The present work demonstrates the possibilities of atmospheric air plasma spraying. It presents various approaches to the development and optimization of spraying modes using diagnostic equipment and provides examples of industrial approbation of the technology.

The wear of piston rings in large marine two-stroke diesel engines is a major maintenance cost. Applying coatings with good oxidation, corrosion resistance and high temperature strength, can lower the total maintenance cost. In the past nickel aluminide with chromium carbide have been applied to pistons by thermal spraying. Using laser cladding a suitable microstructure can be formed while at the same time avoiding cracks and bonding issues. In this report powders and coatings were manufactured in order to be able to investigate the dry-sliding wear behavior. Material with three levels of carbides was atomized. Wear test samples were manufactured by laser cladding. The dry sliding wear-mechanism maps are generated by using block on ring test setup where coated blocks slide against cast iron rings. All alloys exhibited regions of plasticity-dominated wear and oxidational wear with a transition region in-between. The carbide-containing alloys showed lower friction and wear in comparison to the carbide free nickel aluminide alloy.

A thermal cycling test was carried out in an EB-PVD MCrAlY – superalloy system, the result of which showed that a continuous β-NiAl layer formed in the MCrAlY coating near the coating–superalloy interface. Since β phase can be as a reservoir of Al, the formation of the β layer, in which much Al is reserved, is probably beneficial to the coating’s life. An oxidation-diffusion model was adapted to simulate the development of the microstructures in the coating-superalloy system. The simulation results indicate that the formation of the β layer was strongly related to the high Al activity in the substrate; if the Al activity of the substrate was high enough, a β layer could be built up in the coating near the coating-substrate interface.

Surface state plays an important role in particle bonding and formation of the first layer of coatings in thermal spraying. From a chemical aspect as well as a mechanical point of view, in all cases, the substrate surface needs to be optimized to promote the adhesion of the sprayed particles and then the coating. In order to control such parameters, several works have been conducted to avoid drawbacks on sensitive materials. This study aims at developing a laser surface texturation before the spraying process to improve the coating adherence. According to the laser parameters, different surface morphologies (hole diameters, surface roughness, hole depth, etc.) can be developed. The surface material morphologies were characterised by SEM and bond strength was evaluated through ASTM C633 pull tests. This approach has been applied on the system Al 2017 / NiAl and demonstrates a high influence of the laser treatment. However, the thermal effect induced during the laser-matter interaction has to be controlled to avoid negative effects of the substrate properties particularly tribological properties. In this case, a study of the effect of the conventional processes and texturing process on the fatigue properties of substrate were studied.

NiAl-Al 2 O 3 intermetallics based composite coatings were prepared by cold spraying of Ni/Al-Al 2 O 3 composite powders followed by post-spraying annealing treatment. The phase transformation mechanism from Ni/Al mechanical alloy to intermetallics was explored to aim at controlling the microstructure of the composite coating. Results showed that, with the porous Ni/Al and Ni/Al-Al 2 O 3 green compacts, self-propagating high-temperature synthesis (SHS) reaction was ignited at a temperature of 500-600°C. However, SHS reaction was not able to be ignited for the cold-sprayed dense Ni/Al alloy coating with or without substrate. SHS reaction was even not ignited for the Ni/Al-40vol.%Al 2 O 3 composite coating, although the thermal conductivity of the coating was significantly decreased by the addition of Al 2 O 3 ceramic particles. The phase transformation from Ni/Al mechanical alloy to NiAl intermetallics during post-spraying annealing can be evidently attributed to diffusion mechanism.

Post-annealing of cold spray coatings has great potential for wear applications because it produces intermetallic compounds at low temperature far below equilibrium. This study investigates the effects of spraying pressure on the intermetallics formed and their dispersion characteristics. In the experiments, Al and Al-Ni powders were sprayed on Ni and Al substrates at 0.7, 1.5, and 2.5 MPa and a portion of the coating samples were annealed in argon at 500, 550, and 600 °C. Detailed examinations showed that Al particles are subject to peening effects that can interfere with the formation of intermetallic compounds during annealing, but that the effects can be mitigated by controlling gas pressure. Spraying pressure was also found to have an effect on the formation of eutectic pores in Al-Ni composite coatings, with higher pressures corresponding to fewer pores.

Carbon-fiber-reinforced plastic (CFRP) rolls are increasingly employed in manufacturing equipment due to their light weight, high stiffness, and low inertia and flexure. These rolls, however, are rarely used without a surface coating due to their lack of wear resistance and gripping properties. This paper examines the effects of thermal shock on an experimental carbide-type cermet coating deposited by atmospheric plasma spraying on a CFRP test roll. After thermal shock testing, coating cracks and peeling were observed. The underlying cause was determined and an improved coating, a nickel-base composite with high thermal shock resistance, has been developed, tested, and put to use in a papermaking line, where the rolls have been maintenance-free for more than four years.

Coating operations over glass ceramic substrates represent a new field for thermal spray applications. Due to the unique thermal and mechanical properties of glass ceramics, especially the low or even negative CTE, coating processes must be adapted to reduce the distribution of thermal stresses in the system and to not damage the substrate. This study investigates the deposition of a complex-shaped ceramic-metallic multilayer coating system that could potentially serve as a heating element in a glass ceramic cooking plate. To ensure coating adhesion, the substrates are preheated and their surfaces are grit blasted. In order to minimize stresses associated with the deposition of metal, the movement of the spraying mechanism was automated with robot control and new masking concepts were developed to ensure the accuracy of the shape and placement of the coating. The influence of spraying parameters on coating properties and residual stress distribution is analyzed as well.

In this study, Ni-Al powder is plasma sprayed on various substrates prepared by in-situ laser ablation and preheating. Surface topography and splat shape are examined in order to assess how laser induced heat flux affects surface modifications and variations in splat shape. The causes of laser induced surface modifications are identified for Al, Ti, and stainless steel substrates and it is shown that laser preheating improves surface absorptivity, which effectively subjects more defects to the effects of the laser.

The influence of the particle velocity on the formation intermetallic of coatings is discussed. The primary phases of detonation sprayed NiAl coatings are NiAl and Ni 3 Al, and also a solid solution of Ni in NiAl. The lamellar and homogeneous distribution of Al may be due to the oxidation of the powder particles during their flight in the pulsating high temperature, high velocity jet of the gas detonation process. During heating and melting of the powder particles, an aluminum oxide film is formed. This film takes part in the coating formation and affects the Al distribution. Another important observation is the presence of NiAl and Ni3Al phases in the coating structure. The transition zone between the coating and substrate has a thickness of 10-15 µm. The character of the distribution curves of Al and Ni confirms the lamellar distribution of NiAl and Ni 3 Al phases in the coating.

Coatings of Metal-Matrix-Composite (MMC) with enhanced wear resistance were created by thermal spraying. The used powders composed of iron and nickel aluminides reinforced with alumina, Cr- and Ti-carbides were produced before by self-propagating high temperature synthesis (SHS). The fused and crushed composite powders were sprayed by atmosphere plasma spraying (APS) and gas detonation spraying (D-Gun). Spray powder and coating properties like morphology, structure, microhardness, porosity, bond strength, wear and corrosion resistance are examined using optical and scanning electron microscopy, XRD analysis, pin-on-disc (wear resistance). The produced MMC coatings are compared to commercially used wear resistant coatings, e.g. high velocity oxyfuel flame sprayed Cr 3 C 2 -NiCr. The properties of a special coating type depend on the used spraying method. Plasma sprayed MMCs show a slightly higher porosity than D-Gun sprayed coatings. The chemical composition of used powders has a big influence on the coating properties. Fe- and Ni-aluminide matrix coatings reinforced additionally with carbides, especially Cr 3 C 2 , show a better wear resistance compared to coatings containing just oxides as hard material.

Thick thermal spray coatings are used to repair worn parts during aircraft overhaul. The thermal spray coating is used to restore a part to its original dimensions. Characteristics of the as-applied coating that affect the performance of thermal sprayed parts are the residual stress in the coating, the tensile bond strength, the amount of porosity, oxides and impurities near the coating/substrate interface, and the hardness of the coating. An understanding of the relation of these coating characteristics to process variables such as the material used for the coating, spray process, spray angle, and thickness of the applied material is needed. In this paper, four thermal spray coatings, Ni5Al, Ni5Al-atomized, (NiCr)6Al, and Inco 718, on a substrate of Hastelloy X are investigated. These materials are applied using two different thermal spray application processes: plasma spray and High Velocity Oxy-Fuel (HVOF). Spray angles of 90° and 45° are used during spraying. The nominal thickness of the applied coatings ranges from 0.4 mm to 1.8 mm. The thermal spray coatings are evaluated in four types of tests. Residual stresses in the coatings and substrate are evaluated using the modified layer removal method. A tensile bond strength test is performed. Metallographic examination is used to determine the porosity and content of oxides and bond zone impurities (percent) of the applied materials. In addition, the hardness of the coating is measured. For the materials and conditions investigated, it is found that residual stress varies with each of the four process parameters. The bond strength for plasma sprayed coatings is related to the type of material and possibly to the coating thickness. The percent porosity varies with coating material, but, for Ni5Al, it does not depend on application process. Oxide content, as a percentage, varies with material and process, but not with spray angle and thickness. The percentage of impurities near the coating/substrate interface varies with process and, for the specimens that were coated using the HVOF process, with thickness. The hardness of the coating was found to vary with material and spray process. For three of the four coatings, hardness increases with thickness but, for Inco 718, hardness decreases as thickness increases.

Properties of thermally sprayed coatings, including residual stress, are controlled by various parameters of the spraying process. This study is focused on three thermal spraying techniques with significantly different particle temperatures and velocities. These are plasma spraying, twin wire arc spraying and high velocity oxy-fuel spraying. For each method, in-flight particle diagnostics was performed. Through-thickness residual stress profiles in Ni+5%A1 coatings on steel substrates were determined nondestructively by neutron diffraction. The stresses range from high tensile in the plasma sprayed coating to compressive in the HVOF one. Various stress generation mechanisms, including splat quenching, peening, and thermal mismatch, are discussed with respect to process parameters and material properties.

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.

Due to their attractive combination of properties (high resistance to oxidation and wear, high melting point, and lower density) iron and nickel aluminides show promise for the development of advanced materials and coatings However, poor room temperature ductility and susceptibility to intergranular cracking restrict their commercial application. To provide the structure required composite materials produced by the self-propagating high-temperature synthesis (SHS) are promising. In this paper, the potential of thermally sprayed NiAl/aluminum oxide and FeAl/aluminum oxide composite powders produced using the SHS method is evaluated. The results of the structure and property investigations for the synthesized powders as well as for the resulting plasma coatings are presented. Paper includes a German-language abstract.

Current HVOF systems available on the world market are relatively complicated to operate and expensive. At the Bauman State Technical University in Moscow (BMSTU) a new portable HVOF spraying and cutting system MiniJet-30 has been developed. This rugged system offers the ease of operation of conventional gas welding equipment and produces high quality HVOF coatings. In this paper, the results of numerical simulation calculations of supersonic gas/powder flows, with and without a particle mask, are presented and compared with experimental outcomes. Additionally, typical HVOF coatings were sprayed and evaluated for bond strength, porosity, microhardness, abrasive wear, and phase composition (OM, XRD). The results are compared to those of other HVOF systems. Lastly, the cutting efficiencies for stainless steel, cast iron, and non-ferrous metals are discussed.

Magnesium alloys are widely used as lightweight metals in cars and trucks, but they require special surface treatments to offset corrosion and wear limitations. One such treatment, electron beam remelting, is the focus of this present work. As described in the paper, copper and nickel powders were plasma sprayed onto magnesium in a vacuum chamber, then heated to melting temperatures with a swept electron beam. Copper and nickel were chosen because they form hard intermetallic compounds when melted with magnesium. The structure and properties of the remelted Cu- or Ni-alloyed surface layer were found to be dependent on the properties of the plasma sprayed coating and the parameters of the e-beam treatment. In the course of the investigation, the coatings were assessed based on their microstructure, the thickness of the remelting zone, occurring phases, and the determination of hardness and abrasive wear resistance.