Thermally sprayed Cr 2 O 3 coatings have been shown to provide excellent protection against wear in many engineering applications. These coatings are traditionally applied using air plasma spray technology; however, suspension high velocity oxy fuel thermal spraying (SHVOF) is a promising method to improve coating properties as this technique enables powder feedstocks too small to be processed by mechanical feeders to be sprayed, allowing the production of coatings with improved density and mechanical properties. Furthermore, the addition of graphene nanoplatelets (GNPs) to the liquid feedstock has been shown to improve the mechanical properties of SHVOF sprayed ceramic coatings. In this study, an aqueous based nanometric Cr 2 O 3 suspension and a Cr 2 O 3 suspension with 1 wt.% GNP, prepared via a proprietary process, were sprayed by a SHVOF thermal spray onto 304 stainless steel substrates. The microstructure of Cr 2 O 3 and Cr 2 O 3 + GNP coatings was analyzed using SEM and XRD alongside microhardness, fracture toughness and porosity investigations. Dry sliding wear performance was investigated using a ball on flat tribometer against an alpha alumina ball at loads of 16, 30 and 47 N. The GNP containing coating exhibited improved mechanical properties, however its response to sliding wear was very similar to the non-GNP coating.

An air-oxygen controlled high velocity combustion spraying process has been developed that uses a special HVOF gun and a broad range of fuel-oxidant ratios. Extremely low flame temperatures can be achieved while maintaining a supersonic flow of combustion products, thus allowing the solid state deposition of almost all industrially relevant alloys. This work deals with the development of superhard cermet coatings using conventional and fine WC-Co(Cr) powders, optimized spray parameters, and different nozzle geometries. Results are compared based on coating microhardness, toughness, and sliding wear resistance.

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 study assesses the effect of machine hammer peening (MHP) and carbide grain size fraction on the friction and wear behavior of arc-sprayed WC-W 2 C FeCMnSi coatings. SEM examination shows that post-treatment by MHP compresses the coating, reducing both thickness and porosity, particularly in coatings with ultrafine carbides. The treatments also cause cracking, however, especially in carbide phases. Ball-on-disk tests were carried out on as-sprayed and treated samples to determine sliding wear and friction properties, and dry sand rubber wheel tests were used to evaluate abrasion resistance. SEM and EDX analyses before and after wear testing show how coating microstructure and grain size correlate with the friction and wear test results obtained and the given surface treatments.

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.

Chromium carbide-based thermally sprayed coatings are widely used for high temperature wear applications. In these extreme environments at those temperatures, several phenomena will degrade, oxidize and change the microstructure of the coatings, thereby affecting their wear behaviour. Although it can be easily conceived that the Cr 3 C 2 -NiCr coating microstructure evolution after high temperature exposure will depend on the as-sprayed microstructure and spraying parameters, very little has been done in this regard. This study intends to develop a better understanding of the effect of spraying parameters on the resulting chromium carbide coating microstructure after high temperature operation and high temperature sliding wear properties. The microstructures of different coatings produced from two morphologies of Cr 3 C 2 -NiCr powders and under a window of in-flight particle temperature and velocity values were characterized through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Sliding wear at 800°C was performed and the wear behaviour correlated to the spraying parameters and coating microstructure. Vickers microhardness (300 gf) of the coatings before and after sliding wear was also measured.

The dry sliding wear behaviour of two HVOF-sprayed Fe-Cr-Ni-Si-B-C (Colferoloy) alloy coatings was studied by ball-on-disk tests performed at room temperature (against alumina and 100Cr6 steel balls), at 400 °C and at 700 °C (against alumina balls only). HVOF-sprayed Ni-Cr-Fe-B-Si-C and Cr 3 C 2 -NiCr layers were also tested for comparison. Under all test conditions, the wear rate of the Colferoloy coatings is lower than that of the Ni-Cr-Fe-B-Si-C coating but larger than that of the Cr 3 C 2 -NiCr cermet. Specifically, at room temperature, the Colferoloy coatings exhibit a combination of mild abrasion, delamination and tribo-oxidative wear against alumina, whereas, against steel, they undergo very limited delamination with negligible wear loss. By contrast, the Ni-Cr-Fe-B-Si-C coating suffers larger wear against steel and undergoes more severe abrasive grooving against alumina. Although the Colferoloy and Ni- Cr-Fe-B-Si-C coatings possess similar microstructure and micro-hardness, their scratch behaviours, which depend on cracking resistance and plastic deformability, differ, thus explaining the micromechanical reason for the different wear mechanisms. At 400°C and 700°C, all of the metal alloy coatings are softened and suffer more severe abrasive grooving; by contrast, the behaviour of the Cr 3 C 2 -NiCr layer at 700 °C is controlled by the formation and delamination of an oxidised layer.

The HVOF sprayed wear resistant hardmetal coatings with favourable sliding properties are suitable for increasing the lifetime of sliding applications, such as pistons of combustion engines, pumps and other hydraulic devices. In practice, the coatings face the problem of their interaction with other media, in the case of sliding wear usually lubricants. In the paper, the friction properties of five different HVOF sprayed coatings are evaluated by pin-on-disk test according to ASTM G-99 under dry and lubricated conditions and lubricated block-of-ring test according to ASTM G77. Several types of lubricants designed for combustion engines were used to compare their influence on coatings sliding wear behavior. Based on the results, the suitability of coatings for the application on the engines parts is discussed and the effect of counterpart material and different types of lubricants on the coefficient of friction and coatings wear rate is analyzed. It was confirmed, that the CrC-based coating are more suitable for the application under the condition corresponding to combustion engines, e.g. elevated temperature and steel counterpart, than the WC-based coatings. From the group of CrC-based coatings, the superior behavior was observed at the CrC-CoNiCrAlY coating, the matrix material of which offers further enhancement of the sliding wear behavior.

In this study, a TiO 2 (anatase) nanopowder suspension was processed by high velocity suspension flame spraying (HVSFS). The resulting coatings were characterized and compared to conventional HVOF and atmospheric plasma sprayed layers. It is shown that the HVSFS operating parameters can be adjusted to achieve dense titania with a near nanostructure and homogeneous distribution of anatase and rutile phases. These coatings have lower pore interconnectivity and higher wear resistance than the APS and HVOF layers. Alternatively, large unmelted agglomerates of anatase nanoparticles can be embedded in the coating, increasing the porosity and anatase content for enhanced photocatalytic efficiency.

WC-based cermet coatings were deposited by HVOF spraying in order to study the effects of laser remelting on coating microstructure, hardness, and dry sliding wear behavior. It was found that the laser treatment eliminates porosity and contributes to increased hardness and enforced metallurgical fusion between the coating and substrate, effectively improving adhesion and wear resistance.

In this study, two metallic powders, Ni-20Cr and Ni3Al, were plasma sprayed on stainless steel substrates in order to compare their sliding wear properties. The coatings exhibited typical splat morphology prior to wear testing. After wear testing, the coatings were again examined along with an uncoated substrate. It was concluded that although either coating can effectively reduce the wear rate of 309 stainless steel, the Ni3Al coating is a better choice.

The high velocity oxy-fuel (HVOF) combustion spray process has previously been shown to be a successful method for depositing pure polymer and polymer/ceramic composite coatings. Polymer and polymer-ceramic composite particles have high melt viscosities and require the high kinetic energy of HVOF in order to generate sufficient particle flow and deformation on impact. One of the goals of reinforcing polymer coatings with particulate ceramics is to improve their durability and wear performance. Composite coatings were produced by ball-milling 60 µm Nylon-11 together with nominal 10 vol.% of nano and multi-scale ceramic reinforcements and HVOF spraying these composite feedstocks onto steel substrates to produce semi-crystalline micron and nano-scale reinforced coatings of polymer matrix composites. The room temperature dry sliding wear performance of pure Nylon-11, Nylon-11 reinforced with 7 nm silica, and multi-scale Nylon-11/silica composite coatings incorporating 7 to 40 nm and 10 µm ceramic particles was determined and compared. Coatings were sprayed onto steel substrates, and their sliding wear performance determined using a pin-on-disk tribometer. Coefficient of friction was recorded and wear rate determined as a function of applied load and coating composition. Surface profilometry and scanning electron microscopy were used to characterize and analyze the coatings and wear scars.

Plasma sprayed yttria-stabilized zirconia coatings were deposited using nanostructured and conventional powders with optimized process parameters. The sliding wear of both coatings against stainless steel were examined with a block-on-ring test under dry friction condition. It was found that the friction coefficients and wear rates of coatings deposited using the nanostructured powder were lower than that of coatings deposited using the conventional powder. The high wear resistance of the plasma sprayed ZrO 2 coating using the nanostructured powder is attributed to its enhanced cohesion, improved microhardness and homogeneous microstructure.

In the current study, the tribological properties of TiC-based coatings paired with polycrystalline alumina under unlubricated sliding conditions were investigated in order to demonstrate the technological and engineering potential of such coatings. (Ti, Mo)(C, N)-Co coatings were prepared from an agglomerated and sintered spray powder by HVOF spraying using JP-5000 equipment. Cr 3 C 2 -NiCr coatings were studied for comparison. Sliding wear tests were performed over the temperature range from 23°C to 800°C with sliding speeds in the range 0.3-3 m/s, a wear distance of 5000 m and a normal force of 10 N. Wear rates of coatings and sintered alumina counterparts were measured separately. Compared with Cr 3 C 2 -NiCr coatings, (Ti, Mo)(C,N)-Co coatings showed significantly lower total wear rates, corresponding to those found in the region of mixed/boundary lubrication. With few exceptions, the coefficients of friction were found to be lower for (Ti, Mo)(C,N)-Co coatings than for Cr 3 C 2 -NiCr coatings. After tests were performed, the coating microstructures were studied by optical microscopy and SEM. The oxide scales formed on the coating surfaces were investigated by SEM and X-ray diffraction. Comparison of the total wear rates of the couples consisting of sintered alumina and a (Ti, Mo)(C,N)-Co coating with those of other alumina-ceramic and hardmetal-hardmetal tribological systems demonstrates the immense potential of TiC-based coatings for sliding wear applications.

One of the most important uses of HVOF thermal sprayed CrC-NiCr coatings is for wear resistance. In this work Cr 3 C 2 75-NiCr25 coatings were obtained by high-velocity oxy-fuel system from three agglomerated feedstock powders with various powder size distributions (- 30, -10 and –5 µm). The powders were agglomerated, sintered, plasmafused and crushed, in order to increase their density. The coating microstructures were characterised by SEM microscopy. Differences in coating roughness have been determined by profilometry. The ultra-microindentation technique was applied to measure the hardness and the elasto-plastic properties of the coatings. Experiments using a tribometer (pin on disc configuration) under lubricated and dry conditions have been performed in order to evaluate the friction and wear properties of the different coatings. It was found that the coatings obtained with the lowest feedstock powder size presented the best sliding wear resistance under all the conditions. This fact could be explained in terms of differences of cohesion between the carbide particles and the binder phase. The lower feedstock powder presents a lower carbide particle size that involves a better distribution and cohesion of the chromium carbide with the NiCr binder phase. This fact leads a minor production of “third body” hard particles in the wear tests that influenced quite considerably in the final wear rate of the studied coatings.

The microstructure and sliding wear behavior from room temperature up to 650°C of Fe-Al intermetallic coating produced by cored wire and high velocity arc spraying (HVAS) have been investigated. X-ray diffraction (XRD), energy dispersion spectroscope (EDS), optical microscopy (OM) and scanning electron microscopy (SEM) were used to analyze the microstructure and sliding friction and wear mechanism of the coatings. Chemical analysis of the coating indicated the composition to be Fe-20.0Al-14.1O (at.%). The microstructure was found to consist of Fe 3 Al, FeAl and α-Fe regions mainly, together with fine oxide (Al 2 O 3 ) layers and a little Al. The results of sliding wear indicated that the Fe-Al coating exhibited low friction coefficient and low wear rate at elevated temperatures. The reason of the friction coefficient decreasing at elevated temperatures is that protective oxide film formed on the worn surface during sliding wear process. And delamination is the predominant wear mechanism of the coatings. The Fe 3 Al and FeAl intermetallics which have higher strength and hardness at elevated temperatures can effectively resist crack initiation, propagation and splat fracture, thus resulting in excellent high temperature wear resistance of the Fe-Al coating.

PyroGenesis Inc. has been conducting a program on the development of coatings prepared from nanostructured ceramic and cermet materials using atmospheric (APS), vacuum plasma spraying (VPS), and high velocity oxy-fuel spraying (HVOF). In the work presented in this paper, APS and VPS coatings from nanostructured or sub-micron Al 2 O 3 - 13TiO 2 , Cr 2 O 3 -5SiO 2 -3TiO 2 , and TiO 2 feedstock materials were developed and optimized for abrasion wear resistance. They were subsequently tested for sliding wear resistance. The resulting wear properties are discussed in terms of coating microstructure, and compared to those obtained from conventional microstructured feed materials. It is found that the starting powder and the spraying conditions play a major role in the resulting coating characteristics. VPS applied coatings from nanostructured powder were found to generally offer the best performance, most notably under sliding wear conditions.

HVOF sprayed tungsten carbide (WC) thermal spray coatings are finding increasing acceptance for replacement of electroplated chromium on aircraft landing gear parts. In order to replace chrome plating by an HVOF WC coating, the latter should exhibit wear and fatigue characteristics at least as good as those of chrome plating. Sliding wear performance and fatigue life of tungsten carbide coated parts depend on morphology and phase composition of the coating which in turn depend on spray parameters such as powder characteristics, powder feed rate, gas flow rates, and spray distance. A Design of Experiments (DOE) approach for a Jet Kote™ HVOF spray system was used to identify optimal spray parameters for WC-Co and WC-Co-Cr coatings based on best sliding wear and best fatigue characteristics. Best sliding wear was defined as minimum block loss in the standard ASTM-G77 wear test in which a rotating WC coated ring is tested against a stationary Al-Ni-Bz block. Best fatigue characteristics were defined as compressive residual stresses in the coating in the range 250 to 450 MPa. Spray parameters found to strongly affect wear were powder feed rate, oxygen flow rate, powder size, and a powder type-powder size interaction. Spray parameters strongly affecting residual stresses include powder type, hydrogen flow rate, and powder feed rate. Some spray parameters were found to be orthogonal with respect to wear behavior and residual stress. This means some parameters can be adjusted to maximize one performance criterion (wear or residual stress) without adversely affecting the other.

The aim of this study is to find a coating that can improve the wear resistance of bushings and sleeves used in continuous hot-dip galvanizing facilities. In the experiments, a number of wear-resistant alloys and their carbide composites are applied to stainless steel substrates by plasma transferred arc (PTA) surfacing and the resulting deposits are characterized based on XRD and SEM analysis, microhardness measurements, and pin-on-disk sliding wear tests conducted in a molten Zn-Al bath at 470 °C. Changes in microstructure during solidification are discussed and correlations are made with phase composition, hardness, wear behavior, and suspected wear mechanisms. Paper includes a German-language abstract.

Quasicrystalline materials offer outstanding properties: High thermal stability in mechanical behaviour combined with special thermal and electrical conductivity as well as excellent tribological performance. High hardness is accompanied by heavy brittleness - an undesired property when looking for possible applications. A reduction of brittleness can be achieved by embedding quasicrystalline phases into a more ductile material to form a metal-matrix-composite material keeping some quasicrystalline properties. For thermal spraying blended, agglomerated, chemical encased or attrition milled powders as well as filled wires are processable to form such a metal-matrix-composite coating. The research work included spray trials using material-input prepared by the methods described. These different inputs have been processed in different compositions each. Spray trials have been processed by following techniques: Arc-wire-spraying, APS-spraying, wire-flame-spraying and HVOF-spraying. This paper gives an overview about HVOF-sprayed coatings with blended powders. On the one hand investigation were focused on metallurgical analysis for proving the existence of quasicrystal contents as well as determining adherence and embedding behaviour of the matrix-phase. On the other hand tests were centred onto the evaluation of the sliding-wear-behaviour in respect of interdependencies to the coatings composition and microstructure.