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

Damping measurements were carried out on two-phase (y-matrix, y'-precipitates) nickel-base alloys containing different volume fractions of y' in order to achieve a better understanding of the strong elastic modus decrease between 1000°C and 1 100°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 y', like CMSX-4, and the intermetallic phase Ni3A1, the near y'-phase, show two different damping peaks between 1000°C and 1200 "C. The measurements on alloys with a low volume fraction of the y'-phase and of a near-y 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 y'-phase most probably is responsible for the relaxation processes in nickel-base alloys such as CMSX-4.