CREEP OF GAMMA GAMMA-ALPHA EUTECTIC COMPO SITE/

Steady-state creep behaviour of directionally solidified eutectic allo y with chemical composition Ni-30.5Mo-6.3Al [wt.%] was studied at temp eratures between 1223 and 1323 K. Eutectic gamma/gamma'-alpha composit es with aligned fibre structure were prepared at a constant growth rat e 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 tem perature. The measured power-law stress exponents varied between 6.7 a nd 7.0 over the studied temperature range. The apparent activation ene rgy for creep was calculated to be 487 kJ mol(-1). This value is,highe r than that for self-diffusion in the matrix or reinforcing fibres. Wh en the steady-state creep behaviour was analysed in terms of the effec tive stress normalised with respect to the temperature dependence of t he elastic modulus, the stress exponents were calculated to range betw een 4.4 and 5.0. These values are comparable with the values reported for dislocation creep of solid solutions or precipitation and dispersi on strengthened alloys. Calculated value of corrected activation energ y for creep of 436 kJ mol(-1) includes a-contribution of both phases: fibres and matrix.