Creep of Fe3Al-based alloys with vanadium and carbon additions

Creep experiments were conducted on Fe3Al-based alloys with vanadium and carbon additions in the temperature range from 923 to 1023 K, corresponding to the occurrence of B2 lattice. The alloys contained (in atomic %) (i) 27.0 Al, 1.17 V, and 0.02 C and (ii) 27.0 Al, 1.13 V, and 0.73 C (Fe balance). The alloys were tested in the as-cast state and annealed at 1273 K for 50 h. Creep tests were performed in uniaxial compression at a constant load with stepwise loading. Stress exponents and activation energies for the creep rate were determined. The values of the stress exponent in low-carbon alloy correspond to a five-power-law creep. The activation energy is greater than the activation enthalpy of diffusion of both Fe and Al in Fe3Al and is substantially greater than the activation enthalpy of diffusion of V in Fe3Al. The creep rate is impeded in the high-carbon alloy by the presence of tiny carbide particles. Consequently, the creep resistance of the high-carbon alloy in the as-cast state is greater, especially for higher temperatures and lower stresses. The carbide particles coarsen during annealing at 1273 K and are unable to obstruct dislocation motion because the mean distance between them is too large. The high-carbon alloy is then creep-weaker due to the reduced amount of vanadium present in the matrix.