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A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Surface Characterization, Deposition and Modification".

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 28680

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Dr. Chi Wai Chan

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School of Mechanical and Aerospace Engineering, Queen’s University Belfast, University Road, Belfast BT7 1NN, Northern Ireland, UK
Interests: laser surface engineering; laser additive manufacturing; laser welding/joining for high-value manufacturing applications
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Special Issue Information

Dear Colleagues,

Laser surface engineering (LSE) is a promising and effective technique to enhance the surface properties of bulk materials, such as resistance to wear, corrosion, fatigue, high temperature, bacteria, etc. It has been successfully applied across a wide range of industries in modern manufacturing, spanning from applications in aerospace and automotive to electronics and healthcare. LSE possesses the competitive advantages of being a clean (non-contact), fast, low heat input (minimal thermal deformation), highly precise, controllable and repeatable process, and, in addition, being able to retain the bulk properties of the substrate. It can be broadly classified into two classes: The first is to modify/enhance the surface properties without adding new material(s) in the surface or using reactive gases (e.g., N₂) during the LSE process, such as laser surface melting, laser texturing and laser shot peening, whilst the second is to form/deposit new surface layers that involve addition of new material(s) or reaction with reactive gases, such as laser nitriding, laser surface alloying, laser cladding and pulsed laser deposition. The common aims of the aforementioned LSM techniques are to tackle a variety of challenges faced by the industries, particularly to fulfil the tough demands encountered in complex, dynamic and/or extreme environments. With the rapid advancement of fibre laser technology in the last decade, LSE is becoming more cost-effective, efficient and easily adoptable to integrate with robotic systems in a manufacturing production line.

For this Special Issue, we are inviting papers in the field of LSE applied to engineering materials (metals, polymers, ceramics, and composites), particularly welcoming those which involve the use of fibre laser technology, for modifying, enhancing and/or optimising the surface properties.

Topics of interest for this Special Issue include, but are not limited to:

Development of novel, multifunctional coatings by LSE;
Novel experimental setups for process monitoring, control and/or optimisation of LSE;
LSE for enhancing the biocompatibility, bioactivity, osseointegration and/or antibacterial properties of surfaces;
LSE for enhancing the fatigue, fretting fatigue and/or stress corrosion cracking (SCC) resistance of surfaces;
LSE for enhancing the tribological properties of surfaces;
LSE for enhancing the corrosion and/or oxidation resistance of surfaces;
LSE applied as post-process/in-situ surface-treatment in additive manufacturing;
LSE for repairing damaged, high value engineering parts.

Dr. Chi Wai Chan
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 submissions that pass pre-check are 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 2600 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 (10 papers)

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Research

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11 pages, 4075 KiB

Open AccessArticle

Development of Laser Cavitation Peening Using a Normal-Oscillation Nd:YAG Laser

by Hitoshi Soyama

Coatings 2023, 13(8), 1395; https://doi.org/10.3390/coatings13081395 - 08 Aug 2023

Cited by 1 | Viewed by 978

Abstract

The impact induced by cavitation bubble collapse can be utilized for mechanical surface treatment to improve fatigue properties of metals including additive manufactured metallic materials. A peening method using cavitation impact induced by a pulsed laser is called “laser cavitation peening (LCP)”. Normally, a Q-switched Nd:YAG laser, whose pulse width is a few nanoseconds, is used for LCP, which improves the fatigue strength. The problem with LCP is that the processing time is too slow. If a laser pulse whose pulse width is a few hundred microseconds can be utilized for LCP, the repetition frequency can be increased drastically using other types of laser systems such as a fiber laser. In the present paper, in order to reveal the possibility of LCP using a pulsed laser width of a few hundred microseconds, the use of LCP with a normal-oscillation Nd:YAG laser (pulse width ≈ 200 μs) was investigated. It is demonstrated that LCP with the normal-oscillation Nd:YAG laser produced curvature in an aluminum alloy plate. The shock pressure wave and impulsive vibration of the target surface at the first collapse of laser cavitation (LC), which was induced by the normal-oscillation Nd:YAG laser, was 3–4 times larger than those of laser ablation (LA). Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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13 pages, 21415 KiB

Open AccessArticle

Owens–Wendt Characterization of Femtosecond-Laser-Textured Hydrophobic Aluminum Surfaces

by Oleksiy Myronyuk, Denys Baklan, Aleksej M. Rodin, Egidijus Vanagas and Zuo Yong

Coatings 2023, 13(6), 1104; https://doi.org/10.3390/coatings13061104 - 15 Jun 2023

Cited by 2 | Viewed by 1140

Abstract

The eligibility of applying the Owens–Wendt approach to determining the free surface energy of liquid-repellent aluminum surfaces, with micro- and nanotextures formed by a femtosecond laser, was considered. This approach has been shown to be applicable using two essential parameters that can be derived from the graphs. The first is related to the fraction of the contact area between the liquid and the solid surface in the Cassie state. The second is related to the degree of intrinsic polarity of the surface material or the applied organic modifier. The presented interpretation was used to compare the liquid repellency of the obtained textures. A microtexture with a period of 60 μm and a groove width of 45 μm has been shown to be the most liquid repellent. Among the modifiers, 1H,1H,2H,2H-perfluoroctyltriethoxysilane was the most effective, and stearic acid was only slightly inferior, but promising in terms of cost and environmental friendliness. It was shown that spontaneous hydrophobization provided a contact angle with water up to 159°, but the stability of such textures was inferior to the considered modifiers. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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13 pages, 2163 KiB

Open AccessFeature PaperArticle

Enhancing Coating Adhesion on Fibre-Reinforced Composite by Femtosecond Laser Texturing

by Filomena Piscitelli, Raffaele De Palo and Annalisa Volpe

Coatings 2023, 13(5), 928; https://doi.org/10.3390/coatings13050928 - 15 May 2023

Cited by 3 | Viewed by 1358

Abstract

Carbon fibre-reinforced polymers (CFRP), thanks to their properties such as lightness, resistance to corrosion and fatigue, are emerging composite materials in the aeronautic fields, guaranteeing to reduce weight and costs by maintaining high performances in terms of strength and security. For preventing fluid damage and freezing, in aeronautic applications, CFRP parts need to be coated by painting. However, the paint/coating adhesion on CFRP composites is generally poor and affected by surface conditions. In this work, femtosecond laser texturing was investigated as an approach to improve adhesion of superhydrophobic coatings (SHC) to CFRP substrates. The laser textured surfaces show, after coating, a more lasting superhydrophobic behaviour compared to the as received sample, even after several cleaning cycles, demonstrating that the laser pre-treatment is a reliable and green method to enhance the adhesion of the SHC to the composite substrate. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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18 pages, 7333 KiB

Open AccessFeature PaperArticle

Laser Cladding of NiCrBSi/WC + W₂C Composite Coatings

by Aleksander Lisiecki and Agnieszka Kurc-Lisiecka

Coatings 2023, 13(3), 576; https://doi.org/10.3390/coatings13030576 - 07 Mar 2023

Cited by 2 | Viewed by 1805

Abstract

This article presents the results of a study on the laser cladding of metal matrix composite coatings using an experimental custom-made powder composed of NiCrBSi matrix with 65 wt.% reinforcing hard particles of eutectic WC + W₂C. The chemical and phase composition of the powder was designed to ensure high hardness, abrasion wear resistance at moderate dynamic loads and corrosion resistance at high temperature of the coatings. The influence of the basic processing parameters of the laser cladding, especially energy input, on the quality and single bead geometry, the dilution, share of the massive carbides in the matrix, and the fraction share of reinforcing carbides particles on cross-section of the clads, as well as hardness profiles and abrasive wear resistance, were analysed and presented. The microstructure of test coatings, chemical and phase composition were analysed by optical and scanning electron microscopes (OM, SEM), EDS and XRD spectrometers. It was found that the differences in the wear resistance of the coatings produced at different energy inputs of laser cladding were directly related to the share of the massive carbides WC + W₂C in the metal matrix NiCrBSi. The tribological characteristics of the coatings were also studied and described. The test results indicate that the coefficient of friction for carbides is slightly higher than for the metal matrix, and therefore the greater the share of carbides, the higher the value of the coefficient of friction of the coating. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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10 pages, 11427 KiB

Open AccessArticle

Effect of Mo Content on Microstructure and Mechanical Properties of Laser Melting Deposited Inconel 690 Alloy

by Chen Liu, Wenbo Yao, Shuo Shang, Kuaikuai Guo, Hang Sun and Changsheng Liu

Coatings 2023, 13(2), 340; https://doi.org/10.3390/coatings13020340 - 02 Feb 2023

Cited by 1 | Viewed by 1218

Abstract

Inconel 690 alloy is widely used in nuclear power, petrochemical, aerospace, and other fields due to its excellent high-temperature mechanical properties and corrosion resistance. The Inconel 690 alloy with different Mo content was fabricated by laser melting deposition (LMD). The effects of Mo content on the microstructure and mechanical properties were investigated. The microstructure of as-deposited Inconel 690 is composed of columnar dendrites grown epitaxially, and M₂₃C₆ carbides are precipitated in the grain boundaries. With the increase of Mo content, the amount of precipitated carbide increases gradually. At the same time, the grain boundary becomes convoluted. The tensile test at room temperature shows that the high Mo content in the as-deposited Inconel 690 increases the ultimate strength but decreases the ductility. Compared with low Mo content, the alloy with high Mo deposition has better mechanical properties. The present study provides a new method to achieve the preparation of Inconel 690 alloy with excellent integrated mechanical properties. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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15 pages, 5270 KiB

Open AccessArticle

Tailoring Al–Li Alloy Surface Wettability with a Femtosecond Laser and Its Effect on Bonding Performance

by Jun Chen, Yibo Li, Minghui Huang and Lei Dong

Coatings 2021, 11(8), 995; https://doi.org/10.3390/coatings11080995 - 20 Aug 2021

Cited by 2 | Viewed by 2341

Abstract

In this study, a femtosecond laser was used to pretreat the surface of the Al–Li alloy, the surface micromorphology, roughness, contact angle, and surface wettability of which were adjusted by changing the laser scanning speed, and the sample was bonded into a single joint with polyether ether ketone (PEEK) adhesive. The mechanism of the laser surface treatment affecting the bonding strength of the Al–Li alloy was explored through tensile and shear experiments. The results indicated that optimizing the laser surface treatment parameters could change the surface roughness and surface micromorphology of the Al–Li alloy, so as to change its surface free energy and bonding strength. Compared with the untreated sample, the bonding strength of the Al–Li alloy increased by 81%, 95%, 107%, 91%, and 78% under the treatment of laser scanning at 25, 20, 15, 10, and 5 mm/s, respectively. As a whole, femtosecond laser etching of the Al–Li alloy surface had an important influence on its wettability and bonding performance. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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12 pages, 3554 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improving the Laser Texture Strategy to Get Superhydrophobic Aluminum Alloy Surfaces

by Annalisa Volpe, Sara Covella, Caterina Gaudiuso and Antonio Ancona

Coatings 2021, 11(3), 369; https://doi.org/10.3390/coatings11030369 - 23 Mar 2021

Cited by 26 | Viewed by 3758

Abstract

Changing the wetting properties of surfaces is attracting great interest in many fields, in particular to achieve a surface with a superhydrophobic behavior. Laser machining is an emerging technique to functionalize materials with high precision and flexibility without any chemical treatment. However, when it is necessary to treat large area surfaces laser-based methods are still too slow to be exploited in industrial productions. In this work, we show that by improving the laser texture strategy it is possible to reduce the laser processing time to produce superhydrophobic aluminum alloy surfaces. Three different surface texture geometries were micromachined; namely, square, circular and triangular lattice grooves. We found that if the spacing between the grooves is narrow, i.e., when the percentage of the textured surface is high, the volume of air trapped inside the micromachined structures plays an important role in the wetting behavior. Meanwhile, when the groove spacing approaches the droplet dimensions, the texture geometry has a preponderant influence. Based on these findings an appropriate choice of the laser texture strategy allowed the fabrication of superhydrophobic aluminum alloy surfaces with a 10% reduction of processing time. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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16 pages, 6511 KiB

Open AccessArticle

Mechanical Properties and Hydrogen Embrittlement of Laser-Surface Melted AISI 430 Ferritic Stainless Steel

by W. K. Chan, C. T. Kwok and K. H. Lo

Coatings 2020, 10(2), 140; https://doi.org/10.3390/coatings10020140 - 04 Feb 2020

Cited by 4 | Viewed by 3260

Abstract

In the present study, the feasibility of laser surface melting (LSM) of AISI 430 ferritic stainless steel to minimize hydrogen embrittlement (HE) was investigated. LSM of AISI 430 steel was successfully achieved by a 2.3-kW high power diode laser (HPDL) with scanning speeds of 60 mm/s and 80 mm/s (the samples are designated as V60 and V80, respectively) at a power of 2 kW. To investigate the HE effect on the AISI 430 steel without and with LSM, hydrogen was introduced into specimens by cathodic charging in 0.1 M NaOH solution under galvanostatic conditions at a current density of 30 mA/cm² and 25 °C. Detail microstructural analysis was performed and the correlation of microstructure with HE was evaluated. By electron backscatter diffraction (EBSD) analysis, the austenite contents for the laser-surface melted specimens V60 and V80 are found to be 0.6 and 1.9 wt%, respectively. The amount of retained austenite in LSM specimens was reduced with lower laser scanning speed. The surface microhardness of the laser-surface melted AISI 430 steel (~280 HV_0.2) is found to be increased by 56% as compared with that of the substrate (~180 HV_0.2) because of the presence of martensite. The degree of embrittlement caused by hydrogen for the charged and non-charged AISI 430 steel was obtained using slow-strain-rate tensile (SSRT) test in air at a strain rate of 3 × 10⁻⁵ s⁻¹. After hydrogen pre-charging, the ductility of as-received AISI 430 steel was reduced from 0.44 to 0.25 while the laser-surface melted AISI 430 steel showed similar tensile properties as the as-received one. After LSM, the value of HE susceptibility I_δ decreases from 43.2% to 38.9% and 38.2% for V60 and V80, respectively, due to the presence of martensite. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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20 pages, 6182 KiB

Open AccessFeature PaperArticle

Fibre Laser Treatment of Beta TNZT Titanium Alloys for Load-Bearing Implant Applications: Effects of Surface Physical and Chemical Features on Mesenchymal Stem Cell Response and Staphylococcus aureus Bacterial Attachment

by Clare Lubov Donaghy, Ryan McFadden, Graham C. Smith, Sophia Kelaini, Louise Carson, Savko Malinov, Andriana Margariti and Chi-Wai Chan

Coatings 2019, 9(3), 186; https://doi.org/10.3390/coatings9030186 - 12 Mar 2019

Cited by 14 | Viewed by 4789

Abstract

A mismatch in bone and implant elastic modulus can lead to aseptic loosening and ultimately implant failure. Selective elemental composition of titanium (Ti) alloys coupled with surface treatment can be used to improve osseointegration and reduce bacterial adhesion. The biocompatibility and antibacterial properties of Ti-35Nb-7Zr-6Ta (TNZT) using fibre laser surface treatment were assessed in this work, due to its excellent material properties (low Young’s modulus and non-toxicity) and the promising attributes of fibre laser treatment (very fast, non-contact, clean and only causes changes in surface without altering the bulk composition/microstructure). The TNZT surfaces in this study were treated in a high speed regime, specifically 100 and 200 mm/s, (or 6 and 12 m/min). Surface roughness and topography (WLI and SEM), chemical composition (SEM-EDX), microstructure (XRD) and chemistry (XPS) were investigated. The biocompatibility of the laser treated surfaces was evaluated using mesenchymal stem cells (MSCs) cultured in vitro at various time points to assess cell attachment (6, 24 and 48 h), proliferation (3, 7 and 14 days) and differentiation (7, 14 and 21 days). Antibacterial performance was also evaluated using Staphylococcus aureus (S. aureus) and Live/Dead staining. Sample groups included untreated base metal (BM), laser treated at 100 mm/s (LT100) and 200 mm/s (LT200). The results demonstrated that laser surface treatment creates a rougher (Ra value of BM is 199 nm, LT100 is 256 nm and LT200 is 232 nm), spiky surface (Rsk > 0 and Rku > 3) with homogenous elemental distribution and decreasing peak-to-peak distance between ripples (0.63 to 0.315 µm) as the scanning speed increases (p < 0.05), generating a surface with distinct micron and nano scale features. The improvement in cell spreading, formation of bone-like nodules (only seen on the laser treated samples) and subsequent four-fold reduction in bacterial attachment (p < 0.001) can be attributed to the features created through fibre laser treatment, making it an excellent choice for load bearing implant applications. Last but not least, the presence of TiN in the outermost surface oxide might also account for the improved biocompatibility and antibacterial performances of TNZT. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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22 pages, 8667 KiB

Open AccessEditor’s ChoiceReview

Laser-Sustained Plasma (LSP) Nitriding of Titanium: A Review

by Amar M. Kamat, Stephen M. Copley, Albert E. Segall and Judith A. Todd

Coatings 2019, 9(5), 283; https://doi.org/10.3390/coatings9050283 - 26 Apr 2019

Cited by 39 | Viewed by 5777

Abstract

Titanium and its alloys possess several attractive properties that include a high strength-to-weight ratio, biocompatibility, and good corrosion resistance. However, due to their poor wear resistance, titanium components need to undergo surface hardening treatments before being used in applications involving high contact stresses. Laser nitriding is a thermochemical method of enhancing the surface hardness and wear resistance of titanium. This technique entails scanning the titanium substrate under a laser beam near its focal plane in the presence of nitrogen gas flow. At processing conditions characterized by low scan speeds, high laser powers, and small off-focal distances, a nitrogen plasma can be struck near the surface of the titanium substrate. When the substrate is removed, this plasma can be sustained indefinitely and away from any potentially interacting surfaces, by the laser power and a cascade ionization process. This paper presents a critical review of the literature pertaining to the laser nitriding of titanium in the presence of a laser-sustained plasma, with the ultimate objective of forming wide-area, deep, crack-free, wear-resistant nitrided cases on commercially pure titanium substrates. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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