Stony Brook, NY, United States
Stony Brook, NY, United States

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Cinca N.,University of Barcelona | Isalgue A.,Polytechnic University of Catalonia | Fernandez J.,University of Barcelona | Sampath S.,Center for Thermal Spray Research
Materials Science Forum | Year: 2013

Vacuum Plasma Spraying (VPS) 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. © (2013) Trans Tech Publications, Switzerland.


Dwivedi G.,Center for Thermal Spray Research | Dwivedi G.,State University of New York at Stony Brook | Viswanathan V.,Center for Thermal Spray Research | Sampath S.,Center for Thermal Spray Research
Advanced Materials and Processes | Year: 2013

Challenges with thermal barrier coatings (TBC) used in integrated gasification combined cycles (IGCC) for power generation become prominent because these turbines operate under higher moisture conditions than that in natural gas turbines. The composition of these impurities and deposited particles varies and shows significant distribution in quantity. Turbines are derated or operated at lower temperatures to extend service life in such varied environments, resulting in lower turbine efficiency. This requires development of advanced TBCs to ensure turbine sustainability at higher operating conditions. Ongoing research at the Center for Thermal Spray Research at Stony Brook University is addressing these challenges through a multilayer solution enabled via advanced processing. Air born particles ingested into the turbine can cause erosion and large exfoliation resulting in thinning of TBCs. The reduction in TBC thickness causes an increase in bond- coat temperature, which, in turn, accelerates bond coat oxidation leading to TBC failure.


Ghabchi A.,VTT Technical Research Center of Finland | Ghabchi A.,Center for Thermal Spray Research | Ghabchi A.,Boeing Company | Rombouts M.,Flemish Institute for Technological Research | And 2 more authors.
Tribology - Materials, Surfaces and Interfaces | Year: 2013

Laser cladded coatings have been used extensively to extend the service life of components exposed to severe abrasive wear. One of the main wear resistant materials used in laser cladding is ceramic-metallic composite. Despite extensive use of this class of material, there is very limited knowledge regarding mechanical degradation mechanisms, such as cracking and plastic deformation, under different wear conditions. In this investigation a mixture of nickel alloy and tungsten carbide powders were used to deposit the coating. Two types of tungsten carbide powders with spherical and angular carbides were employed. The microstructures of the coatings were analysed thoroughly by optical microscopy, electron probe microanalysis and wavelength dispersive spectrometry. Failure and cracking mechanisms of laser cladded coatings under normal and tangential loading were systematically investigated using scratch testing. In the nickel alloy matrix, fine mixed secondary carbides were formed due to partial dissolution and formation of the secondary tungsten carbide during laser cladding. These secondary carbides were rich in chromium, tungsten and nickel and had a blocky and/or bar-like shape. Failure mechanisms associated with scratch testing were dependent on the microstructure and carbide morphology, applied stress and location of carbide particles with regard to the scratch groove. Owing to the high binder mean free path between the carbide particles, plastic deformation of the binder was the dominant failure mechanism. Additionally, partial or whole fragmentation of carbides, carbide/ binder interface cracking and limited binder fracture were observed. © 2013 W. S. Maney & Son Ltd.


Ghabchi A.,VTT Technical Research Center of Finland | Ghabchi A.,Center for Thermal Spray Research | Varis T.,VTT Technical Research Center of Finland | Turunen E.,VTT Technical Research Center of Finland | And 3 more authors.
Journal of Thermal Spray Technology | Year: 2010

A modified ASTM G 65 rubber wheel test was employed in wet and dry conditions using 220 nm titania particles and 368 μm sand particles, respectively. Both tests were conducted on WC-CoCr coatings produced with two powders with different carbide grain sizes (conventional and sub-micron) to address the effect of carbide size and abrasive medium characteristics on the wear performance. The same spot before and after the wet abrasion wear testing was analyzed in detail using SEM to visualize wear mechanisms. It was shown that the wear mechanism depends on the relative size of the carbide and abrasive particles. Wear mechanisms in dry sand abrasion were studied by analyzing the single scratches formed by individual abrasive particles. Interaction of surface open porosity with moving abrasive particles causes formation of single scratches. By tailoring the carbide size, the wear performance can be improved. © 2009 ASM International.


Ramakrishnan G.,SUNY Stony Brook | Dwivedi G.,Center for Thermal Spray Research | Sampath S.,Center for Thermal Spray Research | Orlov A.,SUNY Stony Brook
Journal of Membrane Science | Year: 2015

We prepared a number of Alumina (Al2O3) microfiltration membranes fabricated using a well-established large throughput thermal spray (TS) technique. In order to study the filtration characteristics and performance of the thermal spray membranes, a variety of microstructures were fabricated by the varying spray process, deposition parameters and the source materials. We characterized the prepared membranes using XRD (X-ray Diffraction), EDX (Energy dispersive X-ray Spectroscopy), SEM (Scanning Electron Microscopy), pore size analysis and dead end filtration tests. Permeability and rejection rate of the sprayed membranes were comparable to some of the commercially available inorganic membranes with the advantage of being highly scalable and potentially orders of magnitude cheaper than the commercially available ceramic membranes. © 2015 Elsevier B.V.


Zois D.,Center for Thermal Spray Research | Wentz T.,Center for Thermal Spray Research | Dey R.,Center for Thermal Spray Research | Sampath S.,Center for Thermal Spray Research | Weyant C.M.,Center for Thermal Spray Research
Journal of Thermal Spray Technology | Year: 2013

The use of factorial design in process parameter development allowed determination of the contribution of key process variables, such as flame energy (combustion pressure and O2/F), spray distance, and feed rate, on in-flight particle properties. The significance of each parameter was used to construct a simple model which enabled the description of particles' temperature and velocity. Particles with velocities ranging by as much as 300 m/s and temperatures ranging up to 350°C were used to produce an array of coatings on an in situ curvature sensor enabling the determination of the evolving - during spraying - and residual stress at the end of the process, correspondingly. These diverse particle states combined with the flame impingement on the substrate, resulted in coatings of similar thickness, but significantly different stress states. Real time evolving stresses - during deposition - and coating properties such as, microhardness, modulus, and corrosion behavior were correlated to particle in-flight properties and, via the use of the introduced model, to spray parameters. © 2013 ASM International.

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