UCLA

Niobium is used in superconducting radio frequency (SRF) structures that operate at cryogenic

temperatures. These structures are continually optimized to increase efficiency and provide cost effective

fabrication. Throughout optimization, material properties of thermal conductivity and mechanical strength

are often jeopardized. Cold spraying has been of interest in coatings, repair, and additive manufacturing

and poses a possible solution to optimization of SRF structures. This process involves deposition of a

desired material onto a substrate through accelerating the material in the form of a powder to high

velocities via pressurized gas. Currently, the combination of copper powder being deposited onto a niobium

substrate via this process has never been studied. This is the first known study of cold-sprayed copper

coatings onto niobium for the application of conductive cooling of SRF accelerating structures. Trials were

conducted to assess the compatibility of cold spray of copper with SRF structures through processing and

operating conditions. The material campaign involved understanding parameters for sample fabrication,

substrate preparation, material deposition, and post-processing that may provide optimal coatings. This

study offers a firm base understanding of the copper and niobium cold spray pair. Effective deposition of

this pair requires mechanical interlocking as there is no metallurgical bonding of these materials at the

processing temperatures. The extent of mechanical interlocking is affected by substrate preparation and

surface roughness, oxygen content of copper powder, particle velocity, gas temperature, powder

morphology, and particle size distribution.