Thick functionally-graded W-316L composite coatings for nuclear fusion applications

Nuclear fusion is a potential pathway to finding a sustainable, carbon-free energy source. Some critical components of the fusion reactors are planned to be coated by tungsten. For the task, thermal spraying in vacuum or protective atmosphere can be employed, offering several advantages such as easy preparation of advanced feedstock for deposition of functionally graded composites. Such coatings could be a viable approach to avoid the thermal expansion coefficient mismatch between the W coating and the steel components. In this study, radio-frequency inductively-coupled plasma spray method was used to deposit W-steel composite coatings of three different W ratios, as well as a functionally graded coating consisting of the three composites and a pure W top coat. The coatings exhibited a high-quality microstructure, without intermetallic or oxide phases formation. Thermal diffusivity and conductivity of the coatings was measured at 100 °C and 600 °C, with the values falling into range between the bulk steel and plasma sprayed W. In conclusion, we have shown that the RF-ICP technology is suitable for preparation of tungsten-steel graded deposits and the outputs are now prepared for other testing and a following upscaling to the industry-relevant size