Influence of Particle Sizes on Properties of Cold Gas Sprayed Aluminum and Titanium Coatings

Under ideal conditions, cold sprayed deposits could reach properties similar to those of respective bulk material. However, solid-state deposition and associated bonding by adiabatic shear instabilities result in inherent internal defects that might limit possible applications. Geometric constraints for shear deformation and bonding result in certain amounts of non-bonded interfaces, their quantity as micro-cracks depending on spray conditions, whereas high degrees of work hardening limit the strain to failure.

For distinguishing influences by overall bonded areas and micro-crack extents on deposit properties, pure titanium and aluminum powders of up to five sizes were cold sprayed under various conditions. The deposits were subsequently analyzed in terms of their microstructures and properties to derive corresponding trends. Higher electrical conductivities for using coarser powder indicate larger amounts of overall bonded interfaces. In contrast, the higher ultimate tensile strength of deposits on basis of the fine powder implies influences by smaller micro-crack sizes on possible crack growth. In general, spray conditions seem to have stronger effects on deposit properties in case of finer feedstock.

In summary, the comparison provides a first view into influences of defect sizes onto the crack propagation within cold gas sprayed deposits and could enable developing concepts for further optimization.