High Pressure Cold Spray Research Articles

Effect of Ratio of Divergent to Parallel Length in Rectangular Cross Section Nozzle and Particle Size on Spray Pattern of Copper Coating by High Pressure Cold Spray

Effect of Ratio of Divergent to Parallel Length in Rectangular Cross Section Nozzle and Particle Size on Spray Pattern of Copper Coating by High Pressure Cold Spray

Silver Tin Copper (Ag-Sn-Cu) Powder Coating on Aluminum Substrate and Teeth Using High Pressure Cold Spray

Silver Tin Copper (Ag-Sn-Cu) Powder Coating on Aluminum Substrate and Teeth Using High Pressure Cold Spray

Effects of annealing temperature on microstructure and mechanical properties of cold sprayed AA7075

This paper examines the softening behaviour of cold sprayed 7075 aluminum alloy after isothermal annealing. The as-received powder was deposited by a high-pressure cold spray device using heated nitrogen as propellant gas. To investigate the effects of post-deposition heat treatment, the excised samples were isochronally annealed in the temperature range of 200 to 400°C. The feedstock powder and the free-standing coatings were initially characterized through various electron microscopy techniques (SEM, EDS, EBSD) and relevant microstructural features were determined. Mechanical properties of the as-sprayed and heat-treated samples were evaluated by quasi-static tensile and microhardness testing. It has been shown that extensive plastic deformation during cold spraying resulted in a dense coating with relatively low internal porosity. Specimens in an as-deposited state possessed a high level of strain hardening and exhibited a brittle rupture associated with intersplat cracking. When subjected to heat treatment, the cold spray deposits showed a general trend of microhardness reduction and progressive sintering of the microstructure with increasing annealing temperature. Furthermore, post-mortem observation revealed a gradual transition in fracture mechanism, manifested by improving material ductility and the occurrence of typical dimple morphology. The aspects responsible for the softening of the cold sprayed 7075 alloys are discussed further.

Microstructure and mechanical properties of cold spray additive manufactured Cu-Cr-Nb and Fe-Ni-Cr alloys

The main objective of this work was to investigate the microstructure and mechanical properties of Cu-Cr-Nb (GRCop-42) and Fe-Ni-Cr (HR-1) alloy deposits produced using a high-pressure cold spray process. GRCop-42 powder blended with varying content of HR-1 powder (0, 15, 25, 50, 75, 85, and 100 wt%) was cold spray deposited, and the microstructure and mechanical properties of the deposits were evaluated. The deposits were characterized using optical microscopy, X-ray diffraction, and scanning electron microscopy. The use of He process gas resulted in relatively lower porosity and better mechanical properties compared to the deposits produced with N2 process gas. In the as-deposited condition, all the cold spray deposits exhibited brittle behavior with no appreciable ductility. Post-deposition heat treatment significantly improved ductility and tensile strength for both GRCop-42 and HR-1 deposits. However, post-deposition heat treatment resulted in coarsening of Cr2Nb precipitates in GRCop-42, the formation of η phase in HR-1, and the formation of σ phase at the interface in GRCop-42 and HR-1 composite deposits.

Mechanical and Tribological Study on Aluminum Coatings with High-Pressure and Low-Pressure Cold-Spray Processes

Cold spray is a promising approach to repair all damages and defects in aluminum (Al) constituent elements. The study aims to investigate the mechanical and tribological properties of Al coatings deposited using high-pressure cold-spray (HPCS) and low-pressure cold-spray (LPCS) techniques. Al powder was sprayed on a cold-rolled plate of aluminum 1100, which was used as the substrate. The results showed that the micro-hardness of the LPCS Al coating reached up to 196.6 HV before the wear test compared to that of HPCS (174.3 HV). Moreover, more low friction coefficients obtained by LPCS (0.798) than HPCS (0.807) indicated good tribological properties with a high amount of oxide composition. Meanwhile, the wear studies reveal that the specific wear rate of the Al coating of LPCS (0.008) was lower than the HPCS (0.009) as the load increased from 3 N to 5 N, thus providing excellent wear resistance. Therefore, the results exhibited greater mechanical and tribological characteristics for Al coatings produced by the LPCS process than by the HPCS process.

Numerical Study on Particle Behavior and Deposition Accuracy in Cold Spray Additive Manufacturing

Cold Spray additive manufacturing (CSAM) is an emerging technique to fabricate freestanding objects by depositing solid-state layers of materials. Thanks to its remarkable deposition rate and maneuverability, it can be tailored to manufacturing intricate geometries in aerospace industries. In comparison to other additive manufacturing techniques, it is the processing speed, solid-state deposition, and the cost that make CSAM unique. In this study, CSAM process was modeled for a system comprised of a high-pressure cold spray gun with axial powder injection. To represent the flow structure around the already built objects and the deposited layers of CSAM, three walls with different profiles are placed on a flat substrate. In this work, the gas-particle behaviors are studied at the vicinity of these non-axisymmetric objects that can be generalized to more complex geometries and the applications of CSAM. The model is 3D and aluminum and copper powders were used for the feedstock. The particles’ conditions upon impact, such as particles’ footprint and normal impact velocities are studied. The numerical results show that the deviation of particles which is caused by the supersonic flow inside the nozzle and the shock waves outside the nozzle defines the accuracy of the deposition. Furthermore, the results manifest the particle’s material and size have a significant influence on the acquired velocities and trajectories of the particles, and consequently on the resolution of the process. It is found that the profile of the deposited layers has some effects on the gas flow near the substrate which plays a role in the dispersion of fine particles.

Cyclic behavior of FeCoCrNiMn high entropy alloy coatings produced through cold spray

FeCoCrNiMn high entropy alloy powders were employed to produce coatings on carbon steel through high pressure cold spray (at 1100 °C and 7 MPa in temperature and pressure respectively). X-ray diffraction of the sprayed material revealed a dense coating with the retention of the original crystallographic structure. Once splatted, particles revealed high flattening ratio with consequent excellent adhesion of the coating to the substrate. Residual stresses and hardness increased through the thickness of the coating. The cyclic behavior of the coatings was evaluated through bending tests. The cyclic bending tests were performed by linearly increase the maximum deformation at a fixed number of loading cycles. Other bending tests were conducted at fixed maximum stroke at the same deformation levels indicated for the previous test up to the coating fracture. For ach 100 cycles the test was stopped in order to observe the coating surface to gain the possibility of evaluating the aspect of the superficial fracture. The fracture surface of the coatings was observed through scanning electron microscopy in order to describe the cracking features related to the different loading conditions imposed to the coatings.

Post treatment of cold sprayed coatings using high-energy infrared radiation: First comprehensive study on structure-property correlation

It is a well-known fact that cold sprayed coatings need post treatment to achieve properties close to their bulk counterparts even when the coatings are obtained using high pressure cold spray. Most often post treatments are conventional furnace heat treatments primarily to relieve stresses and improve splat bonding. However, this methodology cannot be used all the time given the dimensional constraints of a furnace. Use of in tandem heating or mobile heating tools can greatly enhance the commercial potential of cold spray provided the heating tools are cheaper and easily available. In the present study, one such heating tool viz., high energy infrared emitters are used to post treat cold sprayed copper based coatings. A comprehensive study exploring the influence of heating power density and exposure duration on coating properties and microstructure has been taken up in the present work. Furnace heat treatment studies and post treatment of CuAl alloy coatings has also been studied for comparison. Pure Cu coatings respond exceedingly well to the mobile post treatment in terms of amelioration in coating microstructure and properties comparable to and better than furnace. An analysis of the contribution from different microstructural features to the coating properties especially electrical conductivity have been made. In contrast, CuAl alloy coatings respond less favourably to both infrared and furnace post treatments. A discussion towards this anomalous behavior is also provided with the help of the microstructural observations.

High-Pressure Cold Spray Coatings for Aircraft Brakes Application

This paper addresses the potential use of high-pressure cold spray (HP-CS) technology to produce a film of friction material onto a low-carbon steel substrate to allow its use as potential composite material for the stators and rotors of aircraft brake units. Namely, WC-Cr3C2-Ni, WC-Ni, WC-Co-Cr, Cr3C2-NiCr and WC-Co coatings were deposited by using HP-CS, for the purpose of creating high friction and wear resistance composite coatings onto a low-carbon steel substrate. Tribological (friction coefficient and wear rate) and thermal properties as well as coating hardness and adhesion to the low-carbon steel substrate were evaluated to assess the potential use of the coatings as brake surface materials. The tribological and adhesion properties were evaluated by using a pin-on-disk high-temperature tribometer at 450 °C and a scratch test, respectively, whereas coatings hardness was evaluated with a Rockwell C hardness tester. Results obtained show that all coatings exhibit high friction coefficients and low wear rates compared to the low-carbon steel substrate, good adhesion, and elevated microhardness. Furthermore, the WC-Co coating shows better microhardness and thermal properties, while the WC-Co-Cr coating exhibited a better friction coefficient. Unfortunately, it was not possible to quantify the wear resistance due to the elevated roughness of the coatings, but from the analysis carried out on the alumina counterpart of the tribometer, it can be concluded that all the coatings exhibited a very low wear rate. In fact, after the tribological tests, it emerged that the alumina counterpart was more abraded than the investigated coatings.

Effect of substrate surface finish and particle velocity on fatigue performance of cold spray coated A6061 aluminum alloy

Cold spray coatings made with powder of the same material as the substrate can be used to improve fatigue performance and/or to repair damaged parts. The effects of substrate surface finish and particle impact velocity on the bond strength and fatigue performance of Al-6061-T6 substrates coated with Al-6061 powder by using high pressure cold spray (CS) were investigated. To evaluate the effect of particle velocity, coatings were prepared by using both nitrogen (N2) and helium (He) as carrier gases. A new method for substrate surface preparation was introduced by low angle spraying (LAS) with the same powder prior to coating. The bond bar specimens in polished, semi-polished, grit-blasted (GB) and low angle sprayed (LAS) conditions were coated and tested for bonding strength. The microstructural characteristics and microhardness profiles of the coated samples were also evaluated. Fatigue tests on uncoated and coated samples were conducted under fully-reversed axial loading in load-controlled condition. The failure mechanism was identified by evaluating the fracture surfaces using scanning electron microscopy. The results showed that both bonding strength and fatigue performance of the coated specimens prepared by using He-gas were significantly higher than those prepared by using N2. Among the N2-sprayed coatings, the bonding strength of on LAS substrates were significantly higher than that of the other surface conditions, and the bonding strength of coatings on GB substrates was superior to that of polished and semi-polished samples. However, the fatigue performance of LAS-coated samples was inferior compared to uncoated samples due to cracks initiating in the coating and propagating into the substrate. The fatigue behavior of GB-coated specimens was similar to the uncoated samples due to delamination of the coating which resulted in stopping the cracks that initiated in the coating.

Solution and Double Aging Treatments of Cold Sprayed Inconel 718 Coatings

In this study, Inconel 718 coatings were deposited by the high-pressure cold spray technique, and post-process solution and double aging treatments were conducted. The microstructures of the as-deposited and heat-treated IN718 were analyzed, and their mechanical properties were tested. It was found that the micro-dendritic structures in the original powder were severely elongated in the as-deposited IN718 coating due to plastic deformation during the cold spray process. After solution heat treatment, Nb, Mo, and Ti-rich segregations could be dissolved, transforming to MC carbide and a needle-like δ phase. It was found that the needle-like δ phase at the grain boundary had a pinning effect to slow down the grain growth. In addition, strengthening phases could be formed by aging treatments. The mechanical properties of the cold sprayed Inconel 718 could be improved by proper solution and aging heat treatments.

Improved 3D porous structures of Ni electrodes prepared by high-pressure cold spray and post annealing for water splitting

For improving the performance of water splitting, high pressure cold spray was applied to prepare Ni electrodes with controlled 3D porous structures. Al was added as pore former to endow the Ni electrodes with porous structures. Heat treatment was performed to improve the adhesion of the prepared coatings and thus boost the durability of the obtained Ni electrodes. The electrochemical results and characterizations revealed that porous Ni electrodes were successfully obtained. The porosity of obtained electrodes was increased with the addition of Al. Alloy phases such as NiAl and Ni3Al were detected after heat treatment. An oxide layer was found surrounding Ni layers after chemical leaching. The thickness of oxide layer was found increased with heating temperature and Al addition. NiO, Ni(OH)2 and NiOOH were found in the leached samples. With porous coatings, the electrodes possessed an improved current density of HER/OER. The Tafel slops of HER/OER were about 120mv/dec which indicated that the rate of water splitting was controlled by Volmer step. Due to the existence of oxide layers and unconnected pores, some samples exhibited Warburg diffusion behavior. Benefitting from the loose and porous microstructure, N30A sintered at 400 °C performed the best catalytic activity for HER/OER, and is considered the best sample for water splitting in alkaline condition.

Impact Behaviour of Aluminum Particles upon Aluminum, Magnesium, and Titanium Substrates using High Pressure and Low-Pressure Cold Spray

This study is focused on the impact and residual stress behaviour of aluminum component repair using aluminum powder via two different types of cold spray processes; high pressure cold spray (HPCS) and low-pressure cold spray (LPCS). It has been carried out via smoothed particle hydrodynamics simulations, comparing aluminum substrate with other lightweight materials such as titanium and magnesium. The obtained results have shown that the impact behaviour is influenced by velocity, porosity, deformation behaviour, flattening ratio, total energy and maximum temperature. The aluminum particles impacting on aluminum substrates using LPCS is slightly deformed, with the smallest flattening ratio leading to less pore formation between the particles. This has subsequently resulted in good coating quality. Furthermore, HPCS has contributed greatly to the deposition of particles on the heavier and harder substrate, such as titanium substrate. Thus, the overall result indicates that LPCS is better for repairing aluminum component compared to HPCS.

Effect of Gas Propellant Temperature on the Microstructure, Friction, and Wear Resistance of High-Pressure Cold Sprayed Zr702 Coatings on Al6061 Alloy

For the first time, Zr702 coatings were deposited onto an Al6061 alloy using a high-pressure cold spray (HPCS) system. In this work, five different N2 process gas temperatures between 700 and 1100 °C were employed to understand the formation of cold sprayed (CS) Zr coatings and their feasibility for enhanced wear resistance. Results indicated that the N2 processing gas temperature of about 1100 °C enabled a higher degree of particle thermal softening, which created a dense, robust, oxide- and defect-free Zr coating. Across all CS Zr coatings, there was a refinement of crystallinity, which was attributed to the severe localized plastic deformation of the powder particles. The enhanced thermal boost up zone at the inter-particle boundaries and decreased recoverable elastic strain were accountable for the inter-particle bonding of the coatings at higher process gas temperatures. The flattening ratio (ε) increased as a function of temperature, implying that there was a greater degree of plastic deformation at higher N2 gas temperatures. The microhardness readings and wear volume of the coatings were also improved as a function of process gas temperature. In this work, the wear of the Al6061 alloy substrate was mainly plowing-based, whereas the Zr CS substrates demonstrated a gradual change of abrasive to adhesive wear. From our findings, the preparation of CS Zr coatings was a feasible method of enhancing the wear resistance of Al-based alloys.

Inconel 713C Coating by Cold Spray for Surface Enhancement of Inconel 718

Inconel 713C is a nickel-based superalloy usually considered as a material of poor weldability due to its susceptibility to hot cracking in the heat-affected zones. Cold spray, a solid-state deposition technology that does not involve melting, can be proposed as a methodology to deposit Inconel 713C for surface enhancement of other target components. In this study, Inconel 713C coating was deposited on Inconel 718 substrate with a high-pressure cold spray system. The coating was characterized in terms of microstructure, hardness, and wear properties. The cold-sprayed Inconel 713C coating has a low porosity level and refined grain structures. Microhardness of the Inconel 713C coating was much higher than the Inconel 718 substrate. The sliding wear tests showed that the wear resistance of the cold-sprayed Inconel 713C coating is three times higher than the Inconel 718 substrate, making the coating a suitable protective layer. The main wear mechanisms of the coating include oxidation, tribo-film formation, and adhesive wear.

Influence of Cold Spray Parameters on Bonding Mechanisms: A Review

The cold spray process is governed by the impact of high velocity feedstock particles onto a substrate without melting. Hence, the bulk material properties are retained. However, it is challenging to achieve good adhesion strength. The adhesion strength depends on factors such as the cold spray process parameters, substrate conditions, coating/substrate interactions at the interface and feedstock material properties. This review examines fundamental studies concerning the adhesion mechanisms of cold spray technology and considers the effect of cold spray input parameters such as temperature, stand-off-distance, pressure, process gas, spray angle, and traverse speed of the cold spray torch on the bonding mechanism and adhesion strength. Furthermore, the effects of substrate conditions such as temperature, hardness, roughness and material on the adhesion mechanism are highlighted. The effect of feedstock properties, such as feed rate, shape and size are summarized. Understanding the effect of these parameters is necessary to obtain the optimal input parameters that enable the best interfacial properties for a range of coating/substrate material combinations. It is expected that feedstock of spherical morphology and small particle size (<15 μm) provides optimal interfacial properties when deposited onto a mirror-finished substrate surface using high pressure cold spray. Deep insights into each parameter exposes the uncovered potential of cold spray as an additive manufacturing method.

An investigation into microstructure, tribological and mechanical properties of cold sprayed Inconel 625 coatings

In this study, Inconel 625 coatings were successfully deposited on 6061 aluminum alloy using a high-pressure cold spray process. The microstructure, mechanical and tribological properties of the coatings were systematically studied. The cold sprayed Inconel 625 coatings had a low porosity level due to the severe plastic deformation of the splats. EBSD analyses revealed that grain refinement occurred within the coatings and substrates (near the substrate-coating interface), which could be attributed to strain accumulation and fragmentation process. Good adhesion strength of above 57.0 MPa was achieved between the coatings and substrates. Nano-hardness and micro-hardness values were higher than those of bulk Inconel 625 and were uniform along the thickness of the coatings. The effects of normal load and sliding velocity on the tribological properties of cold sprayed Inconel 625 coatings were investigated by sliding wear tests . The wear results demonstrated that both increased sliding velocity and normal load led to higher specific wear rates, which could result from the combined effects of tribo-film delamination , adhesive wear , abrasive wear, and thermal softening. Lower coefficients of friction of the coatings measured under 5 N compared to those measured under 2 N with the same sliding velocity could be explained by transition of wear mechanisms as well as larger coverage of tribo-film on the wear tracks. • Inconel 625 coating was successfully cold sprayed onto aluminum alloy 6061. • Hardness of the coating was much higher than the bulk Inconel 625 alloy. • The adhesion strength greater than 57 MPa was achieved. • Coefficient of friction decreased with increasing normal load. • Wear mechanisms at varying normal load and sliding velocity were revealed.

Improvement of Wear, Pitting Corrosion Resistance and Repassivation Ability of Mg-Based Alloys Using High Pressure Cold Sprayed (HPCS) Commercially Pure-Titanium Coatings

In this study, a compact cold sprayed (CS) Ti coating was deposited on Mg alloy using a high pressure cold spray (HPCS) system. The wear and corrosion behavior of the CS Ti coating was compared with that of CS Al coating and bare Mg alloy. The Ti coating yielded lower wear rate compared to Al coating and Mg alloy. Electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization (CPP) tests revealed that CS Ti coating can substantially reduce corrosion rate of AZ31B in chloride containing solutions compared to CS Al coating. Interestingly, Ti-coated Mg alloy demonstrated negative hysteresis loop, depicting repassivation of pits, in contrast to AZ31B and Al-coated AZ31B with positive hysteresis loops where corrosion potential (Ecorr) > repassivation potential (Erp); indicating irreversible growth of pits. AZ31B and Al-coated AZ31B were most susceptible to pitting corrosion, while Ti-coated Mg alloy indicated noticeable resistance to pitting in 3.5 wt % NaCl solution. In comparison to Al coating, Ti coating considerably separated the AZ31BMg alloy surface from the corrosive electrolyte during long term immersion test for 11 days.

Cold Spraying of IN 718-Ni Composite Coatings: Microstructure Characterization and Tribological Performance

INCONEL 718 superalloy (IN 718) is frequently used in highly aggressive environments, such as aerospace and gas turbine engines, where excellent mechanical properties, creep-, fatigue- and oxidation-resistance performance at high and cryogenic temperatures are required. Recent studies have successfully cold sprayed IN 718, showing great potential mainly in maintenance and repairing fields. However, due to the low plastic deformation, the manufacture of IN 718 cold sprayed coatings often requires the use of expensive propulsive gases or high working parameters to enhance deposition efficiency, with a significant increase in production costs. This paper investigates for the first time the addition of Ni to IN 718 powders in order to increase plastic deformation and interparticle bonding strength. Four composite coatings were deposited via a high-pressure cold spray process using nitrogen as propulsive gas, considering different IN 718 mass fractions in the feedstock: C1 (0 wt%), C2 (25 wt%), C3 (50 wt%), C4 (75 wt%). The coatings are examined in terms of microstructural characteristics and tribological performance. The addition of IN 718 particles significantly improves the mechanical properties of the coatings, despite an increase in porosity, which however does not exceed 1%. The tribological performance of the four coatings is investigated using a pin-on-disk test, demonstrating that the coating wear resistance behaviour improved as the IN 718 content increased. Analysis of the wear mechanism shows that C4 coating has a different wear behaviour than the other coatings, thus achieving the best wear-resistance performance.

Characteristics of spray pattern flattened aluminum coating by the high-pressure cold spray rectangular cross -section nozzle

Characteristics of spray pattern flattened aluminum coating by the high-pressure cold spray rectangular cross -section nozzle