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Kinetic roughening of tantalum films during the initial growth stages has been studied by atomic force microscopy, scanning electron microscopy, and dynamic scaling theory. Different from the time-independent scaling behavior for continuous film growth, an intriguing unstable kinetic roughening occurs during island coalescence. In such case, roughness exponent α increases with growth time, accompanied by lower growth exponent β and higher coarsening exponent η. Detailed analysis of film surface morphology and simple phenomenological models suggests that this unstable behavior is related to the pronounced lateral growth of surface islands, which arises from the combined effect of the formation of grain boundary and the covering of heterogeneous substrate surface.

A strategy integrating structure zone model with dynamic scaling theory was proposed to study the global surface dynamics of polycrystalline Cu films deposited at different homologous temperature Ts/Tm. The evolution of roughness exponent α and growth exponent β reveals a transition from random deposition to surface diffusion dominated smoothening in the lower Ts/Tm regime and then to rapid surface roughening in the higher Ts/Tm regime. In contrast to that of amorphous films, the distinct scaling behavior in higher Ts/Tm regime arises from the change of anisotropic mass transport mechanisms, which could be related to the texture evolution during growth.

The interdiffusion behaviours and oxidation resistance of the NiCrAIY/AI duplex coated specimens during the isothermal oxidation test at 950°C were investigated. It was shown that the NiCrAlY coating system with an AI bondcoat outperformed the NiCrAlY single coating system and the substrate y-TiAl alloy during hot exposure. Analysis techniques such as X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to study the phase formation, microstructure and depth distribution of the elements in the coated specimens.The results showed that the NiCrAIY/AI duplex coating system exhibited better oxidation resistance and adhesion strength with the substrate during scratch test. The SEM-EDS profile analyses further showed that the outward Ti diffusion and the inward Ni diffusion were delayed apparently by the AI interlayer, which was also considered as AI source for forming protective a-Al2O3 scale on the NiCrAIY/AI coating surface.

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