Creep behavior of an oxide-dispersion-strengthened Ni3Al-based alloy

An oxide-dispersion-strengthened (ODS) Ni3Al-based alloy was produced by mechanically alloying a 76Ni-19Al-5Cr-0.1B (at.%) powder with 2 vol.% yttria, Y2O3, and then consolidating by hot extrusion. A microstructure with large elongated grains and an 11:1 grain aspect ratio was developed by secondary recrystallization heat treatments. The creep rate as a function of stress for this coarse-grained material was evaluated at 649, 732, 816 and 982 °C. At 649 °C and stresses of 557–695 MPa, power law creep with a stress exponent of 13.5 ± 0.3 was observed. In the temperature range 732–816 °C a stress exponent of 5.1 ± 0.1 and an activation energy of 239 ± 5 kJ mol−1 were observed. At stresses above 566 MPa at 732 °C, and above 456 MPa at 816 °C, the observed stress exponents were 22 and 13 respectively. At 982 °C and stresses of 133–311 MPa a stress exponent of 9.1 ± was observed. The high stress, high creep rate behavior resulted from the bulk deformation of grains, whereas the low stress, low creep rate behavior resulted from the constrained growth of cavities on transverse boundaries. For all conditions of temperature and stress (except 311 MPa at 982 °C) this coarse-grained ODS Ni3Al alloy exhibited creep rates for a given stress which were at least a factor of 10 less than those of other polycrystalline or single-crystal Ni3Al alloys. The observed creep rates were, however, greater than those of the more complex commercially available superalloys.