Cold Spray: Over 30 Years of Development Toward a Hot Future.

Cold Spray (CS) is a deposition process, part of the thermal spray family. In this method, powder particles are accelerated at supersonic speed within a nozzle; impacts against a substrate material triggers a complex process, ultimately leading to consolidation and bonding. CS, in its modern form, has been around for approximately 30 years and has undergone through exciting and unprecedented developmental steps. In this article, we have summarized the key inventions and sub-inventions which pioneered the innovation aspect to the process that is known today, and the key breakthroughs related to the processing of materials CS is currently mastering. CS has not followed a liner path since its invention, but an evolution more similar to a hype cycle: high initial growth of expectations, followed by a decrease in interest and a renewed thrust pushed by a number of demonstrated industrial applications. The process interest is expected to continue (gently) to grow, alongside with further development of equipment and feedstock materials specific for CS processing. A number of current applications have been identified the areas that the process is likely to be the most disruptive in the medium-long term future have been laid down.

Mechanical and Fatigue Properties of Diamond-Reinforced Cu and Al Metal Matrix Composites Prepared by Cold Spray.

Diamond-reinforced metal matrix composites (DMMC) prepared by cold spray are emerging materials simultaneously featuring outstanding thermal conductivity and wear resistance. In our paper, their mechanical and fatigue properties relevant to perspective engineering applications were investigated using miniature bending specimens. Two different diamond mass concentrations (20 and 50%) embedded in two metal matrices (Al-lighter than diamond, Cu-heavier than diamond) were compared with the respective cold-sprayed pure metals, as well as bulk Al and Cu references. The pure Al, Cu coatings showed properties typical for cold spray deposits, i.e., decreased elastic moduli (50 GPa for Al, 80 GPa for Cu), limited ductility (< 1 × 10-3) and low fracture toughness (3.8 MPa·m0.5 for Al, 5.6 MPa·m0.5 for Cu) when compared to the bulks. Significantly improved properties (strain at fracture, ultimate strength, fatigue crack growth resistance, fracture toughness) were then observed for the produced DMMC. The improvement can be explained by a combination of two factors: changes in the properties of the metallic matrix triggered by the reinforcement particles peening effect and stress redistribution due to the particles presence.