Synthesis and Characterization of W/SiC Compositionally Graded Films As Potential Plasma-Facing Materials

Tungsten (W) is a promising plasma-facing material in a fusion reactor due to its low physical and chemical sputtering yield but it suffers from embrittlement and blistering. A potential alternative is silicon carbide (SiC) due to its low neutron activation and favorable thermomechanical properties but it is more prone to sputtering. In this work we explore the synthesis and benefits of W/SiC compositionally graded films given that W and SiC have a good mechanical and chemical compatibility owing to their similar coefficients of thermal expansion and stable binary compounds. Preliminary W/SiC bilayers have previously been synthesized and exposed to deuterium plasma in the DIII-D tokamak using the Divertor Material Evaluation System (DiMES) manipulator. Sample delamination was observed due to high mechanical strain at the W/SiC interface. The present study improves upon the coating deposition process for the synthesis of W/SiC compositionally graded film using pulsed-DC sputtering deposition. Fabricated films were exposed near the outer strike point of L-mode deuterium plasmas using DiMES. Microstructural images were obtained via scanning electron microscopy (SEM) pre- and post-exposure. The chemical compositions of the W/SiC films were assessed by electron dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS). W/SiC films exposed to L-mode plasmas did not delaminate with a peak heat flux of 1.15 MW/m². Density-functional theory (DFT) calculations were performed to assist in predicting the stability of various structures/phases in the composition regimes of synthesized W/SiC samples. Enthalpies of formation were derived to update the existing W-Si-C ternary phase diagram.