Using EBSD and TKD for New Insights on the Cold Spray Deposition Process

Electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD) are allowing us to uncover details about the cold spray deposition process that cannot be readily addressed by other characterization techniques. Cold spray is a solid-state material deposition process that uses supersonic gas flow to accelerate fine, metallic powder particles. Upon impact, the particles bond to the substrate, and to each other, to form a material that can be used for manufacturing and repair of structural components. We will discuss two examples that highlight how EBSD and related techniques can bring new understanding to the cold spray process. In the first example, we examine Al-Cu binary alloys and use EBSD to relate the microstructure of the starting gas atomized powders to the deformation microstructures present in the deposits. EBSD shows that the grain structure is bimodal and is comprised of highly deformed, micron-sized grains and recrystallized, ultrafine grains. By combining EBSD with TKD and precession electron diffraction in the TEM, we now know that the ultrafine grains are formed during the impact event itself. In the second example, we use EBSD, X-ray, and neutron diffraction to examine how post-deposition laser heating produces recovery and recrystallization in cold-sprayed 304 austenitic stainless steel.