V. Selvarajan

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

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.

Experimental design and performance analysis of alumina coatings deposited by a detonation spray process

The increasing demands for high-quality coatings has made it inevitable that the surface coating industry would put more effort into precisely controlling the coating process. Statistical design of experiments is an effective method for finding the optimum spray parameters to enhance thermal spray coating properties. In the present investigation, an attempt is made to produce high-quality alumina (Al2O3) coatings by optimizing the detonation spray process parameters following a (L16-24) factorial design approach. The process parameters that were varied include the fuel ratio, carrier gas flow rate, frequency of detonations and spray distance. The coating characteristics were quantified with respect to roughness, hardness and porosity. The performance of the coatings was quantitively evaluated using erosion, abrasion and sliding wear testing. Through statistical analysis of the experimental results, performed by the ANOVA method, the significance of each process parameter together with an optimal variable combination was obtained for the desired coating attributes. Confirmation experiments were conducted to verify the optimal spray parameter combination, which clearly showed the possibility of producing high-quality Al2O3 coatings.

Study of Plasma- and Detonation Gun-Sprayed Alumina Coatings Using Taguchi Experimental Design

Atmospheric plasma spraying (APS) is a most versatile thermal spray method for depositing alumina (Al2O3) coatings, and detonation gun (D-gun) spraying is an alternative thermal spray technology for depositing such coatings with extremely good wear characteristics. The present study is aimed at comparing the characteristics of Al2O3 coatings deposited using the above techniques by using Taguchi experimental design.Alumina coating experiments were conducted using a Taguchi fractional-factorial (L8) design parametric study to optimize the spray process parameters for both APS and D-gun. The Taguchi design evaluated the effect of four APS and D-gun spray variables on the measured coating attributes. The coating qualities evaluated were surface roughness, porosity, microhardness, abrasion, and sliding wear. The results show that the coating quality is directly related to the corresponding coating microstructure, which is significantly influenced by the spray parameters employed. Though it is evident that the D-gun-sprayed coatings consistently exhibit dense and uniform microstructure, higher hardness, and superior tribological performance, the attainment of suitable plasma-sprayed coatings can be improved by employing the Taguchi analysis.

Effect of dc glow discharge plasma treatment on PET/TiO2 thin film surfaces for enhancement of bioactivity

In this paper, the surfaces of PET/TiO(2) thin film were modified by DC glow discharge plasma as a function of discharge potentials for improving the bioactivity. The hydrophilicity of the plasma-treated PET/TiO(2) film was measured by contact angle measurement and the surface energy was estimated by using Fowkes method. The structural and chemical composition of the plasma-treated PET/TiO(2) was analysed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Immersion in a simulated body solution (SBF) solution was used to evaluate the bioactivity of the plasma-treated PET/TiO(2) samples in vitro. It was found that the plasma treatment modified the surfaces both in chemical composition and crystallinity which makes surface of the PET/TiO(2) to become more hydrophilic compared with untreated one. Analytical and microstructural investigations of SBF results, showed considerable higher rates of apatite formation on the plasma-treated PET/TiO(2) compared to the untreated films.

Effects of operating parameters on DC glow discharge plasma induced PET film surface

A DC glow discharge plasma surface modification techniques are used to modify surface properties of polymeric materials such as adhesivity, hydrophobicity, hydrophilicity and biocompatibility. The plasma interaction with the surface produces modifications of its chemical structure and morphology. The objective of this study is to examine the effect of operating parameters such as discharge potential, pressure and exposure time on surface properties of polyethylene terephthalate (PET) film. The changes in hydrophilic properties of PET films were studied in detail using contact angle and surface energy measurements. The surface morphology and chemical composition of plasma modified film surfaces were studied by atomic force microscopy (AFM) and X-ray photo electron spectroscopy (XPS). It was found that the efficiency of the surface treatment increases with increasing discharge potential, pressure and exposure time. The AFM and XPS analysis showed changes in surface topography and formation of polar groups on the plasma modified PET surfaces.

Synthesis of Mullite from Laboratory Waste Silica through Transferred Arc Plasma Processing Method

Transferred arc plasma (TAP) processing could be an economic and time saving processing method for waste treatment and recycling of chemical laboratory solid wastes. In this work, three different waste silica powders derived from chemical laboratories which are adsorbed with catalytic amount of ruthenium, palladium, and ferrocene derivatives are recycled in addition with alumina to form mullite (3Al2O3·2SiO2) by TAP processing technique and as well as in conventional method for comparison. The phase and microstructure formation of the processed samples were analyzed by X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) images, respectively. The results show that palladium adsorbed silica has significantly enhanced the formation and densification of mullite rather than ruthenium- and ferrocene-adsorbed silica in TAP processing. The SEM images show that the different kinds of microstructures developed in plasma arc processing mullite due to the direction of the plasma arc formation and solidification.

Synthesis of Mullite by Means of Transferred and Nontransferred Arc Plasma Melting

Arc plasma melting technique is a simple method for the synthesis of high melting point materials. In this article, mullite was synthesized by transferred arc plasma (TAP) and nontransferred arc plasma (non-TAP) melting processes, and the results were compared. The mixes of alumina and silica powders (3:2 mole ratios) were ball milled for four hours and then melted in an arc plasma torch, used in transferred and nontransferred mode, at 5 kW input power and two minutes of processing time. Argon gas was used as a plasma-forming gas. The crystalline phases and the microstructural features of the melted samples were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. A complete crystallization of mullite, with dense, thick whiskers-shaped crystals, was achieved in TAP processing of the alumina/silica system. On the other hand, the non-TAP process produced porous mullite along with a small amount of residual alumina phase. Differential thermal analysis (DTA) curves of the synthesized mullite samples allowed a deeper understanding of the mechanisms of mullite formation during the two different processes.

Effect of Spraying Parameters on Deposition Efficiency and Wear Behavior of Plasma Sprayed Alumina-Titania Composite Coatings

The effects of parameters, in the process of plasma-sprayed ceramic coating, upon the deposition efficiency of alumina-13 wt.% titania composite coatings are reported. The coatings were prepared by the atmospheric plasma spray process. The plasma torch input power, flow rates of primary, secondary and carrier gas, powder feed rate and spraying distance were considered as variables. The results show that the variations in all the selected spraying parameters strongly affect the deposition efficiency. The micro-hardness, as well as erosive and sliding wear rates of the coating are also affected by these parameters. Especially the input power strongly affects the phase and microstructure of the coatings.

Influence of spraying variables on structure and properties of plasma sprayed alumina coatings

Abstract An experimental statistical design study on the plasma spraying of alumina powder has been carried out. Coating experiments were conducted, using a Taguchi full factorial L 16 design parametric approach, to study the effect of four key plasma processing variables on the coating quality, namely, primary gas flow rate, arc current, powder feed rate, and spray distance. Optical microscopy, scanning electron microscopy, XRD, image analysis, and hardness testing were used for characterisation. The resulting as sprayed coating characteristics were quantified with respect to roughness, microhardness, porosity, and microstructure. Through statistical calculation (analysis of variance), the parameters that have significant influence on the structure and properties of the coatings were identified and their relative importance and contribution ratios to overall variance were studied. The Taguchi evaluation employed in the present investigation showed that an improvement in the coating properties could be achieved using an optimum combination of variables.

Application of Taguchi Method to the Optimization of Detonation Spraying Process

Abstract The present study deals with an application of the Taguchi method to the optimization of a detonation spray process for alumina coatings. Coating experiments were conducted using the TaguchUfractional factorial (L8) design parametric study to optimize spray process parameters. The Taguchi design evaluated the effects of four detonation spray process parameters: acetylene to oxygen ratio, carrier gas flow rate, frequency of detonations and spray distance. The coating qualities evaluated were surface roughness, porosity, microhardness, and abrasion mass loss. The influence of process parameters on the as-sprayed coating qualities is discussed. The results of the study indicate that the higher fuel ratio and lower spray distance will result in higher hardness, lower porosity and lower abrasion mass loss. The Taguchi analysis employed in the present investigation led to optimized process parameters for the most abrasive wear resistant alumina coatings.