Iron-based coatings are often considered as replacement of hard chromium and WC-Co, as they pose lower health and environmental impact. In many cases the combination of mechanical and chemical properties of ferrous based alloys may be satisfactory and their relatively low cost make these coatings an interesting candidate for many applications. This study is inspired by opportunities to harden the ferrous base materials by strain hardening, solid solution strengthening, dispersion strengthening, and precipitation hardening. Already commercially available Fe-based coating materials with precipitates of mixed carbides and borides in the metastable austenitic matrix achieve a high hardness. In this study the cavitation erosion and abrasion resistance of various Fe-based coatings produced by HVAF and HVOF processes were investigated. Two experimental precipitation containing materials were prepared, and the sprayed coatings were tested for abrasive and cavitation erosion wear. In addition to precipitations, the importance of proportion of ferrite and retained austenite phases were studied by affecting the microstructure by heat treatments as the ability of different phases to affect hardening and ductility may become crucial in generating desired material properties. The properties of experimental and some commercial Fe-based alloys are compared with WC-Co and Cr 3 C 2 -NiCr coatings by property mapping.

Wear leads to high material and energy losses in various industries. The manufacturing of novel nano-carbide WC/Co powder feedstock materials promises a further increase in the performance of thermally sprayed wear protection coatings. A novel experimental powder and a commercial ultra-fine carbide WC/CoCr reference are thermally sprayed onto a 1.0038 substrate by High Velocity Air Fuel (HVAF) spraying. The specimens are metallographically prepared and analyzed by means of light microscopy (LM) and scanning electron microscopy (SEM). Vickers Hardness testing is conducted by microindentation and the porosities are determined by optical image analysis. X-ray diffractometry (XRD) analysis are used to investigate the phase retention. Fine nanocrystalline WC-structures are preserved in the dense coatings. A significant effect of powder type on the porosity of the coating was found. No systematic relationships could be identified between the coating structure and the parameter settings. It was possible to influence decarburization via both the powder type and the selected parameters. The resulting experimental coatings exhibit high hardness values in the range of the commercial ultrafine carbide WC reference. The novel nano-structured coating can contribute to reduced wear and therefore improve the efficient utilization of critical raw materials like tungsten.

Surface quality lifetime and wear resistance of protective coatings can be improved by decreasing carbide grain size from submicron to nanoscale. In this study, experimental WC-CoCr powders were manufactured via novel powder manufacturing approach using water-soluble raw materials. Produced powders were sprayed with the High-Velocity Air-Fuel (HVAF) spray process to control the particle temperature and to avoid in-flight decomposition of the nanocarbides. As a result, dense and wear resistant coatings with nanosized carbides were produced. Reference coatings were sprayed using commercial sub-micron WC-CoCr powder to compare the properties of the experimental coatings to the current state-of-the-art. Phase composition and microstructural characterization of the coatings were carried out with X-ray diffraction and electron microscopy, respectively. Mechanical properties were studied by using microhardness tester, as well as rubber wheel abrasion and cavitation erosion wear tests. The wear surfaces were characterized after the abrasion and cavitation erosion tests to understand the effect of nano-carbides on degradation mechanisms. Coatings with the nanosized carbides in the structure showed excellent mechanical properties in wear testing, and even outperformed reference coatings in cavitation erosion test. Based on the obtained results, these novel nano-carbide coatings are promising alternatives for demanding applications in which better surface quality lifetime is vital.

Tungsten carbide -based hard metal coatings are extensively used in demanding industrial applications like for wear protection purposes. Continuously increasing demands set new limits and need for materials with enhanced features. One solution is to improve hard metal properties by nanostructures. Presented study is part of a research where novel and safe route to manufacture nanostructural WC-Co powders starting from water soluble raw materials was developed. In this study powders’ workability in thermal sprayings is studied. WC-12Co powder was manufactured using water soluble raw materials: ammonium metatungstate as a tungsten source, glycine as a carbon source and cobalt acetate as a cobalt source. The powder was manufactured via optimized spray drying and heat treatment method producing a correct phase structure and chemical composition. Experimental powder was sprayed by HVAF-spraying to study its workability and functionality. Morphology, microstructure and properties were analyzed from the experimental nanostructural powder and the HVAF-coatings.

Suspension plasma spraying (SPS) is regarded as a promising way to produce new coating structures with improved properties. In this study, SPS was studied as a possible manufacturing process for producing thin MnCo 2 O 4 spinel coatings for used as protective coatings in metallic interconnector plates of SOFC’s. Suspension of nanosized MnCo 2 O 4 powder and ethanol was thermally sprayed by using an F4-MB plasma gun with radial suspension feeding. The influence of spraying parameters, such as plasma gas composition, total gas flow, current and spraying distance for coating architecture was studied by using field-emission scanning electron microscopy (FESEM) and X-ray diffraction method (XRD). Spraying parameters had a strong influence on the coating structure and composition. Coating with the most homogenous structure were formed when sprayed with the low energy spraying parameters whereas high energy parameters resulted in formation of a columnar microstructure containing larger cobalt rich areas.

In low-pressure cold spray (LPCS) process, compressed air is used as a process gas. The most important process parameters are the gas (air) preheating temperature and the gas pressure. Maximum preheating temperature of air is 650ºC and pressure is 9 bar in the LPCS system used in the present study. Powders used in LPCS process contain hard particles (Al 2 O 3 ) with metallic powders. LPCS is the method to spray soft metallic coatings with ceramic hard phase for different application areas. For example LPCS opens a way to produce thick coatings for electrical and thermal conductive applications and for corrosion protection. Aim of this study was to investigate microstructural properties such as microstructure and denseness of LPCS coatings. Also mechanical properties (hardness and bond strength) were studied. One interest of this study was to clarify the effect of hard phase on different coating properties. Coating materials were Cu, Ni, and Zn. Substrate material were carbon steel and copper. LPCS coatings seemed to be dense according to SEM studies but corrosion tests were needed to identify existence of porosity. Through-porosity was observed in the structures of the LPCS coatings during the corrosion tests. Bond strengths of LPCS Cu and Zn coatings were found to be reasonable and furthermore, hardnesses were quite high indicating reinforcement effect of hard phase and work hardening.

Perovskites are considered as potential materials in solid oxide fuel cells (SOFC) for different reasons at different parts of the fuel cells. Perovskites such as La 0.8 Sr 0.2 MnO 3 (LSM) and other compositions are electrically conductive which is necessary for SOFC applications. One possible application is protection coating for interconnect plates (bipolar plate) to avoid chromium oxide evaporation from the surface of ferritic stainless steel. Different commercial and experimental perovskite powders were sprayed by plasma and HVOF spraying under different spray conditions. Spraying of pervoskites was found to be challenging and required careful parameter optimization in both spray methods. Microstructure and phase structure of the coatings were investigated. A very fine crack structure, possibly caused by low mechanical strength and low ductility of the compounds, was easily formed in coatings prepared by plasma and HVOF spraying. Spraying method, parameters and spraying atmospheres were found to affect the stability of the perovskite compounds due to low chemical stability at high spray temperatures. Oxygen deficiency or oxygen surplus was concluded to cause distortion of the compounds crystal structure, causing thus shifting of XRD-peaks due to change of lattice parameters. Electric conductivity was affected by the crystal structure.

In cold spraying, various issues affect the mechanical properties of the coatings. Adhesion strength is usually considered to be the most crucial mechanical property. The aim of this study was to investigate the adhesion strength of cold sprayed copper and nickel chromium alloy coatings. The focus was especially in studying the influence of powders, substrates and heat treatments on adhesion strength. Three different copper and three nickel-20%chromium powders were tested. The substrate materials were carbon steel and copper. Furthermore, effect of substrate pre-treatment to the adhesion strength of the cold sprayed copper coatings was investigated. The influences of the powders and the substrates on the cold sprayed coatings were dependent on the materials. Adhesion strength of the cold sprayed Cu coatings was significantly higher on the Cu substrate than on the steel substrate. Moreover, heat treatment improved the adhesion strengths with increasing annealing temperature.

Cold spraying is quite a new process, which is an effective method to deposit dense and pure coatings. The aim of this study was to investigate microstructures and mechanical properties (hardness and adhesion) of the cold sprayed coatings. The coating materials were aluminium, copper, nickel and zinc. The substrate materials were carbon steel and copper. Influence of heat treatments on mechanical properties was studied, especially different heat treatment times and temperatures. The hardness of the cold sprayed coatings was higher than that thermally sprayed coatings and bulk materials. During heat treatment, the hardness of the cold sprayed coatings decreased and the ductility increased. Corrosion resistance of cold sprayed coatings was also studied. The corrosion resistance was tested with salt spray (fog) testing and open cell potential measurements. The corrosion tests showed some through-porosity but some parts of the cold sprayed coatings appeared to be fully dense, which showed their potential for corrosion protection.

Ceramic deposition produced by cold spraying was studied for functional surface applications. Several oxide materials and metal matrix composite (MMC) powders were used to model the behavior of ceramic powder deposition on soft metallic substrate materials. The manufacturing method, density and size of ceramic powders and matrix material of MMC were found to affect the deposition on soft metal surfaces. The powder density influences the deposition greatly and it is also an important factor in finding an ideal powder particle size. Fusing and crushing the powder can be a good manufacturing method if the fusion does not cause phase transformations in the powder. In that case, spray drying with sintering can give better results. Spraying parameters, such as the process gas parameters and the effect of multiple sweeps of the torch were also studied to optimize the amount of deposition. Cold spraying was found to be a promising manufacturing method for functional surfaces.

HVOF sprayed WC-CoCr coatings are used to in wear and corrosion applications. Commercially available hard metal powders for HVOF spraying are normally manufactured from virgin raw materials. In the present work, the possibility to manufacture WC-CoCr spray powder with excellent properties and quality from recycled cemented carbide tools and tool bits was studied. The powders were manufactured from hard metal scrap by a series of processing steps. The powders were sprayed by using the HVOF process. The properties of the powders and coatings were studied and compared to those of commercially available state-of-the-art WC-CoCr powders and coatings with the same nominal composition. Experimental powders worked well during spraying and the quality of the coatings was equal or even better than that of the reference coatings. Equal or even better corrosion properties compared to reference coatings were obtained with the new spray powder manufactured from recycled hard metal.

Cold spraying is a novel coating method in which coating is formed by mechanical deformation of sprayed metal particles. This heavy deformation causes structures, which need recrystallization heat-treatment in order to gain back the materials natural deformability. Aluminum, copper, nickel and Ni-20%Cr were cold sprayed and heat-treated at several temperatures. Coatings were sprayed using nitrogen as process gas. Substrate material was carbon steel. Heat-treatment temperatures were chosen from near room temperature to below coating materials melting temperature. As-sprayed and heat-treated coatings were characterized in microstructure, hardness, phase structure and electrical resistivity. It was found that 200ºC was enough to increase electric conductivity to 87% of pure copper. By heat treatment ductility was able to be increased and hardness subsequently decreased.