Cermet double carbide coatings (WC-Cr 3 C 2 -Ni) were HVOF sprayed onto magnesium substrate. The variable parameter was spray distance (320, 360 and 400 mm). The microstructure of the coatings has been characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Additional, porosity and residual stress have been estimated. Phase composition of WC-Cr 3 C 2 -Ni cermet coatings consists of hexagonal WC carbide, as well as the Cr 3 C 2 and Cr 7 C 3 carbides. For the longest spray distance, minor presence of WC 6 O 6 was detected, most likely as an effect of higher spraying distance, leading to partially oxidation of WC at powders particles boundaries. Comparing lattice parameters with model data it should be noted that no significant contribution of stress is present, due to minor changes in WC lattice parameters in comparison to ICDD data. It also should be noted that Cr 7 C 3 carbide in WC-Cr 3 C 2 -Ni coating has different lattice parameters than ICDD data what shows its reactive nature. In obtained results it is clearly seen, that residual stress have the lowest values for coating sprayed from the shorter distance. This tendency is visible for both, linear and shear stress. The crystallite sizes are also the smallest for the shorter spray distance. Such fine structure shows a tendency to good redistribute of the thermal stress in the sprayed coating and also on the coating-substrate interface.

In this study, 8YSZ and 24CeYSZ coatings were deposited on stainless steel by suspension plasma spraying. The suspensions were formulated using finely milled powder, water, and ethanol. Spraying parameters were modified by changing spray distance and torch scan speed and were the same for each material. Coating microstructure, phase composition, and porosity were assessed and thermal diffusivity was measured and used to calculate thermal conductivity.

Plasma generated by an SG-100 torch was applied to a spray suspension formulated with the use of ZrO 2 +8 wt% Y 2 O 3 (8YSZ) solid phase. The solids had a mean size of about 4.5 μm and were obtained by milling of commercial Metco 204 NS powder. The suspension was formulated with 20 wt% solid phase, 40 wt% water and 40 wt% ethanol. The plasma spray parameters were optimized with the electric power equal to 40 kW, working gases composition Ar 45 slpm and H 2 5 slpm, spray distance varying from 40 to 60 mm, and torch scan linear speed varying from 300 to 500 mm/s. Coatings with thicknesses ranging from 51 to 106 μm were sprayed onto stainless steel substrates. The porosity of the samples was found from the image analysis of metallographically prepared cross-sections of the samples to be in the range of 8 to 12%. Thermal diffusivity was measured with the use of the commercial NanoFlash system in the temperature range from room temperature to 523 K. The measurements were made with the use of the coatings sprayed on the substrate, and a 2-layer numerical model was developed to determine thermal diffusivity of the coatings. The diffusivity was in the range from 0.196 × 10 -6 to 0.352 × 10 -6 m 2 /s in room temperature depending on the spray parameters. The obtained data were then associated with the literature data of density and specific heat and experimental porosity to find thermal conductivity, which was in the range of 0.47 to 0.86 W/(mK) at room temperature, depending on the spray run.

Plasma generated by an SG-100 torch was applied to spray suspension formulated with the use of ZrO 2 +8 wt% Y 2 O 3 (8YSZ) and ZrO 2 +24 wt% CeO 2 +2.5 wt% Y 2 O 3 (24CeYSZ) as solid phases. The solids have the mean size of about 4.5 µm for 8YSZ and 3.9 µm 24CeYSZ 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% solid phase, 40 wt% water, and 40 wt.% ethanol. The plasma spray parameters were optimized by keeping constant: (i) the electric power at 40 kW (ii) the working gases composition 45 slpm of Ar and 5 slpm of H 2 . On the other hand, the spray distance was varied from 40 to 60 mm and torch linear speed was varied from 300 to 500 mm/s. The coatings were sprayed onto stainless steel substrates to reach the thickness ranging from 70 to 110 µm (8YSZ) and about 70 µm (24CeYSZ). The coating microstructures were analyzed with the use of a scanning electron microscope. Mechanical properties were tested with the use of indentation and scratch tests. The indentation test was carried out with various loads ranging from 100 to 10,000 mN to determine elastic modulus and Martens microhardness. Young’s modulus of the coatings was in the range 71 to 107 GPa for 8YSZ and 68 to 130 GPa for 24CeYSZ. Scratch tests were conducted to determine the scratch macrohardness.

Titanium oxide coatings were suspension plasma sprayed onto different substrates. The suspension was formulated using fine rutile pigment in the mixture of water with ethanol. The zeta potential of the suspension was determined. The spray process parameters were designed using a full factorial plan using spray distance and torch scan velocity as the variables. The temperature at spray process was monitored using a pyrometer. The X-ray diffraction (XRD) analysis enabled to find out the crystalline phases in sprayed deposits and, in particular, the anatase content. Scanning electron microscope (SEM) enabled to characterize the coatings’ microstructure. The coatings included well molten lamellas and zones of loosely agglomerated and sintered grains. The scratch test of the coatings enabled to determine their mechanical properties such as critical load and scratch hardness.

Suspension plasma spraying is a process which enables production of finely grained nanometric or submicrometric coatings. The suspensions were formulated with the use of fine powder of ceramic particles of yttria stabilized zirconia in water with alcohol. The present paper focuses on the theoretical analysis of the formation process of sintering of fine solids impacting the growing coating’s surface. The heat flux input to the coatings was estimated and their surface temperature at spraying was measured. The theoretical analysis of sintering during the coating’s growth was carried out. The different models of sintering were analyzed and adapted to the suspension plasma spraying conditions. The model of surface diffusion was found to be the most appropriate to describe the sintering during suspension plasma spraying. The formation of the necks having the relative size equal to 10 % of the particle diameter was found to be possible during the coatings deposition.