ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2024 50 iTSSe TSS iTSSe TSS Manufacturing processes are in the midst of a paradigm shift—one that integrates the growing trend of fabricating more sophisticated products alongside the emergence of advanced manufacturing technologies, often referred to as Industry 4.0 or the fourth industrial revolution[1]. Within these technologies, metal additive manufacturing (MAM) is a significant contributor. In the MAM process, a 3D shape is created layer by layer through material deposition. When MAM is discussed, thermal technologies such as binder jetting, powder bed fusion, directed energy deposition, wire arc additive manufacturing, and friction stir welding are often the focus[1,2]. In addition, cold spray (CS) is rapidly becoming an important member of the MAM/thermal spray family, although the technology itself has been around for nearly 30 years. During this time, it has developed and matured with significant commercial uptake. COLD SPRAY PROCESS In the CS process, powder particles are accelerated to supersonic speeds in a high velocity gas stream. They impact a solid surface with sufficient energy to cause plastic deformation and bonding with the underlying material, which can be either a substrate or previous layer material. Bonding is a result of high strain rate deformation and adiabatic shear instabilities at the bond interface. CS is commonly referred to as cold gas dynamic spray, high velocity powder deposition, or supersonic particle deposition. Particle velocity is the major contributor to bonding and mechanical properties and this velocity is a combination of gas expansion and pressure. Although defined as a cold gas deposition process, the inclusion of this technology in the thermal spray family is due to temperatures of up to 1100°C. These temperatures can be used to expand the carrier gas and accelerate the metal powder, although the metal powder itself does not get this hot and is in a non-molten state[3]. Compared to commonly used melt-based AM technologies, CS has unique advantages such as shorter production times (high deposition rates), unlimited product size (no build tray or controlled environment required), reduced thermal effects, and high adaptability to different materials and applications. COLD SPRAY JOINS THERMAL SPRAY METAL ADDITIVE MANUFACTURING FAMILY The next generation of additive manufacturing leverages the advantages of cold spray to offer promising options for applications in aerospace, automotive, and biomedical engineering. Neil Matthews, TSS-HoF,* Titomic Limited, Mount Waverly, Australia NEW DEVELOPMENTS Over the past 30 years, CS technology has experienced several scientific and technological breakthroughs leading to new developments in bonding mechanisms, in situ process visualization, materials, apparatus configurations, pre- and post-process treatments, and applications. The current equipment portfolio is designed to meet a wide range of specific requirements. This portfolio includes high performance equipment that can deliver the technology to the point of application for large scale, net shape builds. Modern CS equipment is designated into three categories: high pressure, medium pressure, and low pressure[4]. All of these efforts have resulted in mature CS technology that can be tailored to industry requirements. Its fields of application are increasingly broad, particularly regarding layered materials on substrates for surface engineering applications such as repairs and coatings, 6 *Member of ASM International Metal powder is added to a feeder before a cold spray additive manufacturing operation. Titomic’s D623 is a compact medium-low pressure cold spray system for on-site metal coatings and repair. FEATURE
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