Elevated temperature creep properties of NiAl eryomilled with and without Y2O3

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Abstract
The creep properties of lots of NiAl eryomilled with and without Y2O3 have been determined in compression and tension. Although identical cryomilling procedures were used, differences in composition were found between the lot ground with 0.5 vol % yttria and the lot ground without Y2O3. Compression testing between 1000 and 1300 K yielded similar crecp strengths for both materials, while tensile creep rupture testing indicated that the yttria-containing alloy was slightly stronger than the Y2O3-free version. Both compression and tensile testing showed two deformation regimes; whereas the stress state did not affect the high stress exponent (n ≍ 10) mechanism, the low stress exponent regime n was ∼6 in tension and ∼2 in compression. The strengths in tension were somewhat less than those measured in compression, but the estimated activation energies (Q) of ∼600 kJ/mol for tensile testing were closer to the previously measured values (∼700 kJ/mol) for NiAl-AlN and very different from the Q's of 400 and 200 kJ/mol for compression tests in the high and low stress exponent regimes, respectively. A Larson-Miller comparison indicated that cyromilling can produce an alloy with long-term, high-temperature strength at least equal to conventional superalloys.