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.

The effect of grit blasting exposure time on the adhesion of plasma sprayed Al 2 O 3 and 316L stainless steel coatings was studied in the present work. The steel substrates were grit blasted prior to the coating deposition. Two sets of substrates with exposure time of 1 and 4 seconds were prepared. Both types of coatings were deposited using Water Stabilized Plasma (WSP) torch. Adhesion strength was evaluated using standardized pulloff test. The obtained results showed a slight improvement in the adhesion strength for the blasting time of 4 s. Failure processes taking place in the coatings during the pull-off tests were described based on the detailed fractographic analysis.

Thermal sprayed ceramic coatings are well used as the electrode of corona discharge treatment in order to modify the surface of many kinds of films and papers due to its superior durability and adaptability. Some kinds of Al 2 O 3 -TiO 2 were sprayed by APS on the parallel plate electrodes, and output power of corona discharge generated by the electrodes was measured by using Sawyer-Tower circuit. In addition, discharge output power was calculated with an equivalent circuit of corona discharge. By comparing them, effects of the electrical property of the coating on discharge was researched. As a result, the electrostatic capacitance of the coatings influences the impedance of the whole circuit, and higher relative permittivity of the coating brought higher output power in a constant voltage.

To fully understand particle interactions with both substrate and neighboring particles in Cold Spray (CS), ultrasonic monitoring and acoustic emission of particle agglomerate impact were studied. The results obtained show the influence of particle agglomeration density on stress and strain distribution in the particles and at the particle interfaces. The results are compared with metallographic structures of real coatings. The development of monitoring procedure is made using acoustic methods, specifically testing during the actual spray process itself. It is shown that the final thickness as well as the dynamics of buildup can be evaluated. Cross sections of the coating thickness are also easy to obtain and show true profiles of the coating. Comparisons of real thickness and acoustically estimated thickness show a close linear relationship.

The work deals with the evaluation of strength characteristics of thermally sprayed coatings. The main aim was concentrated on the tensile and shear loading of HVOF (Stellite Alloy 6, Tribaloy 400) and arc sprayed (13%Cr, CuAl8) coatings. The investigation of the coatings behaviour on the coating-substrate interface is important for the evaluation of one of significant coating mechanical properties that influence properties of the whole coating-substrate system. The magnitude of the coating bond strength during tensile and shear stresses predicates the coating stability, reliability, impact resistance, resistance against failure and mostly operating lifetime. The determination adhesive-cohesive strength was performed according to EN 582 and EN 15340 Standards.

The thermal shock resistance of plasma-sprayed thermal barrier coatings (TBCs) with different top coats was investigated according to the Japanese Industrial Standard "Testing methods for thermal cycle and thermal shock resistance of thermal barrier coatings" (JIS H 8451:2008). Three types of ceramics powders, namely, Al 2 O 3 , 8 mass % Y 2 O 3 -stabilized ZrO 2 (YSZ) and La 2 Zr 2 O 7 (LZ) were used in the top-coat spray. After the specimens were subjected to a thermal shock, the tensile adhesive strength of the TBCs was measured and the thermal shock resistance as defined in JIS H8451 was determined. The thermal shock properties of the TBCs were found to depend strongly on the chemical composition of the top-coat material. For TBCs with Al 2 O 3 and LZ, the adhesive strength decreased with increasing thermal shock temperature difference (ΔT). On the other hand, little change in the adhesive strength was observed with increasing ΔT for YSZ TBC. From these results, the thermal shock resistance, ΔTc, was determined to be 480 °C for Al 2 O 3 , 680 °C for LZ and more than 880 °C for YSZ TBC. Furthermore, the influence of thermal shock on the adhesive strength of TBCs was investigated in detail through observations of cross-sectional microstructures and fracture surfaces after adhesive testing.

In this study, the influence of spray parameters on the electrical resistivity of thermally sprayed ceramic coatings from the system Cr 2 O 3 -TiO 2 was investigated. Fused and crushed feedstock powders with contents of 10 wt. % and 20 wt. % chromium oxide were deposited by APS and HVOF. Temperature and velocity of the particles in the spray jet as well as the coating surface temperature were analyzed during the deposition process. Impedance spectroscopy was used to investigate the electrical resistivity of the coatings and the results were correlated to coating microstructure and phase composition. It was found that phase transformations occur during the spray process. In the coatings a high temperature phase (n-phase) and rutile were observed. Though, the ratio of rutile depends on the spray methods employed for coating deposition. The electrical resistivity of coatings obtained by HVOF can be correlated to the content of chromium oxide. Furthermore, the surface temperature of the coating during deposition also shows some influence. Concerning the coatings resulting from APS, the different mixtures of the plasma gases (Ar-H 2 and Ar-N 2 ) are supposed to have the most important influence on the electric resistivity.

Characterization of coatings made with the help of Computer Controlled Detonation Spraying (CCDS) was performed. The applied coatings include hard alloys (WC/Co -75/25, WC/Co - 88/12, WC/Co/Cr - 86/10/4, and Cr 2 C 3 / NiCr), aluminum oxide, nickel-chromium self-fluxing alloy, titanium, bronze, and stainless steel. Tribological investigations of coatings were provided using abrasion test (ASTM standard G65), erosion test (ASTM standard G76), and hydro-abrasive test. To make hydro-abrasive tests special device and method were elaborated based on the interaction of water jet saturated with corundum particles with a coating surface.

New concept and method of testing for the interconnecting porosity of thermally sprayed nonconductive ceramic coatings is proposed. This process is useful to differentiate the open porosity from the closed porosity. Thermally sprayed ceramic coating with metallic substrate is plated, and the intergranular gaps in the coating are filled by deposited metal. Typically, 304 stainless steel substrate deposited with atmospheric plasma sprayed alumina coating is immersed in copper(II) sulphate bath, and electroplated. Inward of the alumina coating, plating solution penetrates toward the interface of coating/substrate via interconnected porosity, and attains the coating-substrate interface to deposit metallic copper. Deposit of copper is gradually grown up along the coating intergranular. The exposure of deposited copper on the coating surface can be visible. Because these phenomena occur only in the interconnected pore structure, it is easy to differentiate the interconnected porosity from the closed porosity. Also the proposed process suggests the unprecedented possibility of manufacturing method of three-dimensional structure of thermally sprayed ceramic coating.

Plasma Transferred Arc is the only thermal spray process that results in a metallurgical bond with the substrate. When compared with other welded coatings finer microstructures are observed after PTA processing, which have been associated with the faster solidification rate imposed by this technique. However, the powdered/atomized material used that forms the thermal spray, can play an important role in the solidification of coatings depending on their chemical composition and their grain size. This study analyzed the solidification of PTA coatings processed with an atomized cobalt based alloy (Stellite 6) with different average grain sizes. Typically, solidification of a welded coating follows solidification principles regarding the nucleation and growth of their microstructure determined mainly by the solidification rate. The role of the powdered feedstock in the solidification of coatings is analyzed based on the assumption that solidification is influenced by the initial interface energy of the atomized grains that melt in the plasma arc before reaching the melt pool. A commercial atomized Stellite 6 alloy was divided in two groups according to their grain size, below and over 125 microns, and deposited with the same processing parameters. Coatings were characterized by laser confocal microscopy and Vickers microhardness. Differences in coatings hardness and microstructure of coatings were associated with the grain size of the deposited alloy and subsequent solidification.