Kinetic Powder Compaction Applying the Cold Spray Process A Study on Parameters

摘要

Supersonic, two-phase flow of a gas/particle mixture directed towards a substrate may enable the deposition of "cold" particles onto a "cold" substrate under certain conditions. The method is commonly known as Cold Gas Dynamic Deposition or Cold Spray. Current research shows that copper can be deposited within a wide range of parameters and velocity regimes, whereas the deposition of other materials may involve difficulties depending on the material properties and substrate characteristics. Although particle velocity is recognized as being the key factor in the deposition of particles with the cold spray process, it alone cannot describe the state of the particle prior to and during impact. A simple analysis shows that the impulse of particles with equal particle velocity and size depends significantly on its density. For common engineering metals, an interval varying by up to a factor of 5 is possible considering, for example, magnesium and molybdenum. The impact force, directly dependent on the particle's impulse, governs the pressures generated during impact. In a simplified calculation, pressure values of around 3000 MPa can be very easily determined. While the particle impulse accounts for the degree of interaction - partial or complete deformation - the particle's and the substrate's lattice structure and its capacity to deform determine the type of particle substrate interaction. Depending on these properties, the substrate, the particle or both will be deformed. Evaluating impact experiments shows distinct differences between the impacts of copper, steel and aluminum particles on aluminum and steel substrates. The paper presented may be seen as a contribution to the discussion of a theory to evaluate coating and substrate combinations prior to spraying in order to predict bonding and coating build-up or to offer guidance concerning the optimum parameter set for deposition.