Surface Erosion of Plasma-Facing Materials Using an Electrothermal Plasma Source and Ion Beam Micro-Trenches

Abstract

Erosion characteristics of tungsten-alternative plasma-facing materials (PFMs) were tested under high heat flux conditions in the electrothermal plasma source facility at Oak Ridge National Laboratory. The PFMs of interest are high-purity β-3C chemical vapor deposition silicon carbide (SiC) and the MAX phases Ti₃SiC₂ and Ti₂AlC [MAX = chemical formula M_n+1AX_n, where M is an early transition metal (such as Ti or Ta), A is an A-group element (such as Si or Al), and X is carbon or nitrogen]. An erosion analysis method was developed using a combination of focused ion beam microscopy and scanning electron microscopy, carving micro-trench geometries into polished sample surfaces. Samples of SiC, Ti₃SiC₂, and Ti₂AlC were exposed to the electrothermal plasma source alongside tungsten and monocrystalline silicon. Samples were exposed to a Lexan polycarbonate (C₁₆H₁₄O₃) electrothermal plasma stream in a He environment, at a specified impact angle, with infrared camera diagnostics. Edge localized mode–relevant heat fluxes of 0.9 to 1 GW/m² over 1-ms discharges were generated on the target surfaces. Tungsten samples exhibited pronounced melt-layer formation and deformation, with measured molten pits 2 to 10 μm in diameter and melt-layer depths of up to 7 μm deep. Surface erosion rates for Ti₃SiC₂ and Ti₂AlC ranged from 80 to 775 μm/s and 85 to 470 μm/s, respectively. Both MAX phases exhibited extreme surface fracture and material ejection, with damage depths past 4 μm for Ti₂AlC and 11 μm for Ti₃SiC₂. SiC displayed the best performance, in one case surviving 15 consecutive electrothermal plasma exposures with an average erosion rate of about 29 μm/s and no surface fracturing. SiC erosion rates ranged from 23 to 128 μm/s.

Keywords:

• Plasma-facing material
• ion beam
• MAX phase ceramics
• silicon carbide
• erosion

Acknowledgments

This material is based upon work supported by the U.S. Department of Energy via UT Battelle, LLC, subcontract 4000145506. C. Parish was supported by an Early Career Award, U.S. Department of Energy, Office of Science, Fusion Energy Sciences, under contract number DE-AC05-00OR22725. This work was performed in part at the Analytical Instrumentation Facility at North Carolina State University, as well as the Low Activation Materials Development and Analysis laboratory at ORNL.