Microstructure, composition and oxidation resistance of nanostructured NiAl and Ni–Al–N coatings produced by magnetron sputtering

Nanostructured NiAl and Ni–Al–N thin films were RF magnetron sputtered from a NiAl compound target in different argon–nitrogen atmospheres. The structure and stoichiometry of as-deposited coatings were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Differential thermal analysis (DTA) was also conducted to study the oxidation kinetics of the films at high temperatures. Microstructural and compositional changes of the coatings after isothermal oxidation were investigated using XRD, SEM, and Rutherford backscattering spectrometry (RBS). The results show that: (1) denser and more completely crystallized Ni–Al–N thin films can be tailored through controlled ion bombardment during deposition, (2) nano-composite NiAl–AlN thin films were synthesized with nitrogen atomic concentrations up to 30%, and (3) the NiAl and Ni–Al–N coatings exhibited good oxidation resistance even at temperatures above 1273 K. The addition of AlN to NiAl resulted in decreased activation energies for oxidation. The oxidation study also revealed different rate controlling mechanisms for NiAl and Ni–Al–N (21.4 at.% N) films isothermally oxidized in air at 1273 K.