HiPIMS Deposition of Protective Tungsten-Based Coatings on Metallic Substrates

Plasma processing of thin films provides unique opportunities to tailor their properties and performances. In the context of Physical Vapor Deposition techniques, High Power Impulse Magnetron Sputtering (HiPIMS) is steadily growing in popularity. Relying on the working principles of magnetron sputtering, HiPIMS applies high voltage cathode pulses at a low duty cycle to enhance plasma density and the ionization of sputtered species [1]. The application of appropriate substrate bias voltages allows to energize the plasma ions and perform substrate treatments to increase coating adhesion. Additionally, the ability to engineer interfaces at the atomic level with HiPIMS contributes to enhanced mechanical properties and thermal stability of the coatings [2].
Thanks to the improved characteristics that can be achieved with HiPIMS, this technique finds one notable application in the production of protective layers for harsh conditions. In the field of innovative nuclear reactors, the proposed concepts rely on fluids with improved thermophysical properties such as liquid metals and molten salts [3,4]. However, compatiblity in these extreme environments remains a concern, particularly because nuclear conditions constrain the choice of materials. The identification of strategies to limit component degradation is therefore an active and multidisciplinary research area, with the deposition of protective coatings emerging as a promising approach.
The use of liquid tin (Sn) as plasma facing material in the context of nuclear fusion experiments is a significant example. [5]. Indeed, solid copper-based materials, chosen to comply with thermomechanical constraints, suffer from liquid tin corrosion under the prospected operating conditions [6]. Concerning the choice of coating material, tungsten and its alloys emerged as reference candidates thanks to their exceptional thermomechanical properties, compatibility with harsh environments and extensive characterization in nuclear fusion conditions [7].
Here we report on the HiPIMS production of tungsten-based coatings on copper substrates and the characterization of their properties and protective performances in the harsh liquid tin environment. Compact pure tungsten and multielemental layers were deposited by HiPIMS on fusion-relevant copper substrates. The morphological and structural properties were characterized by Scanning Electron Microscopy and X-Ray Diffraction, before and after exposure to liquid tin at fusion-relevant temperatures for ten hours.
Our findings indicate that HiPIMS-deposited tungsten-based coatings exhibit enhanced protective properties compared to those obtained by conventional methods. While tungsten confirms its inertness in liquid Sn, the protective layer performance depend on film morphology, structure, and intrinsic stress state. Multi-elemental depositions and plasma processing allows to tune these properties, highlighting the potential of HiPIMS in advancing the field of protective coatings for energy and nuclear fusion applications.
[1] J. T. Gudmundsson, Plasma Sources Sci. Technol. 31 (2022) 083001
[2] O. Pshyk et al., Appl. Surf. Sci. (2024) 160554
[3] "Generation IV Annual Report 2022" at https://www.gen-4.org/
[4] W. Zhou, “Influence of environmental conditions and proton irradiation on molten salt corrosion of metals.” PhD dissertation, Massachusetts Institute of Technology. (2021)
[5] T. W. Morgan et al., Plasma Phys. Control. Fusion 60 (2018) 014025
[6] S. Roccella et al., J. Fusion Energy 39 (2020) 462-468
[7] G. De Temmerman et al., Plasma Phys. Control. Fusion 60 (2018) 044018