Special Issue "Cold Spraying: Recent Trends and Future Views"

A special issue of Coatings (ISSN 2079-6412).

Deadline for manuscript submissions: closed (31 October 2019).

Special Issue Editor

Dr. Heli Koivuluoto
Website
Guest Editor
Materials Science and Environmental Engineering, Faculty of Engineering and Natural Sciences, Tampere University, 33100 Tampere, Finland
Interests: materials science; surface engineering; coating technology; thermal spraying; cold spraying; anti-icing coatings; characterization and testing; coating properties and performance
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Special Issue Information

Dear Colleagues,

Cold spraying is an emerging coating technology, and its development has been very active during the last decades. A larger selection of processes and materials is available, and better technical and functional properties can be achieved with this coating technology. Also, it is raising interest in new application fields, such as additive manufacturing and the medical sector. Improved coating performances, easy manufacturing, understanding of the coating properties and processing factors, as well as assistance processing are some of the main key factors in cold spraying development.

Cold spraying has potential in several industrial sectors and has proven valuable in restoration, repairing, and corrosion and wear protection. The nature of coating formation is a solid-state process, that opens possibilities in a manufacturing of heat sensitive materials and in additive manufacturing. The development and importance of quality are pushing cold spraying technology to the next level.

In the Special Issue, we would like to hear about the latest developments and achievements in the field of cold spraying.

Thus, we cordially invite scientists and academics all over the world to submit original research papers and review articles on cold spraying, its latest developments, applications, as well as coating properties and performance.

In particular, the topics of interest include, but are not limited to:

  • New cold spray processes
  • Process assistance developments in cold spraying
  • Additive manufacturing
  • Feedstock material developments
  • New coating materials
  • Functional coatings
  • Coating properties and performance
  • Quality control
  • Corrosion and wear

Dr. Heli Koivuluoto
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (9 papers)

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Research

Open AccessFeature PaperArticle
Cold-Sprayed Al6061 Coatings: Online Spray Monitoring and Influence of Process Parameters on Coating Properties
Coatings 2020, 10(4), 348; https://doi.org/10.3390/coatings10040348 - 03 Apr 2020
Cited by 2
Abstract
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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Open AccessArticle
Powder Properties and Processing Conditions Affecting Cold Spray Deposition
Coatings 2020, 10(2), 91; https://doi.org/10.3390/coatings10020091 - 21 Jan 2020
Cited by 1
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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Open AccessArticle
Cold Gas Spraying of a High-Entropy CrFeNiMn Equiatomic Alloy
Coatings 2020, 10(1), 53; https://doi.org/10.3390/coatings10010053 - 08 Jan 2020
Cited by 2
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 HV0.3 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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Open AccessArticle
Cold Sprayed Tungsten Armor for Tokamak First Wall
Coatings 2019, 9(12), 836; https://doi.org/10.3390/coatings9120836 - 07 Dec 2019
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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Open AccessFeature PaperEditor’s ChoiceArticle
Effect of Powder Mixture Composition on the Deposition Efficiency in Cold Spay: Modelling and Experimental Validation
Coatings 2019, 9(12), 832; https://doi.org/10.3390/coatings9120832 - 06 Dec 2019
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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Open AccessArticle
Prospects of Low-Pressure Cold Spray for Superhydrophobic Coatings
Coatings 2019, 9(12), 829; https://doi.org/10.3390/coatings9120829 - 05 Dec 2019
Cited by 1
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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Open AccessArticle
Stress Corrosion Cracking Resistance of Cold-Sprayed Al 6061 Deposits Using a Newly Developed Test Fixture
Coatings 2019, 9(7), 445; https://doi.org/10.3390/coatings9070445 - 17 Jul 2019
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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Open AccessArticle
Kinetically Deposited Copper Antimicrobial Surfaces
Coatings 2019, 9(4), 257; https://doi.org/10.3390/coatings9040257 - 17 Apr 2019
Cited by 5
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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Open AccessArticle
Physical and Electrochemical Performances of Cold Sprayed Pb Electrodes
Coatings 2019, 9(3), 174; https://doi.org/10.3390/coatings9030174 - 06 Mar 2019
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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