The powder of HSS (HSS23, AISI M3:2) was deposited by pulsed-PTA method on to low alloyed steel substrate. The influence of pulsation frequency was evaluated on the surface of deposits and on their cross sections by both light microscope and by Vickers hardness measurement apparatus and extreme properties mapping (XPS). Surfacing parameters at current frequency from 0 to 200Hz were tested during deposition of single weld bead. Dilution and heat affected zone were evaluated and compared for all tested parameters. The presence of retained austenite after deposition was determined by X-ray diffraction. The beads deposited with different frequencies differ in their shape, dilution degree, microhardness and penetration depth. It was found that the microhardness increases with current frequency.

TiO 2 nanopowder was used as a feedstock for spraying with the water stabilized plasma (WSP®) in search for superior mechanical properties and wear resistance of titania coatings. It has been proved that good quality coatings can be made even with the high throughput WSP®. Single splats evaluation and the free flight particles were used for the spray optimization. Phase compositions, stoichiometry and selected properties, such as density and elastic modulus, were then studied at the as-sprayed coatings. As for the phase composition of coatings, mainly rutile with possible traces of Magneli phases have been found. A comparison between tension and compression loading shows that values of the Elastic modulus for compression are slightly higher than these for tension, as it is usual in plasma sprayed coatings.

The high cooling rate (>105 - 106 K/s) achieved in thermal spraying makes it possible to deposit coatings that exhibit a high content of amorphous phase and can be, afterwards, heated above the crystallization temperature to form nano-structured coatings. In this study, the relationship between the characteristics (temperature and velocity) of the sprayed particles at impact and degree of amorphization of the as-sprayed coatings was investigated for both plasma and wire-arc spraying techniques A Fe-Cr-based alloy that exhibits a high glass forming ability and is commercially available in the form of powder and wire with close chemical composition was used. The amorphous phase content was higher in plasma sprayed coatings than in wire arc sprayed ones and both types of coatings presented an increase in microhardness after heat treatment.

Amorphous metallic coatings are of high interest because of their good wear and corrosion resistance as well as their high hardness and toughness relative to the crystalline alloys with the same composition. Thermal spray that makes it possible to reach quenching rates in the order of 106-107 K/s, has the ability to deposit coatings with a high content of amorphous phase. However, very few studies dealt with the understanding of the spraying factors that affect the formation of the amorphous phase under thermal spray conditions. In this work, the relationship between temperature and velocity of the spray particles and coating characteristics is investigated. Special attention is given to the degree of amorphisation of the as-sprayed coatings. The latter were produced both by plasma and wire-arc spraying in order to get a larger range of particle parameters at impact and different particle heating history in the gas flow before impingement onto the substrate. A commercial iron-based alloy available both in powder and wire forms was used. Microstructural analyses show that the as-sprayed coatings are partially amorphous and that the proportion of the amorphous phases depends on the sizes of the sprayed particles as they control the heating and acceleration of particles in the gas flow and their cooling rate on the substrate.

CaZrO 3 is a material for thermally sprayed ceramic coatings to which so far only a little attention was paid. This material has a high melting point, good thermal stability and a coefficient of thermal expansion close to that of steel. In this paper water stabilized plasma spraying (WSPR) and atmospheric plasma spraying (APS) were used to prepare CaZrO 3 coatings. The spraying feedstock was prepared from fine CaZrO 3 powder by agglomeration (spray drying) and sintering. Powders with three different particle sizes (- 45 + 20 µm, - 63 + 45 µm and -90+63 µm) were used in the experiments. The coarse fractions were used for WSP spraying, while the fine one was sprayed with the APS process. Plasma sprayed materials were studied from the point of view of phase changes and influence of the powder size on structure of coatings. The changes of phase composition were studied by X-ray diffraction on coatings as well as on free flight particles. Formation of a cubic phase with a reduced content of CaO in comparison to CaZrO 3 was observed. Its formation is probably connected with evaporation of CaO during spraying. This cubic phase is similar to the phase obtained by spraying of ZrO 2 +5%CaO. Plasma sprayed coatings were characterized by light and scanning electron microscopy (SEM) and by density and porosity. Coefficients of thermal expansion of plasma sprayed layers from CaZrO 3 were measured.

An investigation was conducted to assess the potential of water-stabilized plasma (WSP) spraying for applying protective boron carbide coatings to fusion reactor components. This paper describes how test samples were produced and how coating quality was determined. The authors sprayed boron carbide powder onto steel and stainless steel substrates using different powder feeding and spraying distances, substrate preheat temperatures, and carrier gases. They also investigated methods for optimizing the plasma jet and improving coating adhesion. The boron carbide coatings were characterized based on phase composition, porosity, oxygen content, and flexural strength. Paper includes a German-language abstract.

Spraying distance (SD) is one of the main parameters that can affect the spraying process - its efficiency as well as deposit's character. The reason lies in a different thermal history of particles corresponding to different spraying distances. Variation in the structure, preferred orientation, variation of the phase contents and/or in the chemical composition of deposits can be then found for different SDs. Consequently, properties of coatings can greatly vary, not only in the resistance state but also on deposit's annealing. Some materials are, however, more and some less sensitive to that effect. The goal of this work is to compare CaTiO 3 samples produced by plasma spraying with WSP at SD = 350 and 450mm with sintered samples. The following properties were compared: microhardness, thermal expansion coefficient, permittivity and reflectivity. Porosity and the differential thermal analysis of resistance and annealed deposits were also compared. Perovskite CaTiO 3 belongs among materials very stable during spraying - neither chemical nor phase differences were found between the feedstock powder, free-flight particles, as-sprayed deposit and annealed deposit. Despite that there are significant differences in behavior of deposits and freestanding parts sprayed from different SDs. All the recorded differences for CaTiO 3 plasma sprayed deposits with varying SDs must be therefore accounted to the deposit's structural differences, such as pore and splat sizes and shapes and preferred orientation. Additional differences on annealing can be probably attributed to the different amount of "stored" thermal energy in deposits due to the varying SD. However, there is a lower limit for SD assuring a quality deposit on spraying.

Among candidate materials for plasma spraying titanates ATiO3, where A is an element from the alkaline earth group (11), were not systematically tested until today. This paper reports on plasma spraying of synthetic perovskite CaTiO3 and geikielite-perovskite system MgTiO3-CaTiO3. Perovskite CaTiO3 is well known as dielectric material and a basic component of complex dielectric ceramics. Since it is relatively chemically simple and inexpensive material it has been selected for the basic preliminary studies. Mixture of geikielite-perovskite MgTiO3-CaTiO3, with Mg:Ca ratio equal to 94:6, was chosen because its permittivity is independent of temperature. Plasma spraying was done with the water stabilized plasma gun WSP. Plasma spraying conditions were optimized using single splat observation for various substrates and varying substrate temperature. Standard experimental techniques were used for studying of microstructures, chemical and phase compositions and porosity of as-sprayed and annealed deposits. Mechanical properties such as Young’s modulus and microhardness were measured.

For utilization of free-standing ceramic parts produced by plasma spraying it is very important to know the temperature dependence of the linear thermal expansion coefficient and its relation to the porosity of the structure. Zircon ZrSiO4 and gray alumina (96 wt % AI2O3) were plasma sprayed by the water stabilized plasma gun WSP PAL 160. Samples of both materials were cut from thick coatings with respect to their orientation to the gun axis during the gun's horizontal spraying cycling with a constant speed. Thermal expansion coefficients and the differential thermal analysis were performed using SETARAM complex measuring system (up to 1750 °C), the density/porosity was measured by several techniques, such as Archimedean weighing, helium pycnometry, etc. It was found that both, the porosity and the thermal expansion coefficient, change for different locations in the thick deposit due to the varying trajectories of individual particles/droplets in the plasma stream. Measured data for deposits are then compared with data for bulk ceramics. The dependence of the thermal expansion coefficient on porosity in a given location was determined and its general applicability for free-standing plasma spraying is then discussed in the paper.