High Ductility and Strength by Internal Interface Recrystallization of Cold Sprayed Zinc and its Fracture Behavior

Abstract

Tailoring strength and ductility in additive manufacturing or repair is key to successful applications. Therefore, cold spraying must be tuned for maximum amounts of well-bonded internal interfaces as well as sufficient softening of the highly workhardened deposit. Zinc (Zn) with its low melting temperature is an ideal model system to study phenomena associated with high strain rate deformation and local temperature distributions, both, in single impacts and thicker deposits. Bonding and recrystallization can be facilitated by covering selected wide parameter regimes in cold spraying. Despite the low temperatures, Zn single splats already show recrystallization at internal interfaces, the respective amounts then scaling with increasing process gas temperatures. At higher process temperatures, deposits are almost fully recrystallized. The recrystallization seems to improve bonding at internal and at deposit-substrate interfaces. Under optimum conditions, an ultimate deposit cohesive strength of up to 135 MPa and an elongation to failure of 18.4% are reached, comparable to that of laser-manufactured or bulk Zn parts. This demonstrates a welltuned interplay between high amounts of bonded interfaces and softening by recrystallization that allows for deriving bulk-like performance of cold sprayed material without additional posttreatments. Correlations between microstructures, mechanical properties, and fracture mechanisms supply information about prerequisites needed for reaching high ductility as obtained in damage and failure modes of deposits and bulk materials in global and local approaches.