Optimization of Plasma-Sprayed Tungsten Coating on Copper with the Heterogeneous Compliant Layer for Fusion Application
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ali Chong (Submitted June 6, 2012; in revised form November 19, 2012) Structure of 1-mm tungsten (W) coating on copper (Cu) with the different compliant layers was designed and optimized by means of ANSYS code. Three materials of titanium, nickel-chromium-aluminum alloys, and W/Cu mixtures with a thickness of 0.5 mm were selected as the compliant layers to evaluate their effects on the interface stress between W and Cu, strain, and the surface temperature under the heat load of 5 MW/m2. Application of the compliant layers can obviously alleviate the interface stress concentration compared to the sharp interface. The maximum stress reduction of about 25% was obtained from the W/Cu-compliant layer; however, the surface temperature was increased only by 12 °C. Further investigation on the W/Cu-compliant layer revealed that 0.1-0.2-mm 20-35 vol.% W was the optimum structure for 1-mm W coating, which resulted in the smallest peak stress of 299 MPa and the equivalent plastic strain of 0.01%.
Keywords
tungsten, stress
plasma
facing-component,
thermal
employed as compliant layers to evaluate their effects on the stress reduction by means of ANSYS code due to their intermediate CTEs and high compliant nature. Meanwhile, the optimization of W/Cu PFC with W/Cu-compliant layer was also carried out.
1. Introduction Tungsten (W) is a candidate material for the diverter armor of the international thermonuclear experimental reactor (ITER) due to its low physical sputtering rate, low tritium inventory, high melting point, and high thermal conductivity (Ref 1-3). ITER has selected the W as the diverter armor material, and found that the thickness of 1-2 mm can meet the operation demand of ITER. In order to overcome the disadvantages of heavy weight and poor workability, W coating was fabricated on the heat sink by means of plasma-spraying technology, and the technology offers the ability to coat large areas, complex shapes, and in situ repair of damaged parts (Ref 4). However, W coating with copper (Cu) is still a challenge due to the larger mismatch between their thermal expansion coefficients (CTEs), which will induce the stress concentration on the interface of plasma-facing component (PFC). The stress concentration may result in the interface damages, such as micro-cracks, delamination, and even W/Cu PFC failure. Therefore, the use of the compliant layers between W-coating and Cu substrate is very necessary to enhance the bonding strength and avoid the thermal stress concentration. In this paper, titanium (Ti), nickel-chromiumaluminum (NiCrAl) alloys, and W/Cu mixtures were
Fali Chong, Xuzhou Institute of Technology, Xuzhou, Jiangsu 221000, China. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
2. W Coating on Cu, and Condition of Numerical Simulation Vacuum plasma-sprayed W coating on Cu was fabricated via a plasma-spray system (Sulzer Metco AG). The average particle size of W powder is about 40 lm. The scanning electron microscopy (SEM) images of VPS-W coating are shown in Fig. 1. The un-molten
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