Papers by Keyword: Splat

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Authors: W.T. Hsiao, W.H. Liao, M.S. Leu, Cherng Yuh Su
Abstract: The image of thermal spray splats is difficult to collect due to its high velocity of droplets. Especial in High Velocity Oxy-Fuel (HVOF) process, the process present higher velocity of flame jet correlated to other thermal spray process. The system presents at this article describes a useful splats catching method to obtaining splats during thermal spray deposited. Capabilities and advantages of using this instrument are declared at this theme. The final result presented the instrument caught the single spot of HVOF sprayed splats at sub-micro second. Splats of spot were dispersed well on the glass substrate at the obtaining system, and presented various information of droplets impact at different location on the substrate.
Authors: Man Tuiprae, Sittichai Wirojanupatump, Sukanda Jiansirisomboon
Abstract: Characteristics of in flight particle and splat fabricated by arc spraying of three different types of cored-wire including WC-Cr-Ni, WC-Cr-Fe and W-Cr-Fe nano-composite were revealed. In-flight particles and splats were deeply characterized in order to correlate their characteristics that forming coating and affecting coating structure and properties. Starting cored-wires were also characterized prior to being sprayed. Particle size, morphology microstructure, chemical composition and phase identification were investigated through various techniques. The results showed that the size of the in-flight particle did not depend mainly on the size of filler particles as expected, but was instead strongly related to the whole content of metallic phase composed the cored-wire, as the more metal composition the larger size of the in-flight obtained. Splat shapes and characteristics were also found to depend on the metal content; a flower shape splat with a high degree of splashing was predominant for cored-wire having more metal composition. The W-Cr-Fe nano-composite cored wire had the highest content of metallic binder phase, which resulted in the largest in-flight particles produced, and well melted of the metallic phase led to the highest degree of splashing observed.
Authors: Pisit Apichayakul, Sittichai Wirojanupatump, Sukanda Jiansirisomboon
Abstract: Correlations between in-flight particle, splat and coating microstructure of thermally sprayed Ni20Cr were investigated. Flame spray and arc spray systems were employed for spraying Ni20Cr powder and Ni20Cr wire, respectively. The results showed that the arc spray process produced a broader size distribution for both in-flight particles and splats compared to flame process. Flower-like splat morphology was obtained from the arc spray whereas a pancake-like splat was obtained by flame spray. Ni20Cr coating sprayed by arc process had a denser microstructure, lower porosity and better adhesion at the interface. This could be due to the higher temperature and velocity from the arc spray process enhancing the melting and adhering for coating formation.
Authors: Noppakun Sanpo, Jirasak Tharajak
Abstract: Cobalt ferrite sol-gel solution was deposited onto mild steel substrates to form single splats using a solution precursor plasma spray (SPPS) process. It was revealed that the thermal oxidation of cobalt and iron salts occurred mainly into six different formations of deposited splats. These formulations were cobalt monoxide (CoO), maghemite (γ-Fe2O3), cobalt oxide (Co3O4), cobalt oxyhydroxide (CoOOH), goethite (α-FeOOH), hematite (α-Fe2O3), magnetite (Fe3O4), and cobalt ferrite (CoFe2O4). The surface topographies of the splats exhibited burned, unmolten, partially molten, and completely molten splats. The feed rates of SPPS process played the important role on several properties of the splat such as splat morphologies and percentage of the obtained composite splat phases.
Authors: Nuria Cinca, Antonio Isalgué, Javier Fernández, S. Sampath
Abstract: Vacuum Plasma Spraying has been used to produce coatings onto steel substrates. This work deals with the study of splat morphology of the NiTi alloy sprayed by VPS onto different substrates (aluminium, copper, stainless steel, glass and alumina). All the previous characteristics are discussed in terms of wettability and thermal conductivities regarding the rapid cooling involved in the process. Although identical conditions were used during thermal spraying, a wide variety of splat formations were observed; commonly, slushy or splash/disc splats are formed depending on whether the particles have partially or fully melted. The thermal effusivity of the substrate material, which is a measure of its ability to exchange thermal energy with its surroundings, seems to play an important role promoting more or less spreading. The higher the thermal effusivity is, the more rapidly the splats are cooled, thus starting the solidification before they come to rest and, changing their morphology.
Authors: L. Li, A. Vaidya, T. Streibl, S. Sampath, A. Gouldstone, Vladimir Luzin, Henry Prask
Abstract: Thermal spray is a well-established, versatile method of producing protective and functional coatings. As with most thin- or thick-film structures, residual stresses developed during processing play an important role in determining the performance and life of sprayed coatings. Diffraction methods (X-ray or neutron) and in situ curvature measurement have been widely used to measure stresses nondestructively, yet results in coating stress measurements seen in the literatures are sometimes ambiguous or conflicting. This is due not only to the experimental error associated with the measurement and simplifying assumptions, but also the complexity and heterogeneity of the coating structure. During deposition, molten, semi-molten or solid particles successively impinge onto a substrate surface, thus forming a layered structure comprised of ‘splats,’ separated by interfaces, cracks and pores. In this study, X-ray micro-diffraction with a 2-D detector has been used to determine the stress magnitude of both splats and coatings on substrates. Neutron diffraction stress measurements have been made through the entire coating thickness. The process of depositing and cooling has been monitored by in situ curvature measurement. Micro- and macro stresses have been examined. The relation between process and splat and coating residual stresses has been evaluated and interpreted by recourse to microstructural and morphological observations under SEM. This study bridges the behaviors of microscopic single splats and macroscopic coatings, hence helps to fundamentally understand the stress generation during thermal spray process.
Authors: Zhanna G. Kovalevskaya, Evgeny A. Kovalevskiy, Margarita A. Khimich
Abstract: Influence of Fe-Si-Al-C alloy cooling rate on its phase composition, structure and microhardness is shown based on metallographic investigations, electron microscopy and x-ray diffraction analysis. It was determined that the structure will change from dendrite to grained, size of structure elements will decrease, quantity and size of secondary phases precipitations will decrease when cooling rate changes from 103 to 107 K/s. The metastable phases such as primary ferrite, austenite and complex carbides are formed in cooling rate range. The volume ratio of main phases changes in favor of primary ferrite with cooling rate increasing. Hardening of the material occurs more than twice. Hardening is due to the interaction of solid-solution hardening, grain boundary hardening and dispersive hardening by secondary phases particles. The maximum hardening is achieved during formation of the alloy in molten pool at electron-beam melting. The alloy in this case contains 80 vol. % of austenite with dendrite similar structure and precipitations of carbide and silicocarbide phases. It can be assumed than such structure will be formed from the alloy with investigated composition at additive manufacturing.
Authors: Liang Rong Zhu, Hao Ping Zeng, Wen Ji Xu, Hong You Li
Abstract: Mechanical strength and service life of the coatings manufactured by plasma spray forming are significantly reduced by residual stresses. A 2D finite element model constructed for temperature and residual stress simulation of a single stainless steel splat solidifying and cooling on the carbon steel substrate is presented in this paper. Simulated results show that the temperature of the splat rim is higher than that of the central part during the initial stage of solidification, and the temperature difference between the two parts reverse thereafter. The minimum residual stress locates at the rim of the top surface of the splat, and the maximum residual stress, which decreases when the substrate is preheated to a higher temperature, situates at the rim of the interface. Stresses appear as tensile stresses within the splat and compressive stresses within the substrate. The research can provide quantitative understanding of the temperature and residual stress states at the splat level.
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