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Journal ArticleDOI

Influence of process variables on the quality of detonation gun sprayed alumina coatings

10 Jan 2000-Surface & Coatings Technology (Elsevier)-Vol. 123, Iss: 1, pp 44-54
TL;DR: In this paper, a statistical design of experimental study of the D-gun spraying of Al 2 O 3 powder is presented, where the attributes of the coatings are correlated with the changes in operating parameters and their relative importance and contribution ratios to overall variance are calculated.
Abstract: Detonation gun (D-gun) spraying is one of the most promising thermal spray variants for depositing high quality wear resistant coatings. Of all the ceramic materials that can be D-gun sprayed, alumina (Al 2 O 3 ) is the most widely established and these coatings have already gained industrial acceptance for diverse applications. The present study deals with a statistical design of experimental study of the D-gun spraying of Al 2 O 3 powder. Coating experiments were conducted, using a Taguchi-full factorial (L 16 ) design parametric study, to optimize the D-gun spray process parameters. Four selected important spraying parameters were considered in their upper and lower levels of the predefined range according to the test matrix, in order to display the range of processing conditions and their effect on the coating quality. Optical microscopy, scanning electron microscopy, X-ray diffraction, image analysis and hardness testing was used for characterization. Coating qualities are discussed with respect to surface roughness, hardness, porosity and microstructure. The attributes of the coatings are correlated with the changes in operating parameters and their relative importance and contribution ratios to overall variance are calculated.
Citations
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Journal ArticleDOI
TL;DR: In this article, a 33 factorial design experiment was used to establish the effects of the variables on the coatings quality in relation to the corrosion behavior of an HVOF Ni-based self-fluxing alloys coatings in a 3.5% NaCl solution.
Abstract: Experimental design is an effective method for conducting a reduced number of experiments in order to obtain the optimum spraying conditions and enhance the thermally sprayed coatings properties. In the present study, a 33 factorial design experiment was used to establish the effects of the variables on the coatings quality in relation to the corrosion behavior of an HVOF Ni based self-fluxing alloys coatings in a 3.5% NaCl solution. Response surface methodology was employed to describe empirical relationships among variables as the spraying distance, the fuel/oxygen ratio and the powder feed rate. The maps obtained allowed the selection of the optimum operating conditions to achieve the desired specifications of the HVOF coatings for their best corrosion resistance in the chosen environment. The analysis of the results indicates that the spraying distance, the fuel/oxygen ratio and the powder feed rate have a significant effect on the porosity and corrosion resistance of these coatings.

76 citations

Journal ArticleDOI
TL;DR: In this paper, the cyclic oxidation behavior of detonation-gun-sprayed Cr3C2-NiCr coating on three different superalloys namely Superni 75, Superni 718 and Superfer 800H at 900°C for 100 cycles in air under cyclic heating and cooling conditions has been investigated, using thermogravimetric technique.
Abstract: The cyclic oxidation behavior of detonation-gun-sprayed Cr3C2–NiCr coating on three different superalloys namely Superni 75, Superni 718 and Superfer 800H at 900 °C for 100 cycles in air under cyclic heating and cooling conditions has been investigated in the present work. The kinetics of oxidation of coated and bare superalloys was analysed, using thermogravimetric technique. It was observed that all the coated and bare superalloys obey a parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of coated and bare superalloys. The results on the Cr3C2–NiCr-coated superalloys showed better oxidation resistance due to the formation of a compact and adhesive thin Cr2O3 scale on the surface of the coating during oxidation. The scale remained intact and adherent to the partially oxidised coating during cyclic oxidation due to its good compatibility and similar thermal expansion coefficient between Cr3C2–NiCr coating and the superalloy substrates. In all the coated superalloys, the chromium, iron, silicon and titanium were oxidised in the inter-splat region, whereas splats which consisted mainly of Ni remained unoxidised. The parabolic rate constants of Cr3C2–NiCr-coated alloys were lower than that of the bare superalloys as observed in the present work.

71 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarized the results of previous research done by various authors on different coatings done by detonation gun spraying technique, which is one of the most effective method to protect the material from wear, high temperature corrosion, stresses and erosion, thus increasing the life of material in use.
Abstract: Materials are precious resources. Different methods are employed to protect the material from degradation. Thermal spraying is one of the most effective method to protect the material from wear, high temperature corrosion, stresses and erosion, thus increasing the life of material in use. Detonation gun spraying is one of the thermal spraying techniques known for providing hard, wear resistant and dense microstructured coatings. This paper summarizes the results of previous research done by various authors on different coatings done by detonation gun spraying technique.

69 citations


Cites background from "Influence of process variables on t..."

  • ...[41] studied the influence of process variables on the quality of detonation gun sprayed alumina coatings....

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Journal ArticleDOI
Hao Du1, Wei-Gang Hua1, J.D. Liu1, Jun Gong1, Chao Sun1, Lishi Wen1 
TL;DR: In this article, experimental results are presented in terms of the structure, including surface roughness, XRD patterns and porosity, as well as adhesion strength, hardness, and fracture toughness of D-gun-sprayed WC-Co coatings as a function of spraying distance from nozzle exit to substrate and ratio of O 2 :C 2 H 2.
Abstract: Detonation gun (D-gun) spraying is one of the most promising thermal spray technology for high quality wear resistant coatings. Of all the ceramic materials that can be D-gun-sprayed, WC is the most widely established and these coatings have already gained industrial acceptance for diverse applications. The use of D-gun-sprayed WC–Co coating as protection against aggressive environment requires a precise knowledge of the influence of spraying process parameters on the coating characteristics and properties (porosity, adherence, roughness, hardness, etc.). In this article, experimental results are presented in terms of the structure, including surface roughness, XRD patterns and porosity, as well as adhesion strength, hardness, and fracture toughness of D-gun-sprayed WC–Co coatings as a function of spraying distance from nozzle exit to substrate and ratio of O 2 :C 2 H 2 . It is found that both the spraying parameters influence structure and properties of D-gun-sprayed WC–Co coatings. The decarburization of WC–Co powders during the spraying is little even when the highest oxygen–fuel ratio was employed. When the higher oxygen–fuel ratio was employed, hardness and adhesion increase, while, porosity and fracture toughness decrease, which can be attributed to the higher temperature and velocity feed powders obtained from the detonation wave. On the other hand, denser microstructure, higher adhesion strength and higher hardness appear when the coating was deposited at spraying distance of 110–20 mm, while fracture toughness is a little lower, which may come from the best compromise of decreasing velocity and lagging of heat transfer process for the particles to obtain a good molten state.

56 citations

Journal ArticleDOI
TL;DR: In this paper, a series of WC-Co/MoS2-Ni coatings by detonation gun (D-gun) spray, with a proper spray condition in view of both powders were characterized.
Abstract: At present, more and more investigations are being carried out to improve properties of thermal spray coatings, in particular for the dry contact situation. We have deposited a series of WC-Co/MoS2-Ni coatings by detonation gun (D-gun) spray, using a commercial WC-Co powder and a MOS2-Ni powder, with a proper spray condition in view of both powders. The structure, mechanical and sliding wear properties of these coatings were characterized. The results by SEM, EMPA, XRD and XRF indicate that the MoS, composition was kept and distributed homogeneously in the WC-Co/MoS2-Ni coatings and its content is a little higher than the feed powder. The results also indicate that hardness, fracture toughness and adhesion of the WC-Co/MoS-Ni coatings decrease with the increasing MoS2 content in the coating, while porosity and roughness the same, comparing with a pure WC-Co coating deposited under the same condition. It is found that this WC-Co/MoS2-Ni coating possesses self-lubricating property. Furthermore, the MoS2 composition in the WC-Co/MoS2-Ni coatings shows a contribution in lowering wear rate under dry sliding conditions when its content is lower than 4.9 wt.%. However, the wear rate is higher when the content is 7.2 wt.%, which indicate that the MoS, content should be proper for an improvement of the D-gun sprayed WC-Co/MoS2-Ni coating on wear resistance. (c) 2006 Elsevier B.V. All rights reserved.

36 citations

References
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Book
01 Jan 1978

5,151 citations

Journal ArticleDOI
TL;DR: In this paper, a model for the fomation of thermally sprayed alumina coatings is proposed and the spreading and crystallization of liquid droplets on impact with the substrate are analyzed and the thermal history of individual particles related to the kinetics of nucleation of γ-Al2O3 to other forms.
Abstract: A model for the fomation of thermally sprayed alumina coatings is proposed. The spreading and crystallization of liquid droplets on impact with the substrate are analysed and the thermal history of individual particles related to the kinetics of nucleation of γ-Al2O3 to other forms. The results suggest that under the usual spraying conditions undercooling of the liquid droplets is such that γ-Al2O3 nucleates in preference to α-Al2O3 and the cooling rate after solidification is sufficiently rapid to prevent transformation to δ-Al2O3 or α-Al2O3. Transformation of initially formed γ-Al2O3 to α-Al2O3 appears to be possible only if the lamellae formed on impact are thicker than about 10 μm if the substrate is heated to about 1000° C, or if the thickness is greater than about 20 μm on an unheated substrate. The α-Al2O3 generally observed in thermally sprayed coatings is the result of crystallization from pre-existing nuclei arising from incomplete melting of the feed material.

287 citations

Journal ArticleDOI
TL;DR: In this paper, the formation of metastable phases in plasma- and flame-prepared alumina particles is examined in terms of the classical nucleation theory, rate of transformation of the metastable to stable forms, and the thermal history of the particles during solidification.
Abstract: The formation of metastable phases in plasma- and flame-prepared alumina particles is examined in terms of the classical nucleation theory, rate of transformation of metastable to stable forms, and the thermal history of the particles during solidification. It is suggested that homogeneous nucleation of the solidification of liquid droplets at considerable undercooling results in the formation ofγ-Al2O3 rather thanα-Al2O3 because of its lower critical free energy for nucleation. The phase finally observed depends upon the thermal history of the particles during evolution of the heat of fusion and upon the kinetics of the transformation of the nucleating phase to the stable phase. This means that the cooling rate of the particles is relatively unimportant and under the conditions existing in flames and plasmas, metastable alumina will be formed on solidification. The metastable form will be retained on cooling particles less than approximately 10 μm diameter, but particles larger than this may transform toα-Al2O3 during the solidification exotherm

278 citations

Book
28 Nov 1996
TL;DR: This chapter discusses Factorial Experiments, Applications to Industrial Processes, and other DOE Applications to industrial processes.
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138 citations

BookDOI
01 Jun 1993
TL;DR: Fauchais et al. as mentioned in this paper proposed an analytical approach to plasma spraying, Kettunen and Suryanarayanan analyzed the properties of sprayed samarium-cobalt materials.
Abstract: Diagnostics of thermal spraying plasma jets, P. Fauchais et al modelization of plasma-particle transfer, P. Fauchais et al optimizing the APS-process parameters for new Ni hardfacing alloys, Lugsheider et al high velocity oxy-fuel spraying, A.R. Nicoll et al structure of sprayed ceramic coatings, Ohmori properties and applications of plasma sprayed ceramic coatings, Ding experimental design and optimization of plasma sprayed coatings, Kettunen an analytical approach to plasma spraying, S.V. Joshi et al residual stress in the coatings, Kingswell plasma spray applications for electronic materials, R. Suryanarayanan structure and properties of sprayed samarium-cobalt materials, K. Kumar preparation of YBaCuO coating, J. Danroc et al plasma sprayed coatings of YBaCuO, G. Swaminathan et al.

83 citations