High-Performance, No-Helium Cold Spray for Structural Repair Applications

Helium (He) is an expensive and limited resource, but He cold spray achieves very high particle velocities due to the high speed of sound of He that produce as-sprayed mechanical properties acceptable for certain structural repairs. Nitrogen (N2) cold spray deposits currently lack the necessary mechanical properties to implement structural repairs. This work is a collaborative effort between Solvus Global and the University of Alabama (UA), Tuscaloosa with the goal of consolidating existing cold spray process and powder knowledge and engineering experience to achieve comparable mechanical properties to He depositions using N2 cold spray. The proposal team will develop powder feedstock materials and in tandem optimize the deposition process to achieve the desired properties. The Phase I program demonstrated an accelerated evaluation of several different parallel paths for achieving properties of He spray but with N2 process gas using modified powders and processes. These efforts demonstrated the highest reported elongation in an N2-sprayed AL7050 to date and led to a down-selection of the various approaches of interest. There remain several viable paths for achieving He-like properties in the Phase II program; it is Solvus’ belief that the following sequence will be needed to overcome the physics of this process to match He-like properties:Achieve elevated plastic deformation by increasing particle velocity (via increasing gas velocity by pressure and/or temperature increases) and reducing elastic zone (microstructural modification)Achieve comparable peening to He spray (~50% by weight) by blending in non-incorporating phasesAchieve comparable bonding to He by implementing powder with reduced oxide shell and enhanced oxide ejection (jetting) - this will allow for enhanced ductility of as-deposited materialsIn parallel to these fundamental material/process methods focused on N2-based approaches, Solvus will utilize Army Research Laboratory’s Hydrogen (H2)-based cold spray system to develop the best performing materials in a H2-spray environment. This two-prong approach will largely guarantee a successful outcome of this program to replicate He-like properties without using He carrier gas. Upon completion of Phase II, the deployment and transition of a no-He powder/process combination capable of achieving He equivalence and approaching wrought properties will be achieved.