Mechanical Properties of Yttria and Ceria Stabilized Zirconia Coatings Obtained by Suspension Plasma Spraying

Plasma generated by SG-100 torch was applied to spray suspension formulated with the use of ZrO₂+8 wt. % Y₂O₃ (8YSZ) and ZrO₂ + 24 wt. % CeO₂ + 2.5 wt. % Y₂O₃ (24CeYSZ) as solid phases. The solids have the mean size of about 8YSZ - 4.5 µm and 24CeYSZ – 3.9 µm and were obtained by milling of commercial powders Metco 204 NS and Metco 205NS respectively. The suspensions were formulated with the use of 20 wt. % of solid phase, 40 wt. % water and 40 wt. % of ethanol. The plasma spray parameters were optimized with the electric power equal to 40 kW and working gases composition Ar – 45 slpm and H₂ – 5 slpm which were kept constant. On the other hand, the spray distance was varying from 40 to 60 mm and torch scan linear speed was varying from 300 to 500 mm/s. The coatings of the thickness ranging from 70 to 110 µm (8YSZ) and about 70 µm (24CeYSZ), were sprayed onto stainless steel substrates. The coatings microstructure was analyzed metallographically with the use of scanning electron microscope. Mechanical properties were tested with the use of indentation test and scratch test. The indentation test carried out with various loads ranging from 100 to 10000 mN enabled to determine elastic modulus and Martens microhardness. Young modulus of the coatings was in the range 66 to 82 GPa for 8YSZ and 62 to 122 GPa for 24CeYSZ coatings. Scratch test enabled to find the critical load and the scratch microhardness.