Abstract
Nickel-based superalloys are widely used as the heat-resistant materials in various engineering fields. Therefore, it is very important to clarify the viscoelastic properties of these materials because they are often used under elevated temperatures. The final object of this study is to clarify the viscoelastic constitutive relation of Inconel 718 which is one of the most popular nickel-based superalloys. As the preliminary research for this final object, the internal friction (logarithmic decrement) has been measured by the inverted torsion pendulum method with changing the atmospheric temperature. Prior to the measurement, three types of specimens with different grain sizes were prepared by changing the annealing temperature. As the results, it has been clarified that the logarithmic decrement of the large grain size superalloy is smaller than that of the small grain size superalloy and that in some cases, the logarithmic decrement takes a peak value at the atmospheric temperature of approximately 820-850K.
