A contribution to the surface analysis and characterisation of HVOF coatings for petrochemical application (original) (raw)
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Microstructure, Wear Behavior and Corrosion Resistance of WC-FeCrAl and WC-WB-Co Coatings
Metals, 2018
The paper is focused on investigating the quality of two grades of thermally sprayed coatings deposited by high-velocity oxygen fuel (HVOF) technology. One grade contains WC hard particles in an environmentally progressive Ni-and Co-free FeCrAl matrix, while the second coating contains WC and WB hard particles in a cobalt matrix. The aim of the experimental work was to determine the effect of thermal cyclic loading on the coatings' resistance to adhesive, abrasive and erosive wear. Abrasive wear was evaluated using abrasive cloth of two grit sizes, and erosive wear was evaluated by a dry-pot wear test in a pin mill at two sample angles. Adhesion wear resistance of the coatings was determined by a sliding wear test under dry friction conditions and in a 1 mol water solution of NaCl. Corrosion resistance of the coatings was evaluated using potentiodynamic polarization tests. Metallographic cross-sections were used for measurement of the microhardness and thickness and for line energy-dispersive X-ray (EDX) analysis. The tests proved the excellent resistance of both coatings against adhesive, abrasive, and erosive wear, as well as the ability of the WC-WB-Co coating to withstand alternating temperatures of up to 600 • C. The "green carbide" coating (WC-FeCrAl) can be recommended as an environmentally friendly replacement for Ni-and Co-containing coatings, but its operating temperature is strictly limited to 500 • C in air.
The Mechanical Properties and Wear Resistance of HVOF Sprayed WC-Co Coatings
Acta Physica Polonica A, 2016
In this work, the Woka 5810 powders (88% tungsten carbide-12% cobalt) were used to produce coating by high velocity oxy-fuel spraying. WC-Co is widely used as a tribological coating material providing a combination of high toughness, high hardness, and good strength. The treated samples were characterized by using optical micrograph, stereo microscope and scanning electron microscopy, X-ray diffractometry, and microhardness tests. Also the wear performance of the coatings was investigated. The results indicated that the coating shows slight higher microhardness and better abrasive wear resistance than the conventional counterpart. The friction coefficient of coating was low. The scanning electron microscopy and energy dispersive spectroscopy analyses were applied to worn surfaces.
This study is done to investigate the influence of deposition parameter to the hardness and wear resistance of the tungsten carbide nickel (WC-Ni) High velocity oxy-fuel (HVOF) coating which is sprayed on the AISI 1040 medium carbon steel. Three different spraying parameters were used with the oxygen flowrate of each being changed and all other parameters and its value is kept constant. Oxygen flowrate of 30, 45 and 60 LPM were used. The result of hardness, wear rate and surface morphology were compared between the coatings. To compare the surface morphology of the three different parameter HVOF coatings, a scanning electron microscope was used. No significant changes shown on the surface of the coatings where all shows the same lump and crevices structure. X-ray diffraction was used to observe the elemental composition on the three coatings, all the coatings have the same elements present on them. It can be seen that all the coatings contains nickel, tungsten carbide, tungsten (II) carbide and oxygen. The method used for hardness test was the Vickers microhardness tester while weight loss test was used to study the wear resistance. Following the test, it is found that the hardness and wear resistance increased as the oxygen flowrate was increased. The highest hardness and wear resistance can be found in the coating with 60 LPM oxygen flowrate.
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...
Wear and Oxidation Behaviour of Tungsten Carbide Based Coatings: A Review
SSRN Electronic Journal, 2018
Failure of components under severe environment caused by the diversity of wear mechanisms and oxidation necessitated to understand, which is fundamental to estimate durability and reliability of coatings. Abrasive and erosion wear contributed to the maximum failure rate encountered in real life situations. In high-temperature applications, oxidation leads to deterioration in desired properties which causes premature failure of machine or system components. Tungsten carbide (WC) based coatings serve with both types of wears and furthermore deals with high-temperature serviceability. Among the pure metals tungsten exhibits uppermost relative abrasive and erosion resistance which provides the base for utilization of WC based coatings for severe wear applications. The emphasis of this review is on wear and oxidation performance of tungsten carbide based coatings developed by different thermal spray techniques.
Coatings
This work analyzes the differences found in hard metal coatings produced by two high velocity thermal spray techniques, namely high velocity oxy-fuel (HVOF) and high velocity air-fuel (HVAF). Additionally, the effect of the metallic matrix and ceramic composition and the original carbide grain size on coating properties is compared to the most studied standard reference material sprayed by HVOF, WC-Co. For this evaluation, the physical properties of the coatings, including feedstock characteristics, porosity, thickness, roughness, hardness, and phase composition were investigated. Several characterization methods were used for this purpose: optical microscopy (OM), scanning electronic microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and X-ray Diffraction (XRD), among others. The final performance (abrasive wear and corrosion resistance) shown by the coatings obtained by these two methodologies was also analyzed. Thus, the abrasive wear resistance was analyzed by the rub...
Comparative Study into Microstructural and Mechanical Characterization of HVOF-WC-Based Coatings
Crystals
The main objective of this work was to characterize and compare the microstructural and mechanical properties as well as erosion resistance of WC-12Co and WC-10Co-4Cr coatings. The High Velocity Oxy Fuel (HVOF) process was applied to carbon manganese steel API 2H typically used in oil and gas industries. Microstructural characterization of feedstock powder and coatings was conducted using scanning electron microscope (SEM), energy dispersive X-ray spectroscopic (EDS) analysis, X-ray diffraction (XRD) for phase determination, powder particle size distribution, and surface roughness measurement. The average particle size of the former powder was 13.7 µm whereas it was 28.1 µm for the latter. The results showed that the smaller particle size tends to melt easier than the larger one, as deduced from SEM images and surface roughness measurements. EDS and XRD results of both coatings indicated the occurrence of WC decomposition where the powder particle size plays a significant role in th...
Advances in Science and Technology Research Journal
In the field of surface engineering, thermal spraying is very wide adopted in many branches of the industry. The main reasons of such situation are its flexibility as well as cost effectiveness. Among others, high velocity oxy fuel (HVOF) technique is dedicated for spraying hardmetal and cermet coatings, especially for wear-and corrosion resistance. Such type of coating could be a promising candidate as protective layer for magnesium alloys elements. These materials need a strong improvement in the corrosion protection as well as on the field of wear resistance in order to be widely used in the industry. In this work, different WC-based coatings, namely: (i) WC-Co, (ii) WC-Co-Cr and (iii) WC-Cr 3 C 2-Ni manufactured by HVOF spraying, were investigated. The form of all feedstock materials was agglomerated and sintered powder. All coatings were sprayed with the same technological parameters, especially spray distance which was equal to 400 mm on the AZ91 magnesium alloy substrate. The main aim of the studies was to investigate the influence of the powder material on the corrosion resistance of obtained coatings. The manufactured coatings were examined in terms of its microstructure, using scanning electron microscope (SEM) and corrosion performance, which was assessed in the electrochemical corrosion investigations in 3.5% NaCl solution by Tafel method. The study showed that the corrosion resistance increasing in such order: AZ91 < WC-Cr 3 C 2-Ni < WC-Co < WC-Co-Cr. It should be stressed that WC-Cr 3 C 2-Ni coating exhibits very low corrosion performance, which could be effected by relatively high porosity (c.a. 3 vol.%) and because of that the more complex composition promotes creation of many corrosion cells.
Porosity and wear resistance of flame sprayed tungsten carbide coatings
Thermal-sprayed coatings offer practical and economical solutions for corrosion and wear protection of components or tools. To improve the coating properties, heat treatment such as preheat is applied. The selection of coating and substrate materials is a key factor in improving the quality of the coating morphology after the heat treatment. This paper presents the experimental results regarding the effect of preheat temperatures, i.e. 200ºC, 300ºC and 400ºC, on porosity and wear resistance of tungsten carbide (WC) coating sprayed by flame thermal coating. The powders and coatings morphology were analyzed by a Field Emission Scanning Electron Microscope equipped with Energy Dispersive Spectrometry (FE-SEM/EDS), whereas the phase identification was performed by X-Ray diffraction technique (XRD). In order to evaluate the quality of the flame spray obtained coatings, the porosity, micro-hardness and wear rate of the specimens was determined. The results showed that WC coating gives a higher surface hardness from 1391 HVN up to 1541 HVN compared to that of the non-coating. Moreover, the wear rate increased from 0.072 mm 3 /min. to 0.082 mm 3 /min. when preheat temperature was increased. Preheat on H13 steel substrate can reduce the percentage of porosity level from 10.24 % to 3.94% on the thermal spray coatings.
Corrosion and wear behaviour of HVOF spraying WC-12% Ni coating on gray cast-iron
Indian Journal of Engineering & Materials Sciences, 2021
The coatings produced with high-velocity oxygen fuel spraying technology can greatly improve wear and corrosion resistance. In this study, WC-12% Ni coating was applied on the lamellar graphite cast iron substrate. Morphologies and structures of uncoated samples and sprayed coatings were analyzed with light microscopy, scanning electron microscope, energy dispersive spectrometry and X-ray diffraction. Although their micro-hardness, porosity, abrasion and corrosion properties were studied, wear experiments were performed at normal atmospheric conditions (under room temperature and 30% humidity) in the reciprocating wear testing machine. The corrosion resistance of the coatings was measured using potentio-dynamic polarization. The results revealed that the microstructure was porous, had micro-cracks, and contained some inhomogeneous structures such as carbide. Energy dispersive spectrometry analysis revealed that the presence of phases indicated the success in coating process. It was found that the WC-12% Ni coating exhibited lower potential and lower corrosion current density compared to those of the uncoated sample.