Effect of V and Re additions on the creep properties of γ/γ'-α eutectic composites

Alloying a ternary monovariant Ni-Al-Mo eutectic alloy with vanadium and rhenium has been investigated as a means to increase the creep strength at elevated temperature. The creep properties of directionally solidified eutectic γ/γ'-α alloys with nominal composition Ni-31Mo-6Al, Ni-32Mo-6Al-1.4V and Ni-30Mo-6Al-1.6V-1.2Re (wt.%) have been determined using strain rate change test. The tests were conducted under vacuum at temperatures between 1223 and 1323 K. Comparison of the 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 temperature by 11 to 20%. This improvement is higher at higher temperatures and lower creep rates. The steady-state stress has been found to depend strongly on creep rate and temperature. The measured power law exponents varied between 6.7 and 7.9 over the studied temperature range. The 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. (orig.)