Abstract
In this study NiAl coatings containing 0.6 at.% Hf have been deposited onto CMSX-4® substrates via direct current magnetron sputtering. Microstructural analysis using X-ray diffraction (XRD) and transmission electron microscopy (TEM) shows that the as deposited coatings consist of a B2 β-NiAl solid solution phase with no evidence of precipitation. However, it was found that the post-deposition annealing conditions had a great influence on the microstructure of the sputtered coatings. In monolithic coatings extracted from their substrates, nanometer-sized precipitates formed at grain boundaries and within the grain interiors during annealing in argon for 1 h at 1273 K. An increase in the annealing time to 4 h resulted in recrystallization and some grain growth. The microstructure changes of the coatings after isothermal oxidation tests were examined by scanning electron microscopy (SEM) and XRD analysis. The results showed that the heat treatment conditions and Hf concentration in these coatings had a great influence on their oxidation resistance.
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