Dependence of thickness, morphology, and crystallographic properties of Mo and ZrN coatings on U-Mo substrate size

This study reports the size effect of U-7wt.%Mo (U-7Mo) substrates on the thickness, morphology, and crystallographic properties of Mo and ZrN coatings as a diffusion barrier. Each the coating was deposited on 45-90 μm sized U-7Mo particles by direct current magnetron sputtering system. The as-fabricated coated U-7Mo particles were assorted by their size, and then the microstructure of each particle group was analyzed by using scanning electron microscope, energy dispersive X-ray spectrometer, and X-ray diffractometer. The characterization results showed that the thickness of both the Mo and ZrN coatings was proportional to the U-7Mo substrate size. A semi-empirical model to explain the relationship between the coating thickness and substrate size is newly developed with comprehensive considerations for the friction physics and configurations of the deposition system, in which unknown constants were confirmed by fitting the correlation to the measured data. It was shown that the morphology and crystallographic properties of both the Mo and ZrN coatings were various as a function of the U-7Mo substrate sizes, which is due to their different coating thicknesses and deposition rates.