INTERNAL-FRICTION IN NICKEL-BASE SUPERALLOYS IN THE KHZ-RANGE AT TEMPERATURES BETWEEN 20-DEGREES-C AND 1250-DEGREES-C

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