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 In previous studies at McGill University, tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs). A “crack-filling” mechanism was described as the deposition mechanism that allowed deposition of tin onto the CFRP. Improving the coating conductivity for lightning strike protection (LSP) purposes was achieved by adding other metal powders (aluminum, copper, zinc) to tin and cold spraying on the CFRP. At the same time, it was noticed that the addition of this secondary component (SC) provided an increase in deposition efficiency (DE), tamping was initially hypothesized to explain this improvement, thus prompting a study solely on the effect of SC hardness, which is reported elsewhere in this conference. However, it is recognised that other powder characteristics may also be influencing the DE. Thus, in this study, SCs with a wider variety of particle sizes, morphologies, densities and hardness values were mixed with tin and sprayed on CFRPs. The effect of SC properties on tin deposition is discussed and an optimal combination of SC properties for cold spraying of tin is suggested.

Abstract Spark-plasma sintering (SPS) was adopted in this study as a rapid post-spray treatment for yttria stabilized zirconia (YSZ) electrolytes prepared through the direct current (dc) plasma spray process. The lamellar microstructure in the as-sprayed samples was found to significantly reduced the ionic conductivity of the YSZ electrolytes. However, the ionic conductivity (at 1053 °C) increased sharply from 0.065 S/cm for the as-sprayed electrolyte to 0.122 S/cm for electrolyte post-spray treated through SPS at 1400°C for 3 minutes. These phenomena were attributed to the microstructure transformation from lamellar structure of the as-sprayed samples to equi-axial type granular structure of the post-spray samples treated by SPS. Correspondingly, porosity reduced from ~ 10.72 % in as-sprayed coating to ~ 1.38% in the SPS sample treated at 1400°C for 3 min. Majority of the pores in the SPS sample were also found to have contracted to a narrow size range 0.03 – 1 µm. AC impedance spectroscopy demonstrated the effect of the microstructure modification between samples treated in the SPS at temperature 1200, 1300 and 1400°C for 3 minutes with the concomitant reduction of the resistivity, which is consistent with the microstructure changes of the YSZ electrolyte from lamellar structure to granular structure. Overall, the results show that spark-plasma-sintering (SPS) is an effective and rapid post-spray treatment to improve the relative density and electrical properties of plasma sprayed YSZ electrolytes.

Abstract This paper consists of laws of formation of the modified layer on a surface of coatings from zirconium dioxide with the help of laser radiation. The peculiarities of laser processing of TSZ plasma sprayed layers on steel substrates with NiCrAlY bond layers are investigated using CW-carbon dioxide and Nd:YAG as well as pulsed Nd:YAG lasers. The layer surfaces are melted on. These modified layers consisted of macro fragments between 2,000 and 500 micrometer in size. These in turn are composed of micro-fragments between 20 and 70 micrometer in size. In both cases crack gaps are discovered: widths of 10 to 15 and narrow ones of 1 to 5 micrometer. The properties of thermal resistance, hardness, roughness, and density are determined as a function of the laser power output. Paper includes a German-language abstract.

Abstract The influences of process parameters on the microstructure of PEEK coatings deposited by flame spraying were analyzed by different physical and thermal methods, considering the density, the hardness and the Young's modulus. The cooling rate of the coating after spraying leads to large variations of the microstructure which evolves between the crystalline and amorphous states. Amorphous coatings exhibit less residual stress than semi-crystalline ones, which has an influence on the friction behavior.

Abstract In cold spraying, coatings are formed by a high velocity impact of solid particles. The particles are accelerated in a supersonic gas jet at temperatures of only a few hundred degrees centigrade. In contrast to thermal spray processes no melting of the particles and negligible heating of the substrate occurs. A series of spray experiments with copper powders of different particle size ranges were performed to study the effect of various process parameters on microstructure and properties of the coatings. The coatings have been evaluated for their microstructure, density, oxygen content, hardness and bond strength. With nitrogen as process gas and a -25 +5µm powder, dense coatings were obtained within a broad range of gas inlet pressure and gas inlet temperature.

Abstract Ni+Al, Ti+Al, NiCr+AI, and Cr+Al powders react exothermically in the heat zone of thermal spraying systems. Whether such reactions occur between aluminum and superalloy powders is the underlying question of this study. This paper describes composites of this nature and their sprayability to form adherent, metallurgically bonded deposits. Through parametric manipulation, coatings can be produced with a range of properties from dense to open (porous/abradable) structures. The paper also shows how seed particles can be clad with aluminum and sprayed to predictable property limits.

Abstract In order to properly characterize the entire deposition process, evaluation of the coating, including a reliable metallographic preparation technique which reveals the true microstructure, must be performed. Often, recommended metallographic sample preparation methods for thermally sprayed coatings are generic and are not tailored to specific materials. They are time-consuming and, in some cases, may provide inaccurate details (pull-outs, smearing, etc). This could lead to a wrong interpretation of the coating quality. The aim of the investigation was to develop new metallographic sample preparation procedures tailored to different types of coatings (metallic, ceramic, multilayer and composites), in order to reveal a more representative microstructure. A comparative study of different preparation procedures for the examination of various as-sprayed coatings is presented using an optical microscope. The coatings were deposited by atmospheric and vacuum plasma spray (APS and VPS) and high velocity oxygen fuel (HVOF) processes. A separate approach is recommended for choosing the right metallographic preparation procedure for ceramic, metallic, or composite coatings. Applied load and positioning of the mounted sample during preparation are identified as key factors in developing proper procedures. The microhardness of the coating must be considered when determining the applied load. Interesting practical trends in preparation procedures that may lead to superior coating representation and, in some instances, cost and time savings are presented.

Abstract The development and introduction of more advanced spray systems continues to drive the thermal spray market. Most of these developments benefit from an increase in particle velocities. The latest generation of HVOF systems can spray cermet coatings of higher density and higher hardness, wear resistance and corrosion resistance than HVOF systems introduced previously, due to an 30 to 50 % increase in particle velocity. HVAF systems are offered as an cost-effective alternative to HVOF systems. A further increase in particle velocity and the introduction of cold gas spraying can be seen as a transition from thermal to kinetic spraying and may open a wide field of new applications for coatings and structures of oxidation sensitive materials. Advances are also reported for wire spraying. New arc spray systems are capable to increase the density of metal and alloy coatings considerably and to reduce the oxide content of these coatings. Similar improvements but at lower spray rates may be achieved with newly developed HVOF wire systems. Paper text in German.

Abstract This paper describes the technique of anisotropic multiple small-angle neutron scattering (MSANS). Anisotropic MSANS, when combined with anisotropic Porod scattering, electron microscopy, and measurements of elastic modulus and density, has made possible the determination of the porosities, surface areas, mean opening dimensions, mean diameters, and approximate orientation distributions, of the intra-splat cracks and interlamellar pores, as well as the porosity, surface area, and mean diameter, of the globular pores. The changes in these parameters, as a function of annealing, are studied. Paper includes a German-language abstract.

Abstract The demand for highly continuous thermal spray deposition processing to gain manufacturing efficiency and enhanced control of deposition microstructure has driven the search for powder feedstocks that exhibit uniform flow behavior in pneumatic feeding devices even at low carrier gas flow ratios. This paper compares the continuous powder feeding characteristics of one type of feeding device for two different powder alloys fabricated by a representative set of powder processing methods, including spray dried, fused (cast) and crushed, and inert gas atomized. Powders were fabricated by both commercial vendors and Ames Laboratory processing equipment. The powder mass flow rate was found to depend directly on the apparent density of a specific powder type instead of the dry powder flowability, as initially expected.

Abstract The aim of this study is to produce free-standing functionally-graded structures in which density varies continuously from 2.2 to 17.3 g/cm3 through a total thickness of 4.5 mm. In order to optimize material performance, it is necessary to account for the different combinations or ratios of materials (i.e., tungsten and aluminum) in the plasma jet when determining mixture laws. A relationship based on the deposition efficiency, powder feed rate, and density of individually sprayed materials has been established and was used to predict the density, thickness, and deposition efficiency of the combined materials. The mixture laws were found to be in good agreement with experimental results, making it possible to build up coatings with a parabolic density profile and uniform layer thickness.

Abstract A study on induction plasma shape forming with yttria stabilized zirconia (YSZ) was conducted as part of an effort to develop a new method for producing nuclear fuel. YSZ was selected because its melting point is similar to that of UO2. Nuclear fuel pellets were made using a large (70 mm) induction plasma flame that sprays more than 100 pellets simultaneously and a small (10 mm) supersonic plasma flame that produces one pellet at a time. Process optimization for the large induction plasma flame was done based on chamber pressure, plasma plate power, powder spraying distance, sheath gas composition, probe position, and particle size. The best results were 97.11% theoretical density (TD) for 5-mm thick pellets. For the single pellet approach, densities as high as 99% TD have been obtained in 12-mm thick free-standing pellets.

Abstract The Directed Light Fabrication (DLF) process uses a laser beam and metal powder, fed into the laser focal zone, to produce free-standing metal components that are fully dense and have structural properties equivalent to conventional metal forming processes. The motion of the laser focal zone is precisely controlled by a motion path produced from a 3-dimensional solid model of a desired component. The motion path commands move the focal zone of the laser such that all solid areas of the part are deposited and the part can be built (deposited) in its entirety to near net shape, typically within +/-0.13mm. The process is applicable to any metal or intermetallic. Full density and mechanical properties equivalent to conventionally processed material are achieved.

Abstract Densification of plasma-sprayed NiCrAlY coatings was studied from the viewpoint of hybrid spraying combined with YAG laser irradiation. The laser beam was varied while performing low pressure plasma hybrid spraying and the microstructure of each coating was examined and compared with a conventional plasma sprayed coating. Of the various hybrid spraying methods tested, simultaneous irradiation produced the hardest microstructure with the least amount of porosity. The characteristics of the microstructures observed in each coating are explained with respect to their thermal hysteresis behaviors.

Abstract In this study, ethylene methacrylic acid copolymer (EMAA) was used as the matrix to produce EMAA/Al2O3 and EMAA/NiCr composite coatings from dry-blended powder mixtures. This work was conducted to determine processing concerns when using similar sized reinforcement particles of different density in a flame-spray process. This work has utility for applications that require a reduction in mechanical wear and/or to confer upon a polymeric deposit a certain functional property by the introduction of value-added powder. Free-standing coatings were produced to test the mechanical properties of the sprayed deposit. The effects of the filler content on the secant modulus, yield stress, and tensile strength are discussed. The differences in deposition efficiencies among the EMAA, Al2O3, and NiCr are highlighted with respect to particle size and density.

Abstract Pre-alloyed, plasma spheroidized powders were used as feedstock in the plasma spraying of functionally graded ZrO 2 /NiCrAlY coatings. The advantage of using pre-alloyed powders was to ensure chemical homogeneity and promote uniform density along the graded layers, and these pre-alloyed powders could be successfully used to prepare the different inter-layers of functionally graded coatings. The microstructure, density and microhardness changed gradiently in the ZrO 2 /NiCrAlY coatings. The bond strength of ZrO 2 /NiCrAlY coatings with different graded layers was measured. Results showed that for as-sprayed coatings with the same thickness, the bond strength increased with the number of graded layers. The bond strength of the coatings with five graded layers was about twice as high as that of the duplex coatings because of the significant reduction of the residual stress in the coatings. Experimental results also showed that the bond strength of as-sprayed coating increased significantly after hot isostatic press (HIP) and vacuum heat treatments, and the reason can be attributed to the densification of the microstructure, the decrease of defects in the coatings, inter-diffusion between layers and further reduction in the residual thermal stress.

Abstract Addition of CaSi 2 in steel melt leads to a decrease of oxygen content, an increase of the melt flow capability, an improvement of a metal ductility and weldability. For an estimation of CaSi2 and Si additions effect in conditions of thermal spraying composite powders were produced. A base material of these powders particles is nickel, nichrom and iron. CaSi 2 and Si are additional components of the powders (3-12 wt. %). Plasma coatings produced with using of these powders exhibit high density and adhesion. The coatings structure has a high grade of microcrystallinity with a decreasing size of lamels. Oxides content in the coatings decreases with an increasing of CaSi 2 and Si content in the composite powders, moreover this effect is more essential in case of CaSi2 addition. Addition of CaSi 2 and Si to Ni-base coatings increases a microhardness from 1900-2000 MPa to 2200-2850 MPa. In case of NiCr-base coatings this increasing is from 1800-2100 MPa to 2400-3500 MPa.

Abstract High-Z materials such as tungsten are currently considered more suitable for the inner coatings of fusion devices than low-Z materials. The VPS parameters are being optimized for different tungsten powders with respect to uniform pore distribution and distribution of unmelted particles in the coating. High process reliability is aimed at in coating production. Copper is used as the substrate material. The spray efficiencies, coating porosities and unmelted particles in the coatings are being examined and the microstructures evaluated. Spraying parameters are determined for two different powder fractions leading to relative densities ≥ 90 % of the theoretical density.

Abstract A P.S.Z. coating elaborated by r.f. plasma spraying was studied and compared to industrial arc plasma-sprayed P.S.Z. coatings to evaluate the quality of the corresponding thermal barrier coating system for gas turbine applications. One commercial ZrO 2 - 8% Y 2 O 3 powder was sprayed with two industrial d.c. torches (7MB and F4) and one r.f. plasma torch (Tekna PL50). Physical properties such as density, porosity and thermal diffusivity were measured on the three types of P.S.Z. coating. The microstructure and quantitative phase analysis were respectively investigated by S.E.M. and X-Ray diffraction. The burner rig tests on the T.B.C. systems showed that the thermal shocks resistance on the r.f. coating was at least the same as the others. Induction plasma spraying gave a high deposit efficiency (around 80%) and a P.S.Z. coating with very interesting thermal properties. All these facts demonstrate that r.f plasma spraying can be a competitive process to produce high quality thermal barrier coatings.