AVS 50th International Symposium
    Advanced Surface Engineering Tuesday Sessions
       Session SE-TuA

Paper SE-TuA5
Processing and Properties of NiAl-Hf Coatings via DC Magnetron Sputtering

Tuesday, November 4, 2003, 3:20 pm, Room 323

Session: High Temperature Protective Coatings
Presenter: B. Ning, The University of Alabama
Authors: B. Ning, The University of Alabama
M.L. Weaver, The University of Alabama
Correspondent: Click to Email
Crystalline NiAl-0.1Hf coatings (20 µm thick) were deposited onto CMSX-4 substrates at temperatures ranging from room temperature up to 300 °C using direct current (DC) magnetron sputtering. The microstructures of the coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as deposited coatings were single phase, and exhibit dense columnar Zone T microstructures. Column sizes were observed to increase from approximately 250 nm at room temperature to more than 2 µm in diameter at 250 °C. Annealing in argon at 1000ºC for 1h 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 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 and diffusion induced precipitation and phase transformations. The results are discussed relative to conventional CVD aluminide coatings.