Effect of bond coat and preheat on the microstructure, hardness, and porosity of flame sprayed tungsten carbide coatings (original) (raw)
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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.
Microstructure and properties of flame sprayed tungsten carbide coatings
International Journal of Refractory Metals and Hard Materials, 2002
This article reports on feasibility experiments carried out with oxy-acetylene spray system with various oxygen to fuel ratios using two different tungsten carbide powders and powder feeding methods, to evaluate the newly developed fused WC, synthesised by transferred arc thermal plasma method. Transferred arc thermal plasma method is more economical and less energy intensive than the conventional arc method and results in a fused carbide powder with higher hardness. The microstructure and phase composition of powders and coatings were analysed by optical and scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Carbon content of the powders and coatings were determined to study the decarburisation of the material during spraying process. Coatings were also characterised by their hardness and abrasive wear. The effects of metallurgical transformation and phase content are related to wear performance. The results demonstrate that the powders exhibit various degree of phase transformation during the spray process depending on the type of powder, powder feeding and spray parameters. The carbon loss during the spray process in excess of 45% resulted in reduced hardness and wear resistance of the coatings. Coatings with high amount of WC and W 2 C along with FeW 3 C showed higher wear resistance. Thus, coatings of high wear resistance can be produced using fused tungsten carbide powder with WC and W 2 C phases, which can be economically synthesised by thermal plasma transferred arc method.
Journal of Surface Engineered Materials and Advanced Technology, 2013
The microstructure, phase consistence and microhardness of thermal sprayed coatings were investigated. The tungsten and chromium carbide coatings and also composite NiCrSiB coating were analyzed. The microstructure of coatings were observed by using optical microscopy (MO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Almost equiaxial carbide particles settled inside the surrounded material of coating were found. The cracks propagating thorough the particles and along boundaries between the particles and surrounded material were observed. This phenomenon was connected with the porosity of coatings. The decarburization process was detected in coatings by phase composition investigation using X-ray method. The decarburization process was the reason due to which beside initial Cr 3 C 2 the Cr 7 C 3 and Cr 23 C 6 particles were found. In the tungsten coatings beside the initial WC carbides the W 2 C ones were found.
Studies on remelting of tungsten carbide and rare earth modified nickel base alloy composite coating
Surface Engineering, 2012
The Ni base alloy (EWAC 1004EN) was used to develop coatings on the mild steel substrate by flame spraying process. The Ni base alloy powder was modified by adding tungsten carbide (10 and 20 wt-%) and CeO 2 to study their effects on the microstructure, microhardness and abrasive wear behaviour of unmodified and modified coatings. All the coatings were subjected to remelting using tungsten inert gas arc welding. The abrasive wear behaviour of all the coatings in different conditions was studied using different normal loads (5, 10, 15 and 20 N) against 120 and 600 grit size abrasive medium. Scanning electron microscopy analysis of the worn out surfaces was carried out to understand the wear mechanisms. It was observed that the remelting of the coatings increased the hardness of WC and CeO 2 modified flame sprayed coatings by ,35%, while the abrasive wear resistance increased by 1?5-to threefold.
Influence of Thermal Spraying Method on the Properties of Tungsten Carbide Coatings
The main tendencies in the development of tungsten carbide coating applications are presented. General properties of WC based coatings and their dependence on different factors are discussed. For comparative examination of the abrasive wear resistance of thermal spray coatings detailed Taber Abraser wear tests are carried out. Besides HVOF sprayed cermet and APS Cr 2 O 3 also electroplated hard chromium coatings are studied. The best results have been obtained for HVOF sprayed cermet coatings. For this kind of wear conditions the difference in wear behaviour depending on carbide size in WC-CoCr coatings is insignificant compared to the difference depending on the matrix composition.
Surface & Coatings Technology, 2007
In present paper the influence of the tungsten carbide (WC) particle addition on the microstructure, microhardness and abrasive wear behaviour of flame sprayed Co-Cr-W-Ni-C (EWAC 1006) coatings deposited on low carbon steel substrate has been reported. Coatings were deposited by oxy-acetylene flame spraying process. Wear behaviour of coatings was evaluated using pin on flat wear system against SiC abrasive medium. It was observed that the addition of WC particle in a commercial Co-Cr-W-Ni-C powder coating increases microhardness and wear resistance. Wear behaviour of these coatings is governed by the material parameters such as microstructure, hardness of coating and test parameters (abrasive grit size and normal load). Addition of WC in a commercial powder coating increased wear resistance about 4-9 folds. WC modified powder coatings showed better wear resistance at high load. Heat treatment of the unmodified powder coatings improved abrasive wear resistance while that of modified powder coating deteriorated the wear resistance. SEM study showed that wear of coatings largely takes place by microgroove, crater formation and scoring. Electron probe micro analysis (E.P.M.A.) of unmodified and WC modified powder coating was carried out for composition and phase analysis.
Surface & Coatings Technology, 2009
Micron-sized WC-Co powder (powder) was coated onto an 420J2 steel substrate and the bond coats (BCs) of Ni, NiCr, and Ni/NiCr using high-velocity oxy-fuel thermal spraying to study the surface properties, friction behavior, and tensile bond strength of the WC-Co coating (WC-Co) on the 420J2 substrate (sub) and the BCs of Ni, NiCr, and Ni/NiCr. During the spray coating, a small portion of WC decomposed to the less-hard W 2 C, W, and free carbon above its decomposition temperature of 1250°C, decreasing hardness and increasing porosity. The surface hardness of 1120 ± 100 Hv (10,980 ± 980 MPa) depended strongly on the spray parameters. It was three to four times harder than metals and alloys, but less than one-half the hardness of binder-less pure WC (2400 Hv). Free carbon reacted with the sprayed oxygen gas and formed carbon oxide gases, resulting in a coating of 4.3 ± 1.0% porosity. The friction coefficient of the coating increased about 17% with increasing surface temperature: 0.65 ± 0.03 at 25°C to 0.76 ± 0.06 at 500°C because of the increased local cold-welding of the asperities at the higher temperature of 500°C. Sub/WC-Co, sub/Ni/WC-Co, sub/NiCr/WC-Co, and sub/Ni/ NiCr/WC-Co had tensile bond strengths of 9600 ± 300 psi (66.2 ± 3.4 MPa), 6300 ± 200 psi, 6000 ± 200 psi, and 7500 ± 200 psi, respectively. The fracture locations of all coatings were at interfaces with the WC-Co coating, indicating that the adhesion of the WC/Co inside coating was higher than 9600 ± 500 psi and that the adhesion of WC-Co on the substrate (9600 ± 500 psi) was much higher than the adhesion on the BCs.
The wear resistance of thermal spray the tungsten and chromium carbides coatings
Journal of achievements in materials and manufacturing engineering, 2011
Purpose: The objective of the work concerns of wear-resistance of different kinds of thermal spray coatings covering industrial fun blades. The coatings were sprayed onto the fun blades by Plasma Spraying and High Velocity Oxygen Fuel Spraying (HVOF) methods. The Cr3C2, WC and also its compositions were sprayed into the fun blades. The coatings were tested in industry conditions and the effect of influence of centrifugation industry emissions on the stage of the wearing after the exploitation was compared for deposited coatings. Design/methodology/approach: The investigations of coating microstructures by optical microscopy (MO) and transmission electron microscopy (TEM) were performed. The examination of fun blades after the exploitation and the analysis of the obtained results was correlated with the performed microstructure observations and microhardness data of coatings. Findings: The microstructures of Cr and W carbides coatings were observed and analyzed. The microhardness of ...
Advances in Manufacturing Science and Technology, 2011
The aim of the study was to determine the influence of the laser treatment process on the properties of electro-spark coatings. The properties of the coatings after laser treatment were assessed based on following methods: microstructure analysis, adhesion tests, microgeometry measurement, microhardness tests and tribological studies.The tests were carried out on WC-Co coating (the anode) obtained by electro spark deposition over carbon steel C45 (the cathode) and molten with a laser beam. The coatings were deposited by means of the EIL-8A and they were laser treated with the Nd:YAG. The tests show that the laser-treated electro-spark deposited WC-Co coatings are characterized by lower microhardness and friction force, higher seizure resistance, roughness and adhesion. The laser treatment process causes the homogenization of the chemical composition, the structure refinement and the healing of microcracks and pores of the electro-spark deposited coatings. Laser treated electrospark ...
Wear, 2005
Thick composite coatings of carbides (e.g. WC) in a metal matrix are ideal for components subject to heavy abrasive wear. An emerging deposition technique for such wear resistant cemented carbide coatings is laser cladding. This technique has, contrary to surface welding and spraying methods, the potential to coat very locally and on highly complex components. Adhesion and damage resistance is also improved by laser cladding. In this paper the influence of carbide particle size and distribution on the wear resistance of laser clad coatings is discussed. A nickel based matrix reinforced with WC/W 2 C carbides is deposited by a CO 2 laser on low carbon steel substrates. Different coatings are made with three different particle sizes of the carbides and volume fractions ranging from 0 up to 50%. Three different wear modes are evaluated. First, ball-on-disc tests with an Al 2 O 3 ball have been performed. The ball cratering test with 4 m SiC abrasive is used to assess mild abrasive wear. Finally, the resistance against severe two body abrasion is tested in a pin-on-disc test. A clear dependency of the wear resistance on the carbide concentration is found, which is more pronounced for the coatings with the finest WC/W 2 C carbides. The magnitude of the decrease in wear however is highly dependent on the wear mode. In two body abrasion and in the sliding wear, a small amount of carbides is sufficient to improve the wear resistance drastically. Other coating characteristics such as microstructure, hardness and internal stress are assessed.