K. Lee, H. Garich, S. Snyder, M. Inman
Faraday Technology, Inc.,
Keywords: Electrodeposition, Electrochemical Manufacturing, Brazing, Compositionally Graded Alloys
Summary:Brazing is being considered as a method for joining tungsten plasma-facing materials and heat sinks in future fusion reactors. However, direct brazing of tungsten plasma-facing components and potential heat sink materials (e.g., copper, copper alloy, and reduced activation ferritic/martensitic steels) is challenging due to the extreme mismatch in the coefficient of thermal expansion. Incorporating a compositionally graded iron-tungsten alloy brazing interlayer has the potential to alleviate this thermal mismatch and improve the performance of these components. A remaining challenge is the development of a scalable method for manufacturing compositionally graded iron-tungsten alloy interlayers that can achieve a wide composition spectrum and produce materials that are suitable for fusion applications. Electrodeposition is a well-established and scalable manufacturing method that is widely used to manufacture thick, adherent coatings. Electrodeposition offers a number of advantages over other manufacturing methods including the ability to uniformly coat a variety of substrate shapes and the use of simple and inexpensive equipment. In addition, control of the composition, morphology, and microstructure of the electrodeposited material can be achieved through the use of highly tunable pulse and pulse-reverse electric fields. Faraday Technology has significant expertise in the development of novel pulse/pulse-reverse electrodeposition processes for manufacturing alloy coatings for enhanced thermal and corrosion resistance in extreme environments. As part of a current SBIR program, Faraday is developing a novel pulse electrodeposition approach for manufacturing iron-tungsten alloys that can serve as brazing interlayers between tungsten plasma-facing components and heat sinks. In this manufacturing approach, the iron-tungsten alloy is electrodeposited onto tungsten which is then joined to the desired heat sink via brazing. In this presentation, Faraday will discuss the development of this electrodeposition manufacturing approach for fabricating compositionally graded iron-tungsten alloys as well as recent progress in demonstrating the suitability of these iron-tungsten alloys as brazing interlayers. This discussion will include (1) results from electrodeposition trials showing how pulse waveform engineering can be used to control the composition and microstructure of the iron-tungsten alloy, (2) metallographic characterization and ambient temperature mechanical testing of braze joints incorporating these Fe/W alloys, and (3) an overview of current work focused on preparation of samples for high heat flux testing of joint performance under fusion-relevant conditions. A brief overview of pulse/pulse-reverse electrodeposition as a means of manufacturing materials for extreme environments will also be provided.