A preliminary study of DC magnetron sputtered NiAl–Hf coatings

Crystalline NiAl-0.1Hf coatings, ∼20-μm thick, were deposited onto CMSX-4® substrates using direct current (DC) magnetron sputtering. The as-deposited coatings were found to be single phase, consisting of β-NiAl (B2 structure). Annealing in argon at 1000 °C for 1 h resulted in densification of the coatings and in increased adhesion between the coatings and the substrate. Microstructural and compositional changes of the coating system after isothermal oxidation were studied using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. The mechanical properties of the coatings were studied via nanoindentation in the as-deposited condition, after annealing, and following various oxidation heat treatments. The hardness and modulus of the coatings were observed to correlate with oxidation time. Extended oxidation resulted in decreased hardness due to grain growth, precipitate coarsening and the diffusion of solutes into and out of the coating. The results are discussed relative to conventional CVD aluminide coatings.