Iron-based coatings are often considered as replacement of hard chromium and WC-Co, as they pose lower health and environmental impact. In many cases the combination of mechanical and chemical properties of ferrous based alloys may be satisfactory and their relatively low cost make these coatings an interesting candidate for many applications. This study is inspired by opportunities to harden the ferrous base materials by strain hardening, solid solution strengthening, dispersion strengthening, and precipitation hardening. Already commercially available Fe-based coating materials with precipitates of mixed carbides and borides in the metastable austenitic matrix achieve a high hardness. In this study the cavitation erosion and abrasion resistance of various Fe-based coatings produced by HVAF and HVOF processes were investigated. Two experimental precipitation containing materials were prepared, and the sprayed coatings were tested for abrasive and cavitation erosion wear. In addition to precipitations, the importance of proportion of ferrite and retained austenite phases were studied by affecting the microstructure by heat treatments as the ability of different phases to affect hardening and ductility may become crucial in generating desired material properties. The properties of experimental and some commercial Fe-based alloys are compared with WC-Co and Cr 3 C 2 -NiCr coatings by property mapping.

Manufacturing of steel components is often done at high temperatures (HT) posing a serious challenge to components such as forming tools. Thermal spray coatings provide a cost-effective solution for surface protection under HT, corrosive environments and severe wear conditions. Thermally sprayed coatings based on cubic hard materials such as TiC and TiCN can provide an alternative to widely used Cr3C2-NiCr. While the latter possess a superb oxidation resistance and wear resistance at HT, they are prone to degradation in the presence of Mn, an element commonly alloyed in many modern steel grades such as TWIP (twinning-induced plasticity steel). In this study, a (Ti,Mo)(C,N)-29% Ni hardmetal feedstock powder was prepared by agglomeration and sintering. Coatings were deposited using a high velocity air-fuel (HVAF) spray process. The coating was benchmarked against a standard Cr3C2-NiCr coating obtained with the same spray process. Our work comprises analyses of the feedstock powder along with the resulting coating microstructure after deposition and heat treatment. Further, the HT sliding behavior against TWIP steel using a HT pin-on-disc tribometer at 700°C was investigated. The results showed a clear benefit of the TiCN-based coating, with almost no wear detected, while the Cr3C2-coating showed a significant wear loss. Based on these results, the TiCN-based coating is regarded as potential solution for prospective forming applications of modern high Mn steels, such as TWIP.

Minimizing ice adhesion and preventing ice accumulation on different surfaces has remained in scientific focus from the mid 1900’s. Decades after, scientists are combatting the same challenges, which only outlines the complex nature of ice and ice adhesion related research. One approach to exploit passive coating technology for low ice adhesion utilizes slippery surfaces that combine porous solid material with lubricating liquid. This study presents a novel method in creating functional slippery liquid infused porous surfaces, SLIPS, by exploiting flame spray technique. We demonstrate the functionality of these thermally sprayed SLIPS in ice adhesion and wettability. The ice adhesion results confirmed the potentiality of thermally sprayed SLIPS as ice repellent surfaces with an order of magnitude lower ice adhesion strength compared to polished stainless steel.

Oxides are chemically stable and wear resistant materials. Because of these properties, they are often applied as protective coatings in harsh environments. However, their chemical and mechanical stability at high temperature in chlorine containing environments is uncharted. These conditions are present in waste-to-energy and biomass boilers in which the currently available metallic and metal matrix composite coatings provide unsatisfactory protection. To be effective in these conditions the coatings should be chemically inert, erosion resistant and act as environmental barriers. For this purpose, this research studies the corrosion behavior and microstructural features of HVOF and APS-sprayed Al 2 O 3 -, Cr 2 O 3 -, TiO 2 -based coatings. Their chemical stability was evaluated by high temperature corrosion testing of self-standing coatings under KCl salt deposit at 550, 650 and 720 °C for the duration of 72 h.

Thermally sprayed hard metal coatings are the industrial standard solution for numerous demanding applications. Often the performance of thermally sprayed coatings is improved by using finer particle sizes due to improved surface finish and decreased defect sizes. In the aim of utilizing finer particle and primary carbide sizes in thermal spraying of hard metal coatings, several approaches have been studied to control the spray temperature. The most viable solution is to use the modern high velocity air-fuel (HVAF) spray process, which has already proven to produce high quality coatings with dense structures. In HVAF spray process, the particle heating and acceleration can be efficiently controlled by changing the nozzle geometry. In this study, fine WC-10Co4Cr powder (-25+5 µm) was sprayed with three nozzle geometries to investigate their effect on the particle temperature, velocity and coating microstructure. The study demonstrates that the particle melting and resulting W2C formation can be efficiently controlled by changing the nozzle geometry from cylindrical to convergent-divergent. Moreover, the average particle velocity was increased from 780 to over 900 m/s. This increase in particle velocity significantly improved the coating structure and density while deposition efficiency decreased slightly. Further evaluation was carried out to resolve the effect of particle in-flight parameters on coating structure and cavitation erosion resistance, which was significantly improved with the increasing average particle velocity.

Highly corrosion and wear resistant thermally sprayed chromium carbide (Cr 3 C 2 ) based cermets coatings are nowadays a potential highly durable solution to allow traditional fluidised bed combustors (FBC) to be operated with ecological waste and biomass fuels. However, the heat input of thermal spraying processes causes carbide dissolution in the metal binder. This alters the coating structure and forms carbon saturated amorphous and nanocrystalline metastable areas, which can affect the behaviour of the materials under the corrosive chlorides containing environment of the flue gases. This study analyses the effect of carbide dissolution in the metal matrix of MMC coatings and its effect on the onset of chlorine induced high temperature corrosion. Four Cr 3 C 2 -NiCrMoNb coatings were thermally sprayed with high-velocity air-fuel (HVAF) and high-velocity oxygen-fuel (HVOF) spray processes in order to obtain microstructures with increasing amount of carbide dissolution in the metal matrix. The specimens were heat treated in an inert argon atmosphere at 700°C for 5 hours to induce secondary carbide precipitation. As-sprayed and heat-treated self-standing coatings were covered with KCl and their corrosion resistance was investigated with thermogravimetric analysis (TGA) at 550°C for 4 hours. High carbon dissolution in the metal matrix appeared to be a detrimental factor in the initial stage of corrosion. The microstructural changes induced by the heat treatment hindered the corrosion onset in the coatings. Moreover, an optimal amount of oxides and melting degree seemed beneficial.

Thermally sprayed ceramic coatings are used in environments requiring good wear- and corrosion resistance among others. However, a typical issue with ceramic coatings is their low impact resistance and tendency to fail catastrophically by cracking. In bulk ceramics, the Al 2 O 3 -ZrO 2 –composition has been of interest for long since already small additions of ZrO 2 into Al 2 O 3 have shown improvements in fracture toughness compared to pure Al 2 O 3 . Efforts are being made to induce this increased resistance to fracturing in thermally sprayed coatings as well, resulting in higher wear resistance due to a more predictable behavior and damage-tolerance. In this work, Al 2 O 3 -ZrO 2 -coatings have been deposited by atmospheric plasma spray (APS) and high-velocity oxy-fuel spray (HVOF) processes. The wear characteristics of the coatings were evaluated with cavitation erosion, delving into the mechanics of the erosion and the resulting microstructural changes in the coatings. Evidence of phase transformation of t-ZrO 2 to m-ZrO 2 was found during the erosion. The HVOF-sprayed coating exhibited greater wear resistance against the cavitating bubbles due to its finer microstructure.

This study evaluates the anti-icing properties of flame-sprayed polyethylene (PE) coatings. In laboratory scale icing tests, thermally sprayed polymer coatings showed low ice adhesion compared to metals such as aluminum and stainless steel. The ice adhesion of flame-sprayed PE coatings was found to be roughly seven times lower than that of bulk aluminium and five times lower than that of bulk stainless steel.

In this work, a design-of-experiments approach is used to map the main parameters of a high-velocity airfuel (HVAF) spraying process. Chromium carbide based material with a NiFeCrSi matrix was sprayed with varying gas flows and nozzle designs while monitoring their effect on particle temperature, velocity, and coating build-up. It was found that sufficient heating is critical to abrasive wear resistance and that particle temperatures are primarily controlled by fuel flow rates. Nozzle geometry, on the other hand, had the biggest effect on particle velocity, which was found to increase nearly 100 m/s by switching from a cylindrical to a convergent-divergent design.

The aim of this work is to evaluate the brittleness of suspension sprayed aluminum oxide coatings with various methods, including Vickers indentation fracture toughness, four-point bending, and high-velocity particle impact testing. Coatings were applied via high-velocity suspension flame spraying (HVSFS) using suspensions of isopropanol and water solvents. HVOF-sprayed Al 2 O 3 powder feedstock was used as a reference. The tests are described and the results are presented and discussed.

This paper summarizes the results of high-temperature corrosion and erosion tests conducted on a wide range of coating materials, including Cr 3 C 2 -NiCr, Cr 3 C 2 -CoNiCrAlY, TiMoCN-Ni, Stellite 6, NiCrBSi, and Hastelloy C-276. All coatings were deposited on stainless steel substrates by HVOF spraying, and after high-temperature testing, were evaluated by means of SEM and EDX analysis. Of the coating materials evaluated, Hastelloy C-276 provided the best protection against high-temperature corrosion. It also exhibited the highest erosion resistance at a particle impact angle of 90°, but at the sharpest impact angle of 15°, Cr 3 C 2 -NiCr coatings were found to be the most erosion resistant, likely due to the strong bonding of carbide particles in matrix. NiCrBSi coatings, on the other hand, exhibited the highest values of volume loss.

This work evaluates the influence of yttrium on the heat and wear resistance of active arc sprayed (AAS) coatings produced using FeCrBAl cored wire. The AAS process differs from ordinary arc spraying in that it uses propane-air combustion products as a carrier gas instead of compressed air. This increases particle velocity and temperature and forms a reducing atmosphere that protects metal particles in flight and improves coating adhesion and porosity. Coating samples produced with different amounts of yttrium were characterized in terms of surface morphology, microstructure, phase composition, and hardness. They were also subjected to heat resistance, abrasive wear, and corrosion tests in which they performed better than typical wrought steels used in boilers.

Laser-assisted cold-spray has been recognized for over a decade as a technique capable of depositing high quality coatings. By laser heating (and hence softening) the surface being coated, deposition can occur at particle velocities lower than those normally associated with the cold spray process. This can be used to increase deposition rate. However, it can also be used to facilitate the deposition of higher hardness material combinations, normally more out of the reach of the conventional cold spray process. Laser heating can also reduce the requirements of the process on gas usage and gas heating for a given combination, making it more cost-effective. In the work reported below, the capability of a novel co-axially laser-assisted system (COLA) to deposit higher hardness materials, relevant to a range of different industrial applications, has been evaluated. This system can be retrofitted to conventional cold spray equipment.

In this investigation, alumina powders prepared by different methods were sprayed on carbon steel substrates using a conventional plasma torch with radial injection. The spraying process and powder injection parameters were varied and the injection behavior of the powder was studied. Changes in particle acceleration, deceleration, and impact were measured with novel spray diagnostic equipment and are correlated with the structure and properties of the coatings obtained. Dense coatings were achieved with several agglomerated-and-sintered Al 2 O 3 powders, although higher impact velocities and temperatures were recorded for the larger and denser fused-and-crushed particles.

The aim of this study is to evaluate the microstructure and corrosion properties of Fe-based coatings produced using different HVAF spray guns. Differences in microstructure, phase composition, porosity, oxide content, and corrosion behavior were observed among the coatings depending on the gun and spraying parameters. The results are presented and discussed in detail.

This paper presents the results of a study on the tribological properties of TiC-based coatings deposited by HVOF spraying. Four powder feedstocks consisting of (Ti,Mo)(C,N) hardmetal with Ni and Co binders were prepared by agglomeration and sintering. The feedstocks differ in composition and particle size distribution, the latter being optimized for fuel type and equipment requirements. Coating specimens are evaluated based on microstructure, hardness, bonding strength, and friction and wear behavior. The results are presented and correlated with spray parameters, equipment differences, and feedstock characteristics.

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.

The aim of this work is to characterize the performance and durability of Zn-based composite coatings produced by low-pressure cold spraying and evaluate their potential for use in repair and restoration applications. Mechanically blended Zn+Al+Al 2 O 3 , Zn+Cu+Al 2 O 3 , and Zn+Ni+Al 2 O 3 powder mixtures were deposited on grit-blasted carbon steel (Fe52), copper, aluminum, and nodular cast iron substrates using optimized feed rates. In addition, round samples were drilled and the holes were repaired by handheld spraying. Coated substrates are assessed based on microstructural analysis, laser shock adhesion testing (LASAT), and thickness and hardness measurements. Hole repairs are evaluated based on bond strength and gas permeability measurements. The procedures are described and the finding are presented and discussed.

Different feedstock powder compositions of the alumina-chromia system were deposited on steel substrates by various methods, including conventional plasma spraying, three-anode plasma spraying, and HVOF. The powders used for plasma spraying had particle sizes of -38+10 µm and for HVOF spraying -25+5 µm and -25+10 µm. The coatings were evaluated by their microstructure, phase composition, and corrosion, wear, and electrical properties. The study shows that wear properties depend strongly on the spray process and that coatings obtained by HVOF spraying have dense structures and excellent wear behavior. Coatings produced by the three-anode plasma process, despite their higher porosity, were found to be harder than conventional plasma coatings and can be sprayed with higher feed rates. The coating properties do not appear to have a linear dependence on chromia content.

In this study, iron-based coatings are deposited on stainless steel substrates by HVOF and HVAF spraying and are evaluated based on SEM examination, hardness measurements, and corrosion and wear testing and by comparison with WC-CoCr and CrC-NiCr reference coatings. The results indicate that corrosion resistance is insufficient if the coating is not fully dense and has open porosity. During spraying, the particles must be totally melted and rapidly solidified to achieve uniform coating composition. Open porosity and nonuniform distribution of alloy elements, particularly chromium, is seen to induce crevice corrosion in iron-based coatings.