Alkaline water electrolysis is currently the most promising approach to produce hydrogen. However, a main limitation for large-scale application originates from the significant energy loss caused by the coverage of bubbles on the electrode surface. Here, pore-graded Ni electrodes with a positive and negative gradient porous structure that boosts the desorption and release of gas bubble are reported, resulting in a greatly advanced mass transference. The electrodes are obtained from a blend of Ni and Al via high-pressure cold spray. The gradient porosity is realized by varying the addition of Al and chemical etching. As-sprayed electrodes are annealed to eliminate the residual stress and strengthen the adhesion of layers, hence improving their durability. As a result, the electrode with a positive pore-graded structure exhibits a better HER/OER performance when tested with a carbon rob counter electrode. Notably, when tested with an annulus counter electrode of Nickel foam, the electrode with a negative pore-graded structure achieves minimal HER/OER overpotential, outperforming other porous electrodes. This is benefited from improved bubble removal and mass transference capability. All prepared electrodes showed an excellent stability that after 500 cycles of HER/OER test without a large potential fluctuation.

Polymers have proven to be challenging to cold spray, particularly with high efficiency and quality when using inexpensive nitrogen (N 2 ) and air propellants. Helium (He) when used as a process propellant can improve spray deposit properties but is often undesirable due to its limited availability and high cost. In this study, additives of multiple particle sizes and materials were mixed with polymer powder in an effort to improve the performance of polymer sprays using mainly N 2 as a process propellant. The effects of additives on deposit microstructure were investigated by precise ion-beam polishing of deposit cross sections and subsequent electron microscope imaging. Additional metrics including the density and post - spray composition of deposits were investigated to quantify the peening effect and the amount of embedded additive. Additives, regardless of size, were observed to embed in the spray deposits. Additionally, hard-phase additives demonstrated nozzle-cleaning properties that continually remove polymer fouling on the nozzle walls. Inversely, sprays with polymer powder and no additives tended to clog the nozzle throat and diverging section as a result of continual fouling.

Surface texturing is one of the most technologically appropriate laser surface treatment applications. Over the past few decades, texturing has emerged as an attractive surface engineering option and has been used by researchers to generate micro/nanopatterns on operating surfaces. This technique can create simple or complex patterns on component surfaces depending on their aesthetic or functional goals and without altering the overall properties. In addition, this non-contact process can be applied to hard-to-reach areas. Recently, laser surface texturing has been applied to improve the adhesion of contact surfaces. Several authors have demonstrated the impact and benefits of textured surfaces to achieve optimal adhesion of coatings and increase in-service behavior. Nevertheless, based on the laser-matter interaction phenomena, chemical and mechanical transformations of the surfaces can be noticed but are difficult to characterize. Indeed, the affected layers are of the order of a few hundred nanometers. Then, analyses must be performed with variable levels of resolution in order to analyze the structural, chemical and mechanical characteristics of the matter. To develop new applications of unconventional assemblies and improved adhesion of new materials, a control of these local modifications is required.

In the semiconductor industry, plasma etching processes are widely used. Process chamber parts that are located in the plasma etching system are also exposed to the harsh environmental conditions. Thus, parts located close to the process area are typically coated with yttria to increase service life, and thus process performance. However, such yttria coatings are usually porous, and thus can be attacked by fluorine containing plasma. In order to increase the lifetime of the components in the plasma etching system, this research project aimed to improve the protective yttria layer by reducing the porosity of the protective layer. Specifically, a design of experiment was employed in which the porosity was the target value. The main effects of the coating parameters and their interactions including the surface treatment before the coating process were determined. Furthermore, the bonding of the protective coating to the component to be protected, as well as the element distribution and the coating morphology were investigated. The results and their ramifications with respect to the envisaged application will be discussed.

Masking solutions for parts needing special treatments such as shot peening, grit blasting or thermal spray are now commonly used in industrial processes for the aerospace, industrial gas turbine, and medical industries. The ever-evolving special treatment methods require adapting the masking solutions so they retain their efficiency and quality level. This paper will describe the choices made in combining materials, geometry and surface finish of the masks to provide the necessary compliance with the thermal spraying processes or other special treatment requirements. We will demonstrate that successful masking designs are often the result of close collaboration between the operator’s engineering team and the masking solutions provider in order to comply with what is always a bespoke process. Innovations in materials and additive manufacturing enable the process towards tailored solutions which enable these industries to increase their productivity and level of manufacturing quality.

Low pressure cold spraying is an attractive technique for onsite metal coating fabrication due to its compactness and portability. However, the bonding strength of the coating prepared by low pressure cold spraying is generally low, which restricts the further applications in engineering and industrial fields. To improve the bonding strength, pre-treatment on substrate surface can be an effective procedure. In this study, a low-temperature plasma treatment was applied to a pretreatment technique, and the effect of the treatment on particle bonding was compared with that of a laser treatment. Copper coatings on aluminum and copper substrates were selected and studied as basic metal materials. The SEM observation results show that the particle adhesion rate significantly increases by the laser and plasma treatments, due to the removal of the native oxide films on the substrates. The particle bonding on the plasma-treated substrate reveals better interfacial adhesion with less gap compared with the laser-treated one. The pre-treatment by low-temperature plasma can be an attractive technique to assist the cold spraying process due to the oxide removal ability and no thermal effect which can apply a wide range of materials.

Cold spray process was chosen as a good candidate for dimensional restoration and protection of components. Commercially pure aluminum, aluminum-alloy or titanium were recommended for different applications. This paper investigates laser surface texturing association to enhance durability of sprayed coatings. Laser is easy automated, localized and reliable process. It was applied for prior-surface treatment. Textured surfaces were produced and compared to conventional treatments, such as grit-blasting, in terms of deposition efficiency and adhesion bond strength. Patterns promoted direct particle embedment. Particle-substrate interface exhibited significant temperature rate and strain in cavities. Intimate contacts and particle compressive states were assumed responsible for improvement. The particle deformation and bonding behaviors were evaluated and discussed for the different configurations. Thus, window of deposition was increased with laser surface texturing. Anchoring mechanisms increased two fold the adhesion strength compared to conventional pre-treatments. In one case, the interface was stronger than the coating cohesive strength.

Metal surface characteristics play a significant role in interacting with their biological environment. Copper surfaces have been identified for their antimicrobial properties. Improvement of antibacterial and antiviral performances can be tailored by surface microstructure modification. Severe plastic deformation is an effective surface modification procedure to improve the mechanical performance of metal surfaces. This technique can be adapted to obtain surface grain refinement and induce surface roughness. In this work, cold spray shot peening is used to modify copper substrate surfaces and study the effects on their antibacterial properties. To modify the grain structure of copper, different shot-peening parameters were examined. The surface roughness and microstructure were investigated by employing optical and scanning electron microscopy. The bactericidal activity of copper substrates after shot peening treatment is discussed and a comparison between the bacterial load on treated (shot-peened surface and cold sprayed copper coating) and untreated surfaces (as-received) is provided. Testing of the surfaces after their exposure to the biological environment demonstrated improved microbial inactivation performances for surfaces that had undergone grain refinement without exceeding a certain roughness value.

Assemblies containing fiber-reinforced plastic (FRP) and metal parts are typically fastened together via mechanical joining or adhesive bonding. Mechanical joining processes tend to weaken FRP parts by cutting fibers, while adhesives require long cures and often lead to inseparable material compounds. This paper evaluates a new joining method in which plastic parts are laser treated, then metallized via wire-arc spraying, and finally soldered to mating metal parts using a low-temperature process. Due to the effective increase in interface area resulting from laser structuring, bond strengths of up to 15.5 MPa can be achieved.

Metal structures in offshore facilities are usually protected from corrosion using Zn-Al coatings even though they are subjected to collective stress conditions. This paper evaluates a post-treatment called machine hammer peening and its effect on surface finish, induced residual stresses, and near-surface microstructure of thermally sprayed ZnAl4 coatings. As expected, coating roughness was reduced from about Rz = 53.5 μm in the as-sprayed condition to 10.4 μm after treatment and coating densification was revealed in the near-surface zone. Residual stresses, which were surprisingly compressive in the as-sprayed condition, were likewise affected by the peening process, reaching a maximum of 200 MPa. The influence of peening direction and other such parameters were also investigated as part of the study.

In this study, Ni-alloy 718 coatings are deposited on substrates of the same material using laser assisted cold spraying (LACS). The laser heats the substrate surface making it more ductile and expands the metallurgically bonded region. Coatings deposited at various track spacings and surface temperatures are examined to assess coating quality, level of deformation and recrystallisation, and the effect of different track spacings on surface roughness and waviness. A track spacing of 3.5 mm was found to provide the most even coverage with the laser. Surface X-ray diffraction measures residual stress for different layers at various surface temperatures while incremental hole drilling measures stress profiles for coatings of varying thickness. All coatings were found to be well bonded with low porosity.

In this study, NbC coatings, 250 µm thick, were deposited by low-velocity flame spraying on stainless steel substrates and were laser remelted in a controlled argon atmosphere. Isolated passes transverse of the coatings were performed at different focal lengths at speeds of 10, 15, and 20 mm/min. Using the selected laser parameters, layers were recast with eight passes at 10% superposition. Erosion-corrosion tests were performed and coating surfaces and cross-sections were characterized via SEM, EDS, and XRD analysis. Modified surfaces of dense, 800-µm thick coatings with no defects and excellent metallurgical bonding with the substrate were obtained. It was found that dilution of the coating with the substrate formed a gradient of chemical composition and mechanical properties and that erosive-corrosive wear resistance was highest for an erodent impact angle of 90°.

Sand blasting and high-velocity thermal spray processes can produce residual stresses in superalloy substrates that can significantly influence microstructure development. To investigate this effect, single-crystal superalloy substrates were sand blasted using different levels of force (zero, light, and heavy) and then coated with a MCrAlY layer by HVOF spraying. Cross-sectional analysis of an as-sprayed sample revealed a subsurface depletion zone with a composition rich in Mo nano precipitates. Cross-sectional examinations after vacuum heat treating and at various points during oxidation testing showed that elemental interdiffusion occurred between the coating and substrate and that sand blasting intensity has a major influence on the depth of the interdiffusion zones.

In this work, a new cold-spray shot-peening process was used to achieve surface nanocrystallization on a magnesium alloy deposit. The results of various examinations and tests show that nanocrystalline layers up to 40 µm thick with an average grain size in range of 50-80 nm can be prepared on AZ91D deposits using the new process. The nanocrystalline layers also exhibit good microhardness and tribological properties.

In this study, aluminum coatings were cold sprayed, with and without laser assistance, on laser-textured aluminum 6060 and Fe52 steel substrates. The results indicate that laser texturing makes for a cleaner coating interface than grit blasting and that the benefits are greatest when spraying on harder substrate materials. For the steel substrate, the optimized topography achieved through laser texturing assisted in particle deformation, leading to the formation of a much tighter coating structure. Laser-assisted cold spraying, in turn, improved deposition efficiency as well as coating density and adhesion. Separately or together, the two processes have proven to be beneficial for cold spraying.

This paper describes the development of cold-sprayed chromium coatings that are used to increase the corrosion and wear resistance of zirconium-based nuclear fuel cladding tubes. Significant effort was necessary to deposit very thin layers of chromium on 4 m long, 10 mm diameter tubes by cold spraying. As explained in the paper, a final polishing step is used to reduce surface roughness and adjust coating thickness to the desired specifications.

In this study, pure Al coating was deposited via in-situ shot-peening-assisted cold spray method in order to study the effect of the in-situ tamping effect which was caused by the impact of large sized shot-peening particles on grains size evolution of coatings. The microstructures of the as-sprayed Al coating were observed by using Scanning Electron Microscope and Electron Backscatter Diffraction. A commercial gas atomized Al powder with a grain size range of 10-20 μm was used as the spraying powder. The cross section of the as-sprayed Al particles presented elongated rectangular morphologies, which indicated that the nearly spherical particles experienced severe plastic deformation by the impact of large sized shot-peening particles. It was found that dynamic recrystallization of dislocations-ridden regions was responsible for the grain refinement of cold sprayed coating. Aluminum grains with size of several tens to several hundred of nanometers can be apparently recognized at the whole cross section of the particle. Therefore, in-situ shot-peening-assisted cold spray method can deposit completely nanocrystalline coating using micrometer-grain powder, and thus can be employed to develop high quality coatings of commercial importance.

NiCoCrAlY coatings are widely used as bond coats for ceramic thermal barrier coatings (TBCs) and oxidation and corrosion protective overlay coatings in industrial gas turbines. High temperature oxidation behaviour of NiCoCrAlYs has a great influence on the coating performance and lifetime of TBCs. A promising route to decrease the oxidation rate of such coatings is post-coating surface modification which can facilitate formation of a uniform alumina scale with a considerably slower growth rate compared to the as-sprayed coatings. In this work, the effect of surface treatment by means of shot peening and laser surface melting (LSM) on the oxidation resistance of high velocity air-fuel (HVAF) sprayed NiCoCrAlY coatings was studied. Isothermal oxidation was carried out at 1000 °C for 1000h. Results showed that the rough surface of as-sprayed HVAF sprayed coatings was significantly changed after shot peening and LSM treatment, with a compact and smooth appearance. After the exposure, the oxide scales formed on surface-treated NiCoCrAlY coatings showed different morphology and growth rate compared to those formed on as-sprayed coating surface. The oxidation behaviour of surface treated HVAF-sprayed NiCoCrAlY coatings were revealed and discussed.

Three Fe-based powder alloys, Höganäs Fe SP529, Fe SP586 and 6AB, have been deposited by HVOF and HVAF spraying onto mild steel plates. The sprayed samples were first ground and then shot peened using glass shot in order to seal the surface interconnected pores and other surface imperfections. The samples as ground and ground/glass shot peened were tested by salt spray (fog) exposition for 238 h according to ASTM B117/ISO 9227. FeSP586, HVOF and HVAF sprayed and glass shot peening samples achieved surface sealing enough to pass the test with appearance rating RA = 9 according to ISO 10289. All other samples achieved moderate to excessive pitting and/or moderate to excessive staining types of corrosion defects.

In this study, pure Al coatings were deposited on ZK60-T5 Mg alloy substrates via in-situ shot-peening assisted cold spray in order to study the effect of the Al coating on fatigue behavior of coated samples. Fatigue behavior of the coated and un-coated samples has been investigated through experimental tests. The size and shape distribution of powders, microstructural characteristics of coatings and fractography of fatigue test samples have been studied using scanning electron microscopy. The average microhardness of pure Al coating is higher than 70 HV50. In order to obtain the fatigue S-N diagram for each set, coated and un-coated samples have been tested in a load-controlled condition. The tension-compression fatigue experiments reveal that the fatigue property of ZK60-T5 alloy coated with pure Al coatings has significantly deteriorated compared with un-coated samples.