Creep and rupture of an advanced fiber strengthened eutectic composite superalloy

Abstract

Creep and rupture tests have been conducted on NiTaC-13, an advanced TaC fiber strengthened composite. A simple equation is developed to describe the creep behavior in argon for strains up to about 1 pct at temperatures between 871 and 1093°C. This equation may readily be incorporated in a nonlinear analysis of the deformation of a body subjected to nonsteady and nonuniform stresses and temperatures. The creep rates in air show a progressive increase relative to those in argon due to a loss in cross-section resulting from oxidation. The Larson-Miller parameter is shown to be unreliable for either correlation or extrapolation of rupture data. This is especially true for air tests. A modified parameter is, however, shown to give a good correlation with all the data. Although metallurgical instabilities are present, they have no clear effect on rupture strength and are not uniquely linked with the parametric representation. There is a systematic increase in ductility with increase in temperature and the generally high level of ductility is reflected in pronounced notch strengthening. Some load relaxation tests indicate that fiber failure occurs in excess of 1 pct composite strain. It is suggested, therefore, that 1 pct could be an appropriate design limiting strain for this class of material.