This study aims to comprehensively examine and analyze the basic mechanical properties, oxidation resistance, high-temperature hardness, fretting wear, and simulated operating conditions of CuAl/PHB coatings. The objective is to investigate the optimal combination of resistance to fretting wear and abradability for these coatings.

Cu and Cu-MoS 2 coatings were fabricated by cold gas dynamic spray and the fretting wear performance of the two coatings was compared. A mixture (95 wt.% Cu + 5 wt.% MoS 2 ) was used as feedstock for the composite coating. Coatings were sprayed with identical gas flow conditions on the substrates preheated to approximately 170°C. The cross section of the coatings was analyzed by scanning electron microscope (SEM) and MoS 2 concentration was measured, as well as coating microhardness. Fretting tests were carried out under gross slip conditions in ambient environment. SEM observation on wear scars and counterspheres revealed the development of third bodies, by which the sliding was accommodated. For the Cu-MoS 2 coating, solid lubrication effects in the form of friction drops occurred in early cycles (< 5k), but eventually (> 5k) the coating's friction behavior was similar to the pure Cu coating. Third body morphology and wear of the two coatings were distinctly different, which could largely be attributed to the hardness reduction of the Cu-MoS 2 composite due to poorly bonded interfaces induced by the effect of MoS 2 during particle impact and coating formation.

This study evaluates candidate coatings for potential use in the manufacture of metal-seated ball valves for hydrometallurgy service. All coatings were deposited on grit-blasted titanium coupons by air plasma spraying to a nominal layer thickness of 500 µm. The feedstock powders used were selected based on literature review and field experience and include Cr 2 O 3 , TiO 2 -Cr 2 O 3 , nano TiO 2 , and a novel mixture of nano TiO 2 and conventional Cr 2 O 3 . The resulting coatings are compared based on microhardness, shear strength, friction properties, and wear resistance. Specimen preparation procedures and test methods are described in the paper along with the findings and potential implications of the study.

This study assesses the abrasive wear resistance of Cr 3 C 2 -NiCr coatings produced by HVOF spraying. Abrasion tests were conducted in a three-body solid-particle rubber-wheel test rig using silica and alumina grits under different loads. The results indicate that abrasion performance is controlled by cohesion between splats, which can be further improved. The removal of carbide particles was the main wear mechanism and is controlled by the content and size of the Cr 3 C 2 particles. It is shown that the abrasive wear resistance of carbide-based cermet coatings is significantly higher than that of mild steel.

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%.

Minimizing wear of mining components in the oil sands industry is key to increasing productivity and decreasing excessive maintenance costs. A significant amount of research has gone into the selection of appropriate materials for improved wear protection. Tungsten carbide overlays are applied to the most critical components, typically by plasma transferred arc welding (PTA-W). This study aims at investigating the effects of several commercial PTA torches in terms of overlay microstructure and performance. A commercial tungsten carbide-NiCrBSi metal matrix composite (MMC) was used as the overlay material. A variety of parameters were studied when comparing the torches; including heat input, powder delivery, and deposition pattern. The effect of the overlay microstructure was examined using optical, digital and electron microscopy. The overlay performance was gaged using dry sand abrasion testing (ASTM G65-04). The type of torch, powder delivery method or power source did not have any significant effect on the quality or performance of the overlay in terms of microstructure or abrasion resistance.

Magnesium and magnesium alloys are the lightest structural materials with an approximate density of 1.7 g/cm³ (density of aluminium ~2.7 g/cm³). Due to the poor corrosion and wear resistance properties, they need to be coated for usage in lightweight constructions. AlSi20 was found to be a suitable coating material to improve the properties of parts made of the magnesium alloy AZ31B. Within this work, coatings are applied by thermal spraying, laser cladding and the combination of both processes. These coatings were investigated regarding corrosion protection in 3.5 % chlorine solution in a three electrode setup to obtain electrochemical corrosion characteristics. Abrasive wear was investigated using a pin-on-disc tribometer and abrasion rate was calculated. Resistance against shock loads was tested by applying a cyclic load at 50 Hz in order to investigate the resistance against impact stresses.

Characterization of coatings made with the help of Computer Controlled Detonation Spraying (CCDS) was performed. The applied coatings include hard alloys (WC/Co -75/25, WC/Co - 88/12, WC/Co/Cr - 86/10/4, and Cr 2 C 3 / NiCr), aluminum oxide, nickel-chromium self-fluxing alloy, titanium, bronze, and stainless steel. Tribological investigations of coatings were provided using abrasion test (ASTM standard G65), erosion test (ASTM standard G76), and hydro-abrasive test. To make hydro-abrasive tests special device and method were elaborated based on the interaction of water jet saturated with corundum particles with a coating surface.

Mechanical properties of WC-Co coatings prepared by cold spraying (CS) and warm spraying (WS) have been studied with changing material parameters of Co content (12~25%), powder size (-45+15 and -20+5 µm) and WC particle size (0.2 and 1.8 µm) in this paper. The study reveals that a formation of undesirable phases such as W 2 C, W, and amorphous or nanocrystalline Co-W-C (eta) phase has been suppressed in the CS and WS coatings. Both coatings have high hardness, which is comparable to or superior to HVOF coatings as well as higher density (low porosity) than the HVOF. Abrasion wear test has shown that WS coatings has higher resistance than CS coatings within this study. As for powder properties, smaller powder and smaller WC particle sizes are effective to produce hard and dense coatings leading to higher wear resistance.

WC-Co thermal sprayed coatings are mainly used for wear protecting functions in various industries, for which high velocity oxy fuel (HVOF) spray is considered to be the best suited process. However, WC-Co HVOF coatings still have some defects as compared with sintered bulk, such as decarburization of WC and porous structure. Recently, experiments of WC-Co coatings using warm spray (WS) and cold spray processes have demonstrated some improvements in reduction of these defects. In particular, WS process seems to be a more promising process for WC-Co coatings from the previous work. In this study, wear resistant functions of WC-12%Co coatings prepared by HVOF and WS were investigated by abrasion and erosion tests. In addition, in-flight particles were captured and their characteristics such as the amount of decarburization, crystal phase, particle strength and particle size distribution were investigated to clarify the difference between HVOF and WS processes. The result shows that the wear resistances of the WC-Co WS coatings are comparable or superior to those of the HVOF coatings, which can be attributed to the difference in the amount of W 2 C and coatings porosity revealed by the in-flight particles and the coating microstructure. The result of the in-flight particle analysis also indicates that wear resistance of WS coatings can be further improved by optimizing the powder shape and chemical composition.

WC-Co cermet coatings were fabricated by using Warm Spraying, which is a modification of HVOF spraying to lower the temperature of the propellant gas below the melting point of Co. By changing the processing parameters, specimens were prepared for hardness, abrasion wear and particle erosion tests. Their microstructures were examined by SEM and XRD. The microstructure clearly showed the effects of suppression of the dissolution of WC into the Co phase, which is the major cause of embrittlement of the conventional HVOF sprayed WC-Co coatings. By combinations of adequate feedstock powder and processing parameters, it was possible to take advantage of fine WC grain size to prepare coatings with higher hardness (HV > 1400), smoother surface (Ra < 2 μm), and moderately improved wear performances compared with conventional HVOF coatings.

The fretting phenomenon was investigated experimentally in contacts between nitrided, coated and nitrided-coated Ti-6-4 rods against uncoated M50 rods generating a circular Hertzian contact. A fretting wear test rig was designed and developed to facilitate mounting of rod specimens of different coating thicknesses. Fretting wear tests were performed on low temperature and high temperature nitrided Ti-6-4 rods as well as on T-800 (CoCrMoSi) thermal spray coated Ti-6-4 and T-800 coated M50 rods. Finally, tests were carried out on Ti-6-4 rods nitrided at low and high temperatures and T-800 thermal spray coated on the top. The results obtained from fretting tests of each surface against uncoated M50 are studied and compared. Fretting wear volumes and surface profiles are presented for the contacts studied. The fretting wear resistance of each surface is quantified and compared with Archard’s wear equation. The role of amplitude of motion and number of cycles on the fretting wear of coatings is discussed. It was observed that increase in fretting wear resistance of uncoated Ti-6-4 rods by nitriding is greater than thermal spray coating. The fretting wear resistance was found to be higher for high temperature nitrided-coated rods than for low temperature nitrided-coated rods.

This study assesses the effect of carbide grain size on the wear performance of HVOF-sprayed WC-CoCr coatings. The coatings were produced from two powders, one of conventional grain size and one with submicron carbide. Both coatings were subjected to abrasive rubber wheel wear tests in wet and dry conditions with 220 nm titania particles and 368 μm sand particles, respectively. Detailed examination before and after wear tests shows that the wear mechanism depends on the relative size of the carbide and abrasive particles.

Different post treatment methods are developed up to now to improve the properties of thermally sprayed coatings. In this work, arc sprayed aluminium coatings on aluminium substrates are post-treated by plasma electrolytic oxidation. To estimate the wear resistance of resulting oxide coatings, two abrasive wear tests (ASTM G65 and ASTM C1624) are carried out. Worn surfaces are examined by scanning electron microscopy in order to establish the wear mechanisms. These results of the abrasive wear tests are correlated with the parameters of the PEO process and the hence resulting micro structures of the coatings.

Microscale wear mechanisms in thermally sprayed hard coatings were examined. A test procedure for examining microwear with various abrasives was developed. Different abrasivity of kaolin, precipitated calcium carbonate and titania was found to affect wear mechanisms. Fine-particle abrasion caused the surface to loose its gloss and smoothness. Coatings subjected to fine-particle abrasion were examined with optical gloss measurements and scanning electron microscopy. It was shown that in tungsten carbide based hard coatings the microscale wear was governed by preferential wear of the soft binder phase. However, also coating defects like pores or poorly adhered splats tended to provide nucleation points for microscale wear. It was found that coatings that performed well in dry-sand rubber wheel abrasion or wet abrasion tests did not necessarily have good microwear resistance. The results showed that different abrasives had effect on the wear phenomena and wear rate of hard coatings. Coatings also behaved differently and novel modifications in the composition affected the wear behaviour. In conclusion, the results provided deep understanding of the role of various abrasives in the wear phenomena of thermally sprayed hard coatings.

Based on the previous studies of nanostructured WC based coatings, various improvement methods of the coatings were attempted. On of the method was to improve the feedstock materials via a partial flocculation method. This method uses a special technology to form spherical spray dried powders using nanostructured starting materials. According to this method, morphology and porosity level of the feedstock material was controlled. In addition, the basic principle of this method will be introduced. A few other methods are tried to improve the feedstock materials including carbon addition and a Co coating method. The coating morphology and characteristics are analyzed and wear performance is compared. The carbon contents, porosity, phases, and wear loss by a sand abrasion test will be presented in details. Abstract only; no full-text paper available.

Thermal spray coatings were deposited by the HVOF technique using two grades of WC-VC-Co powders (WC- 10VC-12Co and WC-10VC-17Co), produced by agglomeration and sintering, from WC, VC and Co starting powders. The coatings were sprayed by a commercial enterprise producing WC-Co thermal spray coatings, using the same spray parameters as for WC-Co coatings. This paper presents results from the characterization of the powders as well as the results of abrasion and erosion tests performed under identical conditions on the new WCVC- Co coatings and on standard WC-Co coatings of equal cobalt content. Under many conditions, the WC-VC-Co coatings performed better than the standard coatings, despite their deposition conditions not having been optimized.

A microplasma spraying torch with a hollow cathode electrode is designed to melt completely the refractory materials and deposit coatings at plasma power level up to several kilowatts. The designed torch permits spray material to be fed into plasma arc jet through axial powder injection. In the present study, molybdenum is used as a typical refractory spray material. The effects of the main processing parameters including plasma arc power, plasma gas flow and spray distance on the particle velocity during spraying, and the microstructure and properties of the coatings are investigated. The microstructure of coating is characterized with optical microscopy and scanning electron microscopy. The properties of the coating are characterized by microhardness and abrasive wear tests. The particle velocity during in-flight is carried out using a particle velocity/temperature measurement system based on thermal radiation. The comparison of the microstructure and property of micro-plasma sprayed Mo coatings with those of the coating deposited by the conventional plasma spraying operated at a power of 42 kW is performed. The results show that the abrasive wear loss of the Mo coatings deposited by the micro-plasma spray torch is comparable to that of the coating deposited by the conventional plasma spraying disregarding the one order difference in the plasma operating power.

Controlled scratch testing, dry abrasion tests and hardness measurements were performed on WC-12Co coatings produced by the high velocity oxy-fuel spraying of nanostructured and conventional feedstock powders. The information obtained employing these different evaluation techniques was used to provide insight into coating behaviour and identify the most abrasion-resistant coatings. The results indicated a correlation between scratch hardness and the microhardness determined by Vickers indentation for the coatings. There was good agreement between the scratch test and the abrasion test in identifying the best coatings for use in dry abrasion. Observation of the scratched surfaces and wear scars indicated material removal by splat debonding and fracture. The results demonstrate the usefulness of the scratch test for assessing the abrasion resistance and wear behaviour of coatings.

Thermally sprayed hard coatings, including tungsten carbide and chromium carbide cermets and other hard metallic materials, were studied in two types of wear tests. Surfaces of the coatings were worn by coarse and hard quartz sand in a rubber-wheel dry abrasion wear test, and by fine and soft kaolin abrasive in a wet slurry abrasion wear test. The aim of the work was to study how the surfaces retain their high polished finish and gloss, and the type of wearing of different coatings and materials. The results showed that coatings with hard tungsten carbides were worn preferentially by removal of the the binder material. Cermet coatings with softer chromium carbides, and with another types of uniform microstructures showed more uniform wear and better retained their glossy finish.