M. J. Yadegari

The cold spray technique involves accelerating micron-sized particles to high speeds of 300-1200 m/s, resulting in plastic deformation upon impact with the substrate and adherence to its surface. The spraying nozzle is scanned along the substrate to achieve uniform thickness. Cold spray can deposit various materials such as metals, polymers, ceramics, composites, and nanocrystalline powders. A schematic image of the procedure in this manufacturing method is presented below.

This thermal spray-based method has impressive advantages that make it potentially very competitive. These include the absence of a heat-affected zone and no reaction at the interface due to the solid-state deposition method at relatively low temperatures. It also minimizes oxidation and phase changes during deposition. Additionally, almost every metallic material, metal matrix composite, and metal/ceramic mixture can be deposited using this method. It is fast, cost-effective, and flexible, making it suitable for additive manufacturing and repairing parts. On the other side, some difficulties can be found. For instance, it is difficult to spray hard and brittle materials because, in this case, mechanical adhesion through plastic deformation could be less effective than it is for ductile particles.

Several aspects of the cold spray process are of great interest to researchers in this field, such as:

• Impact and bonding in angle and deposition efficiency
• Deposition in the interior of parts
• Optimization of properties for best performance
• Optimization of post-spray processes

In this regard, Moridi [1] investigate experimentally and numerical behavior of as-built and treatment parts fabricated by cold spray, such as fatigue. Ghelichi et al. [2] studied the microstructural and fatigue behavior of cold spray-coated Al5052. The results indicate that the fatigue strength was significantly improved by up to 30% in the case of Al7075 coatings. Finally, Nikbakht et al. [3] explore the process-structure relation of mixed Ni-Ti powders in a cold spray. Single/multi-particle impact experiments and FEM modeling were employed to investigate particle deformation and microstructure evolution. They observed that splats in dissimilar multi-particle impacts experience more deformation than those of similar materials.

Understanding materials’ fundamental behavior during deposition is essential for the process development, which must be addressed more for mixed powders. Therefore, this project emphasizes optimizing the properties of the components fabricated by cold spray additive manufacturing technique with two or more constituent phases for achieving the best functional performance (e.g., mechanical properties).

Particular challenges need to be addressed before achieving complete control over the deposit characteristics in cold spray. Although the chemical composition of the powder mixture can be accurately regulated prior to spraying, the yield of the composition in the deposit is still being determined. This is primarily due to variations in the thermo-mechanical and morphological properties of different phases. Moreover, the mechanical performance of the integrated structure is affected by the varying mechanical properties of each step.