Nowadays, Cr 3 C 2 -based cermet coatings by HVOF process are widely recognized for their corrosion and erosion resistance, particularly at high temperatures. These coatings also offer the advantage of being lightweight and exhibiting superior wear, corrosion and cavitation resistance in room-temperature applications. Their lightweight nature and high temperature capability make them an attractive alternative to WC-based alloy coatings and hard Cr plating coatings. The objective of this study is to develop optimal Cr 3 C 2 -NiCr coatings by comparing different feedstock materials, including feedstock with nanocrystalline and/or submicron sized Cr 3 C 2 phases. The focus of the investigation is on understanding the impact of feedstock features such as particle size, morphology, and carbide sizes, as well as sliding abrasive wear conditions (specifically SiC grit size and working load), on the coating properties and sliding wear performance. The results of the study indicate that the sliding wear resistance of the Cr 3 C 2 -NiCr coatings is highly influenced by the features of the Cr 3 C 2 carbides. The presence of nano, submicron and few microns sized carbides in the coatings improves their density and hardness, leading to a significant reduction in wear rates under test conditions. Furthermore, the size of the abrasive SiC grit on the counter surface plays a significant role in determining the sliding wear behavior of these coatings. Based on the analysis of the test data, the mechanisms behind the performance of the Cr3C2-NiCr coatings have been investigated and used to interpret their sliding wear behaviors. A high microhardness in the coating is considered a reliable indicator of high quality, full density, and satisfactory wear resistance. This study has identified and recommended optimized materials for improved coating properties based on the key findings. These findings contribute to the understanding of the relationship between feedstock features, sliding abrasive wear conditions, and the wear rates of HVOF-sprayed Cr 3 C 2 -NiCr coatings.

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.

This paper evaluates and compares five wear-resistant coatings produced by HVOF spraying for high-temperature use. CrC-NiCr, CrC-CoNiCrAlY, Stellite 6, NiCrBSi, and TiMoCN-Ni coatings were sprayed on grit-blasted carbon steel substrates. Abrasive, sliding, and fretting wear resistance were measured and changes in microstructure and hardness due to high-temperature exposure were recorded. CrC-NiCr coatings exhibited the best wear properties, but the oxidation of carbides at high temperatures proved to be a problem. Based on test results, alternative coatings would include CrC-CoNiCrAlY for abrasive wear, Stellite 6 for erosive wear, and NiCrBSi for sliding wear.

By use of homemade arc spraying system patented, which could make melted metal droplets atomized fully and make its flying velocity achieve ultrasonic velocity, TiAl alloy coatings were manufactured on the aluminum alloy (LY12) substrate surface. The slide wear resistance of TiAl alloy coatings was investigated. The effect of spraying parameters, coatings' chemical composition and microstructure on the slide-wear resistance of coatings was examined. Then the slide-wear mechanism of the coatings was discussed. The results showed that the slide wear resistance of TiAl alloy coatings by ultrasonic arc sprayed is 17 times higher than it of the aluminum alloy (LY12) substrate under the condition of dry slide-wear.

This paper investigates the mechanical properties of plasma-sprayed Al 2 O 3 -TiO 2 coatings. Micro and nano powders were deposited on hot and cold substrates under different conditions using atmospheric and vacuum plasma spraying. The coatings were then characterized based on microstructure, hardness, phase composition, abrasive wear rate, and adhesion strength. It is observed that Al 2 O 3 -TiO 2 layers are very dependent on the coating system, powder form, and spray parameters used. The layers sprayed with nanopowder in a vacuum were found to have the best combination of properties. Paper includes a German-language abstract.

WC-CoCr coatings are deposited by HVOF process for improving surface resistance of low alloyed steels. In this study we examined the wear characteristics of WC-CoCr coatings on low alloyed steel substrate under different test conditions, using a sliding wear test unit with abrasive ball. In experimental studies discussed the effects of test load, temperature, work medium and sliding distance on the wear characteristics of coatings. Weight loss, wear track depth and width were observed . It was found that the weight loss of coatings increased in dry medium conditions. Wear weight loss was significantly reduced in lubricated condition due to decreasing friction. The wear track surface profile changed with lubrication and increasing temperature in test conditions. Under the base oil lubricated conditions the WC-CoCr coating performed well.

Gas atomized Al 63 Cu 25 Fe 12 powders of varying size fractions were plasma sprayed to study the relationships between coating microstructure and tribological behavior. After spraying, annealing was performed on one of the coatings. Abrasion and sliding wear tests were performed on the coatings. The results indicate a correlation between the abrasion resistance and hardness of the coatings. Furthermore, sliding wear tests reveal lower coefficients of friction for the as-sprayed coatings compared to the annealed coatings.

A tungsten carbide/cobalt hard coating was deposited on steel substrates using plasma-arc and high velocity oxyfuel flame (HVOF) spraying. The characteristics of the coatings made by the two spraying methods were evaluated under identical conditions. The microstructure and the chemical composition ofthe coatings were different depending on the powder heating temperature and the velocity of particles. The sliding wear properties of the coatings against hardened steel at high sliding speeds showed different tendencies from those at low speeds. The plasma sprayed coatings resulted in better abrasive wear properties than HVOF coatings did. Material removal by solid particle erosion depended on the striking angle of particles on the substrate surface but there are no clear differences in wear properties between the two coatings.

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.

Plasma transferred arc welding (PTA) is used to produce coating for wear resistance application in earth moving equipment. The coating is designed to have balanced toughness and hardness, optimal microstructure to perform in the wear modes the components are subject to. 4~ 6 times improvement in wear life compared with hardened steel was achieved as demonstrated in dry sand/rubber wheel test and Caterpillar proprietary abrasion wear test

This paper describes the development of novel engineered surfaces based on thermal spray coatings for sliding wear resistance under conditions of high loading and starved lubrication. As specific examples, piston ring elements for internal combustion engines and radial bearings for medium-lubricated pumps are discussed. The properties of two coatings, SUME SOL 220 and SUME SOL 320, are compared with existing materials and coatings. It was found that SUME SOL 220 exhibited excellent sliding wear resistance under boundary (oil) lubrication. As a consequence, they are considered as attractive candidates for piston ring applications in heavy duty engines. For more corrosive applications, such as encountered in sea water environments, the SUME SOL 320 coating exhibited superior combinations of sliding wear and corrosion resistance. Paper includes a German-language abstract.

Thermal sprayed chromium carbide (Cr3C2)-25% NiCr (Ni-20%Cr) coatings are extensively used in wear resistant applications especially under conditions wherein operating temperatures are likely to be higher than 500°C . The performance of the Cr3C2-NiCr coatings under such conditions depend on a variety of coating properties like the porosity, microstructure, extent of decarburization of Cr3C2 phase and hardness. One of the parameters which affects the above mentioned coating properties is the characteristics of the powder utilized for thermal spraying. In the present study, Cr3C2-25% NiCr powders obtained from four different sources has been utilized to form Cr3C2-NiCr coatings on steel substrates utilizing the detonation spray coating (DSC) system. The Cr3C2-NiCr powders utilized vary from each other in terms of manufacturing route employed (sintered and crushed, pre-alloyed, blended, etc.), particle size distribution, particle shape and even phases present. The influence of each of these powder characteristics on the coating microstructure, porosity, hardness, extent of carbide dissolution and ultimately on coating performance (i.e. sliding and abrasive wear resistance) has been evaluated.

Iron aluminides have been lately proposed as promising materials for wear applications. Many authors have focused their investigations on the friction behaviour of FeAl coatings emphasizing the role of this intermetallic as a new matrix to embed ceramic particles and replace for high temperature the extensively studied WC-Co cermet system. However, few works deal with the evaluation of the different tribological properties and their relationship with the coating microstructure. Thus, in the present study, the near stoichometric Fe40Al was successfully sprayed by means of HVOF using different spraying parameters and the tribological behaviour was assessed through solid particle erosion, abrasive and dry sliding tests. The wear mechanisms that took place in the produced coatings are discussed with regard to the obtained results. The friction coefficient versus sliding distance was obtained. In addition, isothermally treated samples in air were tested showing both lower friction coefficient and lower wear rate.

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.

Plasma Transferred Arc hardfacing (PTA) is an excellent tool for surface tailoring as it allows for the manipulation of coatings chemical composition. In particular in-situ alloy development can be achieved during the deposition of different powder mixtures. In this work powder mixtures of Ni-Al, Nb-Al and Fe-Al were deposited by PTA. Coatings were characterized for their mechanical features at room temperature evaluated by Vickers microhardness under 300gf load, nano- (0.04gf) and macro- (10kgf) scratch tests and pin-on-abrasive disc tests under 1kgf. Results showed very high dilution for the processed coatings with Vickers microhardness varing with the chemical composition of the deposited powder, mixtures, with the Fe based deposits exhibiting the lower hardness (below 400Hv) and the Nb-based deposits reaching 900HV. Scratch hardness followed Vickers micro hardness only for the Nb based coatings. Abrasion mechanism also varied for each alloy system and within each alloy system, the harder the coating the better the abrasive wear resistance. However when comparing the full set of coatings the Nb based coatings exhibited a superior performance and the Ni based deposits the poorer wear resistance.

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.

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.

A ball-milled mixture of glass and alumina powders has been plasma sprayed to produce alumina-glass composite coatings. The coatings have the unique advantage of a melted ceramic secondary phase parallel to the surface in an aligned platelet composite structure. The alumina raises the hardness from 300HV for pure glass coatings to 900HV for a 60wt% alumina-glass composite coating. The scratch resistance increases by a factor of three and the wear resistance by a factor of five. The glass wears by the formation and intersection of cracks. The alumina wears by fine abrasion and supports most of the sliding load. The wear resistance reached a plateau at 40-50vol% alumina, which corresponds to the changeover from a glass to a ceramic matrix. Keywords: glass composite coatings, wear, thermal spraying

Air plasma spray coatings of three different WC-12%Co powders based on the powder manufacturing methods were conducted. S&F (Sintered and Crushed) WC-12%Co and NiCrSiB mixed powder with different ratio were also sprayed. The best wear resistance of S&F WC-12%Co coating was mainly due to its high hardness related with large amount of homogeneously and uniformly distributed retained carbides. The wear resistance of blend coatings increased with increasing WC-12%Co weight percent which was associated with the fact that the wear resistance of all coatings increased with increasing hardness and decreasing friction coefficient. But the exact relation of wear resistance with cohesive bond strength could not be found. The dominant wear mechanisms of WC-12%Co coatings were adhesive wear, tribo-film formation by material transfer, fatigue crack, particle (splat) fracture and delamination (spallation of coating layers). In the case of blend coatings, when the weight percent of WC-12%Co was small plastic deformation and abrasive mark (or scratching) by asperity and/or hard particle were observed. with increased weight percent of WC-12%Co the wear mechanism was closer to that of WC-12%Co coatings where no plastic deformation and abrasive mark was observed.

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.