In this study, nitrogen is employed rather than helium to cold spray MCrAlY coatings at relatively low process settings. Recycling of the non-deposited particles during the spray is also explored, and the characteristics and cold sprayability of recycled powder are compared with that of as-received feedstock powder. The resulting MCrAlY coatings from the two powders, though different thicknesses, show similar dense microstructures, low oxide inclusion, and smooth surface finish, all of which contribute to improved oxidation behavior.

In this study, different sets of plasma-sprayed YSZ thermal barrier coatings were deposited via Ar/H 2 and N 2 /H 2 plasmas and compared based on deposition efficiency (DE), thermal conductivity (TC), and furnace cycle testing (FCT). The top-performing coatings exhibited equivalent FCT lifetimes with TC values in the range of 1.15-1.25 W/mK at 1200 °C, but the deposition efficiency of those produced with N 2 /H 2 plasma was twice as high, resulting in a 55% reduction in production costs.

This study assesses the viability of using nitrogen instead of helium to cold spray NiCoCrAlTaY coatings onto single-crystal superalloy substrates. The process, though feasible, has a low deposition efficiency, leading to a high level of deformation that affects the microstructure of both the coating and substrate. SEM and TEM analysis revealed metallurgical and mechanical bonding at the interface and grain refinement in the coating. A fine grain structure that developed in the substrate after deposition was also observed possibly caused by dynamic recrystallization during the deposition process. Evidence of element segregation in the substrate, identifiable as zones with a deformed γ/γ’ structure, was found as well.

This research demonstrates the use of cold spray (CS) as an additive manufacturing process to manufacture reflective aluminium coatings. Nitrogen was used as a carrier gas at various gas heating temperatures. Following deposition, the coatings were finished using a number of machining and/or polishing processes to surface roughness values of 20-150 nm. The samples were characterised with respect to total reflectivity within the wavelength range of 400-1800 nm, porosity, surface roughness, and density. The reflectivity of the coatings approached that of bulk material, and 99% dense coatings were obtained. Increasing the gas heating temperature did not decrease the porosity with the lowest gas heating temperature found to deliver the best reflectivity. This work demonstrates that CS can be used to coat thin layers of aluminium onto various materials, which can be subsequently polished to create composite reflectors. This provides a novel reflector with the reflectivity of aluminium, and the structural and thermal properties of the substrate material, allowing for greater flexibility in the manufacture of reflectors.

This study investigates the influence of particle temperature and velocity during reactive plasma spraying and the effect of plasma gases on coating properties. Using hydrogen gas with low flow rate was found to be better for reactive plasma spraying of fine Al 2 O 3 -AlN mixtures. The H 2 gas increased in-flight particle temperature, affecting in-flight vaporization, AlN content, phase transformation, deposition efficiency, and coating thickness. N 2 gas, on the other hand, increased particle velocity, thereby reducing particle residence time in the plasma, which affects melting, nitride conversion, and phase transformation.

This study demonstrates a new approach for producing thick copper coatings on steel by cold spraying via nitrogen gas. To overcome delamination problems without resorting to helium, substrate surfaces are treated prior to deposition using a forced-pulse waterjet. Samples with different levels of roughness were prepared using both conventional and waterjet surface treatments. The samples were then coated with thick Cu using only N 2 and adhesion tests were performed. Test results show good coating adhesion on all waterjet treated substrates with bond strengths ranging from approximately 25 MPa to 58 MPa, depending on surface roughness. Consistent with previous studies, cold spray Cu did not adhere to any substrates that had been polished or grit blasted. It is shown that the pulsed waterjet creates a surface with anchoring features that interlock with incoming particles to form a strong mechanical bond.

This study compares the deposition behavior of kinetic sprayed bronze-diamond composite coatings produced using different mixtures of helium and nitrogen gas. To determine impact properties of the diamond particles, bare and nickel-coated diamonds are deposited on bronze layers and the effects of plastic deformation are examined using SEM and finite-element analysis. The results indicate that the deposition efficiency of diamond is determined by several factors and depends more on the angle and shape of the diamond particles than on the deformation properties of the bronze matrix.

Nitrogen-alloyed steels have outstanding properties, but are rarely used in thermal spraying. In this study, high-nitrogen duplex and austenitic steels are sprayed using APS and HVOF techniques and the resulting layers are evaluated based on microstructure, composition, and corrosion and wear properties. HVOF layers outperformed the APS layers in corrosion and wear testing, with austenitic steel having the highest corrosion resistance, and duplex steel the highest wear resistance. Paper includes a German-language abstract.

A free falling experiment was conducted as a simulation of a thermal spray process. A flattening behavior of the freely fallen metal droplet impinged onto a flat substrate surface was fundamentally investigated. The substrates were kept at various designated temperatures, and the substrates coated with gold by PVD were also prepared in order to investigate the effect of a wetting at the splat/substrate interface on the flattening behavior of the droplet. A falling atmosphere was atmospheric pressure nitrogen to prevent the oxidation of the melted droplet, and the experiments under low-pressure condition were also conducted. A transition of the splat morphology was recognized in atmospheric pressure nitrogen experiments, that is, the splat morphology on a room temperature substrate was a splash type, whereas that on a high temperature substrate was a disk type. The cross-section microstructure of the splat obtained on the room temperature substrate was an isotropic coarse grain, whereas that on the high temperature substrate was a fine columnar. The grain size changed transitionally with increasing the substrate temperature. Transition temperature on the gold-coated substrate was higher than that on the substrate without coating. The cross-section microstructure of the splat obtained under low-pressure was a fine columnar even on the room temperature substrate. The results indicate that the metal droplet wets better under low-pressure condition than in atmospheric pressure nitrogen condition, and the wetting has a significant role in the flattening of the droplet.

Air entrainment in the first 30 mm of a dc Ar/ H 2 plasma jet has been studied by emission spectroscopy. The tests were conducted using 6, 7 and 10-mm diameter nozzles and plasma arc currents of 400 and 600 A. Oxygen, nitrogen, and argon spectral lines were recorded 20 and 30 mm downstream of the nozzle exit during spraying, and the corresponding atom density ratios were estimated based on plasma population temperature and volumetric emission coefficients. The results indicate that at 20 mm air entrainment is mainly due to piston flow for the 10-mm nozzle and both piston flow and engulfment for the 7-mm nozzle. At 30 mm, the engulfment process is found to have 4 to 6 times the impact that it does at 20 mm and is directly linked to the jet velocity. At both locations, the atom density ratios differ from that observed in air due to the time required to dissociate N 2 .

Among the different wires used in arc spraying, copper is a material of choice in some applications. Its malleability is used to allow an easy machining procedure after spraying. This article focuses on the limitations of the oxidation of copper during arc spraying and its influence on coating process and properties. The aim of this series of experiments was to improve coating properties of copper sprayed with the electrical wire arc spraying process by substituting compressed air with nitrogen. These experiments show that coating properties, as well as electric wire arc spraying process, are strongly influenced by the gas employed as the atomising element.

Thermally sprayed Fe-based coatings can be applied in conditions ranging from almost solid to complete molten droplets. While spraying under atmospheric conditions, the oxygen content in the coating varies depending on the spray parameters and the portion of molten phases in the droplets. Using vacuum-plasma technology, Fe-based alloys can be sprayed with a significant amount of molten phase without oxidation. This capability can also be used for alloying Fe-based sprays with nitrogen as is done during reactive vacuum plasma spraying. Such alloying promotes the formation of dispersed vanadium-nitride which greatly improves corrosion and wear resistance.

Properties of MCrAlY coatings obtained by High Velocity Oxy-Fuel (HVOF) thermal spray process operated in a standard configuration were compared with those obtained using a gas shroud attachment to the HVOF gun. Our measurements show that the attached gas (nitrogen) shroud nozzle considerably reduces the oxygen content in the coating without an appreciable change in the microstructure. The particle temperatures were decreased by an average of 100 °C at a standoff distance of 0.275 m (11 inches). There was also a large reduction in the particle velocity at this distance. Both these effects were related to the excessive amount of nitrogen used for shrouding.

When spraying is conducted in the ambient atmosphere, the entrainment of air cools down the plasma jet and affects its expansion. It may also cause the oxidation or the chemical decomposition of the sprayed materials. Inert Plasma Spraying (IPS), generally conducted in argon atmospheres, prevents these phenomena. However, the main drawbacks of IPS in comparison with air plasma spraying are the capital and apparating costs. To reduce the latter by 25 to 30%, nitrogen atmospheres may be used as a substitute for the conventional argon atmosphere. This paper presents a study in which titanium carbide and niobium powders were sprayed in argon and nitrogen atmospheres. Cryogenic cooling of the substrate was used during the spray process. This helps to maintain a low temperature in the chamber, produces thick coatings and allows the use of substrate materials that are sensitive to heat. The adhesion, roughness and microstructure of the coatings produced in both atmospheres are compared as well as their nitrogen content.