Microstructural Dependence of Spallation in Kinetic and Plasma Sprayed Refractory Metal Deposits

Thermal spray (TS) processing of metals and metal blends has become a cost-effective versatile process to produce thick coatings with minimum oxidation. Furthermore, microstructural features inherent to the spray process result in unique properties such as increased yield strength, low ductility, and differences in tensile and compressive strengths thus enabling tailorability of fatigue behavior and dynamic performance. Historically, wrought and additively manufactured tantalum have been extensively studied under dynamic compression over a range of pressures, but there has been little effort to understand the microstructural dependence of TS materials under these conditions. Here we report the results of spallation experiments applied to Cold Spray (CS) and Controlled Atmosphere Plasma Spray (CAPS) deposits of tantalum (Ta), niobium (Nb), and a tantalum-niobium blend (TaNb). The deposition methods differ in that CS utilizes kinetic-based deposition whereas CAPS uses melt deposition via a direct current plasma torch in either vacuum or an inert environment. Both techniques produce unique porous and stochastic microstructures, with CS resulting in a build-up of denser work-hardened material, while CAPS is less dense with a more lamellar microstructure. Postmortem materials characterization was conducted to investigate the primary fracture mechanisms of CS and CAPS deposited materials during tensile loading. These results provide insight into the effects that TS microstructures have on the dynamic performance compared to traditional manufacturing and higher temperature additive techniques. This provides a base for the development of structural component materials with unique mechanical properties for aerospace and military applications.