The elastic modulus correction term in creep activation energies: applied to oxide dispersion strengthened superalloy

Abstract

Creep properties of Inconel alloy MA 753 were studied. It was found that below 1500$sup 0$F, where elastic modulus is weakly dependent upon temperature, the modulus correction term to creep activation energy is small. Accordingly, for superalloy systems such as INCONEL alloy MA 753 and Mar-M 200, which show high apparent creep activation energies at this temperature, modulus corrections are unimportant and their true activation energies remain high. In contrast, at very high temperatures, as a consequence of the high temperature values and the sharper changes in the slope of the young modulus vs. temperature curve, the elastic modulus correction term can be significant--it is found to be about -142 kcal/ mole for INCONEL alloy MA 753 at 1900$sup 0$F and thus reducing the creep activation energy at this temperature from 202 kcal/mole to that of vacancy self-diffusion. It is noted that in general and especially at high temperatures the creep equation used to analyze creep data and creep activation energies must include the elastic modulus terms. Up to now, the neglect of these terms have by-in-large been justified. However, with the advent of very high temperature creep tests on the high temperature dispersion strengthened systems, the modulus terms mustmore » be taken into consideration. With respect to alloy designing for high temperature creep resistance, in addition to other considerations to obtain high temperature creep resistance, a high value of elastic modulus with a weak dependence on temperature at high temperatures is required. (auth)« less