Tribological Properties of Hard Metal Coatings Sprayed by High-Velocity Air Fuel Process (original) (raw)
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Tribology of HVOF- and HVAF-sprayed WC–10Co4Cr hardmetal coatings: A comparative assessment
Surface and Coatings Technology, 2015
This paper provides a comprehensive assessment of the sliding and abrasive wear behaviour of WC-10Co4Cr hardmetal coatings, representative of the existing state-of-the-art. A commercial feedstock powder with two different particle size distributions was sprayed onto carbon steel substrates using two HVOF and two HVAF spray processes.
Tribology of FeVCrC coatings deposited by HVOF and HVAF thermal spray processes
Wear, 2018
This work studies FeVCrC-based coatings as potential alternatives to conventional Ni-and Co-based alloys for wear protection. Specifically, the microstructure and tribological properties of the coatings are characterized as a function of the particle size distribution of the feedstock powder, of the deposition technique-High Velocity Oxygen-Fuel (HVOF) or High Velocity Air-Fuel (HVAF) sprayingand of specific processing parameters. HVOF-sprayed coatings obtained from fine feedstock powder exhibit numerous oxide inclusions, which provide high hardness (≈ 900 HV 0.3) but do not excessively impair fracture toughness, as determined through scratch testing techniques. HVAF-sprayed coatings obtained from the same feedstock powder contain much fewer oxide inclusions, and some of them possess simultaneously high hardness and high toughness. Defects (e.g. speckles) are instead formed in case unsuitable HVAF torch hardware is employed. A coarse feedstock powder always results in unmelted inclusions, which impair the cohesion of the coatings, particularly of the HVAFsprayed ones. Most coatings anyway exhibit very low sliding wear rates < 3 × 10 −6 mm 3 /(N m); abrasive grooving and surface fatigue-induced pitting are the main wear mechanisms. Oxide inclusions do not affect negatively the response of HVOF coatings, whereas too many unmolten particles increase pitting under severe test conditions. Rubber-wheel abrasion testing produces comparatively more severe grooving.
Tribological behavior of HVOF- and HVAF-sprayed composite coatings based on Fe-Alloy+WC–12% Co
Surface and Coatings Technology, 2014
Fe-based coatings are promising alternatives to Ni-based ones, because of lower cost and lower toxicity. Following a previous research, where the sliding wear resistance of HVOF-sprayed Fe-Cr-Ni-Si-B-C alloy coatings was found to compare favorably with that of a Ni-Cr-B-Si-C alloy and of electroplated chromium, the present study investigates the wear resistance of Fe-Cr-Ni-Si-B-C + WC-Co composite coatings. The Fe-alloy feedstock powder was therefore blended with 0, 20 and 40 wt.% of a WC-12 wt.% Co powder and sprayed by HVOF and HVAF processes. HVAF-sprayed coatings exhibit less structural alteration than HVOF-sprayed ones, which results in lower intrinsic nanohardness of both Fe-alloy and WC-Co splats; however, HVOF-and HVAF-sprayed coatings exhibit similar Vickers microhardness. Somewhat poorer interlamellar bonding in HVAF-sprayed coatings results in a greater tendency to microcracking during dry sliding wear testing at room temperature; however, dry sliding wear rates of HVOF-and HVAF-sprayed samples never differ significantly. The reinforcing effect of WC-Co decreases the wear rate of composite coatings (≈10 −6 mm 3 /(Nm)) by more than order of magnitude, compared to unreinforced ones (≈1-2 * 10 −5 mm 3 /(Nm)). As the test temperature is increased to 400°C and 700°C, the dry sliding wear rates of all samples increase (up to 10 −4 mm 3 /(Nm) or greater). The greatest changes are observed when the WC-Co content is larger, as it suffers from oxidation and thermal alteration more than the Fe-alloy matrix. The abrasive wear resistance of the Fe-based coatings, evaluated by rubber-wheel testing, is also significantly improved by the addition of WC-Co.
The Wear Resistance of HVOF Sprayed Nickle Chromium and Boron Carbide Coatings
International Journal of Engineering Tehnology Science and Research, 2017
Pin-on-disk dry sliding wear tests were performed under dry conditions against steel counter material for different loads, speed & sliding distances. Sliding speeds ranging from 1.88 to 5.65 m/s and under loads ranging from 10 to 50 N were conducted for pin specimens of Al6061 alloy MMC pin substrate reinforced with ball milled Nickle Chromium & Boron Carbide particles. This paper describes the dry slide wear behavior of Al6061 alloy composite coatings deposited by HVOF coating technique. It was evident from the experiment that the wear resistance of the coatings produced using Nickle Chromium & Boron Carbide powders is greatly improved compared with the substrate material. The highest wear resistances of the coatings were also determined in the coating. Construction and structure of coatings were studied using electron microscopy (SEM) & EDX analysis. The research results showed that all coatings exhibit comparable increase in the wear resistance property of the pin due to the presence of Nickle Chromium & Boron Carbide particles 1. INTRODUCTION Superior wear resistance is one of the attractive properties in MMCs. It has been found that particulate-reinforced MMCs show wear resistance on the order of 10 times higher than the un-reinforced materials in some load ranges. Many studies have been performed in order to understand the effects of various factors such as the particle size [3], the fraction of the reinforcing particles the load and the sliding speed on the wear resistance of the particulate-reinforced MMCs with Aluminium matrices.[1] J. Brezinová et al found that the HVOF coating of WC-Co-Cr showed the highest hardness than the coating Cr3C2-25NiCr. Tungsten carbide and chromium carbide-based coatings are frequently used for many of the applications in gas turbine, steam turbine and aero-engine to improve the resistance to sliding, abrasive and erosive wear. The former is used up to 500°C and the latter up to 800°C. Also, for sliding wear and abrasive wear resistance, the carbide coatings are considered to be a viable alternative to hard chrome plating due to the
Coatings, 2014
Thermally-sprayed Fe-based coatings have shown their potential for use in wear applications due to their good tribological properties. In addition, these kinds of coatings have other advantages, e.g., cost efficiency and positive environmental aspects. In this study, the microstructural details and tribological performances of Fe-based coatings (Fe-Cr-NiB -C and Fe-Cr-NiB -Mo-C) manufactured by High Velocity Oxygen Fuel (HVOF) thermal spray process are evaluated. Traditional Ni-based (Ni-Cr-Fe-Si-B-C) and hard-metal (WC-CoCr) coatings were chosen as references. Microstructural investigation (field-emission scanning electron microscope FESEM and X-Ray diffractometry XRD) reveals a high density and low oxide content for HVOF Fe-based coatings. Particle melting and rapid solidification resulted in a metastable austenitic phase with precipitates of mixed carbides and borides of chromium and iron which lead to remarkably high nanohardness. Tribological performances were evaluated by means of the ball on-disk dry sliding wear test, the rubber-wheel dry particle abrasion test, and the cavitation erosion wear test. A higher wear resistance validates Fe-based coatings as a future alternative to the more expensive and less environmentally friendly Ni-based alloys.
HVOF sprayed WC-CoCr coatings on aluminum: tensile and tribological properties
IOP Conference Series: Materials Science and Engineering, 2017
This paper provides a comprehensive assessment of the tensile and sliding wear behaviour of WC-10Co4Cr agglomerated and sintered powder deposited on aluminum by Hyper Velocity Oxy-Fuel (HVOF) process. Microstructural analysis (SEM) identified grains of tungsten carbide (WC) in the metal matrix of the cobalt-chromium (Co-Cr). A transformation of the WC in the W 2 C phase was observed and decomposition of WC in the metal matrix. The HVOF WC-Co-Cr coating was found to decrease tensile strength of the aluminum substrate. Transverse cracks were observed to initiate on the coating surface, increasing rapidly with the increase in tensile strain and stopped on the coating-substrate interface causing decohesion. Tribological properties were examined using the pin-on-disk method under various loads. The friction coefficient rose abruptly at the start-up phase and stabilized at almost the same sliding distance independently of the applied load. Both the friction coefficient and the wear volume were found to increase with increasing applied load. Study of the wear mechanisms revealed surface micro-cracking and fragmentation of flattened coating layers with subsequent gradual pull out of the carbide particles.
Effect of Co Content on the Properties of Hvof Sprayed Coatings Based on Tungsten Carbide
2012
Thermal sprayed coatings based on tungsten carbide are the most durable materials in terms of wear resistance. Although they are not suitable for high temperature applications, they can be applied in many areas of industry due to the combination of very hard carbides and tough matrix. The good wettability of carbides WC in Co matrix contributes to the high cohesive strength of WC-Co cermets. The hardness and toughness rate of WC-Co coatings is, in the case of thermal sprayed coatings, determined by mutual proportion of carbide phase and matrix, and by spraying parameters. Depending on the application, either hardness of coating (abrasive wear) or higher level of toughness (erosive wear) can be preferred for different types of wear. The presented study was conducted to determine the effect of cobalt matrix content on the resulting coating mechanical properties. Samples were prepared using the HVOF (high velocity oxy-fuel) spraying equipment HV-50. Three powder types with different co...
Journal of Thermal Spray Technology, 2017
The use of nanoscale WC grain or finer feedstock particles is a possible method of improving the 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 standoff distances. Three WC-10Co-4Cr coatings, with two different powder particle sizes and two different carbide grain sizes, were sprayed using a high velocity oxyair fuel (HVOAF) thermal spray system developed by Castolin Eutectic-Monitor Coatings Ltd., UK. Powder and coating microstructures were characterized using XRD and SEM. Fracture toughness and dry sliding wear performance at three loads were investigated using a ball-on-disk tribometer with a WC-Co counterbody. It was found that the finer powder produced the coating with the highest microhardness, but its fracture toughness was reduced due to increased decarburization compared to the other powders. The sprayed nanostructured powder had the lowest microhardness and fracture toughness of all materials tested. Unlubricated sliding wear testing at the lowest load showed the nanostructured coating performed best; however, at the highest load this coating showed the highest specific wear rates with the other two powders performing to a similar, better standard.
Assessment Tribological Properties of Coatings Applied by Hvof Technology
Acta Mechanica et Automatica, 2013
In this article, the attention is paid to the HVOF (High Velocity Oxygen Fuel) thermal spraying method by which the progressive coatings are applied on basic material C15E (STN 412020). These coatings are based on C-17CO, WC-CO-Cr and Cr3C2-25NiCr. There was made determination of the chemical composition of the coatings and assessment of coatings quality-adhesion, microhardness, porosity and wear resistance at room temperature (21°C) and also at operational elevated temperature (900°C). Results of adhesive wear showed high quality of all evaluated coatings and their suitability to extreme tribological conditions.