Microscale particle-target interactions and the resulting modifications of the target material play a crucial role in the domains of industrial manufacturing and application process. As know that the processing and manufacturing, failure prevention, and even the spacecraft protection against hypervelocity micrometeorites and orbital microdebris. Based on such an interesting, noteworthy, and profoundly applied research, it quickly followed up and compiled a series of relevant studies for particle-target interactions of high-speed microparticle impact. Here, it discussed the gas-based, laser-based, and electrostatic-based of the high-speed microparticle impacts. Among these, laser-induced particle impacts stand out for their high throughput and the suitability for operation in small facilities or even on standard laboratory optical benches. Various behaviors have been observed with smaller projectiles, relatively high velocities, and extreme strain rates, which involved the description of launching system, dynamic capturing of high-speed videography, triggering and characterization of material response, and resulting material modification. Subsequently, it conducted a summary and future prospect of the focused topics. As expected that the particle-target interactions will become an effective tool for the study of microprocessing, multi-field coupling, material strengthening and modification, it will bridge multidisciplinary to understand the scientific phenomena involved in the impact process, also provides a novel strategy for the development of next-generation of ballistic impact testing.

Cold spray coatings are the sum of countless individual bonding events between single particles impacting on top of one another at high velocities. Thus, the collective behavior of microparticles must be considered to elucidate the origins of coating flaws at the scale of the particles and larger, or the dynamic evolution of the overall coating microstructure. Laser-induced particle impact testing (LIPIT) has been extensively used to study single-particle impacts, and in this work is adapted to study the accumulation of numerous particles with knowledge of each individual particle's impact parameters (particle size, velocity). The method reproducibly deposits stacks of gold particles (>20 particles) with different characteristic spectra of impact velocity. The observation of impactinduced erosion lets us define a critical velocity for material-build-up that is higher than that for singleparticle bonding. The quantitative single-particle data are analyzed in a correlative manner to the structure and flaws in the resulting stacks, providing some first statistical connections between, e.g., strain and recrystallization, or aberrant particle characteristics and defects. The results highlight opportunities for the study of many-particle phenomena in microparticle impact-from interaction of particles in cold spray to multi-step erosion processes-with a quantitative view of the behavior of single particles.

Across disciplines and length scales, alloying of metals is a common and necessary strategy to optimise materials performance. While the manufacturing of alloys in bulk and thin film form is well understood, the fabrication of alloyed 3D nanostructures with precise control over the composition remains a challenge. Herein, we demonstrate that electrohydrodynamic redox 3D printing from mixed metal salt solutions is a versatile approach for the 3D nanofabrication of alloys. We propose that the droplet-by-droplet nature of the electrohydrodynamic redox printing process allows straightforward electroplating of alloys with composition solely controlled by the composition of the electrolyte solution, independent of the reduction potential of the involved cations. As a demonstration of the direct control of composition, we deposit binary and ternary alloys of Ag, Cu and Zn. TEM microstructure analysis indicates homogeneous alloying at the nanoscale and the formation of a metastable solid-solution phase for Ag-Cu and a two phase system for Ag-Cu-Zn alloys. The straightforward approach to alloying with an electrochemical technique promises novel opportunities for optimisation of properties of 3D nanofabricated metals.

In the first decade of high-velocity microparticle impact research, hardly any modification of the original experimental setup has been necessary. However, future avenues for the field require advancements of the experimental method to expand both the impact variables that can be quantitatively assessed and the materials and phenomena that can be studied. This work explores new design concepts for the launch pad (the assembly that launches microparticles upon laser ablation) that can address the root causes of many experimental challenges that may limit the technique in the future. Among the design changes contemplated, the substitution of a stiff glass launch layer for the standard elastomeric polymer layer offers a number of improvements. First, it facilitates a reduction of the gap between launch pad and target from hundreds to tens of micrometers and thus unlocks a reproducibility in targeting a specific impact location better than the diameter of the test particle itself (±1.75 µm for SiO2 particles 7.38 µm in diameter). Second, the inert glass surface enables experiments at higher temperatures than previously possible. Finally—as demonstrated by the launch of thin-film Au disks—a launch pad made of materials standard in microfabrication paves the way to facile microfabrication of advanced impactors.

Electrohydrodynamic redox 3D printing (EHD-RP) is an additive manufacturing (AM) technique with submicron resolution and multi-metal capabilities, offering the possibility to switch chemistry during deposition “on-the-fly”. Despite the potential for synthesizing a large range of metals by electrochemical small-scale AM techniques, to date, only Cu and Ag have been reproducibly deposited by EHD-RP. Here, we extend the materials palette available to EHD-RP by using aqueous solvents instead of organic solvents, as used previously. We demonstrate deposition of Cu and Zn from sacrificial anodes immersed in acidic aqueous solvents. Mass spectrometry indicates that the choice of the solvent is important to the deposition of pure Zn. Additionally, we show that the deposited Zn structures, 250 nm in width, can be partially converted into semiconducting ZnO structures by oxidation at 325 °C in air.

The control of materials’ microstructure is both a necessity and an opportunity for micro/nanometer-scale additive manufacturing technologies. On the one hand, optimization of purity and defect density of printed metals is a prerequisite for their application in microfabrication. On the other hand, the additive approach to materials deposition with highest spatial resolution offers unique opportunities for the fabrication of materials with complex, 3D graded composition or microstructure. As a first step toward both—optimization of properties and site-specific tuning of microstructure—an overview of the wide range of microstructure accessed in pure copper (up to >99.9 at.%) by electrohydrodynamic redox 3D printing is presented, and on-the-fly modulation of grain size in copper with smallest segments ≈400 nm in length is shown. Control of microstructure and materials properties by in situ adjustment of the printing voltage is demonstrated by variation of grain size by one order of magnitude and corresponding compression strength by a factor of two. Based on transmission electron microscopy and atom probe tomography, it is suggested that the small grain size is a direct consequence of intermittent solvent drying at the growth interface at low printing voltages, while larger grains are enabled by the permanent presence of solvent at higher potentials. 

3D printing research targets the creation of nanostructures beyond the limits of traditional micromachining. A proper characterisation of their functionalities is necessary to facilitate future implementation into applications. We fabricate, in an open atmosphere, high-aspect-ratio gold nanowalls by electrohydrodynamic rapid nanodripping, and comprehensively analyse their electronic performance by four-point probe measurements. We reveal the large-grained nanowall morphology by transmission electron microscopy and explain the measured low resistivities approaching those of bulk gold. This work is a significant advancement in contactless bottom-up 3D nanofabrication and characterisation and could also serve as a platform for fundamental studies of additively manufactured high-aspect-ratio out-of-plane metallic nanostructures.

Many emerging applications in microscale engineering rely on the fabrication of 3D architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge toward the implementation of AM in microfabrication. Here, a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution ≤10 μm is presented. Standardized sets of samples are studied by cross-sectional electron microscopy, nanoindentation, and microcompression. It is shown that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials' performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects—a significant step toward the potential establishment of AM techniques in microfabrication.