TEMPERATURE-DEPENDENCE OF DYNAMIC YOUNGS MODULUS AND INTERNAL-FRICTION IN LPPS NICRALY

The piezoelectric ultrasonic composite oscillator technique (PUCOT), operating near 80 kHz, was used to measure the temperature dependence, in the range 23-1000 degrees C, of dynamic Young's modulus, E, and internal friction, Q(-1), in three compositions of low-pressure plasma-sprayed NiCrAlY: Ni-15.6Cr-5.2Al-0.20Y (16-5), Ni-17.2Cr-11.6Al-0.98Y (17-12), and Ni-33Cr-6.2Al-0.95Y (33-6). Ambient temperature (23 degrees C) dynamic Young's moduli for the three alloys were 205.0, 199.8, and 231.0 GPa, respectively. In each case, dE/dT was found to be - 0.06 GPa degrees C-1 over temperature ranges 23-800, 23-400 and 600-900, and 23-700 degrees C, respectively. Internal friction was essentially independent of temperature to about 600 degrees C (700 degrees C for the 16-5 alloy), at which point a temperature dependence of the form Q(-1) = A exp( - Cl RT) was observed. The constant A for the three alloys was determined to be 62.7, 555, and 2.01 x 10(6), respectively. The constant C for the three alloys was determined to be 82.8, 111, and 170 kJ/mol(-1), respectively. While the physical mechanism is not fully understood, both the pre-exponential constant A and the activation energy C correlate with durability in thermal barrier coatings (TBCs) wherein these alloys are used as bond coats.