Abstract Acquisition of a new LVPS and APS coating system at Delta Air Lines necessitated optimization of the coating parameters on both systems, especially for application of bond coat (LVPS) and top coat (APS) for a TBC coating system. To expedite the coating optimization, it was determined that a design of experiments (DOE) approach would best enable the establishment of the operating window for the two systems. Samples prepared were primarily evaluated for their performance while exposed to a cyclic oxidation cycle. Samples were also evaluated for the microstructure and composition using energy dispersive spectroscopy (EDS) analysis. Samples from the ceramic coating DOE were also evaluated for their erosion characteristics. Results indicate a low correlation between the individual bond coat parameters evaluated to the furnace cycle life. However, the top coat spray parameters were found to have a greater correlation to furnace cycle life and erosion performance.

Abstract Tungsten heavy alloy (WHA) of W-Ni composition was deposited from a blend of standard thermal spray powders using a radio frequency inductively coupled plasma torch in a protective atmosphere. The coating contained a fully developed WHA structure, i.e., spherical W particles embedded in a Ni-rich matrix. Bending tensile strength R m , bending yield strength R p,0.2 , and elastic modulus were measured and compared with W-Ni-Co references fabricated by sintered and quenched (SQ) and forged and annealed (FA) powder metallurgy (PM) processes. The fatigue and fracture properties of the plasma spray deposits are comparable with those of the SQ-PM reference material, but inferior to those of the FA-PM reference. The results of various property tests are presented and analyzed in the paper.

Abstract Three different coatings were deposited using the Detonation Gun Spraying (DGS) technology from steel powders alone, and steel powers mixed with Fe3C and SiC particles, respectively. The microstructural characteristics of these coatings were examined and the hardness of each type of coating was studied. The morphology and structure of the feedstock powders were affected by the exposure to high temperature during the spraying process and rapid solidification of steel powders that resulted in the formation of an amorphous structure. The unreinforced steel coating had the highest hardness among the three types of coatings, possibly due to a higher degree of amorphization in the coating compared to the other two samples. The microstructural observation confirmed the formation of dense coatings with a layered structure with good connectivity between layers with minimum defects and porosities in the interfacial regions.

Abstract Cold gas spraying is a solid-state deposition process developed for metallic powders as feedstock materials. For ceramic materials; such low temperature-high velocity kinetic process is still questionable but could have interesting advantages. In the CERASOL project (ANR-19-CE08-0009); the nature and the architecture of porous ceramic powders involving agglomerated sub-micrometric grains are investigated. To that purpose; three oxide ceramics powders (alumina; zirconia and yttria) have been prepared for cold spray. These powders were analyzed in order to assess their architecture (composition; particle size; porosity; density; crystallite sizes…). Preliminary cold spray experiments were carried out implementing velocities measurements for various stand-off distances and spraying of coupons with line experiments. The characteristics of the deposited layers have been examined by SEM and XRD in order to discuss the role of the powder architecture on the impact behavior of the nanostructured agglomerated particles. The role of the gas stream that affects the kinetic and the trajectory of the particles are also discussed.

Abstract Thermal spray coatings are widely used to protect materials from corrosion, wear, and oxidation, but they have yet to reach their full potential because of porosity limitations and the detrimental effects of oxidation on interlamellar bonding. This paper investigates an atmospheric plasma spraying process that deposits oxide-free dense metallic coatings with well bonded lamellae. The process produces ultrahigh temperature metallic droplets, up to 2650 °C, using specially designed powders that are deoxidized in-flight through the evaporation or gasification of oxides. The impact of these oxide-free ultrahigh temperature droplets has a spreading-fusing, self-metallurgical bonding effect resulting in fully dense bulk-like metallic coatings. Various coating materials, including NiCrMo, 304SS-Mo, NiCrBSi, and Al, are investigated, demonstrating the versatility of the new technique.

Abstract Microstructure and physicochemical properties of a thermally sprayed coating depend on the dynamics of the particles interacting with the spray jet. This is especially the case for electrical properties. In this study, different spraying processes were used to spray p-type and n-type half-Heusler powders. Thermoelectric powders, Hf20Zr75Ti05CoSb80Sn20 (p-type) and Hf60Zr40NiSn98Sb02 (n-type), were selected due to their interesting electrical properties. The spray processes were evaluated based on coating composition and mechanical property measurements. The only coatings of practical interest were those that were plasma sprayed and they were examined in detail to assess the effect of process parameters on coating properties.

Abstract In subzero conditions, atmospheric ice naturally accretes on surfaces in outdoor environments. This accretion can compromise the operational performance of several industrial applications, such as wind turbines, power lines, aviation, and maritime transport. To effectively prevent icing problems, the development of durable icephobic coating solutions is strongly needed. Here, the durability of lubricated icephobic coatings was studied under repeated icing/deicing cycles. Lubricated coatings were produced in one-step by flame spraying with hybrid feedstock injection. The coating icephobicity was investigated by accreting ice from supercooled microdroplets using an icing wind tunnel. The ice adhesion strength was evaluated by a centrifugal ice adhesion tester. The icing performance was investigated over four icing/deicing cycles. Surface properties of coatings, such as morphology, topography, chemical composition and wettability, were analyzed before and after the cycles. The results showed an increase in ice adhesion over the cycles, while a stable icephobic behaviour was retained for one selected coating. Moreover, consecutive ice detachment caused a surface roughness increase. This promotes the formation of mechanical interlocking with ice, thus justifying the increased ice adhesion. Finally, the coating hydrophobicity mainly decreased as a consequence of the damaged surface topography. In summary, lubricated coatings retained a good icephobic level after the cycles, thus demonstrating their potential for icephobic applications.

Abstract Thermally sprayed WC-Co coatings provide excellent wear resistance and corrosion protection under heavy loads, but their application usually involves additional grinding and polishing steps, which can be 3-4 times costlier than the spraying process itself. There is thus the motivation to develop a process that produces smooth, near-net-shape carbide coatings. This contribution is an investigation of WC-12Co coatings obtained by suspension HVOF spraying. Significant work was devoted to the development and characterization of water-based hardmetal suspensions synthesized from commercially available WC and Co powders. The suspensions produced were sprayed using the HVOF process, and the resulting coatings were evaluated based on microstructure, hardness, and phase composition.

Abstract This study investigates the effect of composition on the antibacterial and antiviral properties of hydroxyapatite/titania composite coatings deposited by suspension plasma spraying. Hydroxyapatite is a bioceramic material used as a plasma-sprayed coating to promote osseointegration of femoral stems. TiO2 has promising photocatalytic activity and good efficiency in destroying bacteria, viral species, and parasites. Prior to coating, substrates were grit blasted, ultrasonically cleaned, and heated to enhance adhesion strength. The microstructure of the resulting coatings was then characterized using XRD and Raman spectroscopy. Test results indicated that SPS transformed Ti2O3 into TiO2 with mixed phases. Ti4O7 and Ti3O5 phases were also identified, which show photocatalytic activity due to oxygen vacancies. Antibacterial and antiviral tests were conducted as well.

Abstract Grinding wheels are usually manufactured by powder metallurgical processes, i.e. by moulding and sintering. Since this requires the production of special moulds and the sintering is typically carried out in a continuous furnace, this process is time-consuming and cost-intensive. Therefore, it is only worthwhile for medium and large batches. Another influencing factor of the powder metallurgical process route is the high thermal load during the sintering process. Due to their high thermal sensitivity, superabrasives such as diamond or cubic boron nitride are very difficult to process in this way. In this study, a novel and innovative approach is presented, in which superabrasive grinding wheels are manufactured by thermal spraying. For this purpose, flat samples as well as a grinding wheel body were coated by low-pressure (LP) cold gas spraying with a blend of a commercial Cu-Al2O3 cold gas spraying powder and nickel-coated diamonds (8-12 μm). The coatings were examined metallographically in terms of their composition. Afterwards, the grinding wheel was conditioned for the grinding application and the topography was evaluated. This novel process route offers great flexibility in the combination of binder and hard material as well as a costeffective single-part and small-batch production.

Abstract Plasma spraying was used to deposit Li3PO4 coatings from sintered dense powders in three size ranges to study the effects of particle size and spraying distance. Coating microstructure, crystal structure, and composition were characterized using SEM, XRD, ICP-MS, and FTIR. It was found that sintered dense powders have a high temperature orthorhombic phase (γ-Li3PO4) that differs from the β-Li3PO4 phase associated with agglomerated Li3PO4. Plasma-sprayed coatings produced from these powders have similarly dense microstructures with fracture-surface morphology like that of sintered bulk. The effect of particle size and spraying distance on atomic ratio is also investigated in the study.

Abstract The unique combination of the properties of iron aluminides opens up a multitude of novel applications at elevated temperatures in oxygen and sulphurous atmospheres. FeAl composites have excellent wear and corrosion resistance paired with the intermetallic phases of the Fe-Al system, which, however, tend to hydrogen embrittlement. In this paper, intermetallic phases are produced from FeAl using the self-propagating high-temperature synthesis process, which is reinforced with inclusions from other intermetallic phases, which prevent cracks from spreading. In addition, layers are deposited by means of thermal spraying, which are analyzed with regard to their composition and structure. Paper includes a German-language abstract.

Abstract This paper aims to achieve Ti-6Al-4V nitrided coatings using high-pressure plasma spraying coupled with reactive plasma spraying in a reactive nitrogen atmosphere, namely High Pressure Reactive Plasma Spraying. The influence of chamber pressure and the influence of chamber atmosphere with some experiments using air atmosphere are studied. The spraying was carried out with four pressure variations up to 250 kPa in a nitrogen atmosphere in order to determine the influence of the spraying pressure and the spraying atmosphere. The microstructure and the phase composition of the Ti-6Al-4V layers are examined with the aid of X-ray analysis, microprobe measurement, SEM, and TEM. The investigations show that the pressure-supported nitrogen application during spraying led to the formation of fine and coarse TiN in the Ti matrix. Paper includes a German-language abstract.

Abstract The aim of this investigations was to increase the wear resistance and the corrosion resistance of magnesium alloys. It can be noticed, that the coating of magnesium alloys is practicable with PTA welding and laser welding. The quality of coatings depends on the composition of the strap material, on the composition of the coating material (matrix material, carbides) and the welding parameters. The magnesium alloys AM50 and AZ31 are suitable for coating. But microporosity is not available. The best results were obtained with a coating matrix material of AlSi12 and addition of B4C. This coatings have a fine and homogeneous structure. Paper text in German.

Abstract This paper examines plasma-sprayed layers for the production of which powder mixtures were used, which, in addition to NiCrSiB alloys, contained impurities that resulted from the abrasion caused by the blasting of cast iron rollers produced by centrifugal casting. The structure and mechanical properties of composite layers of different compositions are investigated. A tribo-technical test is carried out using a friction device that worked according to the "coated disc clamping device" scheme. The clamping device is made of hardened carbon steel (C45) with a hardness of HRC 58 to 60. The tests are carried out in the area of boundary friction with bath lubrication and with limited lubrication. Another test is carried out in the absence of lubrication in the friction zone and in conditions that simulated abrasive wear. Paper includes a German-language abstract.

Abstract Since its commercial introduction in the early 1980s, it has been known that HVOF spraying can produce layers with low oxide levels, high toughness, and excellent adhesive strength. Compared to low-pressure plasma and vacuum plasma spraying, the HVOF process is based on different melting dynamics, which do not require the use of a controlled atmosphere. As a result, the original oxygen content of the wettable powder plays a significant role with regard to the layer quality. In this paper, the oxygen content of normal MCrAlY powder is varied and its influence on the quality of the sprayed coating is examined. It is concluded that, by controlling and limiting the initial oxygen content in the spray powder, better layer qualities with lower oxide proportions and higher density can be achieved. Paper includes a German-language abstract.

Abstract The HVOF spraying process is used to produce NiCoCrAlYRe layers, which serve as adhesive layers for plasma-sprayed thermal insulation layers. This paper investigates the influence of the HVOF spray parameters on the structure and properties of the layers. The parameters are optimized to produce high layer densities with low degrees of oxidation and the same surface roughness for subsequent TBC coatings. High-temperature oxidation of HVOF-sprayed NiCoCrAlY Re layers by means of TBC layers is investigated at temperatures of 950 and 1000 deg C in time cycles of up to 3000 hours. A vacuum-sprayed layer with the same composition is examined as a reference. Oxidized layers are characterized, and peculiarities such as oxide layer thickness, proportion of the NiAl phase, and imperfections at the boundary layer are measured. It turned out that the less expensive HVOF layer offers the same protective properties as a VPS layer. Paper includes a German-language abstract.

Abstract In this paper, a study on the spraying of Hastelloy C-276 is carried out using the Axial III plasma spray method. The aim is to develop a layer with a low oxide content. The oxide content is related to the microhardness of the spray coating. In various test series, a Hastelloy C-276 layer with low hardness could be achieved with the help of plasma spraying in a protected and unprotected atmosphere. Paper includes a German-language abstract.

Abstract Arc spraying is a possible method for the cost-effective coating of large-area metallic components. Arc-sprayed layers are also used for highly stressed gas turbine parts as adhesion promoters or as protection against corrosion. In many arc-sprayed applications, the oxidation of the sprayed material during the spraying process proves to be disadvantageous. The oxidation has a negative effect on the spraying process, as it causes a reduction in the mechanical properties as well as the corrosion resistance. In some cases, however, a high degree of oxidation in the layer can be advantageous as it increases the layer's resistance to abrasive wear. In this paper, the possible alternatives for adjusting the degree of oxidation of the layers are considered. This is primarily achieved through the use of non-oxidizing nebulizer gases. The measured oxide content of the layer varied from 0.8 to 3.41 percent by weight when Ni18Cr6Al2Mn is used. Paper includes a German-language abstract.

Abstract This paper investigates technologies of wear-resistant coatings and types of cored wire. Novel layers with low porosity and small particle size are produced using the arc spray process. FeCrB + Al and FeCr + Al + C cored wires with steel sheathing and a modified burner are used. The phase composition of the layers and their change due to friction are investigated using the XRD method. Wear tests are carried out with the block-on-ring configuration with different lubrication under a normal pressure of 5 MPa. The results showed good wear resistance of both layer systems. Paper includes a German-language abstract.