was studied between room temperature and 1000 ~ in laboratory air. t131Fatigue life in air at 1000 ~ was studied over a wide range of frequency (4 10-3 to 2 Hz) and using tensile strain hold time tests. [131 Low cycle fatigue life was found to be strongly frequency dependent in air. This frequency dependence of fatigue life vanishes in vacuum and fatigue life in vacuum was found to be much longer than in air except for high frequency tests, t13j Oxidation was shown to reduce the crack propagation period and more drastically the crack initiation period. [1
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