In glass mold industry, a surface treatment by laser cladding of a Ni based powder on cast iron is performed with a 4-kW continuous diode laser. For this, a robot programming method named "Wavering" was used. This method allows to cover large surfaces (higher than 5 mm). The cast iron substrate used during this work is employed for its heat exchange properties in glass mold Industry. However, it has drawbacks which are weak wear, corrosion, and abrasion resistance. Conventional techniques used to protect the molds, like Plasma Transferred Arc (PTA), affect the molds microstructure, but also the thermal and mechanical properties. The laser cladding of the Ni based alloy allows to protect the molds without affecting the cast iron thermal properties (and reduce the Heat Affected Zone length). The purpose of this research is to produce a well bonded Ni based melted powder without pores or cracks on large and curvilinear surfaces with the wanted geometry. The impact of the process parameters such as laser power, scanning speed and frequency on the coating geometry was investigated with an experimental design technique using the ANOVA (Analysis of variance) method. It was used to determine and represent the influence of each process parameter on the coating geometry (width, height, and circularity). This ANOVA analysis led to a parameter combination to optimize the Ni coating and the cast iron substrate quality by considering the industrial geometrical constraints. The bonding quality and the cracking behavior are also investigated on optimized parameters. Finally, it appears that laser cladding process leads to a better coating on curvilinear surfaces than other process like PTA.

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 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.

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 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.

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.

This study examines the structural and corrosion properties of Ni and NiCu coatings produced by high-pressure cold spraying. It also assesses the effect of heat treatment. FE-SEM images of coating cross-sections show tightly bonded particles with only a minor presence of open or oxidized boundaries. Polarization measurements in alkaline salt and acid solutions show that the Ni and NiCu coatings have good potential for corrosion protection applications. Corrosion behaviors of as-sprayed and heat treated coatings are compared with corresponding properties of bulk and substrate materials.

In this study, atmospheric and suspension plasma spraying are used to create nickel-based electrodes with enhanced surface area as required for hydrogen production. Optimal spraying conditions were determined using a Taguchi design-of-experiments approach. Electrochemical double-layer capacitance measurements by cyclic voltammetry show that suspension plasma spray coatings have more surface area than coatings produced by atmospheric plasma spraying. SEM micrographs show that the surface microstructure of the sample with the largest surface area contains high amounts of cauliflower-like aggregates with an average diameter of 10 µm. In general, the combination of melted, semi-melted, and resolidified particles leads to the formation of deposits with high porosity, rougher surfaces, and consequently larger surface areas.

This study ranks a number of common thermal surfacing materials for soil tillage applications based on the results of dry-sand rubber-wheel testing for abrasion resistance. Test specimens were prepared by plasma transferred arc (PTA) and powder welding deposition of a nickel-based self-fluxing matrix with and without tungsten carbide (WC) additions. For comparison, PTA coated M2 tool steel and quenched and tempered spring steels were also tested. PTA and PW deposition produced coatings with a similar level of abrasive wear resistance. Hardfacing with M2 and nickel-based 1560 deposited by PTA showed ~30% and ~15% wear respectively compared to the reference steels, while nickel-based grades with additions of 50% carbide showed only ~5% wear. Moreover, by increasing the amount of WC from 50 to 60 wt%, abrasive wear resistance was increased by 25%.