In this study, 316 stainless was deposited by low-pressure plasma spraying under various conditions to obtain different coating structures and by cold gas dynamic spraying for comparison. The coatings were characterized by cross-sectional metallography to assess porosity, oxidation, particle flattening, and elemental composition. The samples were also subjected to flyer plate impact testing in a gas gun to determine their shock propagation and porosity compaction properties. Comparing the results with that of the reference sample shows the effect of deposition conditions on the dynamic behavior of the coatings.

Plasma sprayed zirconium (Zr) metal coatings onto uranium-molybdenum (U-Mo) alloy nuclear reactor fuel foils act as a diffusion barrier between the fuel and the aluminum fuel cladding. Neutron diffraction was performed to investigate the crystallographic phase composition, crystal orientations and lattice parameters of the plasma sprayed Zr and the U-Mo substrate. The neutron diffraction results show that the plasma sprayed Zr coating is crystalline, phase pure (alpha-Zr) and has preferred crystalline orientation likely due to directional solidification. Also, there is a slight (~0.01 Å for a direction and ~0.016 Å for c direction) increase in the plasma sprayed Zr lattice parameter indicating oxygen in the lattice and some residual thermo-mechanical strain. There is little or no modification of the underlying U-Mo following plasma spraying. In particular, there is no detectable allotropic transformation of the starting gamma-U (body-centered cubic) to alpha-U (orthorhombic). The unique neutron diffraction capabilities at LANL are well suited for nuclear fuel characterization offering distinct advantages over conventional X-ray diffraction and destructive metallography.

The measurement of the spatial distribution of coating thickness of thin coatings applied by thermal spraying can be challenging. For non-magnetic metallic substrates and coatings, X-Ray Fluorescence (XRF) was employed for measuring coating thicknesses in the range of 15 to 60 μm. XRF is used to measure the ratio of atomic fluorescence peaks for an element in the substrate to an element in the coating. With appropriate calibration, the ratio of peak intensities gives the coating thickness for the spot sampled. Mass gain and cross sectional metallography are compared to XRF to determine accuracies and sensitivities of the techniques for plasma sprayed coatings.

Coating porosity is an important parameter to optimize for plasma-sprayed ceramics which are intended for service in molten metal environments. Too much porosity and the coatings may be infiltrated by the molten metal causing corrosive attack of the substrate or destruction of the coating upon solidification of the metal. Too little porosity and the coating may fail due to its inability to absorb thermal strains. This study describes the testing and analysis of tungsten rods coated with aluminum oxide, yttria-stabilized zirconia, yttrium oxide, and erbium oxide deposited by atmospheric plasma spraying. The samples were immersed in molten aluminum and analyzed after immersion. One of the ceramic materials used, yttrium oxide, was heat treated at 1000°C and 2000°C and analyzed by X-ray diffractography and mercury intrusion porosimetry. Slight changes in crystal structure and significant changes in porosity were observed after heat treatments.