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A. Cavasin
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Proceedings Papers
ITSC1998, Thermal Spray 1998: Proceedings from the International Thermal Spray Conference, 957-961, May 25–29, 1998,
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The development of nuclear fusion reactors is presently considered to be the only possible answer to the world's increasing demand for energy, while respecting the environment. Nuclear fusion devices may be broadly divided into two main groups with distinctively different characteristics: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) reactors. Although the two nuclear fusion technologies show similarities in energy levels (as high as 3 J/cm2) and type of environment (high temperature plasmas) to be contained, the materials of choice for the protective shields (first wall in the ICF and deflectors in the MCF) differ significantly. In ICF reactors, multiple laser beams are used to ignite the fuel in single pulses. This process exposes the first wall to microshrapnel, unconverted light, x-rays, and neutrons. B4C is a low Z material that offers high depth x-ray absorption to minimize surface heating, is not activated by neutrons (will not become radioactive), and offers high hardness and vapour temperature. The long term operation envisioned within MCF reactors, where a continuous nuclear fusion of the fuel is sustained within the confinement of a magnetic field, favours the use of high Z materials, such as W, to protect the plasma exposed deflectors. The reason is a lower erosion rate and a shorter ionization distance in the plasma, which favours the redeposition of the sputtered atoms, both resulting in a lower contamination of the plasma. The production of the first wall and the deflector shields using solid B4C and W materials respectively, is obviously unthinkable. However, ProTeC has developed high density coatings for both ICF and MCF nuclear fusion reactors. W coatings with less than 2% porosity have been produced for both, the Tokamac MCF reactor and its Toroid Fueler. The toroid fueler is a plasma generating device designed to accelerate particles and inject them into the centre of the operating fusion reactor in order to refuel. For the application in an ICF reactor, B4C coatings exhibiting porosity levels below 3% with a hardness above 2500 HV have been deposited directly onto Al substrate. Properties such as outgassing, resistance to erosion and shrapnel, and the influence of x-rays have been studied and showed exceptional results.
Proceedings Papers
ITSC1998, Thermal Spray 1998: Proceedings from the International Thermal Spray Conference, 1229-1232, May 25–29, 1998,
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Many of the recent improvements in gas turbine engines have been attributed to the introduction of thermal barrier coatings (TBC) for superalloy components. There exists, however, some limitations in current fabrication methods for closed hot-section components: less than ideal coating quality, the need for welding, and limited choice of superalloy material. This paper describes a vacuum plasma near-net-shape process that overcomes these limitations. The process is used to fabricate closed components from yttria-stabilized-zirconia with a CoNiCrAlY bond coat and IN-738LC outer layer. The results from the study show that it is possible to produce near-net-shape superalloy parts with good coating properties and the absence of welds. The mold was reusable after minor reconditioning and the coatings were uniform in thickness and microstructure with a smooth surface finish. The bond coat and structural superalloy layers were very dense with no signs of oxidation at the interface. After heat treatment, the mechanical properties of the IN-738LC compare favorably to cast materials.
Proceedings Papers
ITSC1998, Thermal Spray 1998: Proceedings from the International Thermal Spray Conference, 1645-1650, May 25–29, 1998,
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Zirconia-based thermal barrier coatings (TBCs), produced using Vacuum Plasma Spray (VPS) technology, were recently subjected to burner rig testing. The VPS TBC performance was compared to TBCs deposited using conventional Atmospheric Plasma Sprayed (APS) and Electron Beam Physical Vapor Deposition (EB-PVD) techniques. All of the coatings consisted of an MCrAlY bond coat and a partially stabilized ZrO 2 -8%Y 2 O 3 (PSZ) top coat. The TBC coated pins (6.35 mm in diameter) were tested using gas temperatures ranging from 110CC to 1500°C. The pins were tested to failure under severe conditions (1500°C gas temperature, with no internal cooling). The initial testing indicated that under typical operating gas temperatures (1400°C), the VPS TBC performance was comparable, if not superior, to conventional TBCs. Following the encouraging results, thick composite TBCs, produced in a single-step operation, were investigated. Preliminary work on ZrO 2 -8% Y 2 O 3 /Ca 2 SiO 4 composite TBCs with interlayer grading included thermal shock testing and temperature drop measurements across the TBC. The composite TBC thicknesses ranged from 850µm to 1.8 mm. Initial results indicate that thick adherent composite TBCs, with high resistance to severe thermal shock, can be produced in a single step using the VPS process.