The applicability of Norton's creep power law and its modified version to a single-crystal superalloy type CMSX-2

Creep experiments at 982°C indicate that the Norton creep power law and its modified version can be used to describe the creep behavior, over an extensive amount of deformation, of the nickel-base precipitation-strengthened single-crystal (SC) superalloy type CMSX-2 by continuously changing the parameters in the equations describing these laws. The exponent n in Norton's law keeps changing with the amount of total creep deformation of the alloy, reaching a peak value upon rafting of the initially cuboidal precipitates. A new empirical exponential relation was observed between the two parameters of the Norton creep power law. This exponential relation indicates that the activation energy for the creep process is linearly proportional to the exponent in Norton law, it changes continuously as the deformation of the SC progresses and it also peaks during rafting of the precipitates.