Internal Friction in Nickel-Base Superalloys in the kHz-Range at Temperatures between 20 °C and 1250 °C

Abstract
Damping measurements were carried out on two-phase (γ-matrix, γ'-precipitates) nickel-base alloys containing different volume fractions of γ' in order to achieve a better understanding of the strong elastic modus decrease between 1000°C and 1100°C. For the investigation of the damping a free-free beam flexural vibration technique was applied. Nickel-base alloys with a high volume fraction of γ', like CMSX-4, and the intermetallic phase Ni₃Al, the near γ'-phase, show two different damping peaks between 1000°C and 1200 °C. The measurements on alloys with a low volume fraction of the γ'-phase and of a near-γ matrix material lead to only one damping maximum in this high-temperature range. A comparison of the evaluated damping parameters leads to the assumption that the diffusion of nickel and aluminium atoms in the γ'-phase most probably is responsible for the relaxation processes in nickel-base alloys such as CMSX-4.