Ni-Al intermetallics have excellent corrosion and oxidation resistance, but their use in thermal spraying has been limited due to issues with in-flight oxidation. In this study, a novel approach is proposed to remove oxide from Ni-Al droplets in-flight by adding a deoxidizer (diamond) to the feedstock powder. A mixture of nickel, aluminum, and diamond powders was mechanically alloyed using a combination of cryogenic and planetary ball milling. The resulting Ni/Al/diamond composite powder was then plasma sprayed via the APS process, forming Ni-Al coatings on Inconel 738 substrates. Phase composition, microstructure, porosity, and microhardness of the coatings were characterized by X-ray diffraction, scanning electron microscopy, image analysis, and hardness testing, respectively. Oxygen content measurements showed that the coatings contained significantly less oxygen than coatings made from ordinary Ni/Al powders. In-flight particle temperatures were also measured and found to be higher than 2300 °C. The low oxygen content in the coatings is attributed to the in-situ deoxidizing effect of ultrahigh temperature droplets which are also oxide-free.

The focus of this study is the formation of a solid solution and metallic nickel in the cobalt-nickel mixed oxide coatings during suspension plasma spray (SPS) deposition. The (Co,Ni)O solid solution is a potential material for inert anode applications in aluminum production. SPS coatings and in-flight collected particles are studied to gain further insight into the melting and mixing phenomena of the NiO and CoO powders as well as phase formation in the deposited coatings. Moreover, the role of suspension feedstock particle sizes on the microstructure of coatings is discussed. SEM, EDS and X-ray diffraction studies helped better understanding the formation of different crystalline phases within the as-sprayed coatings. It was found that the formation of metallic nickel is possible in the coatings. The results support the importance of substrate temperature on the formation of metallic Ni, so that keeping the substrate at low temperature results in an increase of the Ni content in the coatings. In this study, possible causes for the formation of metallic Ni during spraying are discussed.

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.

Developing effective heating systems to prevent ice accretion on the surface of wind turbine blades and aircraft wings is of great significance for extreme cold environments. However, due to high velocity impingement of water droplets and solid particles on the surface of these components, an appreciable degree of surface material degradation may occur. In this study, nickel-chromium-aluminum-yttrium (NiCrAlY) was chosen as a metal matrix material for a coating-based heating system. Pure ceramic powders, namely, alumina and titania, and a cermet powder, tungsten carbide-cobalt (WC-12Co), were mechanically admixed with NiCrAlY powder and deposited to fabricate reinforced metal matrix composite (MMC) coatings. The powders were deposited on cylindrical low carbon steel bars by using flame spraying. The specimens were placed in a wind tunnel to conduct a comparative investigation of their erosive wear resistance under water droplet impact. A cold spraying unit was used for solid particle impact erosion tests. The erosive wear rates were quantified by measuring mass loss. The experimentally obtained results showed noticeably lower wear rate in NiCrAlY-WC-12Co and NiCrAlY-titania coatings compared to the other coatings. The results suggest that certain MMC coatings could be effectively employed to decrease the erosion rate of coating-based heating elements.

The purpose of this work is to study the effect of laser radiation on powder particles transported by gas during laser cladding. The temperature and velocity of particles entering the light field of a CO 2 laser were determined by measuring particle radiation as well as the scattered radiation of the diode laser, two independent methods. It is shown that under the action of laser radiation, the particles acquire additional acceleration due to the vapor pressure from the irradiated part of the particle surface. This sonic recoil vapor pressure can significantly affect the in-flight characteristics of powder particles in a gas jet. Particle velocities due to laser acceleration exceeded 100 m/s in a carrier gas with a flow rate less than 30 m/s. Particle temperature depends on several factors and was found to vary from ambient temperature to the boiling point of the powder.

This study shows how HVOF-sprayed NiAl coatings produced using chemical and electrochemical activation processes can serve as oxygen evolution electrodes in alkaline water electrolysis systems. Freestanding hierarchical NiAl structures produced without chemical binders exhibit electrocatalytic performance comparable to state-of-the-art noble catalysts characterized by very low overpotential and high current density without degradation.

WC-Ni metal-matrix composite coatings were deposited by low-pressure cold spraying using feedstock powders with different amounts of carbide. Uniaxial quasi-static tensile testing was conducted on the as-sprayed coatings to investigate the effect of porosity, particle size, and mean free path on mechanical properties. The evolving strain fields were measured via digital image correlation and image analysis was used to characterize coating microstructure. The coatings with higher carbide content exhibited better tensile properties, which is attributed to significant consolidation of the matrix, increased interfacial area, smaller average carbide size, and reduced mean free path between carbide particles.

The fracture toughness of pure Al, Cu, Ni, and Ti deposited by cold spraying was investigated to gain a better understanding of the damage process and quantify material performance. Rectangular specimens of self-standing deposits with fatigue pre-cracks were tested in three-point bending. KIC values were obtained from J-R curves and stress-strain curves were plotted. The cold-sprayed deposits exhibited significantly lower fracture toughness than the same wrought materials, and fractographic analysis revealed either ductile or cleavage intergranular fracture as the major failure mode.

The aim of this study is to evaluate the effect of electromechanical treatment on the structure and wear behavior of plasma-sprayed nickel coatings. The coatings were air plasma sprayed on low carbon steel substrates, then electromechanically treated using different values of current density. Erosion resistance was assessed based on volume loss and coating microstructure and phase composition were evaluated via SEM and XRD. Erosion mechanisms were compared by analyzing coating cross-section and surface microstructures and wear resistance was associated with features such as defects, porosity, and cracks.

Commercial available Ni and Ti powder were blended together and deposited on stainless steel by atmospheric plasma spray(APS). Subsequently the as-sprayed coatings were laser remelted with a Nd -YAG pulsed laser source. Cross-sections of as-sprayed and laser-remelted coatings were characterized by scanning electron microscopy (SEM). Prior to SEM observations, the laser remelted coatings were polished and etched by Kroll etchant. Meanwhile, the energy dispersive spectrometer (EDS) was employed to analyze the chemical distribution of the coating both as-sprayed and laser remelted. The results indicated that APS sprayed NiTi coatings presented a dense microstructure with Ni splats and Ti splats distributing uniformly. Oxygen partial pressure in the argon leads to the burning of Ti splats during the laser remelting process. And Ti oxides located at the bottom of the laser molten pool because of the laser stiffness and molten flow. Moreover, the top part of the molten pool mainly involved in Ni columnar grains.

In this work, a mechanically clad NiCr powder feedstock was deposited on alumina substrates by atmospheric plasma arc spraying. The resultant splats were analyzed for features such as interfacial bonding, splat classification and, critically, Cr distribution. Using a slice-and-view sectioning technique in a dual-beam FIB-SEM system, a representative splat exhibiting discrete Ni and Cr regions was physically deconstructed then reconstructed with visualization software to analyze individual layers with the splat. Although the powder feedstock contained Ni particles clad with clusters of Cr, the splats solidified into distinct layers of Ni and Cr with no signs of interaction between them. A model formulated based on this observation shows that the distribution of Cr cladding on the Ni particulates influences the amount and location of Cr around the solidified Ni splats.

In this investigation, Ni-Al 2 O 3 powder mixtures containing different amounts of alumina were cold sprayed onto Al 7075 substrates. SEM analysis showed that the Al 2 O 3 particles were mainly distributed between elongated nickel grains although some were found fragmented on the surface due to impact with embedded Al 2 O 3 particles. All coatings exhibited high surface roughness while those with 40 wt% Al 2 O 3 had the best balance between embedded particle content and coating porosity. Nanoindentation tests revealed significant variations in hardness and Young's modulus over the surface of the coatings.

In this study, a 30 kW RF plasma reactor is used to synthesize metallic (Ni) and intermetallic (Mg 2 Ni) nanoparticles along with carbon-encapsulated Ni. The system was configured with injection probes at the top and bottom of the torch to facilitate the synthesis of compounds as well as core-shell particle structures. Materials used as precursors include methane, Ni, Mg, and pre-alloyed Mg 2 Ni powder. By feeding Ni together with methane, nickel nanoparticles encapsulated with 6-10 layers of graphite were produced. The core-shell particles and other samples collected were analyzed using X-ray diffraction and electron imaging techniques and were found to be spherical in shape and less than 100 nm in diameter.

In this study, nickel and Inconel coatings were deposited on aluminum and steel substrates by cold gas spraying. Fine, standard, and coarse nickel powders and two standard Inconel (625 and 718) powders were selected as feedstock materials and sprayed at different gas pressures and temperatures. A coaxial air-cooled nozzle was used in spray trials, except for the fine Ni powder, which required a water-cooled nozzle to prevent clogging at high temperatures. Coating microstructures were examined and various properties were measured including shear strength, adhesive tensile strength, hardness, and porosity. Cross-sectional images of different coating samples are presented and discussed along with test results.

In this investigation, particle image velocimetry (PIV) and direct imaging are used to measure particle velocities during cold spraying. Four feedstock powders were sprayed, including Ni, WC-Co, carbonyl Fe, and Cr steel. Multiple exposures at 500 ns intervals were used to measure in-flight particle velocities via direct imaging with a high shutter speed camera. Velocimetry measurements were made with a double-pulse laser and a high-resolution camera. With the minimum frame straddling time set to 100 ns, a maximum particle velocity of 1052 m/s was measured.

Intrinsically active nickel electrodes with large porous surface areas have shown promise for producing hydrogen by alkaline water electrolysis. In this study, Ni powder and NiO suspensions were sprayed on Inconel 600 substrates with an atmospheric plasma gun, producing single (Ni, NiO) and double layer (Ni-NiO) coatings. Top surface morphologies were examined, revealing both micro and nano scale features. Based on kinetic parameters obtained from steady-state polarization measurements, APS-SPS coated electrodes are the most catalytically active and thus have the most potential for hydrogen evolution. It is believed that the nanoscale structure increases effective surface area while the microporous structure facilitates mass transport and overcomes hydrogen bubble blockage.

The practical experience with the new Castolin Eutectic CJK5 High Velocity Oxy Fuel thermal spray unit has grown since its successful launch in 2011. It has many design features that simplify the user interface and servicing, but maintaining outstanding coating quality. The technical and practical features are described with detailed microstructural characterization of the resulting carbide based coatings using an established powder composition from several powder sources. With the recent development of a state-of-the-art metal powder manufacturing plant in Europe, highest quality “satellite-free” metal powders can be manufactured. New self-fluxing chemistries have been developed that are also low in Nickel and are designed to have good wear resistant properties. With the growing practical experience and parameter optimization, several innovative powders and coatings have been developed and are presented. Microstructural and mechanical properties and their relationship to processing parameters are presented.

Comparative studies on the intermetallic compound (IMC) formations of nano- and micro-size Sn with Ni and Cu in cold gas dynamic sprayed (CGDS, or Cold Spray) coatings were carried out. High purity pure nano (average 150 nm) and micro (under 45 μm) Sn were selected and prepared as raw materials mixture in order to be sprayed onto Ni and Cu plate-shape substrates. Nano particles of Sn were successfully coated under conventional coating parameters when they are mixed with microsize materials. And thermodynamic predictions regards to compound formation similarly worked out for both nano and micro Sn mixture. However, the kinetics of formation reaction were turned out to be different. In all case, nano particle showed more sluggish behavior. After post-annealing, microsize Sn formed larger amount of IMC with Ni than nanosize Sn although, owing to larger interfacial area, more intensive reactivities were expected. Also, there were significant differences in the size and distribution of eutectic pores as well.

In cold spray, feedstock powders are accelerated by supersonic jet with solid phase and deposited onto substrate. Compare with the conventional thermal spray, the coatings have low porosity without oxidation and decomposition. This study examines the effect of the powder compressive strength of each particle on coating deposition characteristics using two types of Ni powders, manufactured in a different process, in cold spray. The result indicated that heat treatment reduced the powder compressive strength, and the decrease of the powder compressive strength was related to the increase of bond strength of particles and deposition efficiency. In addition, it was shown that the powder compressive strength has an influence of deposition mechanism.

This paper presents a life cycle assessment comparison of electroplating and various thermal spray processes for the formation of nickel coatings. The comparison was carried out using a peer-reviewed database of upstream materials and energy and commercial LCA software. Material and energy use and the corresponding emissions of each coating process were converted to impact scores by means of the Eco-Indicator-99 method.