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16 pages, 4143 KiB

Open AccessFeature PaperArticle

Cold-Sprayed Al6061 Coatings: Online Spray Monitoring and Influence of Process Parameters on Coating Properties

by Heli Koivuluoto, Jussi Larjo, Danilo Marini, Giovanni Pulci and Francesco Marra

Coatings 2020, 10(4), 348; https://doi.org/10.3390/coatings10040348 - 3 Apr 2020

Cited by 27 | Viewed by 4932

Process optimization and quality control are important issues in cold spraying and coating development. Because the cold spray processing is based on high kinetic energy by high particle velocities, online spray monitoring of particle inflight properties can be used as an assisting process [...] Read more.

Process optimization and quality control are important issues in cold spraying and coating development. Because the cold spray processing is based on high kinetic energy by high particle velocities, online spray monitoring of particle inflight properties can be used as an assisting process tool. Particle velocities, their positions in the spray jet, and particle size measurements give valuable information about spraying conditions. This, in turn, improves reproducibility and reliability of coating production. This study focuses on cold spraying of Al6061 material and the connections between particle inflight properties and coating characteristics such as structures and mechanical properties. Furthermore, novel 2D velocity scan maps done with the HW CS2 online spray monitoring system are presented as an advantageous powder and spray condition controlling tool. Cold spray processing conditions were similar using different process parameters, confirmed with the online spray monitoring prior to coating production. Higher particle velocities led to higher particle deformation and thus, higher coating quality, denser structures, and improved adhesions. Also, deposition efficiency increased significantly by using higher particle velocities. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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19 pages, 4572 KiB

Open AccessArticle

Powder Properties and Processing Conditions Affecting Cold Spray Deposition

by Alessio Silvello, Pasquale Daniele Cavaliere, Vicente Albaladejo, Ana Martos, Sergi Dosta and Irene G. Cano

Coatings 2020, 10(2), 91; https://doi.org/10.3390/coatings10020091 - 21 Jan 2020

Cited by 24 | Viewed by 6752

Abstract

The cold spray coating properties and performances are largely affected by feedstock characteristics and the employed processing parameters. Starting from experimental results obtained from the bibliographic data, the relationships between starting particles, processing conditions, and coating properties obtained by cold gas spray were [...] Read more.

The cold spray coating properties and performances are largely affected by feedstock characteristics and the employed processing parameters. Starting from experimental results obtained from the bibliographic data, the relationships between starting particles, processing conditions, and coating properties obtained by cold gas spray were analyzed. The relationships among these properties and particle velocity were described for various material systems. The effect on particle flattening, hardness, and porosity were largely described. Finally, the influence of the different parameters on the process output and on the coating properties was analytically defined through the employment of the multi-objective simulation tool modeFRONTIER. The analysis of data from the bibliography is a new trend that can also be applied to cold spray in order to analyze the effect of powder properties and spraying parameters on the cold spray (CS) process. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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12 pages, 5635 KiB

Open AccessArticle

Cold Gas Spraying of a High-Entropy CrFeNiMn Equiatomic Alloy

by Joonas Lehtonen, Heli Koivuluoto, Yanling Ge, Aapo Juselius and Simo-Pekka Hannula

Coatings 2020, 10(1), 53; https://doi.org/10.3390/coatings10010053 - 8 Jan 2020

Cited by 43 | Viewed by 5346

Abstract

Cold gas spraying was used to make a coating from an equiatomic CrFeNiMn high-entropy alloy. This four-component alloy was chosen because it is Co-free, thus allowing application in nuclear industries as a possible replacement of currently used stainless steel coatings. The feedstock material [...] Read more.

Cold gas spraying was used to make a coating from an equiatomic CrFeNiMn high-entropy alloy. This four-component alloy was chosen because it is Co-free, thus allowing application in nuclear industries as a possible replacement of currently used stainless steel coatings. The feedstock material was gas atomized powder with a particle size distribution from 20 to 45 µm. A number of parameters were tested, such as the powder feed rate and gas feed pressure, in order to obtain as dense a coating as possible with nitrogen as the process gas. Spraying was performed using a gas preheating temperature of 1000 °C, gas feed pressure ranging from 50 to 60 bar, and two powder feeding rates. The coating thicknesses ranging from 230 to 490 µm and porosities ranging from 3% to 10% were obtained depending on the powder feed rate and gas feed pressure. The hardness of the cross-section of the coating was usually lower than that of the surface. The highest coating hardness obtained was above 300 HV_0.3 for both the surface and the cross-section. The as-atomized powder consisted of a face-centered cubic (FCC) phase with a minute amount of body-centered cubic (BCC) phase, which was no longer detectable in the coatings. The microstructure of the coating was highly stressed due to the high degree of deformation occurring in cold gas spraying. The deformation leads to strain hardening and induces a pronounced texture in the coating. The {111} planes tend to align along the coating surface, with deformation and texturing concentrating mainly on particle boundaries. A high-entropy alloy (HEA) coating was successfully sprayed for the first time using nitrogen as a process gas. The coating has the potential to replace stainless steel coatings in nuclear industry applications. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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15 pages, 17252 KiB

Open AccessArticle

Cold Sprayed Tungsten Armor for Tokamak First Wall

by Jan Cizek, Monika Vilemova, Frantisek Lukac, Martin Koller, Jan Kondas and Reeti Singh

Coatings 2019, 9(12), 836; https://doi.org/10.3390/coatings9120836 - 7 Dec 2019

Cited by 23 | Viewed by 8047

Abstract

Harnessing nuclear fusion is a challenging task, in particular because of the demands put on the used materials. In tokamaks, future energy sources, the inner-most chambers are to be coated with dense coatings of W, or W-Cr-based alloys. So far, the attempts for [...] Read more.

Harnessing nuclear fusion is a challenging task, in particular because of the demands put on the used materials. In tokamaks, future energy sources, the inner-most chambers are to be coated with dense coatings of W, or W-Cr-based alloys. So far, the attempts for such coatings formation by other methods failed due to oxidation, high porosity, insufficient adhesion, high specific surface, or even insufficient thickness below 10

μ

m. Cold spraying seems a promising technology for the task. In our study, we demonstrate the first successful fabrication of thick pure W coatings. W-Cr and W-Cr-Ti coatings were further prepared without oxidation of the metals. All coatings exhibited high hardness levels, good interface quality with three tested substrates and, importantly, a promising potential for formation of stable Cr

_{2}

WO

_{x}

phases. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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13 pages, 3405 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Powder Mixture Composition on the Deposition Efficiency in Cold Spay: Modelling and Experimental Validation

by E. Lapushkina and A. Sova

Coatings 2019, 9(12), 832; https://doi.org/10.3390/coatings9120832 - 6 Dec 2019

Cited by 7 | Viewed by 3501

Abstract

In this paper, a new semiempirical probability model, allowing for prediction of the composition of multimaterial cold spray coating in dependence on the initial percentage of blend components, is developed and applied. The proposed modeling approach takes into account the deposition efficiencies and [...] Read more.

In this paper, a new semiempirical probability model, allowing for prediction of the composition of multimaterial cold spray coating in dependence on the initial percentage of blend components, is developed and applied. The proposed modeling approach takes into account the deposition efficiencies and the particle sizes of each component of the spraying powder blend. The experimental validation using several Cu/Cr₂C₃NiCr mixtures with different percentages of copper and cermet powders showed that the simulation results were in a good agreement with the experimental data. It was demonstrated that the deposition efficiency of the Cr₂C₃NiCr cermet powder strongly decreased when its mass percentage in the Cu/Cr₂C₃NiCr mixture increased from 5% to 75%. It was also shown that the dependence of the Cr₂C₃NiCr content in the coating on the initial percentage in the blend was nonlinear and the standard rule of mixtures was not applicable for prediction of copper–cermet coating composition. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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21 pages, 7328 KiB

Open AccessArticle

Prospects of Low-Pressure Cold Spray for Superhydrophobic Coatings

by Anna Gibas, Agnieszka Baszczuk, Marek Jasiorski and Marcin Winnicki

Coatings 2019, 9(12), 829; https://doi.org/10.3390/coatings9120829 - 5 Dec 2019

Cited by 14 | Viewed by 5071

Abstract

A major challenge in materials engineering is the development of new materials and methods and/or novel combination of existing ones, all fostering innovation. For that reason, this study aims at the synergy between low-pressure cold spray (LPCS) as a tool for coating deposition [...] Read more.

A major challenge in materials engineering is the development of new materials and methods and/or novel combination of existing ones, all fostering innovation. For that reason, this study aims at the synergy between low-pressure cold spray (LPCS) as a tool for coating deposition and sol-gel technique for fabrication of the feedstock powder. The complementarity of both methods is important for the examined topic. On one side, the LPCS being automized and quick mean provides the solid-state of feedstock material in nondestructive conditions and hence the hydrophobicity imparted on the sol-gel route is preserved. On the other side, the sol-gel synthesis enables the production of oxide materials with enhanced deformability due to amorphous form which supports the anchoring while LPCS spraying. In the paper, several aspects including optimal fluoroalkylsilane (FOTS) concentration or substrate roughness are examined initially for altering the superhydrophobicity of produced coatings. Further, it is shown that the appropriate optimization of feedstock powder, being submicron silica matrices covered with two-layer FOTS sheath, may facilitate the anchoring process, support roughening the substrate or cause enhancement the coating hydrophobicity. All the discussion is supported by the characteristics including surface morphology, wettability and thermal behaviour examined by electron microscopy, water contact angle measurements and thermal analysis (TGA/DSC), respectively. The coatings presented in the paper are characterized by an uneven thickness of up to a few silica particles, but final hydrophobicity is provided uniformly on the surface by the formation of multi-level roughness by a detachment of outer layer from the SiO₂ particles. Thus, the presented approach constitutes a simple and fast solution for the fabrication of functionalized coatings using LPCS including industrial potential and fundamental research character. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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19 pages, 14067 KiB

Open AccessArticle

Stress Corrosion Cracking Resistance of Cold-Sprayed Al 6061 Deposits Using a Newly Developed Test Fixture

by Mala Sharma, Jeremy Schreiber, Timothy Eden and Victor Champagne

Coatings 2019, 9(7), 445; https://doi.org/10.3390/coatings9070445 - 17 Jul 2019

Cited by 3 | Viewed by 5608

Abstract

The stress corrosion cracking (SCC) response of Al 6061 bulk deposits produced by high-pressure cold spray (HPCS) was investigated and compared to commercial wrought Al 6061-T6 material. Representative tensile coupons were stressed to 25%, 65% and 85% of their respective yield strength and [...] Read more.

The stress corrosion cracking (SCC) response of Al 6061 bulk deposits produced by high-pressure cold spray (HPCS) was investigated and compared to commercial wrought Al 6061-T6 material. Representative tensile coupons were stressed to 25%, 65% and 85% of their respective yield strength and exposed to ASTM B117 salt fog for 90 days. After exposure, the samples were mechanically tested to failure, and subsequently investigated for stress corrosion cracking via optical and scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). The results were compared to the wrought Al 6061-T6 properties and correlated with the observed microstructures. Wrought samples showed the initiation of stress corrosion cracking, while the cold-sprayed deposits appeared to be unaffected or affected by general corrosion only. Optical microscopy revealed evidence of stress corrosion cracking in the form of intergranular corrosion in the wrought samples, while no significant corrosion was observed in the cold-sprayed deposits. Fractography revealed wrought samples failed due to multiple mechanisms, with predominant cleavage and intergranular failure, but cold-sprayed samples only failed by ductile dimple rupture. The difference in SCC response between the differently processed materials is attributed to the documented benefits of the cold spray process, which includes maintaining fine grain structure of the feedstock powder and high density after consolidation, low oxidation, and work hardening effect. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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9 pages, 3025 KiB

Open AccessArticle

Kinetically Deposited Copper Antimicrobial Surfaces

by Victor Champagne, Kristin Sundberg and Dennis Helfritch

Coatings 2019, 9(4), 257; https://doi.org/10.3390/coatings9040257 - 17 Apr 2019

Cited by 39 | Viewed by 6399

Abstract

Bacterial and viral contamination of contact surfaces increases the risk of infection. A great deal of work has been done on the capabilities of copper and its alloys to protect against a variety of microorganisms endangering public health, particularly in healthcare and food [...] Read more.

Bacterial and viral contamination of contact surfaces increases the risk of infection. A great deal of work has been done on the capabilities of copper and its alloys to protect against a variety of microorganisms endangering public health, particularly in healthcare and food processing applications. This work has conclusively shown the effectiveness of copper for touch surface disinfection; however, the optimum microstructural characteristics of the copper surface have not been established. The sterilization effectiveness of three kinetically sprayed copper surfaces and two copper feedstocks were examined. The surfaces were inoculated with methicillin-resistant Staphylococcus aureus (MRSA) and influenza A virus. After a two-hour exposure to the surfaces, the surviving microorganisms were assayed, and the results contrasted. These tests showed substantial antimicrobial differences between the coatings generated by the spray techniques and those obtained by different feedstock powders. The significance of the copper spray application was demonstrated, and the application-dependent mechanism for antimicrobial effectiveness was explained. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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13 pages, 4190 KiB

Open AccessArticle

Physical and Electrochemical Performances of Cold Sprayed Pb Electrodes

by Guosheng Huang, Yaowei Zhuang and Wei Fu

Coatings 2019, 9(3), 174; https://doi.org/10.3390/coatings9030174 - 6 Mar 2019

Viewed by 3611

Abstract

Titanium-based PbO₂ electrodes are widely used for chemical industries, such as electrodialysis, electrolysis, and electrodepositing, to improve the mechanical and life cycle properties of Pb metal electrodes. However, PbO₂ electrodes are usually electrodeposited onto rigid metals due to its soft characteristic, [...] Read more.

Titanium-based PbO₂ electrodes are widely used for chemical industries, such as electrodialysis, electrolysis, and electrodepositing, to improve the mechanical and life cycle properties of Pb metal electrodes. However, PbO₂ electrodes are usually electrodeposited onto rigid metals due to its soft characteristic, which results in severe passivation problems requiring thin thickness and high porosity. It is of great importance to develop a rigid Pb metal electrode system since thermal spraying and welding methods fail to manufacture such a promising electrode. In the present work, the cold spraying method was used to deposit a pure Pb metal coating with thickness of above 500 μm on Q235 steel substrate. The coating has good physical performances, the porosity is less than 1%, and the bonding strength ranges from 6.25 to 7.75 MPa. The cross-sectional morphology suggests that no through-thickness pores exist in the coating. The oxygen evolution potential is larger than 1.5 V vs. SCE, which is similar to the potential of the titanium-based PbO₂ electrode. Dynamic polarization curves and cyclic voltammetry curves of coated sample in sodium sulfate solution indicate that cold sprayed Pb coating is a good electrode for electrochemical reduction reactions. All our results mean that cold spraying is capable of manufacturing electrode materials for electrochemical industries. Full article

(This article belongs to the Special Issue Cold Spraying: Recent Trends and Future Views)

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