Assessing critical process condition for bonding in cold spraying

Cold spray bonding mechanism is often correlated with adiabatic shear instability and jetting at inter-splat boundaries. In this work, the role of in-flight temperature on the deposition characteristics is synergistically addressed with the in-flight velocity of the impacting powders. The fraction of inter-splat bonding and the properties of the coatings are correlated as a function of total energy of the powder upon impact rather than in-flight velocity alone. Fraction of inter-splat bonding is used to obtain normalised electrical conductivity and normalised elastic modulus for variety of materials ranging from low melting point zinc (Zn) to high melting point tungsten (W). Onset of deposition is characterized with the dimension less parameter estimated by normalising the total energy of the impacting powder with the Ebond (critical energy). The data is correlated with the experimental results. For instance, the critical velocity (VCr) and critical energy (Ebond) for bonding of copper are estimated to be 451 m/s and 27.25 μJ respectively. One can tailor the process condition to deposit the metallic powder in cold spraying by selecting either in-flight velocity or in-flight temperature. The synergistic effect of velocity and temperature can be corroborated with the bonding state in cold sprayed coatings.