Vacuum Kinetic Spraying Research Articles

A nozzle design for mitigating particle slowing in the bow shock region during micro-cold spray of 8 YSZ films

During micro-cold spray deposition, also referred to as the aerosol deposition method or vacuum kinetic spraying, performed with conventional nozzles, the particle impact velocities decrease drastically with particle size for fine particles <500 nm in diameter due to slowing in the stagnation region. A new design for a nozzle that contains pressure relief channels is proposed that allows the pressure in the stagnation region downstream of the bow shock to be reduced. This reduced stagnation pressure results in less particle slowing compared to conventional nozzle geometries, particularly for smaller or less dense particles. The effects of the channel geometry on the particle impact velocity are systematically investigated by independently varying the channel parameters. Calculations show that the impact velocities for 100 and 200 nm yttria stabilized zirconia particles is increased by 111% and 31%, respectively, for a selected pressure relief channel nozzle when compared to a comparable conventional nozzle. Although impact velocities are increased, a tradeoff exists with this nozzle design in that the particle focusing in the nozzle is decreased and some of the particles may be removed from the aerosol by the channels. Experiments using a nitrogen as a carrier gas at ∼40 kPa upstream pressure show that, despite the loss of larger particles into the relief channels, the deposition efficiency is improved by 300% when depositing films from fine 8 YSZ powder with the pressure relief nozzle compared to a conventional nozzle.

Effect of an oxide layer on high velocity impact of tantalum particles characterized using molecular dynamics

Micro-cold spray, also commonly referred to as the aerosol deposition method or vacuum kinetic spraying, is a process for depositing nanostructured films of metals and ceramics by impacting solid nanoparticles at high velocity onto a substrate at room temperature and at low pressures. Tantalum films deposited by micro-cold spray are desirable because tantalum is non-reactive to certain molten metals and can therefore serve as a non-reactive barrier coating. However, unlike most other metals deposited by micro-cold spray, tantalum quickly forms an oxide layer when exposed to air. In the deposition of films using traditional cold spray with much larger particles, native oxides must fracture for particle–substrate bonding to occur. The fraction of the particle that is oxidized in micro-cold spray and the strain rates experienced by the particles upon impact are both much larger than in cold spray, suggesting that the role of the oxide on film deposition may be distinct. The effect of this oxide layer on particle deformation and adherence to a substrate under high strain rates is studied using molecular dynamics simulations. The effect of oxide layer thickness, particle diameter, and impact velocity are examined.

Microstructural features correlated with the electrical properties and plasticity-based deposition of silver particles through the vacuum kinetic spray process

Although the vacuum kinetic spraying (VKS) process is primarily used to fabricate thin films from ceramic materials, other materials or material combinations have also been deposited through this method. However, the detailed deposition process is not yet fully understood. In this study, the Ag particle deposition process and subsequent electrical resistivity of the patterned Ag coating fabricated on Al2O3 and Si substrates were investigated. Although Ag film was formed on both substrates, Ag coating on the Si substrate with a low roughness of 1.7 nm was easily peeled off while that on Al2O3 having a high roughness of 222.0 nm was well preserved, implying the importance of an anchoring layer for the film adhesive strength. Under gas flow rates of 10 and 18 L/min, patterned films formed on the Al2O3 substrate with the thickness of 1.37 and 2.26 μm, and accordingly, the measured electrical resistivities were 3.08 × 10−5 and 7.86 × 10−5Ω−Cm, respectively. In the coating microstructure, relatively large crystallites of 63.79 nm, high boundary/interface fractions, and interfacial nanopores were observed (unlike on typical VKSed films), which can deteriorate the electrical resistivity in addition to low pattern thickness and its shape. Furthermore, based on the findings, the deposition features of soft particles and hard substrates are discussed in terms of anchoring layer formation, initial weak bonding, deposited particle delamination, and bonding consolidation, and a plasticity-based deposition process is hypothesized.

Gas and ceramic particle velocities for micro-cold spray

The particle impact velocity is a critical parameter in assessing deformation and particle adhesion mechanisms that occur during the micro-cold spray process (also referred to as the aerosol deposition method or vacuum kinetic spraying) for depositing fine ceramic particles. In this study, the influence of operating parameters including inlet gas pressure, gas pressure ratios, gas type, and nozzle-to-substrate distance on gas velocities is studied. The gas velocities are then used to calculate maximum particle velocities, slowing that occurs as the particle travels through compressed gas near the substrate, and particle impact velocities. The drag laws used are appropriate for the full range of particles sizes used in micro-cold spray and related processes from 50 nm to 5 μm. The process parameters that maximize particle impact velocity for particles with a range of sizes and densities are delineated, and the influence of nozzle geometries is assessed.

Aerosol Deposition of Thin-Film Single- and Bi-layered Solid Electrolytes for Intermediate Temperature Planar Solid Oxide Fuel Cells

One of the main limiting factors determining an increase in the specific power and efficiency of solid oxide fuel cells (SOFCs) is the development of deposition technique for thin-film gas-tight electrolytes. Hence, the development of inexpensive and scalable technologies to form thin-film electrolytes is the key direction of SOFC improvement. Despite existence of well-developed techniques, such as chemical vapor/solution deposition (CVD/CSD), electrochemical deposition (ED), thermal spray (TS), physical vapor deposition (PVD), all of them have a trend in rising deposition temperatures or establishing high vacuum that causes an increase in cost. The aerosol deposition (AD) also known as vacuum kinetic spraying (VKS) is a technique for deposition of thin and thick, gas-tight and porous layers. The deposition occurs due to the impact of high-energy particles to substrate and their consequent fragmentation and consolidation, this phenomenon is called room temperature impact consolidation (RTIC). The AD method is distinguished by the ability to lower the formation temperatures of a gas-tight electrolyte layer down to room temperatures by using a high-energy aerosol jet under conditions of low vacuum (1 – 1000 Pa) and room temperature. In addition, the method is characterized by low equipment cost and easy scaling. The possibility to deposit gas-tight films and films with controlled porosity in a wild range of thickness makes it possible to create all functional SOFCs layers without intermediate sintering steps. In the present work, the aerosol deposition technique was used to deposit thin-film electrolytes for anode-supported SOFCs. Two types of anode-supported SOFCs were manufactured. Type-1: thin-film electrolyte with the composition 8 mol.% yttria-stabilized zirconia (8YSZ) deposited on a bilayered anode substrate (current-collecting and functional sublayers) using the AD method followed by the screen-printing of a composite cathode with the composition of (La0.8Sr0.2)0.95MnO3-δ (LSM) and zirconia co-stabilized with 10 mol.% of scandia and 1 mol.% of yttria (10Sc1YSZ). Type-2: bilayered thin electrolyte made of 8YSZ and 10 mol% gadolinia doped ceria (GDC) protective layer deposited on a bilayered anode substrate using the AD method, followed by the screen printing of an active cathode with the composition of (La0.80Sr0.20)0.95CoO3–δ (LSC). The high quality of electrolyte layers of both types of SOFCs was confirmed by scanning electron microscopy, as well as electrochemical measurements, including the measurements of current-voltage characteristics and impedance spectroscopy. At 800 °C the anode-supported cells with humidified hydrogen as a fuel, and air as an oxidant demonstrated the open-circuit voltage of more than 1.04 V for both types of SOFCs, as well as specific power of more than 420 mW/cm2 and 780 mW/cm2 for type-1 and type-2 of SOFCs, respectively. Based on the studies carried out, further steps were determined to improve the electrochemical parameters of the cells, as well as to scale up to deposition on substrates with an area of 100x100 mm2.This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071. Figure 1

Shock Absorption Effect on Particle Fragmentation and Microstructural Features of Vacuum-Kinetic-Sprayed Al2O3 Film on Polycarbonate Substrate

As the demand for flexible devices has increased, polymers have become very promising materials for these applications because they have excellent flexibility, lightweight, and low cost. Vacuum kinetic spraying can be a good alternative technology for film fabrication on polymers as dense ceramic films can be fabricated even at room temperature without thermal degradation of the polymer substrate. However, there is a lack of understanding of the deposition process of ceramic films on a polymer substrate. In this regard, the deposition behavior and microstructural features were investigated by comparing Al2O3 particle deposition on glass and polycarbonate (PC) substrates by using simulations and experimental methods. Simulations demonstrated that hard particles were prone to penetrate or be only embedded in the soft substrate without sufficient fragmentation. This is attributed to the shock absorption effect of the substrate. Particle kinetic energy was transferred mostly to the internal energy of the soft substrate but not to particle internal energy (plasticity and/or failure), which prevents particle fragmentation. Consequently, unusual interface microstructural feature was attributed to insufficient particle fragmentation by the shock absorption of the soft substrate.

Impact Behavior for Successful Particle–Particle Bonding in Vacuum Kinetic Spraying

This study investigated the impact behavior of ceramic particles in vacuum kinetic spray (VKS), also known as aerosol deposition method, for successful coating build-up using both experimental methods and numerical simulations. A coating trial and fluid dynamics simulation results showed that there existed a critical impact velocity at which successive coating build-up was possible. This indicated that particle–particle bonding could be achieved through sufficient kinetic energy of impacting particles. According to the results in this study, it is suggested that the critical velocity values for deposition of Al2O3 and SiO2 in VKS were 400 and 300 m/s, respectively. The AUTODYN simulation results revealed that the initial kinetic energy of particles at high impact velocity should be consumed by fracture and deformation of both impacting particles and the pre-deposited layer. Above critical impact velocity, it is expected that high von Mises stress, pressure, and temperature values contribute to dynamic fragmentation of impacting particles, additional size reduction of crystallites, and consolidation for uncontaminated intimate inter-crystallite faying surface bonding. It is expected that these material responses contributed to the dense and strong VKS coating fabrication.

One-step deposition of a Ni(OH)2-graphene hybrid prepared by vacuum kinetic spray for high energy density hybrid supercapacitor

Hybrid supercapacitors (HSCs) that use the nickel hydroxide-graphene hybrid (NGH) as an anode material and reduced graphene oxide (rGO) as a cathode material are a promising HSC structure. The NGH electrode is synthesized by one-step, binder-free deposition of a micro-size hydroxide powder and graphite powder mixture on nickel foam by the nanoparticle deposition system (NPDS). The NPDS is classified as a vacuum kinetic spraying approach. The electrochemical performance of the NGH-10 electrode in a 3-electrode cell demonstrates a specific capacitance of 3408 F/g at 1 A/g. The NGH-10//rGO HSC displays a specific capacitance of 180 F/g at 1 mA/cm2 in a high operating potential from 0 V to 1.6 V. The NGH-10//rGO HSC has an energy density of 64 Wh/kg @ 411 W/kg, and still 20 Wh/kg @ 8230 W/kg.

Computational Research on Factors Affecting Particle Velocity in a Vacuum Kinetic Spray Process

In vacuum kinetic spraying (VKS) systems, also called aerosol deposition, the particle velocity is crucial because kinetic energy determines successful deposition. However, various factors simultaneously affect particle velocity, which complicates prediction. To address this issue, the factors affecting particle velocity in the VKS process were investigated via computational simulation. The factors were analyzed in terms of particle variables (i.e., particle material, size, and shape factor) and process variables (i.e., process gases and the pressure difference between the two chambers). Consequently, how and to what extent each factor influenced particle average and impact velocity are discussed.

Room temperature impact‐induced deposition of pure SiC coating layer by vacuum kinetic spraying

AbstractThis study successfully manufactured a thick, pure SiC coating layer with a thickness of 83.3 μm using vacuum kinetic spray process and investigated the unique impact‐induced deposition behavior at room temperature. The simulated result of SiC particle collides with the metallic matrix, or predeposited SiC layer confirmed that particle shock pressure could increase up to the maximum pressure of 27.2 GPa. Moreover, the particles were predicted to fracture to submicrometer size after plastic deformation and those characteristics also matched microstructural observations made with a transmission electron microscope. The SiC coating layer formed an unexpected microstructure composed of bent lattices, fractured submicrometer‐sized particles, and amorphous layers. Correlating the microstructure and simulation results suggested that a pure SiC coating layer could be formed using mechanical anchoring and amorphous bonding at room temperature.

Roles of Particle Size Distribution in Bimodal Feedstocks on the Deposition Behavior and Film Properties in Vacuum Kinetic Spraying

Vacuum kinetic spray (VKS), also called aerosol deposition method, is a spray process that makes it possible to fabricate dense ceramic films at room temperature. Although the deposition rate of VKS is better than conventional ceramic coating processes, the deposition properties are still poor for industrial use. In this respect, this work investigates the role of particle size on the deposition behavior by blending two alumina powders having different sizes. It results in suggestions for increasing the deposition efficiency and rate. The microstructure and mechanical properties of films revealed that nanosized particles directly took part in deposition and participated in increasing the deposition rate despite the low adhesion between crystallites. In contrast, relatively large submicron-sized particles mainly contributed to the coating consolidation via severe friction, which strengthened the fragment bonding. Submicron-sized particles also were indirectly deposited as crystallites after sufficient fragmentation. Therefore, it is suggested that the deposition behavior and film properties in VKS can be controlled by adjusting the mixing ratio of two alumina powders with different particle size ranges.

Correlation of Fracture Mode Transition of Ceramic Particle with Critical Velocity for Successful Deposition in Vacuum Kinetic Spraying Process

Vacuum kinetic spraying (VKS) is a promising room-temperature process to fabricate dense ceramic films. However, unfortunately, the deposition mechanism is still not clearly understood. In this respect, the critical conditions for successful deposition were investigated. Based on simulation and microstructural analysis, it was found that as the particle velocity increased, fracture mode transition from tensile fracture to shear fracture occurred and particle did not bounce off anymore above a certain velocity. Simultaneously, particle underwent shock-induced plasticity and dynamic fragmentation. The plasticity assisted to prevent the fragments from rebounding by spending the excessive kinetic energy and fragmentation is essential for fragment bonding and film growth considering that the deposition rate increased as the fraction of fragmentation increased. Accordingly, plasticity and fragmentation take a crucial role for particle deposition. In this respect, the velocity that fracture mode transition occurs is newly defined as critical velocity. Consequently, for successful deposition, the particle should at least exceed the critical velocity and thus it is very crucial for film fabrication in VKS process at room temperature.

진공상온분사 공정을 이용한 세라믹 도료 분말의 장식용 코팅 및 패터닝 제조

진공상온분사 공정을 이용한 세라믹 도료 분말의 장식용 코팅 및 패터닝 제조

Dynamic fragmentation process and fragment microstructure evolution of alumina particles in a vacuum kinetic spraying system

In a vacuum kinetic spraying (VKS) system, submicron ceramic particles impact the substrate and undergo dynamic fragmentation within nano-seconds, resulting in a nano grain film. In this report, a hypothesized mechanism for dynamic fragmentation generated during Al2O3 particle deposition is suggested and tested via Auto-dyn simulation linked to an analysis of distinct fragment microstructures and debris size calculations. Based on this data, shock-induced dynamic fragmentation, one of the crucial elements of clarifying the deposition mechanism, was investigated.

Shock-induced plasticity and fragmentation phenomena during alumina deposition in the vacuum kinetic spraying process

In a vacuum kinetic spraying system, plasticity and fragmentation have been considered as the main deposition mechanisms because the deposited layer exhibits a flattened morphology with nanosized grains. In this research, Al2O3 film was fabricated, and the microstructure was analyzed using Auto-dyn simulation to investigate the deposition mechanism. Plasticity was generated in a ceramic particle by shock loading, and the particle impact intensity affected the fragmentation behavior and consolidation of a previously deposited layer.

Room Temperature Synthesis of Highly Compact TiO2 Coatings by Vacuum Kinetic Spraying to Serve as a Blocking Layer in Polymer Electrolyte-Based Dye-Sensitized Solar Cells

Vacuum kinetic spraying (VKS) was used to form a blocking layer (BL) in order to increase the efficiency of dye-sensitized solar cells. Nano-sized TiO2 powders were deposited on fluorine-doped tin oxide (FTO) glass while varying the coating parameters including the mass flow, substrate transverse speed, and number of coating passes in order to control the thickness of the BL. Compared to the cell without a BL, the open-circuit voltage and short-circuit current density of the solar cell with a VKS-coated BL were noticeably improved. Consequently, the photoconversion efficiency increased up to 5.6%, which is significantly higher than that of a spin-coated BL.

Deposition Behavior and Microstructure of Fe-based Amorphous Alloy Fabricated by Vacuum Kinetic Spraying Process

Deposition Behavior and Microstructure of Fe-based Amorphous Alloy Fabricated by Vacuum Kinetic Spraying Process

Microstructure Evolution of Titanium Nitride Film during Vacuum Kinetic Spraying

Single crystal titanium nitride powder was used to fabricate titanium nitride films using a vacuum kinetic spray (VKS) process. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (FETEM) were used to investigate the microstructure of the as‐fabricated films under different process conditions. Plastic deformation features (i.e., amorphization, rotated grain, slip bands, and distorted lattices in the transition structure) revealed an elastic‐to‐inelastic transition of titanium nitride particles at high strain rate and high pressure induced by hypervelocity impact, which was considered vital for grain refinement and film growth during the process.

Phase evolutions of bulk amorphous NiTiZrSiSn feedstock during thermal and kinetic spraying processes

Abstract An inert gas atomized NiTiZrSiSn powder was sprayed using vacuum plasma spraying, high velocity oxy-fuel (HVOF) spraying, and kinetic spraying. Through this study, the effects of thermal energy and kinetic energy of in-flight particles and oxidizing power of the working environment on the amorphous phase formation were evaluated. In view of the melting state of the impacting particle, the processes are divided into thermal spraying and kinetic spraying. On the other hand vacuum plasma and kinetic spraying can be considered to be inert processes while the HVOF process is regarded as an oxidation process. For the former classification, the peak temperature experienced by the in-flight particles during flight is the critical factor for amorphous formation. The preferential oxidation of Ti and Zr was observed during the oxidative process and this made the chemical composition of the feedstock deviate from the optimum composition. The more in-flight oxidation there was, the less amorphous phase fraction there was.