EFFECT OF V-ADDITION AND RE-ADDITION ON THE CREEP-PROPERTIES OF GAMMAGAMMA'-ALPHA EUTECTIC COMPOSITES/

Alloying a ternary monovariant Ni-Al-Mo eutectic alloy with vanadium a nd rhenium has been investigated as a means to increase the creep stre ngth at elevated temperature. The creep properties of directionally so lidified eutectic gamma/gamma'-alpha alloys with nominal composition N i-31Mo-6A1, Ni-32Mo-6Al-1.4V and Ni-30Mo-6A1-1.6V-1.2Re (wt.%) have be en determined using strain rate change test. The tests were conducted under vacuum at temperatures between 1223 and 1323 K. Comparison of th e stress-strain rate behaviour to that for directionally solidified Ni -Al-Mo eutectic alloy has revealed that the additions of vanadium and rhenium increase the steady-state stress at given creep rate and tempe rature by 11 to 20%. This improvement is higher at higher temperatures and lower creep rates. The steady-state stress has been found to depe nd strongly on creep rate and temperature. The measured power law expo nents varied between 6.7 and 7.9 over the studied temperature range. T he activation energies for creep were calculated to range between 471 and 517 kJmol(-1). The ductility of these eutectic composites was high , typically ranging from 40 to 60% reduction of area and from 15 to 38 % elongation..