Ductility and fracture behavior of cold spray additive manufactured zinc

Tailoring part strength and ductility in additive manufacturing or repair is vital to successful applications. Therefore, applying cold spray as a deposition technique must be tuned for maximum amounts of well-bonded internal interfaces and sufficient softening of the highly work-hardened deposit. With its low melting temperature, Zinc is an ideal model system for studying phenomena associated with high strain rate deformation and local temperature rise effect, both in single impacts and thicker deposits. Despite the low temperatures, Zn single splats already show recrystallization at internal interfaces. The respective amounts scale with increasing process gas temperatures. At higher process temperatures, deposits are almost fully recrystallized. The recrystallization obviously improves bonding at internal and at deposit-substrate interfaces. Under optimum conditions, an ultimate deposit strength of up to 135MPa and an elongation to failure of 18.4% are reached, comparable to that of laser-manufactured Zn parts. However, the presence of defects in the form of a high density of high-angle grain boundaries and a certain amount of nonbonded splats interfaces results in a lower ductility than that of bulk Zn. This demonstrates a well-tuned interplay between the minimization of defect densities and softening by recrystallization that would allow for deriving bulk-like properties of cold sprayed material without additional post-treatments. Correlations between simulation and experimental results of microstructures, mechanical properties, and fracture mechanisms supply information about the prerequisites for reaching high ductility.