High-pressure die casting (HPDC) is a manufacturing process used in the automotive sector to make high-precision components. Corrosion induced by molten metal and heat-checking cracks are two of main failure modes for die casting molds, changing the die's geometry and surface quality. Thermally sprayed coatings can improve the surface properties and recover the geometry of the die caused by aluminum attack. The main objective of this work is to observe the behavior of the H13, Cr3C2-25NiCr, and WC10Co4Cr coatings deposited by HVOF and HVAF processes in aluminum corrosion and die soldering tests. During corrosion and die soldering tests, chromium carbide in the Cr3C2-25NiCr coating reacts with the molten aluminum, creating a tough intermetallic interface and raising the extraction stress. After tests, it was observed that the WC 10Co 4Cr HVAF coating presented low adhesion to aluminum with no observed coating failure due to the formation of intermetallic. Die soldering tests indicated that the WC 10Co 4Cr coating protects the substrate, resulting in lower extraction stress than H13 base material and other HVOF coatings. It was observed that WC 10Co 4Cr HVAF coating showed results comparable to AlCrN PVD coating.

Thermal barrier coatings (TBC) are an essential part of modern gas turbines for aviation and power generation. As such, there is an incessant demand for improved TBC performance and longevity. Of the possible coating microstructures, the columnar structure first produced by electron beam physical vapour deposition was found to be most durable. The subsequently developed suspension plasma spray coatings are seen as an alternative method for producing columnar TBCs but typically utilise flammable solvents to achieve such structures. Aqueous solution precursors have also been used as a feedstock to deposit yttria stabilised zirconia (YSZ) TBCs; however, columnar structures have proven elusive, with solution precursor plasma spray (SPPS) deposition conditions and throughputs involving radial feed spray torches also being industrially unattractive. This study illustrates the first columnar coatings of single-layer yttria stabilised zirconia from an aqueous solution precursor using an axial feed capable plasma torch. Coatings have been shown to be columnar structured over a robust operating window, fully tetragonal in phase constitution and capable of being deposited at rates that can be commercially interesting. These initial results lay a great foundation for further TBC development utilizing an aqueous, powder-free, feedstock.  

This study investigates the tribological behavior of WC-CoCr coatings deposited using High-Velocity Air Fuel (HVAF) thermal spraying. Three distinct types of feedstock powders were employed to examine the influence of powder morphology on coating performance: a dense, angular fused-and-crushed powder; a spherical, porous agglomerated-and-sintered powder, and a newly developed powder with intermediate features. All powders had analogous particle size distribution approximately in the range of 7–20 μm. Two coating thicknesses were deposited with each powder (50 μm and 150 μm), additionally aiming to verify the possibility of depositing thin hardmetal coatings. The coatings microstructure was characterized, their hardness and porosity were measured and their tribological properties were evaluated by means of ball-on-disk sliding tests and dry jet erosion tests at various impact angles.

The results demonstrated that powder morphology significantly affects deposition efficiency. The newly developed powder offers notable advantages, such as higher deposition efficiency, which accelerates the spraying process and boosts production productivity, along with reduced sensitivity to parameter variations. In fact, the newly developed powder exhibited more consistent deposition rates across varying process conditions. Coatings derived from the new manufacturing route powder also showed improved cohesion and hardness due to stronger interparticle bonding and peening effects. On the other hand, surface roughness was unaffected by the powder type, and the coatings produced from the three powders had comparable wear resistance under erosion and sliding conditions. Coating thickness, rather than powder morphology, appeared to play a greater role in determining wear performance. The thicker coatings demonstrated superior resistance under both test conditions, due to reduced substrate influence.

This study aims to demonstrate the feasibility of the atmospheric plasma spraying (APS) technique to fabricate individual constituents of solid-state batteries (SSBs) such as anode, solid electrolyte (SE) and cathode as well as further produce their half-cell (anode|SE) and full-cell (anode|SE|cathode) configurations. The materials targeted in this work were Li4Ti5O12 (LTO) as an anode, Li7La3Zr2O12 (LLZO) as a SE and LiNi1/3Mn1/3Co1/3O2 (NMC111) as a cathode, with aluminium substrates being used as current collectors. The microstructure of the LTO and LLZO layers exhibited a characteristic lamellar structure along with the presence of a secondary phase attributed to delithiation at high temperatures, whereas the NMC111 layer was found to undergo substantial structural change. X-ray diffraction (XRD) analysis suggested that both LTO and LLZO layers retain most of the characteristic peaks along with the presence of secondary phases while NMC111 layers undergone significant change in the crystal structure. The XPS analysis confirms the presence of expected elements and oxidation states for the LTO layer. In the case of the LLZO layer, a metal carbonate surface reaction layer was observed, while the NMC111 layer reveals the presence of Li, Ni, Mn, Co, and O along with feeble metal carbonate. Fabrication of half-cell and full-cell configurations shows encouraging results by revealing a well-intact interface demonstrating the feasibility of the APS technique to accomplish such layered structures. This proof-of-concept effort provides valuable insights into the efficacy of APS for fabricating SSB components for further development, benefiting both the battery and thermal spray communities.

Spinel Li4Ti5O12 (LTO) is a promising anode material for solid state thin film batteries (SSTB) due to its almost-zero volume change and promising Li-ion mobility. However, preparing LTO anodes for SSTB demands tedious vacuum-based processing steps that are not cost effective. In this context, the present study embarks on evaluating the versatile suspension plasma spraying (SPS) approach to fabricate LTO coatings without using any binder. The microstructure and stoichiometry of the fabricated LTO coatings developed through the SPS route reveals retention of ∼76 wt.% of the spinel LTO from the starting feedstock, with minor amounts of rutile and anatase TiO2. The SPS experiments yielded varying thickness build up rates of the LTO coatings depending on the processing parameters adopted. The electrochemical data of the produced LTO based electrode tested in a half-cell through galvanostatic cycling show reversible lithiation and delithiation at expected potential, thereby validating the promise of the SPS technique for potential fabrication of SSTB components once fully optimized.

Thermal spray technology, a versatile coating technique, significantly impacts diverse industries and is pivotal in modern manufacturing processes. Like other technologies, it must continuously evolve to address new challenges and market demands. In this context, “hybrid thermal spraying” utilizing distinct feedstocks (such as powders, wire, suspensions, and solution precursors) offers a novel pathway to conveniently combine dissimilar materials at very different length scales to realize coatings with unique properties and enhanced performance.

This approach seamlessly integrates into all thermal spray techniques. Introducing two or more distinct feedstocks simultaneously or sequentially with independent control over each can deposit coatings with varied architectures and novel microstructures. The present-day industry constantly demands enhanced performance and longevity of established wear-resistant coatings, thermal barrier coatings (TBCs), etc., and novel functionalities for emerging fields such as batteries. Hybrid thermal spray can potentially address these needs by elegantly combining established material systems with additional constituents.

This review discusses the different variants of hybrid thermal spraying, and their relevance to practical applications is explored based on a comprehensive assessment of available literature. This review is intended to serve as a bridge between traditional and innovative approaches for inspiring further research to harness the advantages of hybrid thermal spray processes gainfully. It also discusses the challenges and limitations associated with this approach.

This study investigates the phase and elemental distribution in a suspension plasma-sprayed (SPS) Li4Ti5O12 (LTO) thin-film anode for solid-state lithium batteries, deposited on an SS-304 substrate. Advanced synchrotron-based µXRD and µXRF techniques were employed for micro-scale characterization, revealing distinct phase regions influenced by thermal exposure during the SPS process. The dominant Li4Ti5O12 phase was retained across most of the film, with localized transformations to secondary phases Li2Ti3O7, Li2TiO3, and TiO2 near the substrate interface, primarily due to prolonged high-temperature exposure and subsequent lithium loss. These findings underscore the importance of controlling SPS parameters to minimize lithium loss and optimize phase stability and interfacial integrity in solid-state battery components.

High-velocity air fuel (HVAF)-sprayed SiC coatings have been investigated as a potential approach to address challenges associated with their successful application through thermal spraying, since SiC can potentially serve as a sustainable replacement for WC in tribological hard coatings. Ni-P capped SiC feedstock was processed to fabricate composite coatings using HVAF, which is a relatively recent versatile and cost-effective spray technique. Three coatings, Ni-SiC-1, Ni-SiC-2, and Ni-SiC-3 were sprayed using various parameters to investigate the relationship between the processing conditions, microstructure, and wear performance. The extent of SiC retained in each of the coatings, albeit fragmented, was determined to be ~25 % for each of the three coatings compared to the 54 wt % SiC presence in the feedstock. However, despite the similarity in the quantity of SiC retained in the respective coatings, two of the coatings (Ni-SiC-1 and Ni-SiC-2) showed mixed amorphous and crystalline phases, whereas the Ni-SiC-3 coating was fully crystalline. The microindentation hardness of the coatings in the as-sprayed and annealed forms was noted to be in the range of 800–850 HV0.1. The specific wear rates for the respective coatings in the as-sprayed and annealed forms were found to be promising but of the same order of magnitude, revealing no significant role of annealing on their tribological behaviour. The results establish that it is possible to process a suitably designed SiC feedstock using HVAF to realize a sustainable wear-resistant coating.

A new technique combining wire and powder in the form of a ‘hybrid’ feedstock during arc spraying has been explored in this study. The primary goal of this research was to investigate the feasibility of incorporating a second phase in a Babbitt matrix by spraying wire and powder simultaneously. While Tin-based Babbitt alloys have excellent tribological properties, such as a low friction coefficient and frictional resistance, making them popular materials for sliding bearings, dual-phase/composite coatings have been of interest due to their potential to perform better than corresponding single constituent coatings. A further objective was to assess the effect of copper (Cu), molybdenum (Mo), and tungsten carbide (WC) contents as second-phase reinforcements on composite Babbitt coatings’ microstructure and tribological properties. These effects were systematically investigated through scanning electron microscopy (SEM), microhardness tests, and dry sliding, as well as lubricated wear tests. The study demonstrated that a hybrid arc spray process effectively incorporated Cu, Mo, and WC particles into the coating. The wear test results indicated that adding the second phase enhanced the wear resistance of the coating.

NiCrAlY as a coating is often used to improve the high temperature strength and oxidation performance of superalloys. Traditionally these coatings are deposited using various thermal spray techniques. Producing these coatings with Additive Manufacturing methods like the Directed Energy Deposition with Laser Beam (DED-LB) process improves the coating-substrate bonding. Subsequently, it enhances the high-temperature capability. To achieve this, understanding the correlation between process parameters and microstructure is crucial. The commercially available NiCrAlY powder is deposited on the alloy 718 substrate in this study. A two level three factor design of experiments was conducted for single track and three-layer track depositions. Statistical analysis was used to understand the effect of the primary process parameters (laser power, scan speed and powder feed rate) on the geometrical characteristics such as height and width of the deposition, and dilution of the substrate. Microstructural studies revealed the transformation in grain morphology from intra-dendritic mode of precipitation to inter-dendritic mode of precipitation with dilution from the substrate. From the Energy Dispersive Spectroscopy analysis, the formation of γ-Ni matrix phase and β-NiAl precipitate phase was confirmed. Samples with low dilution exhibited high hardness in accordance with high β phase content. In the three-layer tracks, the presence of hard and brittle β phase along the dendritic boundaries led to surface cracking due to stress build up.