High-Temperature Creep of Nickel-Chromium Alloys (On the Relation Between High-Temperature Creep and Diffusion in Nickel Base Solid Solutions, IV)

Tensile creep properties of nickel-chromium alloys containing up to 30 at% of chromium have been studied. Tests were carried out in argon atmosphere over the temperature range from 650° to 1150°C, and the stress range from 1.3 to 6.0 kg/mm2. Little changes in general trend of creep curves are observed with increase of the chromium content. The steady state creep rate (\dotεs) decreases with the increasing chromium content. Temperature and stress dependences of the steady state creep rate were analysed using Dorn’s equation, \dotεs=Cσnexp(−Qs⁄RT). Activation energies (Qs) are independent of both applied stress and grain size (from 0.05 to 1.2 mm in average diameters). Qs having a value of 66 kcal/mol for pure nickel scarcely vary with the increasing chromium content at a low concentration range. In alloys containing more than 20 at% of chromium, however, Qs show slightly higher values than of the low concentration alloys (e.g. about 74 kcal/mol for alloys containing 25∼30 at% of chromium). Stress exponents (n), having a value of about 5, show a tendency to decrease slightly with the increasing chromium content.