Creep of gamma/gamma-alpha eutectic composite

Steady-state creep behaviour of directionally solidified eutectic alloy with chemical composition Ni-30.5Mo-6.3Al [wt.%] was studied at temperatures between 1223 and 1323 K. Eutectic gamma/gamma'-alpha composites with aligned fibre structure were prepared at a constant growth rate of 2.78 x 10(-6) m s(-1) in a modified Bridgman-type apparatus. The steady-state stress was found to depend strongly on creep rate and temperature. The measured power-law stress exponents varied between 6.7 and 7.0 over the studied temperature range. The apparent activation energy for creep was calculated to be 487 kJ mol(-1). This value is,higher than that for self-diffusion in the matrix or reinforcing fibres. When the steady-state creep behaviour was analysed in terms of the effective stress normalised with respect to the temperature dependence of the elastic modulus, the stress exponents were calculated to range between 4.4 and 5.0. These values are comparable with the values reported for dislocation creep of solid solutions or precipitation and dispersion strengthened alloys. Calculated value of corrected activation energy for creep of 436 kJ mol(-1) includes a-contribution of both phases: fibres and matrix.