In this study, an internal powder injection was employed with a modified anode nozzle. The effects of the anode geometry and spray particle size on spray particle temperature were investigated. Moreover, the effect of spray particle temperature on the in-situ in-flight deoxidization and intersplat bonding formation were examined with both boron and carbon deoxidizers.

In this study, a high-entropy alloy (HEA) powder containing boron (NiCrCuMoB) was developed for atmospheric plasma spraying to produce coatings with minimal oxide formation in the molten droplets. The in-situ deoxidizing effect of boron during flight was investigated by analyzing collected HEA particles. The oxidation behavior of individual splats deposited on polished stainless-steel substrates was also examined. The resulting coating microstructure and mechanical properties were characterized. The results demonstrate that the addition of boron effectively suppresses in-flight oxidation of the molten particles, leading to the production of HEA particles with low oxide content. Consequently, bulk-like HEA coatings exhibiting strong metallurgical bonding and a reduced oxide content were achieved due to the deoxidizing action of boron.

All solid-state sodium-ion batteries (ASS-SIBs) have great potential for application to large-scale energy storage devices due to their safety advantages by avoiding flammable organics and the abundance of sodium. In this study, plasma spraying was used to deposit Na 3 Zr 2 Si 2 PO 12 (NZSP) electrolyte for assembling high performance ASS-SIBs. NZSP electrolyte layers were deposited at different spray conditions using NZSP powders in different particle sizes. The factors influencing the microstructure and compositions of NZSP layers were examined by characterizing the compositions of splat and cross-sectional microstructures of the deposits. It was found that the preferential evaporation loss of Na and P elements occurs severely to result in a large composition deviation from initial powders and spray particle size is key factor which dominates their evaporation loss. The APS NZSP electrolytes present a dense microstructure with well bonded splats which is attributed to low melting point of NZSP. The apparent porosity of the as-sprayed NZSPs was lower than 3 %. The effect of annealing on the microstructure of APS NZSP was also investigated. The performance of typical APS NZSP was also evaluated by assembling an ASS-SIB battery with APS NaxCoO2 (NCO), Na 3 Zr 2 Si 2 PO 12 (NZSP) and Li 4 Ti 5 O 12 (LTO) as cathode, electrolyte and anode, respectively. Results showed that columnar-structured grains with a chemical inter-splat bonding were formed across the interfaces between electrodes and electrolyte. There is no evidence of inter-diffusion of zirconium, cobalt and silicon across the NCO/NZSP interface. With the preliminary battery, the solid electrolyte exhibited an ionic conductivity of 1.21 × 10 -4 S cm -1 at 200 o C. The SIB can operate at 2.5 V with a capacity of 10.5 mA h g -1 at current density of 37.4 μA cm -2 .

MCrAlY coatings prepared by plasma spraying have been commonly utilized as a thermal protective coating for crucial heated end components due to their high mechanical properties and excellent high-temperature oxidation resistance in aggressive environments. However, the oxides introduced during the preparation process have an adverse impact on the properties of the MCrAlY coatings. In the present work, an attempt was made to deposit NiCrAlY coatings by air plasma spraying (APS) with a low oxide content achieved by introducing carbon as a deoxidizing element. During spraying, the carbon is preferentially oxidized and the formed gaseous CO is completely removed rapidly. Thus, the in-flight oxidation of metal elements can be suppressed to achieve oxide-free particles. Individual in-flight droplets were collected with liquid N 2 to clarify the deoxidation effect. Results demonstrate that the oxygen-free NiCrAlYC droplets can be achieved by adding deoxidizing element carbon. The oxide content of NiCrAlYC particles is 0.43 wt.%, being much lower than the 2.87 wt.% of conventional NiCrAlY particles. The adhesive strength test yielded an adhesive strength higher than 71 MPa for NiCrAlY coatings APS-prayed by the oxide-free NiCrAlYC molten droplets, which is much higher than 53 MPa for the conventional NiCrAlY coatings.

Plasma spraying is the most versatile coating process for depositing a wide range of materials to enhance material performance in harsh conditions. However, severe oxidation during the plasma spraying of metal coatings often results in coatings with high oxide content, limiting interlamellar bonding. Consequently, as-sprayed metal coatings offer inadequate protection against severe corrosion and wear. To address this challenge, we developed Ni-, Cu-, and Fe-based materials containing boron as a deoxidizer. This innovative approach effectively suppresses in-flight oxidation, producing oxide-free molten droplets and enabling the formation of bulk-like metal coatings with sufficient metallurgical bonding between splats. We employed a modified tensile test to evaluate the adhesive and cohesive strengths of these coatings. The Ni-based coatings exhibited adhesive strength exceeding 150 MPa on Fe-based substrates, while cohesive strength surpassed 260 MPa with a novel bond coat. Corrosion and gas penetration tests confirmed the creation of dense, bulk-like Ni-based alloy coatings, demonstrating their potential for various applications in severe service environments.

A new challenge in the transport systems concerns with improving efficiency. Thermal swing coatings are interesting candidates for internal combustion engines due to their potential to reduce cooling requirements and increase efficiency. K 2 Ti 6 O 13 (KTO) thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying through powder structure design and optimization of deposition conditions. The thermophysical properties of plasma-sprayed KTO deposits and their effect on the thermal swing have been investigated. Their thermal conductivities were tested by a laser flash method and the thermal performance of the coatings was further examined by thermal swing test. The phases, nominal chemical compositions and microstructure of KTO deposits were characterized by X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS). The results indicated that the chemical composition change occurs to the coatings resulting in a deviation from nominal stoichiometry due to chemical reactions between the plasma gas and particles. The thermal conductivity of the coating is very sensitive to the coating compositions, and the coating prepared using porous powder under pure argon presents a single K 2 Ti 6 O 13 phase and high porosity, and the lowest thermal conductivity of 0.85 W/m·K.

The metallic bond coat is generally utilized to increase the coating adhesion and the adhesion of thermal spray bond coat is of essential importance to applications. However, it usually depends on mechanical bonding with a low adhesive strength. In this study, a novel metal bond coat with high cohesion strength is proposed by plasma-spraying Mo-clad Ni-based or Fe-based spherical powder particles. Mo-cladding ensures the heating of spray particles to a high temperature higher than the melting point of Mo and prevents metal core from oxidation during spraying. Theoretical analysis on the splatsubstrate/ splat interface temperature and experimental examination into coating-substrate interface microstructure were performed to reveal the metallurgical bonding formation mechanism. The local melting of substrate surface and resultant bond coating by impacting high temperature droplets creates metallurgical bonding throughout the interfaces between substrate and bond coat, and within bond coat. The experiments were conducted with different substrates in different surface processing conditions including Ni-based alloy, stainless steel and low carbon steel. All pull-off tests yielded strong adhesion higher than the adhesives strength of 80 MPa. The present results revealed that Mo-clad metal powders can be used as new bond coat materials and high performance bond coat can be deposited by atmospheric plasma spraying.

The previous results have shown that dense bismuth oxidebased electrolytes can be fabricated simply by plasma spraying owing to their low melting point. In this study, the Bi 2 O 3 – Er 2 O 3 –WO 3 electrolyte of high ionic conductivity was deposited by the cost-effective plasma spraying to assemble the SOFC for examining its electrochemical performance. The SOFC cell consisted of FeCr 24.5 metal support, NiO-YSZ anode, 10 mol% scandium oxide-stabilized zirconium oxide (ScSZ) electrolyte, (Bi 2 O 3 ) 0.705 (Er 2 O 3 ) 0.245 (WO 3 ) 0.05 (EWSB) electrolyte, and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) cathode. The ScSZ electrolyte interlayer was introduced between the anode and EWSB electrolyte to hinder the reduction of EWSB in the anode environment. NiO-YSZ, ScSZ, EWSB, and LSCF were deposited by plasma spraying on the metal support which was prepared by a press-forming-sintering process. The NiO-YSZ/ ScSZ/ EWSB/ LSCF single cell assembled with the as-sprayed ScSZ presented an open circuit potential of 0.90V at 600 °C and the maximum power density of 1130 mW cm -2 at 750 °C, 450 mW cm -2 at 650 °C, and 128 mW cm -2 at 550 °C. The plasma sprayed ScSZ electrolyte was then densified through impregnating using yttrium and zirconium nitrate solutions followed by annealing treatment. The single cell assembled with the densified ScSZ presented an open circuit potential up to 1.004V at 600 °C and the maximum power density of 1356 mW cm -2 at 750 °C, 619 mW cm -2 at 650 °C, and 163 mW cm -2 at 550 °C. The performance of the cell was significantly improved by the post-spray densification treatment of the ScSZ electrolyte. The present result shows that the high performance NiO-YSZ/ScSZ/EWSB/LSCF cell at intermediate temperatures can be successfully fabricated by plasma spraying.

Atmospheric plasma sprayed (APS) CuNiIn coatings have been widely used for fretting wear protection in many important areas such as aircraft engines for decades. The oxides in CuNiIn coating prepared by APS hinder splat bonding formation and thus degrade the coating fretting performance. In this study, CuNiIn powders of different boron contents were designed to realize the self-oxide-cleaning effect for in-flight molten droplets and thus deposit the dense CuNiIn coating with high fretting performance. Scanning electron microscope was used to characterize the microstructure. The oxygen content in the coating was measured by the inert gas fusion technique. Fretting test was performed for three coatings under different loadings. The results show that CuNiIn2B and CuNiIn4B coatings presented the oxide content of 0.40wt% and 0.38wt%, which are lower than 1.6wt% of the CuNiIn coating. The oxygen content in the CuNiIn4B coating decreased with the increase of spray distance while the oxygen content in CuNiIn coating increased with the increase of the spray distance. Such results clearly reveal the boron in-situ deoxidizing effect of inflight molten droplets. As a result, the dense CuNiIn2B and CuNiIn4B coatings were deposited with oxide-free molten droplets. The test results showed that the fretting wear performance of B-alloyed CuNiIn coatings were increased by a factor over three comparing with conventional CuNiIn coating.

Since the plasma sprayed coatings always present a limited interlamellar bonding, it is difficult for a plasma sprayed coating to be applied in corrosion environment without any post-spray treatment. In this study, a NiCr powder alloyed with boron was employed to fabricate fully dense corrosionresistant coating by plasma spraying through in-situ deoxidation effect of boron. As reported previously, plasma sprayed Ni 20 Cr 4 B coating presents fully dense microstructure with few isolated pores. Due to the oxide-free state of the inflight particles by the deoxidation effect of boron, the splats were effectively bonded upon impact so that the inter-splat boundaries were indiscernible. A long-term immersion corrosion test in NaCl solution was conducted for 80 days to confirm that the plasma sprayed Ni 20 Cr 4 B coating presents the superior resistance against the corrosion, which was comparable to the flame spray-fused NiCrBSi coating. Furthermore, the cross-sectional microstructure of the Ni 20 Cr 4 B coated Al alloy samples after 80 days immersion revealed that the plasma sprayed Ni 20 Cr 4 B coating was dense enough to completely block the penetration of corrosive substance in such an aqueous corrosion environment.

Thermal spray coatings are widely used to protect materials from corrosion, wear, and oxidation, but they have yet to reach their full potential because of porosity limitations and the detrimental effects of oxidation on interlamellar bonding. This paper investigates an atmospheric plasma spraying process that deposits oxide-free dense metallic coatings with well bonded lamellae. The process produces ultrahigh temperature metallic droplets, up to 2650 °C, using specially designed powders that are deoxidized in-flight through the evaporation or gasification of oxides. The impact of these oxide-free ultrahigh temperature droplets has a spreading-fusing, self-metallurgical bonding effect resulting in fully dense bulk-like metallic coatings. Various coating materials, including NiCrMo, 304SS-Mo, NiCrBSi, and Al, are investigated, demonstrating the versatility of the new technique.

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.

Plasma spraying was used to deposit Li3PO4 coatings from sintered dense powders in three size ranges to study the effects of particle size and spraying distance. Coating microstructure, crystal structure, and composition were characterized using SEM, XRD, ICP-MS, and FTIR. It was found that sintered dense powders have a high temperature orthorhombic phase (γ-Li3PO4) that differs from the β-Li3PO4 phase associated with agglomerated Li3PO4. Plasma-sprayed coatings produced from these powders have similarly dense microstructures with fracture-surface morphology like that of sintered bulk. The effect of particle size and spraying distance on atomic ratio is also investigated in the study.

The effect of deposition pressure on the microstructure and ablation behavior of ZrB2 coatings deposited by very low pressure plasma spraying is investigated. The results show that under a chamber pressure less than 50 kPa, as the spray chamber pressure decreases, the porosity of the coating deposited at the same distance decreases, and the coating prepared under 100 Pa presents the lowest porosity of 1.79 %. Furthermore, among the ZrB2 coatings deposited at 100 Pa, 5 kPa, 10 kPa and 50 kPa, the dense coating deposited at 100 Pa showed the lowest ablation rate of 0.33 μm/s, 0.75±0.08 mg/s.

In this study, high-strength aluminum alloy AA7055 deposits are prepared using a recently developed cold spray process that employs in-situ microforging. The in-situ hammering effect is achieved by mixing large shot-peening particles into the spray powder and is shown to enhance interparticle bonding along with the plastic deformation of deposited particles. The underlying mechanisms are discussed based on the characterization of interface microstructure and the distribution of oxide film at the interparticle interface.

This study assesses the durability of superhydrophobic surfaces that possess a scalable architecture similar in morphology to branching or corymbose coral. In the experiments, electrolytic copper powders with a coral-like morphology are cold sprayed onto metal, ceramic, and glass substrates, forming a textured copper layer with a structural hierarchy based on the morphology of the powder. After cold spraying, a flame treatment is applied, creating a porous layer of Cu 2 O over the pliable Cu surface, which further increases roughness. As a final step, a fluoroalkyl silane spray is applied to reduce surface energy. It is shown that the fluorinated surface retains its excellent water repellency after cyclic bending and folding, sand-grit erosion, knife-scratching, and even heavy loading with simulated acid rain. It also retains its adhesion to glass (17 MPa), ceramic (12 MPa), and metal (34 MPa) substrates.

In this study, NiCrBSi powders with a size range of 30-50 μm were deposited on mild steel substrates by self-fusing atmospheric plasma spraying. Particle temperatures exceeded 2400 °C and the deposits were remarkably dense with low oxygen content. Based on the results, a novel strategy is proposed to directly deposit dense, oxide-free coatings by plasma spraying without the need of post-spray fusing processes.

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.

Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) with lamellar structure exhibit low thermal conductivity and low stiffness. However, high temperature exposure for certain long duration causes the sintering which heals two-dimensional (2D) inter-lamellar pores and intrasplat pores. Such sintering effect increases the stiffness and thermal conductivity of the coatings and consequently reduces the stability and durability of TBCs. It can be expected that large 2D pores with a wide opening is difficult to be eliminated. In this study, inter-lamellar 2D pores with large opening width were fabricated in the La 2 Zr 2 O 7 (LZO) coatings through spraying LZO+SrO coatings and removing the SrO splats in the water. Then, the conventional LZO coating and the porous LZO coating were subjected to high temperature exposure in the air at 1300 °C for different durations. The microstructure evolution especially in terms of the shape and density of inter-lamellar 2D pores was examined. In addition, the change of thermo-physic properties and the mechanical properties of the coatings with increasing exposure duration were studied. Results show that the 2D pores in LZO coating created by those SrO splats inherit primarily large opening width from 200nm to about 1 µm which endows the LZO coating with high sustainability at high temperature environment. Under thermal exposure at 1300°C, it was found that 2D pores resulting from SrO splats are free from healing while conventional 2D inter-lamellar pores with small opening width formed during splat cooling became healed rapidly. Thus, thermal conductivity and Young's modulus of the conventional LZO coating increased rapidly, while unhealed 2D pores in the highly porous LZO coatings contributed to the low Young's modulus and low thermal conductivity of LZO coating with remarkably high stability. With addition of 30% SrO in spray powder, a LZO coating with a thermal conductivity of about 0.39 W.m -1 .K -1 in the as-prepared state was obtained. The coating maintained a thermal conductivity of 0.57 W.m -1 .K -1 even after 100 hours exposure at 1300°C. The present results indicated that high sintering-resistant thermal barrier coating can be fabricated though designing inter-lamellar 2D pores with large opening width in the coating by the present novel approach.

The corrosion resistance of thermal barrier coatings against CMAS deposit at high temperature is significantly affected by the microstructure of the coatings. Enhancing the bonding ratio between splats can reduce the inter-connected pores and then obstructs the penetration of the molten CMAS into the coatings. In this study, atmospheric plasma sprayed ZrO 2 contains 8 wt. % Y 2 O 3 (8YSZ) coating with improved lamellar bonding ratios was deposited with full-molten droplets at an enhanced deposition temperature. The microstructure of the dense 8YSZ coating and conventional 8YSZ coating before and after thermal exposure with CMAS were characterized. It was clearly revealed that by adjusting the microstructure and designing a ceramic layer with high bonding ratio, the corrosion resistance of the thermal barrier coating could be enhanced. Moreover, by designing double-ceramic-layer (DCL) TBCs composed of a porous ceramic layer and well-bonded ceramic layer, the TBCs with high CMAS corrosion resistance and low thermal conductivity can be achieved.