Composite coatings using mixed alloy matrices reinforced with carbon-based solid lubricants as feedstock materials were prepared by atmospheric plasma spraying. The aim of the present study was to investigate the tribological characteristics of such coatings exploring potential benefits of CNTs as nano-additive to reduce friction and wear, improving lubrication conditions during operation in tribosystems, such as piston ring – cylinder liner systems. The chemical composition of feedstock materials and the thermal spray parameters during coatings deposition are correlated to friction coefficient and wear rate using pin-on-disk measurements. The developed coatings hybrid behaviour is studied. Co-based cermet as well as metal alloy anti-wear performance along with the promoted lubrication conditions during operation is revealed. The dependence of the developed coatings quality and performance on the characteristics of the feedstock powder is thoroughly discussed.

Thermally sprayed WC-based hardmetal coatings offer high hardness, good sliding wear and abrasion performance and find large applications in mechanical engineering, valve construction, or offshore applications. WC-Co coatings are mainly produced by high-velocity oxy-fuel spraying (HVOF) from conventional spray feedstock powders. In our previous work, the potential of the suspension-HVOF spraying (S-HVOF) to produce dense-structured WC-12Co coatings has been shown. Significant work was devoted to the development of appropriate aqueous hardmetal suspensions starting from commercially available fine WC and Co raw powders feedstock. This contribution proposes a step forward in the development of the S-HVOF WC-12Co coatings and evaluation of their microstructural and tribological properties. Suspension spraying trials were carried out using gas-fuelled HVOF TopGun system. For comparison purposes, liquid-fuelled HVOF K2 was employed to spray WC-12Co coatings starting from commercial available spray powder. Microstructural characterization, X-Ray diffraction and microhardness of the coatings were evaluated. Oscillating sliding wear tests were conducted against sintered Al 2 O 3 and WC-6Co balls. The sliding wear performances of the WC-Co sprayed coatings were discussed in term of the microstructure, phase composition and coating-ball test couples.

Impact testing appears as a most promising tool for gaining information on coating behavior in load-bearing applications. During dynamic impact test an indenter impacts successively the surface of the coating with constant force and frequency. The deformation of the coated specimen during impact testing is affected by the mechanical properties of both the substrate and the coating. Varying the impact load and the number of impacts, the evolution of coating surface deformation and contact fatigue failures can be observed. In the paper, the influence of dynamic impact load and number of impacts on the resulting impact crater volume and morphology is analysed, and the interpretation of the results in form of Wohler-like dependance is suggested and demonstrated on two types of HVOF sprayed Co-based alloy coatings. The low-number impact craters evolution and subsurface cracks propagation of HVOF sprayed Co-based alloy coatings is analyzed in more detail, by means of 3D optical microscopy and SEM. The results showed, that the higher ability to deform plastically increased the coatings dynamic impact fatigue lifetime. The cracks, responsible for coatings destruction, spread predominantly along the intersplat boundaries in the pile-up area.

Deposition of hybrid plasma-sprayed coatings employing both dry powder and liquid feedstocks enables preparation of innovative coating architectures. Using this technique, miniature domains of additional (secondary) material may be introduced via the liquid feedstock route into the more conventional powder-deposited coating, providing potential benefits for the coating functionality. In this contribution, we have explored the tribological properties of hybrid coatings sprayed from alumina powder with additions of chromia (Cr 2 O 3 ), zirconia (ZrO 2 ), yttria-stabilized zirconia (YSZ), and titania (TiO 2 ) delivered from liquid feedstocks. The coatings were subjected to dry sliding wear testing and a subsequent analysis of the wear tracks to determine their wear resistance and coefficient of friction, as well as a qualitative assessment of the wear mechanisms. The hybrid coating doped with the chromia addition matched the remarkable wear resistance of highly-dense suspension-sprayed coatings. This is a significant result, especially when considering the order of magnitude better production efficiency of the hybrid coatings.

The use of nanoscale WC grain or finer feedstock particles are two possible methods of improving the properties and performance of WC-Co-Cr coatings. Finer powders are being pursued for the development of coating internal surfaces, as less thermal energy is required to melt the finer powder compared to coarse powders, permitting spraying at smaller stand-off distances. Three WC-10Co-4Cr coatings, with two different particle sizes and two different carbide grain sizes, were sprayed using a high velocity oxy-air fuel (HVOAF) thermal spray system developed by Monitor Coatings Ltd. in the UK. The powder and coating microstructure were characterised using XRD and SEM. Fracture toughness and dry sliding wear performance were investigated using a ball-on-disc tribometer with a WC counter-body. It was found that the finer powder had a higher hardness but relatively lower fracture toughness. When performing sliding wear testing at the lower 96N load the nanostructured coating performed best; however at 240N this coating was displayed the highest specific wear rates, with the other two powders performing to a similar, better standard.

This study compares the wear performance of thermally sprayed iron coatings with that of electrolytic hard chrome (EHC) plating. Three Fe-based alloy powders (FeSP529, FeSP586, 6AB) were deposited on S355 structural steel plates by HVOF and HVAF spraying and the resulting coatings and plating samples were subjected to dry sliding wear tests using a block-on-ring setup. Wear maps for all three Fe-based powder alloys are similar, showing regions of plasticity dominated wear, wear transition, and oxidational wear as a function of sliding velocity. More importantly, the wear rates of the sprayed coatings were ten times lower than those of the EHC plating samples.

This work investigates the sliding wear resistance of alumina coatings deposited on stainless steel substrates by HVOF and air plasma spraying, using fine (1-5 μm) and conventional (10-45 μm) powders. Sliding wear tests were carried out using a sintered WC-Co ball as the counter-body and the wear tracks were examined to obtain a better understanding of wear mechanisms. HVOF coatings showed an order of magnitude improvement in wear resistance compared to their APS counterparts. The disparity in wear performance is correlated to differences in phase composition, porosity, hardness, and fracture toughness as revealed by SEM and XRD analysis and nanoindentation testing. The development of tribofilms and their role in wear behavior is also discussed.

This study assesses the microstructure and mechanical properties of tungsten boride (WB) powder and cemented carbide coatings with WB additions. HVOF-sprayed layers produced from 60WC-30WB-10Co composite powders are compared with conventional 88WC-22Co and 86WC-10Co-4Cr coatings based on phase composition, hardness, wear resistance, and wear surface structure. The results indicate that Co reacts with WB during spraying, forming ternary phases (WCoB, W 2 CoB 2 ) that increase hardness as well as sliding wear resistance.

Cu and Cu-MoS2 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.% MoS2) 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 MoS2 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-MoS2 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-MoS2 composite due to poorly bonded interfaces induced by the effect of MoS2 during particle impact and coating formation.

Lowering the thermal energy and increasing the kinetic energy of sprayed particles by newly developed HVAF systems can significantly reduce material decarburization, and increases sliding wear and corrosion resistance of hard metal coatings, making HVAF coatings attractive both economically and environmentally over its HVOFs predecessors. Two agglomerated and sintered feedstock powder chemistries, respectively WC-Co (88/12) and WC-CoCr (86/10/4), with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Respective dry sliding wear behaviours and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against Al2O3 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviours were evaluated via standard Neutral Salt Spray (NSS), Acetic Acid Salt Spray (AASS), accelerated corrosion test and electrochemical polarization test at room temperature. Optimization of coating tribological properties are discussed regarding the suitable selection of primary carbide size for different working load applications.

The wear resistance of thermal spray coatings mainly depends on coating properties such as the microstructure, hardness, and porosity, as well as on the residual stress in the coating. The residual stress is induced by a variety of influences e.g. temperature gradients, difference of the thermal expansion coefficient of the coating / substrate materials, and the geometry of the components. To investigate the residual stress, the Impulse Excitation Technique was employed to measure the Young’s and shear moduli. The residual stress was determined by using the hole-drilling method and X-ray diffraction. Pin-on-Disc and Pin-on-Tube tests were used to investigate the wear behavior. After the wear tests, the wear volume was measured by means of a 3D-profilometer. The results show that the value of the residual stress can be modified by varying the coating thickness and the substrate geometry. The compressive stress in the HVOF-sprayed WC-Co coatings has a significant positive influence on the wear resistance whereas the tensile stress has a negative effect.

Sprayed deposits using conventional wire and powder materials open a wide range of possibilities to solve wear problems in engineering equipment. The option for new different spray technologies and consumables like nanostructured powder materials and nanocomposite cored wires has expanded the engineering possibilities. Cored wire technology allows the use of compositions that cannot be drawn into wire form like carbides in metallic matrix and high-temperature materials, thus intensifying the use of low operating cost welding and spraying processes to demanding wear applications. The objective of this work was to compare the mechanical characteristics and erosive wear performance of coatings obtained by Flame Spray and High Velocity Oxygen Fuel Spray using some selected powder and flexi-cord wire materials. The wear resistance of the coatings was determinate by slurry erosion wear test.

High-temperature tribology plays an important role in many engineering applications such as metal forming operations and aerospace industry. Several problems in hot-metal forming of high strength steels occur such as oxidation of tool and workpiece surfaces, increased wear of tools and scaling of workpiece. Moreover, operations at elevated temperatures can significantly influence frictional behavior of tool steels [1]. Present research attempts to analyze experimentally and understand tribological behavior of AISI H11 and AISI H13 under dry conditions at room temperatures. High velocity oxy-fuel (HVOF) thermal spray NiCrBSi coating was developed on tool steels. The room-temperature wear performance of uncoated and coated tool steels was evaluated on pin-on-disc tribometer in the laboratory. In-depth analysis of exposed as-sprayed samples was examined with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS).

Titanium aluminium based nitride (Ti, Al)N coatings possess excellent tribological behaviour with respect to metal cutting and polymer forming contacts. In the present work TiAlN coatings were deposited by plasma spray process. Three coatings of TiAlN were deposited on AISI-347 grade boiler steel substrate out of which two were thin nano coatings deposited at different temperatures of 500°C and 200°C and one conventional coating was deposited by plasma spraying. The as sprayed coatings were characterized with relative to coating thickness, microhardness, porosity and microstructure. The optical microscopy (OM), the XRD analysis and field mission scanning electron microscope (FESEM with EDAX attachment) techniques have been used to identify various phases formed after coating deposited on the surface of the substrate. Subsequently the sliding wear behaviour of uncoated, PVD sprayed nanostructured thin TiAlN coatings deposited at 500°C and 200°C and plasma sprayed conventional coated AISI-347 grade boiler steel were investigated according to ASTM standard G99-03 using pin on disk wear test rig. Cumulative wear volume loss and coefficient of friction, μ were calculated for the coated as well as uncoated specimens for 10, 15 and 20 N normal loads at a constant sliding velocity of 1 m/sec. The worn out samples were analysed with SEM/EDAX. Wear rates in terms of volumetric loss (mm³/g) for uncoated and coated alloys were compared. The nanostructured TiAlN coatings deposited at 500°C and 200°C has shown minimum wear rate as compared to conventional TiAlN coating and uncoated AISI-347 grade boiler steel. Nanostructured TiAlN coatings were found to be successful in retaining surface contact with the substrate after the wear tests.

The main objective of this study is to determine the optimum conditions for cold spraying a WC-Co nanopowder on aluminum alloy and carbon steel substrates. XRD tests were run on the powder and coatings to determine if phase changes occurred during spraying. Coating samples were evaluated via adhesion, corrosion, and wear testing. Cold spraying proved to be very competitive with conventional thermal spray techniques, producing thick, dense, hard WC-Co coatings on steel as well as aluminum with excellent tribological and electrochemical properties.

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 investigates the effects of operating environment and temperature on the friction behavior of self-mated WC-CoCr coatings in sliding contact. Nickel superalloy substrates were coated with 86WC-10Co-4Cr powder using a warm spray gun. Coating cross-sections and surfaces were examined by SEM, XRD, EDX, and x-ray photoelectron spectroscopy (XPS). Tribological tests were conducted on a high-load tribometer at various temperatures in air, nitrogen gas, and distilled water. Test samples were examined by SEM and XPS, revealing wear patterns and elemental compositions while providing insights on oxide formation.

A special pin-on-disc test setup designed for vacuum environments was used to conduct wear tests in a large chamber scanning electron microscope. Arc-sprayed NiCrBSi and HVOF-sprayed WC-12Co coatings were tested using a pin with an Al 2 O 3 ceramic ball as the wear counterpart. During testing, different wear mechanisms were identified and the processes were recorded in short video streams.

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.

Thermal spray coatings are widely used in sealed constructions where a specific seal material is sliding on the coating surface in aqueous conditions. Such applications are often highly corrosive and therefore limit the lifetime and increase the wear of the seal and the coating. In this work special test equipment was manufactured to study corrosion and wear performance of the specific test materials used under chlorine containing conditions at low pH-values. In the test procedure, a rotating seal material was pressed with certain pressure against the thermal spray coating material in the test solution and the wear of the seal and the weight loss of the coating material was measured during the test. Coating samples for the tests were prepared using HVAF, HVOF, twin wire arc spray and atmospheric plasma thermal spray techniques. Corrosion resistant stainless steel material EN1.4404 was tested as a reference together with the thermal sprayed coatings. Altogether four different seal materials were tested and the seal material was found to affect the weight loss of the tested base material and also to the coated material during the corrosion wear tests. Pure graphite seals were seen to accelerate the wear rate of both bulk stainless steel material and the thermal spray coatings, as compared to the other seal materials involved in the tests. The HDPE polymer seal gave the lowest weight loss in the tests. Clear differences in corrosion wear resistance were found between tested thermal spray coatings. Clearly the best performance was achieved with plasma sprayed chromium oxide coating compared to the other tested coatings when glass fibre reinforced teflon was used as the seal material.