Vacuum Cold Spray Research Articles

Crystallographic/Morphological Changes and Performance of Lithium Iron Phosphate Deposited By Vacuum Cold Spray

Cold spray offers several advantages for material deposition, including the ability to deposit a wide range of materials without the need for high temperatures, minimizing heat-related distortion and maintaining material properties. Additionally, cold spray is a highly efficient and environmentally friendly process, as it reduces waste and energy consumption compared to traditional thermal spray methods. Lithium iron phosphate (LFP) has been gaining popularity as a cathode material for lithium-ion batteries due to its stable cycling performance, lack of oxygen generation, thermal stability, and use of environmentally friendly iron over nickel or cobalt. In this study, LFP was deposited by vacuum cold spray onto aluminum foil substrate to investigate the viability of cold spray as a possible method of manufacturing all-solid-state batteries. Results were obtained through in-situ X-ray diffraction (XRD), scanning electron microscopy (SEM), and in-situ transmission electron microscopy (TEM). Electrochemical results were obtained by assembling cold spray deposited LFP into half-cells with Li-metal anode and liquid electrolyte before being tested on electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and C-Rate. Due to the high impact velocities during cold spray, crystalline LFP was observed to undergo changes to an amorphous phase. Using in-situ X-ray diffraction (XRD), scanning electron microscopy (SEM), and in-situ transmission electron microscopy (TEM) the crystallographic and morphological changes to cold spray deposited LFP were investigated across various temperatures. In-situ XRD initially showed a decrease in crystallinity with crystallinity being restored with elevated temperatures, with in-situ TEM further supporting these findings. Investigation with SEM showed LFP particles undergo deformation upon impact with a mix of intact particles interspersed throughout to create a dense layer. Electrochemical impedance spectroscopy (EIS) of assembled half-cells show low resistance of 90Ω with further reduction to 60Ω upon cycling of the cell. In terms of cycling performance, initial discharge capacities showed 80 mAh/g and 20mAh/g at 0.1C and 1C respectively. These capacities dropped further with repeated cycling. Future work will be focused on improving capacity, annealing post deposition to restore crystallinity, and incorporation of solid electrolyte.

Influence of the Gas Preheating Temperature on the Microstructure and Electrical Resistivity of Copper Thin Films Prepared via Vacuum Cold Spraying

Vacuum cold spraying (VCS) has emerged as an environmentally sustainable method for fabricating ceramic and metal films. A high particle impact velocity is a critical factor in the deposition of metal particles during the VCS process, which can be significantly enhanced through gas preheating. This study employs Computational Fluid Dynamics (CFD) simulations to investigate the substantial impact of gas preheating temperature on particle impact velocity and temperature. Elevating the gas temperature leads to higher particle impact velocity, resulting in severe deformation and the formation of dense copper films. The experimental results indicate improvements in both film compactness and electrical properties with gas preheating. Remarkably, the electrical resistivity of the copper film deposited at a gas preheating temperature of 350 °C was measured at 4.4 × 10−8 Ω·m. This study also examines the evolution of cone-shaped pits on the surface of copper films prepared on rough substrates. VCS demonstrates a self-adaptive repair mechanism when depositing metal films onto rough ceramic substrates, making it a promising method for ceramic surface metallization.

Study on the performance of Lead zirconate titanate piezoelectric coating prepared by vacuum cold spraying

By utilizing the force-electric conversion capabilities of piezoelectric materials, piezoelectric ceramic coatings are intended to monitor the state of component damage. In this study, lead zirconate titanate [Pb(Zr, Ti)O3, PZT] piezoelectric ceramic coatings were prepared on the SUS304 substrate by vacuum cold spraying (VCS). The phase structure, microstructure, and electrical properties of the PZT coating were analyzed. According to the findings, the PZT coating has a typical tetragonal perovskite structure, and the Xi photoelectron spectrometer (XPS) findings show that the room-temperature deposition characteristics of VCS techniques do not affect the elemental valence state of PZT materials, making it a non-destructive way to create the coating. The surface of the PZT coating is uniform and smooth, and the surface roughness Ra is about 195 nm. The PZT coating has a microhardness of around 1,510 Hv and an elastic modulus of about 73.9 GPa. Meanwhile, the piezoelectric coefficient d33 of the PZT coating was about 46 pC/N. The maximum saturation polarization of the PZT coating was 16.2 μC/cm2, the remnant polarization was 3.1 μC/cm2, and the coercive field was 59.3 kV/cm, which showed some ferroelectricity. The dielectric constant/dielectric loss of the PZT coating was about 425/0.35. The Curie temperature of PZT coating is 392.6 °C, which improves the application temperature range of PZT coating. This demonstrates that the PZT coatings created by VCS have certain electrical capabilities, offering a novel way to create and enhance the piezoelectric ceramic coating system for later-stage part monitoring.

Microstructure and properties of vacuum cold sprayed lead zirconate titanate coating with different pre-annealing of the powder

The effect of powder pretreatment on lead zirconate titanate (PZT) coatings was reported. Annealed powder and the annealed powder of ball milling were used to form PZT coating by vacuum cold spraying. The results show that the coatings were prepared successfully. The thickness range of coatings were 11 μm–13 μm. The d33 values of annealed powder coating and untreated powder coating are 11 pC/N and 55 pC/N. The remnant polarizability (Pr) and dielectric constant (εr) of the PZT coatings exhibited the same trend as that of d33. The PZT coatings formed with annealed powder existed looser agglomerate structures. The agglomerated powder has obvious influence on the performance of PZT coating. The density of coating with milled after annealing powder is higher than that of coating with annealed powder, which was due to the dispersion of agglomerates. The reduction of porosity can improve the electrical properties.

Vacuum cold sprayed nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ as a high-performance cathode for porous metal-supported solid oxide fuel cells operating below 600 °C

Porous metal-supported solid oxide fuel cells (PMS-SOFCs) demonstrate potential to dramatically reduce their costs while simultaneously enhancing the durability of SOFCs. However, owing to the unsatisfactory performance improvement of PMS-SOFCs at low temperatures and available fabrication processes, their commercial applications are limited. In this study, exceptional performance of PMS-SOFCs for electricity generation at low temperatures (400–600 °C) with vacuum cold sprayed (VCS) nanostructured La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) as the high-activity cathode, the plasma-sprayed Ce0.8Gd0.2O2−δ/La0.8Sr0.2Ga0.8Mg0.2O3−δ (GDC/LSGM) bilayer as the electrolyte, and a cermet consisting of the nickel–gadolinium-doped-ceria (Ni–GDC) composite as the anode. By carefully controlling the spray particle size, a nanostructured LSCF cathode is obtained, and the oxygen reduction reaction (ORR) is activated. Consequently, the microstructurally optimized cell exhibits remarkable peak power densities of >1 W/cm2 at 600 °C and >0.2 W/cm2 at 450 °C. Moreover, this nanostructured cathode maintains high activity over 1000 h at 550 °C due to the stable microstructure, strontium (Sr) surface segregation, and the exceptional stability of PMS-SOFCs. Our results demonstrate a simple route to dramatically improve the performance and stability of PMS-SOFCs operating at low temperatures by using a nanoscale cathode for activity toward the ORR.

Narrow and Thin Copper Linear Pattern Deposited by Vacuum Cold Spraying and Deposition Behavior Simulation

Compared with ceramic materials, the fabrication of dense metal films requires higher impact velocity in vacuum cold spraying (VCS), also known as aerosol deposition method. In this study, a supersonic nozzle for the fabrication of dense, thin and narrow copper lines was designed. The acceleration behavior of gas and copper particles was investigated through CFD numerical simulation. And the impact behavior of copper particles was studied through finite element analysis. The copper lines with the width of about 200 μm and the height of about 4 μm were directly fabricated on silicon wafers at room temperature without masking. The results show that there is an optimum particle diameter for the impact velocity in particle collision deposition systems. In order to obtain a higher particle impact velocity in VCS, the substrate should be placed behind the high-pressure region of gas shock wave, so that the position of the high-pressure region of the free jet and the position of the bow shock with the substrate coincide as much as possible. Copper particles undergo plastic deformation and particle flattening upon impact and subsequent particle compaction. The width of copper line increased with increasing standoff distance, and maximum height decreased with increasing standoff distance.

La0.8Sr0.2Ga0.8Mg0.2O3 electrolytes prepared by vacuum cold spray under heated gas for improved performance of SOFCs

High impact velocity of particles has found its common way into the vacuum cold spray (VCS), but heating gas may further intensify this function, resulting in significantly higher impact velocity. That's the original design idea to realize denser ceramic deposition at low temperature in this paper. In this study, a ~ 10 µm thick La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) electrolyte layer for SOFCs is prepared by VCS under heated gas. The effects of gas temperature on the deposition behavior, mechanical and electrical properties of the coatings are investigated. Results show improvements in coating density, hardness and ionic conductivity at elevated temperature. Additionally, the output performance of cell with LSGM electrolytes deposited at gas temperature of 400 °C achieved an open circuit voltage of ~ 1.0 V and the maximum power density of 855 mW/cm2 at 750 °C. Overall, these findings testify of the promising aspects of VCS method for preparing solid electrolyte films for IT-SOFCs.

MD Simulation on Collision Behavior Between Nano-Scale TiO2 Particles During Vacuum Cold Spraying

Particle collision behavior influences significantly inter-nano particle bonding formation during the nano-ceramic coating deposition by vacuum cold spraying (or aerosol deposition method). In order to illuminate the collision behavior between nano-scale ceramic particles, molecular dynamic simulation was applied to explore impact process between nano-scale TiO2 particles through controlling impact velocities. Results show that the recoil efficiency of the nano-scale TiO2 particle is decreased with the increase of the impact velocity. Nano-scale TiO2 particle exhibits localized plastic deformation during collision at low velocities, while it is intensively deformed by collision at high velocities. This intensive deformation promotes the nano-particle adhesion rather than rebounding off. A relationship between the adhesion energy and the rebound energy is established for the bonding formation of the nano-scale TiO2 particle. The adhesion energy required to the bonding formation between nano-scale ceramic particles can be produced by high velocity collision.

Microstructure and Transparent Super-Hydrophobic Performance of Vacuum Cold-Sprayed Al2O3 and SiO2 Aerogel Composite Coating

In this study, vacuum cold spraying was used as a simple and fast way to prepare transparent super-hydrophobic coatings. Submicrometer-sized Al2O3 powder modified by 1,1,2,2-tetrahydroperfluorodecyltriethoxysilane and mixed with hydrophobic SiO2 aerogel was employed for the coating deposition. The deposition mechanisms of pure Al2O3 powder and Al2O3-SiO2 mixed powder were examined, and the effects of powder structure on the hydrophobicity and light transmittance of the coatings were evaluated. The results showed that appropriate contents of SiO2 aerogel in the mixed powder could provide sufficient cushioning to the deposition of submicrometer Al2O3 powder during spraying. The prepared composite coating surface showed rough structures with a large number of submicrometer convex deposited particles, characterized by being super-hydrophobic. Also, the transmittance of the obtained coating was higher than 80% in the range of visible light.

Room-temperature deposition of hydroxyapatite/antibiotic composite coatings by vacuum cold spraying for antibacterial applications

To develop implants with long-term antibacterial property, hydroxyapatite (HA)-gentamicin sulfate (GS) composite powder were synthesized and deposited onto titanium substrates by vacuum cold spraying at room temperature. The successful fabrication of the HA-GS composite powder and coatings was confirmed by transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis, respectively. Gentamicin release kinetics, antibacterial property and biocompatibility were systematically investigated in vitro. Results indicate that we can effectively load the coating with antibiotic and the coating shows long-term antibacterial capacity. Moreover, the HA-GS composite coatings displayed excellent biocompatibility. The approach in this study provides an alternative to fabricate an efficient bioactive drug delivery system for biomedical applications.

Effect of Deposition Temperature on the Microstructure and Performance of Vacuum Cold Sprayed Nano-Structured LSCF Cathodes for Solid Oxide Fuel Cells

Here, we investigate the feasibility of using vacuum cold spray process as a novel method for the cost effective fabrication of a nano-structured La0.4Sr0.6Co0.2Fe0.8O3 (LSCF) as a high-performance cathode for low-temperature solid oxide fuel cells (LT-SOFCs). Nano sized LSCF particles were used as feedstock. The effects of deposition temperature and particle size on the phase composition, microstructure, and electrochemical performance of the resulting cathodes were studied. The results indicate that 10~20 μm nano-structured porous LSCF cathodes can be successfully prepared by vacuum cold spray process. However, the deposition temperature shows significant influence on the microstructure. When the cathode was deposited at room temperature, there were many unbonded interfaces between the cathode and electrolyte. With the increase of deposition temperature, the interface bonding was improved. At a deposition temperature of 300 °C, it can be found that the cathode and electrolyte were bonded well. Besides, the results indicate that the cathode polarization resistance decreased significantly with the decrease of spray particle size. When particle size decreased from 150 nm to 50 nm, the cathode polarization resistance decreased from 11 Ωcm2 to 1.5 Ωcm 2 at 450 °C. Our results suggest that vacuum cold spray has potential to be a low-cost and flexible process suitable for the fabrication of nano-structured cathodes for LT-SOFCs.

Microstructure and Electrochemical Properties of La0.8Sr0.2Ga0.8Mg0.2O3 Thin Film Deposited by Vacuum Cold Spray for Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFC) has attracted considerable attention in recent years as a power conversion system, owing to its high-energy conversion efficiency, fuel flexibility and low pollution emissions as well. Recently, the intermediate temperature-solid oxide fuel cell (IT-SOFC), which operates at lower temperatures (600~800 °C) to reduce cost and to improve efficiency, appears to be an alternative choice for the development of SOFC. La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM), with a perovskite structure, presents a high ionic conductivity at intermediate temperatures. However, the common methods to fabricate the LSGM electrolyte (e.g., solid state method) often lose their advantages owing to the depletion of Ga and the interfacial reaction between the LSGM and electrodes. Vacuum cold spray (VCS), based on the impact adhesion of fine particles to build up ceramic film at room temperature, is a new and promising method to fabricate thin (﹤20 mm) and dense (LSGM) electrolyte membrane. In the present study, the LSGM electrolyte layer with a thickness of ~10 mm is prepared by a home-developed VCS system assisted with in-situ particle heating approach (25~400 °C). The output performance of cells assembled with VCS-LSGM is determined at 500~750 °C. Results show that the OCV value is above 1.0 V, suggesting that the VCS-LSGM electrolyte is dense enough for the application to SOFC. Meanwhile, the ionic conductivities of LSGM coatings prepared by different in-situ particle heating temperatures were determined by an electrochemical impedance spectroscopy system. In addition, the microstructure and phase structure of LSGM coatings was characterized by scanning electron microscopy and X-ray diffraction. Based on this study, it is possible to conclude that the VCS is a promising method to prepare the LSGM electrolyte applied in the IT-SOFC.

Synthesis and Vacuum Cold Spray Deposition of Biofunctionalized Nanodiamond/Hydroxyapatite Nanocomposite for Biomedical Applications

Insufficient biological performances of titanium alloys have been the long‐standing problems for their clinical applications. Here, we report synthesis of novel hydroxyapatite/nanodiamond‐bone morphogenetic protein 2 (HA‐ND/BMP2) composite powder and their coatings deposited by vacuum cold spray operated at room temperature. The microstructure and chemistry of the HA‐ND/BMP2 powder and coatings are characterized by transmission electron microscopy, field‐emission scanning electron microscopy, thin‐film X‐ray diffraction, Raman spectrometry, and X‐ray photoelectron spectroscopy. In vitro growth assay of osteoblasts on the coatings showed that the biofunctionalized nanodiamonds promoted cell adhesion and proliferation. This study provides a promising technical route for constructing biofunctionalized nanocomposites coatings for potential biomedical applications.

Enhanced sintering behavior of LSGM electrolyte and its performance for solid oxide fuel cells deposited by vacuum cold spray

How to obtain dense La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) electrolyte at low sintering temperature (<1300°C) is a challenge to improve solid oxide fuel cell (SOFC) performance at intermediate operation temperature. In this study, a double-layer design method for vacuum cold spray (VCS) prepared-LSGM electrolyte assisted with two-step sintering at a low temperature was proposed. The sintering behavior of VCS deposited LSGM layers at 1200°C was investigated. The LSGM layers became denser in most regions except the appearance of some cracks. Subsequently, the effect of a second LSGM layer on the sintered top layer was studied to block cracks. Results showed that the co-sintered layer with a thickness of approximately 5μm presented a maximum open circuit voltage of ∼0.956V at 650°C and a maximum power density of 592mW/cm2 at 750°C. Result indicates that the sintering assisted VCS is a promising method to prepare the LSGM electrolyte applied in intermediate temperature SOFCs.

Superhydrophobic nanocoatings prepared by a novel vacuum cold spray process

A superhydrophobic TiO2-oleic acid (OA) nanocomposite coating was fabricated by a novel vacuum cold spray (VCS) process at room temperature. The content of OA immobilized on TiO2 nanoparticles could influence the deposition effect during the VCS process, in turn controlling the wettability of nanocoatings acquired. The wettability of the nanocoatings could be adjusted by altering the content of OA in the starting nanocomposite powder. The maximum static water contact angle and the minimum sliding angle were obtained at 151.2°and 1.2°, respectively, with the molar ratio of OA to TiO2 at 1:10. Additionally, it was observed that the newly constructed superhydrophobic coatings display mechanical durability. This study presents a promising approach for fabricating inorganic-organic nanocomposite superhydrophobic coatings for long-term functional applications.

Effect of Deposition Temperature on the Microstructure and Performance of Vacuum Cold Sprayed Nano-Structured LSCF Cathodes for Solid Oxide Fuel Cells

Here, we investigate the feasibility of using vacuum cold spray process for the cost effective fabrication of a nano-structured La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) as a high-performance cathode for solid oxide fuel cells (SOFCs). The results indicate that the deposition temperature shows significant influence on the microstructure. When the cathode was deposited at room temperature, there were many unbonded interfaces between the electrolyte and cathode, and inside the cathode. At a deposition temperature of 300 °C, it can be found that the cathode and electrolyte were bonded well and the cathode showed the lowest polarization resistance (0.5 Ωcm2 at 600 °C). However, with the further increase of deposition temperature, a dense microstructure was obtained and resulted in a polarization resistance increase. Our results suggest that vacuum cold spray has potential to be a low-cost and flexible process suitable for the fabrication of nano-structured cathodes for SOFCs.

Microstructure and Electrochemical Properties of La0.8Sr0.2Ga0.8Mg0.2O3 Thin Film Deposited by Vacuum Cold Spray for Solid Oxide Fuel Cells

Doped lanthanum gallate (La0.8Sr0.2Ga0.8Mg0.2O3, LSGM) is considered as a promising electrolyte material for the intermediate temperature-solid oxide fuel cell (IT-SOFC), due to its high ionic conductivity at 600~800 °C. However, the common methods to fabricate the LSGM electrolyte (e.g., solid phase sintering) often lose their advantages owing to the depletion of Ga and the interfacial reaction between the LSGM and electrodes. Vacuum cold spray (VCS) is an emerging method to fabricate thin (﹤20 μm) and dense ceramic electrolyte membrane. In the present study, the LSGM electrolyte layer with a thickness of ~10 μm is prepared by VCS system assisted with in-situ particle heating approach (25~400 °C). The coating density and the ionic conductivities were increased with heating temperature. The results showed that VCS is a promising method to prepare the electrolyte film applied in the IT-SOFC.

Thin film of Yttria stabilised zirconia on NiO using vacuum cold spraying process for solid oxide fuel cell

Yttria stabilised zirconia (YSZ) was fabricated on a glass and NiO-YSZ anode support substrate using the vacuum cold spraying (VCS) technique at room temperature. The field emission scanning electrode microscope (FESEM) analysis revealed a dense microstructure and several vertical cracks within 0.1 μm width of the YSZ film. The transmission electron microscopy (TEM) was used to analyse the grain size and it was found to be 20 nm which was finer size compared to the average particle size of the starting YSZ powder. The x-ray diffraction (XRD) analysis showed lacking of phase transformation during the VCS process. The YSZ film fabricated by VCS technique showed better gas tightness compared to that fabricated by atmospheric plasma spray process. The Young's modulus of the YSZ film was found to be 172 GPa.

Thin film of Yttria stabilised zirconia on NiO using vacuum cold spraying process for solid oxide fuel cell

Thin film of Yttria stabilised zirconia on NiO using vacuum cold spraying process for solid oxide fuel cell

Effect of the powder particle structure and substrate hardness during vacuum cold spraying of Al2O3

In this paper, the effect of the powder particle structure and substrate hardness during vacuum cold spraying (VCS) of Al2O3 is investigated. Our results help understand the underlying deposition mechanism during VCS in more detail and enable the tailoring and improving of the resulting coatings. Two structurally different alumina feedstocks were used for this study. We find that the loosely agglomerated powder bonds to the substrate primarily through coordinated deformation of the nano-sized powder particles. The sintered powder, on the other hand, bonds to the substrate through severe fracture and deformation of the particles. High-resolution transmission electron microscopy (HR-TEM) was employed to observe details in the interfacial microstructure of the coatings on the two substrates with differing hardness. The hard steel substrate facilitates particle fracture, which leads to cohesive particle/particle-bonding in the coating region close to the substrate. The softer aluminum substrate leads to strong interfacial coating/substrate-bonding because the particles are embedded into the substrate. In summary, the fracture and deformation of the feedstock as well as the substrate hardness affect both adhesion (coating/substrate bonding) and cohesion (particle/particle bonding) considerably.