Wear and friction properties of aluminium titanate, zirconium silicate and magnesium zirconate atmospheric plasma sprayed ceramic (APS) coatings in contact with 100Cr6 steel were investigated under dry sliding conditions as a function of high temperature. The tribological tests were performed at different temperatures varying from 20 °C up to 800 °C using an High Temperature Ball on Disk Tribometer. The wear scar diameters of the 100Cr6 steel ball were measured by optical micrograph. The cross sections of the worn ceramic coated disks were determined with a Laser Profilometer. Results show that as a result of the higher temperature (up to 400 °C), the material yields more readily (softening effects ) and so adhesion is the dominant wear mechanism. For hybrid bearing, operating temperature of about of 200 °C must therefore be avoided.

Plasma spraying was carried out on aluminium alloy substrates using high silicon aluminium alloy powders (Al- 40Si-Cu-Mg) to improve the wear resistance of the aluminium alloy. The coating exhibits superior more wear resistant to cast A390, and a low friction coefficient ranging from 0.2 to 0.25. The sprayed coating is much higher hardness of HV260 compared with that of cast A390, because of its quenched microstructure with sub-micron size silicon particles. The coating hardness does not decrease as annealing temperature up to 573 K, above 573 K it decreases rapidly. This drop in coating hardness is related to the coarsening of silicon particles and thus expanded interparticle distance. The wear resistance of coatings after annealing is inferior to that of sprayed coating. This is attributed to decrease in hardness value and coarsening of the microstructure. After annealing, the friction coefficient of the coatings shows a remarkable increase with increasing sliding distance. Since the plasma sprayed coating is in a non-equilibrium state, it maintains low friction coefficient even with a long sliding distance. Therefore, improvement in tribological properties is considered here to be due to change in wear mechanism brought by the formation of film-like layer, which prevents coating surface from adhering to iron.

Lightweight materials play a special role thanks to their low density. In recent years considerable development has been conducted using Al, Mg and their alloys. The increasing use of these materials enlarges the requirements related to the high wear resistance accompanied by good formability and ductility as well as the high corrosion resistance. A fulfillment of such demands can be attained through surface treatments. Among the currently available wide variety of surface treatment processes thermal spraying techniques play an important role. This study presents a comparison of light weight materials coated through Detonation-Gun and Atmospheric Plasma Spraying Processes. The influence of coating parameters, coating type and coating thickness on tribological properties are studied. The behavior of coatings under different bending angle regarding cohesion and adhesion is analyzed. Corresponding SEM- and LM-analyses are conducted to understand the underlying mechanisms.

Particulate erosion tests were conducted on coatings of heat/wear resistant materials (Cr 3 C 2 -NiCr (HVOF), Fe-Cr–Mn-B-Si (Arc spray), Fe-Cr-B-Si (HVOF)) and comparing materials (stainless steel, carbon steel). The erosion test was given under comparatively mild test conditions such as catalyst impinging in consideration of actual plants. In the previous paper, the particle erosion mechanism on using angular particulate erodent has been conjectured that it was similar to a cutting phenomenon of grinding process between the particle and surfaces with plastic/elastic properties. As the shape of erodent is an important factor as well as hardness of erodent and surfaces, the particulate erosion properties were investigated using three types erodent (angular/spherical silica and angular alumina). The materials of erodent were selected commercially available silica-filler and alumina grit. The erosion wastage depends on the shape and hardness of the particles. We considered the erosion mechanism of thermally sprayed coatings and metal materials depending on the shape and hardness of erodent.

Nanostructured and conventional titania feedstocks were thermally sprayed using APS, VPS and HVOF techniques to study the effects of processing, microstructure and properties on the abrasion behavior. The in-flight characteristics (temperature and velocity) of the APS and HVOF-sprayed particles were also investigated. For the nanostructured coatings, a process map was developed relating the in-flight particle characteristics during coating deposition to the abrasion resistance. This map showed that the particle velocity and particle temperature had an important influence on the volume loss in abrasion tests. Coatings were characterized using SEM to investigate the microstructural features, image analysis to measure coating porosity and Vickers indentation to determine hardness. The abrasion behavior of the coatings was evaluated using the ASTM standard dry sand/rubber wheel test. The abrasion results indicated that the VPS and HVOF-sprayed nanostructured titania coatings exhibited the highest abrasion resistance among the 14 coatings studied.

The abrasion and erosion resistance of six different coatings were evaluated in relation to their microstructure. The coatings were produced from six different powders: four containing WC and two containing CrC. Microstructural analysis highlights the relationship between the starting powder morphology and chemistry and the spray conditions in the development of the final coating microstructure. The wear performance of the coatings was evaluated according to the ASTM G-65 standard for the abrasion resistance and a slurry containing 0.66% of 180 μm alumina particles flowing at 20 m/s for wet erosion resistance. The results show that for all tested coatings the abrasion wear resistance is mostly governed by the hardness distribution. For the chrome carbide, coatings having the lowest hardness are the lest abrasion resistant. For the WC containing coatings, carbide debonding and pullout is the main wear mechanisms. The most resistant material being the WC-6Co-8Cr. All the coatings performed better than the D2 tool steel reference sample. The erosion wear resistance is controlled by the local hardness, the matrix properties and the droplet debonding. The most wear-resistant materials are the WC-Co-Cr cermets. The least wear-resistant materials are the clad CrC-20(NiCr) and the WC-Ni cermets.

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.

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.

A bulk amorphous NiTiZrSiSn produced using an inert gas atomization was sprayed onto the Cu substrate. As the oxygen to hydrogen gas fraction was increased, oxide phase fraction was increased at the expenditure of amorphous phase fraction. The phase evolution was mainly due to the in-flight particle oxidation according to flame gas composition. Tribological behaviors were investigated in view of friction coefficient and weight loss by a pin-on-disc dry sliding test. Both friction coefficient and weight loss were largely dependent on the phase composition of the coating. As the amorphous phase fraction was increased, the friction coefficient was decreased with the increase of the transfer film formation. On the other hands, major weight loss mechanism was changed from transfer film formation to pull-out of coat material as the amorphous phase fraction was decreased.