Study of Tribological Properties of Detonation Nanostructured WC-Co-Based Coatings (original) (raw)
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A review on nanostructured WC–Co coatings
Surface and Coatings Technology, 2002
Unique mechanical properties of nanostructured materials motivate a worldwide interest to synthesize nanostructured coatings. Nanostructured WC-Co coatings have been extensively investigated because of the importance of WC-Co coatings in industrial applications, usually with respect to wear resistance requirements. The present paper has reviewed the studies in this field, including synthesis of nanostructured WC-Co powder, concern on decomposition of nanostructured WC particles, influence of spraying parameters on microstructure and mechanical properties of nanostructured coatings. Significant achievements in this field are: (1) It is possible to produce nanostructured WC-Co powders without non-WCyCo phases in quantities although a high percentage of non-WCyCo phases is frequently reported in conventional WC-Co powder; (2) By controlling agglomerate size of feedstock powder, fuel chemistry and fuel-oxygen ratio, the decomposition of WC particles can be reasonably eliminated so as to synthesize near nanostructured WC-Co coating with a low amount of non-WCyCo phases; and (3) Increased hardness, toughness and wear-resistance can be obtained in near nanostructured WC-Co coatings that are properly synthesized.
Transactions of FAMENA, 2020
Samples of nanostructured hardmetals were sintered as a substrate material by applying two different powder metallurgy processes. The starting powders had an average grain size from 95 nm to 150 nm. The plasma-assisted chemical vapour deposition technique was used for the deposition of coatings and two coating systems, i.e. the 2 µm titanium nitride and 3.8 µm titanium carbon nitride were produced. Scratch tests were conducted with an increasing load ranging from 5 to 200 N. Critical normal loads of coating delamination during the scratch tests were registered. The sliding wear resistance was investigated with a ball-on-disc test. The ball-on-disc test showed that the porosity of the sintered product had the highest impact on the wear volume loss. Nanostructured hardmetals showed a great potential for application of plasma-assisted chemical Vapour deposition.
Surface & Coatings Technology, 2007
Twelve commercially available WC-Co powders with different average WC grain sizes (0.2, 2, and 6 μm) and cobalt contents (8, 12, 17 and 25 wt.%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying process. Hardness, Young's modulus, and fracture toughness of the coatings were measured. While the hardness and Young's modulus decreased with increasing cobalt content from 1600 to 1100 Hv and from 400 to 300 GPa respectively, the fracture toughness remained in the range from 4 to 6 MPam 1/2 . The coatings with 2 μm carbide showed lower hardness than those deposited from 0.2 and 6 μm carbide. These measured mechanical properties were discussed with the help of microstructures of the coatings investigated by scanning electron microscopy, X-ray diffraction and chemical analysis. Finally, the hardness of the binder phase in these coatings was estimated to range from 1000 to 1300 Hv by applying the mixture rule for composites to the experimental data, demonstrating that such hardening of the binder phase is a key factor affecting the mechanical properties of the coatings.
Metallurgical and Materials Transactions A, 2000
A nanostructured WC-12 pct Co coating was synthesized using mechanical milling and high velocity oxygen fuel (HVOF) thermal spraying. The variation of powder characteristics with milling time and the performance of the coatings were investigated using scanning electron microscope (SEM), X-ray, transmission electron microscope (TEM), thermogravimetric analyzer (TGA), and microhardness measurements. There is no evidence that indicates the presence of an amorphous phase in the sintered WC-12 pct Co powder, and the binder phase in this powder is still crystalline Co. Mechanical milling of up to 20 hours did not lead to the formation of an amorphous phase in the sintered WC-12 pct Co powder. During the initial stages of the milling, the brittle carbide particles were first fractured into fragments and then embedded into the binder phase. This process gradually formed polycrystal nanocomposite powders of the Co binder phase and W carbide particles. The conventional cold welding and fracturing processes primarily occurred among the Co binder powders and polycrystal composite powders. The nanostructured WC-12 pct Co coatings, synthesized in the present study, consist of an amorphous matrix and carbides with an average particle diameter of 35 nm. The coating possesses an average microhardness of 1135 HV and higher resistance to indentation fracture than that of its conventional counterpart.
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.
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.
Tribological Characterization of WC-Co Plasma Sprayed Coatings
Journal of the American Ceramic Society, 2009
Atmospheric plasma spraying of WC coatings is typically characterized by increased decarburization, with a consequent reduction of their wear resistance. Indeed, high temperature and oxidizing atmosphere promote the appearance of brittle crystalline and amorphous phases. However, by using a high helium flow rate in a process gas mixture, plasma spraying may easily be optimized by increasing the velocity of sprayed particles and by reducing the degree of WC dissolution. To this purpose, a comparative study was performed at different spray conditions. Both WC-Co powder and coating phases were characterized by X-ray difraction. Their microstructure was investigated by scanning electron microscopy. Mechanical, dry sliding friction, and wear tests were also performed. The wear resistance was highly related to both microstructural and mechanical properties. The experimental data confirmed that high-quality cermet coatings could be manufactured by using optimized Ar-He mixtures. Their enhanced hardness, toughness, and wear resistance resulted in coatings comparable to those sprayed by high velocity oxygen-fuel.
Materials Science and Engineering: A, 2004
Single-layered coatings of WC-Co and multi-layered coatings of NiCrAl/WC-Co were manufactured by high-velocity oxy-fuel (HVOF) and detonation spraying (DS) techniques. The residual stress, mechanical properties, and wear resistance of these coatings were evaluated and the effects of coating structure and spraying method on coating properties were analyzed. Experimental results show that the coatings made by HVOF excel corresponding DS coatings with respect to mechanical and thermal shock properties. Both the spraying method and coating structure affect the residual stress markedly. Compared with the single-layered coatings, multi-layered ones exhibit better wear resistance under light-load conditions.
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.