The paper discusses the screening of experimental variables leading to formation of a columnar microstructure in suspension plasma sprayed zirconia coatings. These variables tested in 12 experimental runs included: (i) 2 types of zirconia powder; (ii) 4 concentration of solids in suspensions; (iii) 4 substrate preparation methods; and (iv) 2 plasma spray setups. Two different, commercially available, powders were used to formulate the suspensions. Yttria and ceria stabilized zirconia of composition ZrO 2 + 24 wt.% CeO 2 + 2.5 wt.% Y 2 O 3 (YCSZ) was milled the decrease the particles sizes. The yttria stabilized zirconia of composition ZrO 2 + 14 wt.% Y 2 O 3 (14YSZ) was used as received. The coatings were deposited on 304L stainless steel substrates which had the surface prepared by: (i) grid blasting; (ii) grinding; (iii) turning; and (iv) laser treatment. The 3D topographies of substrates' surfaces were characterized and their roughnesses were measured. The suspensions were plasma sprayed using the following plasma torches: SG-100 of Praixair and Triplex of Sulzer-Metco. The microstructure of powders and coatings was analyzed by optical microscopy, scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM) as well as by X-ray diffraction. The columnar microstructure was formed in coatings sprayed with both plasma setups sprayed using finer 14YSZ powder suspensions. The substrate surface preparation as well as low concentration of solids in suspension promoted their formation. Rietveld method was applied to determine the quantity of different phases in the structure of coatings and to calculate the lattice parameters. The YCSZ coatings crystallized in mainly tetragonal phase with a small content of monoclinic phase. The 14YSZ crystallized in cubic phase. Finally, the thermal diffusivity of coatings was characterized up to 523 K with the use of laser flash method and thermal conductivities of coatings were determined. The conductivities were in the range from 0.6 to 1.1 W/(mK) depending on temperature for YCSZ and 14YSZ coatings.

The paper briefly describes major thermal spray techniques used to spray functionally graded coatings such as atmospheric plasma spraying, high velocity oxy-fuel spraying, suspension and solution precursor plasma spraying, and finally low and high pressure cold gas spray method. The examples of combined spray processes as well as some examples of post spray treatment including laser and high temperature treatments or mechanical one, are described. Then, the solid and liquid feedstocks used to spray and their properties are shortly discussed. The reviewed properties of functional coatings include: (i) mechanical (adhesion, toughness, hardness); (ii) physical (porosity, thermal conductivity and diffusivity, thermal expansion, photo-catalytic activity), and; (iii) bioactivity and simulated body fluid (SBF) corrosion. These properties are useful in present applications of functionally graded coatings as thermal barriers, the bioactive coatings in prostheses, photo-catalytic coatings in water treatment, coatings used in printing industry (anilox and corona rolls). Finally, some of the future possible fields of functional thermal sprayed coatings applications are discussed, e.g., to coat polymer substrates or to use the cheap technology of low pressure cold gas spray method instead of expensive technology of vacuum plasma spraying to obtain bond coatings.

The paper presents our actual knowledge and experience in joining dissimilar materials with the use of friction welding method. The joints of aluminium and aluminium alloys with the different types of steel were studied. The structural effects occurring during the welding process were described. The mechanical properties using, for example, (i) microhardness measurements, (ii) tensile tests, (iii) bending tests, and (iv) shearing tests were determined. In order to obtain high-quality joints the influence of different configurations of the process such as (i) changing the geometry of bonding surface, (ii) using the interlayer, or (iii) heat treatment was analyzed. Finally, the issues related to the selection of optimal parameters of friction welding process were also investigated.

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The present paper is focused on the characterization of the differences between two microstructures that can be obtained using SPS technology, namely (i) columnar and (ii) two-zone microstructure including lamellas and fine unmelted particulates. The optimization of spray parameters was made, and the advanced microstructural studies of obtained coatings were performed. The work was focused on zirconia stabilized by yttria (YSZ, ZrO 2 + 14 wt.% Y 2 O 3 ) and both by yttria and ceria (YCSZ, ZrO 2 + 24 wt.% CeO 2 + 2.5 wt.% Y 2 O 3 ) which are frequently used as thermal barrier coatings. Two types of microstructure were achieved using two different plasma torches, namely SG-100 of Praxair and Triplex of Oerlikon Metco. The microstructure of prepared coatings was analyzed using scanning electron microscopy with secondary electrons detector and backscattered electrons. Energy dispersive spectroscopy was performed to analyze the chemical composition of sprayed coatings. By electron backscatter diffraction grain shape, size, and crystal orientation were determined. The analysis enabled the discussion of the coatings growth mechanism. Finally, the Shape From Shading technique was applied to recreate and to analyze 3D views of coatingsÕ topographies, and using laser confocal microscopy, the surface roughness was examined.

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The Al2O3 + TiO2 coatings are of the interest of surface technology and tribology due to their good wear resistance and enhanced toughness comparing to pure Al2O3 coatings. However, the detailed effect of the used feedstock powder, is often neglected. Here, this work focuses on the deposition of Al2O3 + 13 wt % TiO2 coatings by atmospheric plasma spraying (APS) method as well as on their microstructure, phase composition and selected mechanical properties, in the reference to the route of the powder feedstock preparation. The commercial powder Metco 6221 in agglomerated and sintered form was used as a feedstock material during spraying, due to the fact that, so far, sintered or cladded powders are the most studied ones. The 2k + 1 spray experiment allowed to evaluate the influence of two variables, namely spray distance and torch linear velocity, on the coating microstructure. Afterwards, the coating adhesion was measured by the means of pull-off test. The correlations between Vickers microhardness, fracture toughness (Kc) as well as the coating morphology and phase composition were investigated. Finally, the dry sliding wear resistance was studied by using Ball-on-Disc method.

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