Cold Spray Additive Manufacturing: Microstructure Evolution and Bonding Features

Abstract

Conspectus Most metal additive manufacturing (AM) methods involve the melting or sintering of feedstock powder or wire using an energy source (laser, electron beam, or electric arc). Solid-state AM, sometimes also known as non-beam-based AM, is a process in which the deposited material does not melt and is built up layer-by-layer, typically through severe plastic deformation. Initially considered to be a coating technique, by virtue of its high deposition rate, cold spray additive manufacturing (CSAM) is attractive as a solid-state AM technology. In the CSAM process, metal powder particles are impacted onto a substrate at a supersonic velocity and relatively low temperature. The CSAM process reduces or eliminates many problems associated with melting or beam-based AM methods, making the CSAM technically attractive for a wide range of applications, such as in the aerospace, automobile, marine, biomedical, machinery, and energy sectors. In this Account, the author briefly reviews the setup of a cold spray system and discusses the strengths and drawbacks of CSAM compared with thermal sprays and beam-based AM processes, as well as applications in relevant industries. The author summarizes the bonding mechanisms proposed for the cold spray process. The focus of this Account is to review the microstructure evolution of several typical model metals (copper, nickel, aluminum, and titanium) during the cold spray process. The author shows a large variety of microstructure characteristics (recrystallized grains, annealing twins, shear bands, submicron-sized grains, deformation twins, and nanometer-sized grains) in cold-sprayed copper, dynamic recrystallization of cold-sprayed nickel, and the formation of refined grains even below 10 nm in size in cold-sprayed aluminum. The magnitude of the stacking fault energy of as-sprayed materials considerably influences the microstructure after cold spray and postprocessing. Due to the relatively low thermal conductivity and ductility of titanium, cold spraying of titanium shows both a high deposition efficiency and relatively high porosity of as-sprayed parts, as well as a heterogeneous microstructure. Moreover, the Account introduces the postprocessing heat treatment and nanoindentation characterization of cold-sprayed materials. A fundamental understanding of microstructure evolution during and after the cold spray process is essential for optimal mechanical properties. Lastly, the author provides a perspective on applying old lessons and taking advantage of new techniques and materials, including powder characterization, hybrid additive manufacturing, machine learning for searching process windows, nanomechanical testing, and emerging alloys (high-entropy alloys, nanocrystalline alloys, and quasicrystals), to advance the research and applications of CSAM.

Metal Additive Manufacturing for Electrical Machines: Technology Review and Latest Advancements

“…However, all these techniques have different levels of maturity as shown in Figure 2c. For instance, some techniques are still in their early stage such as NanoParticle Jetting [12] and cold spray (CS) [13]. Other techniques has already reached a high level of maturity such as Laser-Beam Powder Bed Fusion (LB-PBF) [14].…”

Cold-Sprayed Composite Metal-Fluoropolymer Coatings for Alloy Protection against Corrosion and Wear

“…Powder melting does not occur in this method. In contrast to the thermal spray method [63] and beam (laser or electronic) deposition methods, in the CS, the particles remain in a solid state (at least for the vast majority of metallic materials) throughout the entire process [64]. Due to the application of low temperatures, the coating obtained by the CS method has unique properties [15,61,65,66].…”

Solid-State Cold Spray Additive Manufacturing of Ni-Based Superalloys: Processing–Microstructure–Property Relationships

“…The advantage of such a practice is that the typical defects of oxidation, grain growth, thermal stresses (in the form of tensile stresses), and phase transformations can be effectively avoided, in contrast to fusion-based techniques, such as DED and PBF [ 53 ]. From a deposition rate perspective, CSAM also yields the advantage of having greater deposition rates (up to 50 kg/h [ 54 ]) compared with fusion-based AM processes (which were reported to be up to 10 kg/h with processes such as DED) [ 55 , 56 , 57 ]), which can be visually seen in Figure 3 . For reference, the fusion-based AM processes listed pertain to PBF-related (consisting of sintering and full melting) and DED-related (consisting of a laser beam, electron beam, and arc plasma) techniques [ 58 ].…”