Vacuum plasma spray deposition of YSZ-NiO-Ni coatings at different Ar and H2 gas flow rates

The work presents results of the experimental investigation of vacuum sprayed yttria stabilized zirconia, nickel oxide, nickel (YSZ-NiO-Ni) ceramic composite coatings deposited on Al₂O₃ ceramic and stainless steel substrates produced at different Ar and H₂ gas flow rates. The Ar and H₂ gas flow was varied according to the factorial plan design. It is shown that for the used vacuum plasma spray YSZ and NiO powder mixture the produced coatings were composed of three phases mainly: cubic YSZ (c-YSZ), cubic NiO (c-NiO), and cubic Ni (c-Ni). The quantitative X-ray diffraction (XRD) analysis was used to evaluate each phase amount in the coatings. It was found that the vacuum spray technique enables formation of composite layers with a variable composition and that phase content in the coatings can be controlled choosing the Ar and H₂ gas flow rates. The electrical conductivity measurements revealed that a variation of the phase content in the YSZ-NiO-Ni composites is responsible for the existence of different electrical conduction mechanism and rapid change in the conductivity of coatings with the used powder content. The surface morphology and the cross-section analysis by scanning electron microscope (SEM) have shown porous structures of the deposited coatings.