A comparative study of tribological behavior of plasma and D-gun sprayed coatings under different wear modes
01 Jun 1998-Journal of Materials Engineering and Performance (Springer-Verlag)-Vol. 7, Iss: 3, pp 343-351
TL;DR: In this paper, the authors compared the tribological behavior of detonation gun (D-gun) spray coatings and their plasma spraying counterparts in different wear modes, and found that the D-gun coatings consistently exhibit denser microstructures and higher hardness values than their plasma sprayed counterparts.
Abstract: In recent years, thermal sprayed protective coatings have gained widespread acceptance for a variety of industrial applications A vast majority of these applications involve the use of thermal sprayed coatings to combat wear While plasma spraying is the most versatile variant of all the thermal spray processes, the detonation gun (D-gun) coatings have been a novelty until recently because of their proprietary nature The present study is aimed at comparing the tribological behavior of coatings deposited using the two above techniques by focusing on some popular coating materials that are widely adopted for wear resistant applications, namely, WC-12% Co, A12O3, and Cr3C2-MCr To enable a comprehensive comparison of the above indicated thermal spray techniques as well as coating materials, the deposited coatings were extensively characterized employing microstructural evaluation, microhardness measurements, and XRD analysis for phase constitution The behavior of these coatings under different wear modes was also evaluated by determining their tribological performance when subjected to solid particle erosion tests, rubber wheel sand abrasion tests, and pin-on-disk sliding wear tests The results from the above tests are discussed here It is evident that the D-gun sprayed coatings consistently exhibit denser microstructures and higher hardness values than their plasma sprayed counterparts The D-gun coatings are also found to unfailingly exhibit superior tribological performance superior to the corresponding plasma sprayed coatings in all wear tests Among all the coating materials studied, D-gun sprayed WC-12%Co, in general, yields the best performance under different modes of wear, whereas plasma sprayed Al2O3 shows least wear resistance to every wear mode
TL;DR: In this paper, a dense ceramic oxide coating approximately 100 mm thick was prepared on a 7075 Al alloy by microarc oxidation in an alkali-silicate electrolytic solution.
Abstract: A dense ceramic oxide coating approximately 100 mm thick was prepared on a 7075 Al alloy by microarc oxidation in an alkali-silicate electrolytic solution. Coating thickness and surface roughness (R ) were measured during coating formation. The a influence of current density, electrolyte temperature and inter-electrode distance on coating kinetics was investigated. Microstructure and phase compositions were analysed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microhardness of the coating was also measured. The tribological performance of the coatings was evaluated using a dry sand abrasion test, a solid particle erosion test and a pin-on-disc sliding wear test. In addition, the results are compared to detonation-sprayed alumina (Al O ) coating and bulk Al O . The basic mechanism of microarc coating formation is explained. The material removal 23 2 3 mechanism during solid particle erosion was investigated, and structure–property correlations were established. 2002 Elsevier Science B.V. All rights reserved.
TL;DR: In this paper, the mechanical and tribological properties of HVOF CrC75 (NiCr20) 25 coatings were compared with hard chromium plating in piston rings and valve stems applications, and it was found that the CrC-NiCr coating, obtained with the lowest feedstock powder size, presented the best wear resistance under all the studied conditions.
Abstract: Automotive manufacturers have specified chromium plating for decades because of its appearance, wear and corrosion resistance, however chromium plating cause effects on human health because of the use of substances in the galvanic process whose toxicological features have not always been recognised. The improvements of the high-velocity oxy-fuel thermal spray process allow the chromium coating replacement with a comparable or superior surfaces and more environment friendly. The present study describes and compare the mechanical and tribological properties of HVOF CrC75 (NiCr20) 25 coatings sprayed from three different agglomerated feedstock powders with various powder size distributions. These results have been compared with conventional hard chromium plating. The objective of the present work is applying these new HVOF coatings in piston rings and valve stems applications. Furthermore, the studied HVOF coatings are produced with fine-powders in order to avoid the blasting and regrinding operations necessary when plasma spray coatings are used. The coating microstructures were characterised by BSE–SEM microscopy. Differences in 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 pin on disc tribometer 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 CrC–NiCr coating, obtained with the lowest feedstock powder size, presented the best wear resistance under all the studied conditions. The Fine CrC–NiCr coatings have demonstrated superior performance to hard chrome with regard to mechanical and tribological properties, and they can be proposed as an alternative to hard chrome coatings.
TL;DR: In this article, the authors present a review of the test methods used to evaluate thermal spray coatings and highlight the extrinsic nature of mechanical property measurements with regard to thermal spray coating.
Abstract: The primary focus of this review concerns the test methods used to evaluate thermal spray coatings. Techniques to measure coating intrinsic properties such as (i) porosity and (ii) residual stress state; as well as extrinsic mechanical properties that include (iii) hardness, (iv) adhesion, (v) elastic modulus, (vi) fracture toughness, and (vi) the Poisson’s ratio of thermal spray coatings are presented. This review also encompasses the feedstock and thermal spray method since process variants create a specific microstructure. An important aspect of this work is to highlight the extrinsic nature of mechanical property measurements with regard to thermal spray coatings. Thermal spray coatings exhibit anisotropic behaviour and microstructural artefacts such as porosity and the splat structure of coatings influence the mechanical characterisation methods. The analysis of coating data variability evolving from the different measurement techniques is of particular relevance to interpret the character of...
TL;DR: In this paper, a Miller Thermal/UTP Top Gun high velocity oxy-fuel spray system was used for the deposition of Cr x C y -Ni-Cr coatings from three commercially available powders, namely a sintered and crushed powder, a blended powder and a composite powder.
Abstract: Cr x C y –NiCr cermet coatings are commonly utilised in industry as a means to provide wear resistance in high temperature environments. Such coatings are usually deposited by thermal spraying. In this work, Cr x C y –NiCr coatings have been deposited using a Miller Thermal/UTP Top Gun high velocity oxy-fuel spray system from three commercially available powders, namely a sintered and crushed powder, a blended powder and a composite powder. The characteristics of the powder feedstock have a strong influence on the coating microstructures, although the coating microstructure is often very different to that of the powder due to processes that occur during spraying and rapid solidification of the splats. Coating microstructures were assessed by X-ray diffraction, scanning electron microscopy and microhardness measurements. The abrasive wear performance of the coatings was assessed using a dry sand–rubber wheel test with both alumina and silica abradents. It was found that, under all conditions, the coating deposited from the blended powder exhibited the highest wear rates and the coating deposited from the composite powder exhibited the lowest wear rates. Wear mechanisms were assessed by SEM examination of the wear surfaces and cross-sections through the wear scars and understood in terms of the different coating microstructures.
TL;DR: In this article, chromium carbide was applied on X20CrMo V121 steel for high temperature applications such as steam turbine valve spindle and the wear behavior of surface coated and treated materials have been studied at an elevated temperature of 550°C while rubbing against graphite-filled stellited steel.
Abstract: Various coatings such as chromium carbide (deposited by plasma spraying and detonation gun techniques), chromium oxide, chromium oxide+titania+silica, NiCrAlY, and Al2O3+NiAl, all deposited by plasma spraying; stelliting, and surface nitriding have been applied on X20CrMo V121 steel. This steel is used for high temperature applications such as steam turbine valve spindle. Friction and wear behavior of the surface coated and treated materials have been studied at an elevated temperature of 550°C while rubbing against graphite-filled stellited steel. These studies have been carried out on SRV Optimol reciprocating tribometer. Test parameters for tribological studies have been selected with a view to simulate operating conditions encountered in operation. Additionally, the structure, porosity, hardness, bond strength, and thermal cycling behaviour of these surface coated/treated materials have been characterised. Based on these laboratory investigations, chromium carbide coating deposited by plasma spraying technique has been identified as the most suitable coating for steam turbine valve spindle application. Process parameters have been established for deposition of chromium carbide coating by plasma spraying technique on actual valve spindles. The field results obtained are found to be commensurate with the laboratory findings.
01 Jan 1988
TL;DR: In this article, high-energy plasma (HEP) and high-velocity oxygen fuel (HVOF) thermal spray techniques were used for tungsten carbide-12 wt.% cobalt coatings.
Abstract: Tungsten carbide-12 wt.% cobalt coatings were deposited using optimized high-energy plasma (HEP) and high-velocity oxygen fuel (HVOF) thermal spray techniques. The coatings were evaluated using transmission electron microscopy, differential thermal analysis, X-ray diffraction, and subjected to wear tests to relate the coating structure to wear performance. Coatings were evaluated in the assprayed condition, as well as after heat treatments in inert atmosphere. The results indicate that a substantial amount of amorphous matrix material is created during the thermal spray process. Carbon and tungsten, liberated through the dissociation of the WC, combine with cobalt present in the starting powder to form amorphous material on solidification. Differential thermal analysis revealed an exothermic reaction for both the HVOF and HEP coatings at approximately 853 and 860 °C, respectively, which did not occur for the powder. Post-coating heat treatment in an inert atmosphere resulted in the recrystallization of the amorphous material into Co6W6C and Co2W4C, which was dependent on the time and temperature of the heat treatment. Wear testing showed improvement in the wear performance for coatings that were subjected to the heat treatment. This was related to the recrystallization of the amorphous matrix into eta phase carbides.
TL;DR: In this article, a new parameter called erosion efficiency, capable of identifying the dominant micromechanism leading to solid particle erosion, has been introduced, and the objective of this paper is to demonstrate the usefulness of this parameter by considering the large body of data in the literature pertaining to the solid particle degradation of metallic materials, ceramics, cermets and coatings under normal impact conditions.
Abstract: A new parameter called erosion efficiency, capable of identifying the dominant micromechanism leading to solid particle erosion, has been introduced in this paper. The objective of this paper is to demonstrate the usefulness of this parameter by considering the large body of data in the literature pertaining to the solid particle erosion of metallic materials, ceramics, cermets and coatings under normal impact conditions.
TL;DR: In this article, the science and technology of detonation spraying are reviewed relative to other associated methods of thermal spraying (e.g., plasma spraying). Special attention will be centred on optimization methods for a range of engineering applications.
Abstract: Detonation gun spraying, a technique of thermal spraying, achieves well-bonded dense protective coatings through ultrahigh velocity, medium temperature deposition of powders. The powdered feedstock materials range from metallic alloys to hard ceramics, enabling wear-resistant coatings to be formed. In this paper the science and technology of detonation spraying will be reviewed relative to other associated methods of thermal spraying (e.g. plasma spraying). Special attention will be centred on optimization methods for a range of engineering applications. The mechanism of formation of detonation-sprayed coatings will be discussed.
TL;DR: In this article, the wear and friction behaviours of detonation-gun and plasma-sprayed hard coatings were investigated under dry sliding conditions, and the results indicated that D-gun-sprays had higher hardnesses, densities and wear resistances than the corresponding plasma-Sprayed coatings.
Abstract: The wear and friction behaviours of detonation-gun- (D-gun) and plasma-sprayed hard coatings were investigated under dry sliding conditions The coating materials studied included Cr 2 O 3 , WC-12%Co, WC-20%Co, Al 2 O 3 , TiO 2 , Al 2 O 3 -40%TiO 2 , TiC-20%Ni and Cr 3 C 2 -25%NiCr Sintered WC-6%Co and steel MoCN315M were also investigated as references Scanning electron microscopy analysis was carried out to study the wear mechanisms The results indicated that D-gun-sprayed hard coatings had higher hardnesses, densities and wear resistances than the corresponding plasma-sprayed coatings D-gun-sprayed Cr 2 O 3 showed the highest wear resistance among the materials studied The wear resistance of D-gun-sprayed Cr 2 O 3 was even higher than that of sintered WC-6%Co As a result of this study, the wear-resistant order of D-gun- and plasma-sprayed hard coatings as well as sintered WC-6%Co was given
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