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

Deadline for manuscript submissions: closed (10 November 2020) | Viewed by 39027

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Dr. Sara Ferraris

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Department of Applied Science and Technology, Politecnico di Torino, 10129 Torino, Italy
Interests: biomaterials; metallic materials; surface modifications; surface functionalization; surface characterizations; coatings; joining; titanium; aluminum foams; natural molecules
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Special Issue Information

Dear Colleagues,

It is my pleasure to announce you the Special Issue of Coatings dedicated to "Surface Engineering of Light Alloys" and invite you to submit your valuable contribution.
Light alloys (aluminum, magnesium, and titanium alloys) are gaining increasing interest in the scientific and technological community, in many different application fields from automotive to medicine, thanks to their light weight coupled with interesting mechanical properties. The functional performances of light alloys can be significantly affected by their surface properties; in fact, the surface can be considered as the “visiting card” of the material for its working environment (e.g., it can drive the biological response upon implantation for titanium alloys intended for biomedical implants or it can affect the joining ability of aluminum and magnesium alloys) as well as for its further material working steps (e.g., coatings). Surface engineering is a versatile tool for the modification of materials surface in order to tailor and improve their functional properties.
The aim the present Special Issue is to present the latest development in this field through research and review papers.
In particular, the topics of interest include, but are not limited to:

Surface engineering of light alloys for biomedical applications;
Surface engineering of light alloys for joining and coatings applications;
Surface engineering of light alloys for corrosion protection;
Surface engineering of light alloys for antibacterial/antifouling purposes.

Dr. Sara Ferraris
Guest Editor

Manuscript Submission Information

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Related Special Issue

Surface Engineering of Light Alloys: Innovation Starts at the Surface in Coatings (1 article)

Published Papers (12 papers)

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Editorial

Jump to: Research

2 pages, 154 KiB

Open AccessEditorial

Special Issue: Surface Engineering of Light Alloys

by Sara Ferraris

Coatings 2020, 10(12), 1177; https://doi.org/10.3390/coatings10121177 - 1 Dec 2020

Cited by 1 | Viewed by 1576

Abstract

Light alloys (mainly aluminum, magnesium and titanium alloys) are of great interest in applications where lightweight has an high impact, such as automotive, aerospace and biomedical fields [...] Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

Research

Jump to: Editorial

16 pages, 4045 KiB

Open AccessArticle

Bioactive Bilayer Glass Coating on Porous Titanium Substrates with Enhanced Biofunctional and Tribomechanical Behavior

by Ana M. Beltrán, Paloma Trueba, Flora Borie, Ana Alcudia, Belén Begines, José A. Rodriguez-Ortiz and Yadir Torres

Coatings 2022, 12(2), 245; https://doi.org/10.3390/coatings12020245 - 14 Feb 2022

Cited by 5 | Viewed by 1995

Abstract

The use of porous titanium samples fabricated by space-holder powder metallurgy with bioactive coatings has already been reported to prevent resorption of the bone surrounding the implant and improve osseointegration, respectively. However, the presence of pores as well as the poor adherence and the brittle behavior inherent to glassy coatings affect the service behavior of implants fabricated from these samples. Therefore, they need to be optimized. In this work, 50 vol.% of porosity titanium substrates were manufactured with different pore range size (100–200 and 355–500 µm) spacer particles and coated with a bilayer of bioactive glasses (45S5/1393). The effect of the pores on the tribomechanical properties and infiltration of the bioactive glass 1393 along with the bioactivity of the bioactive glass 45S5 were evaluated by instrumented micro-indentation and scratch tests and the formation of hydroxyapatite in simulated body fluid. The results obtained were very promising as potential implants for the replacement of small tumors in cortical bone tissues, mainly due to the smaller pores that present an improved biomechanical and biofunctional balance. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys: Innovation Starts at the Surface)

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10 pages, 2365 KiB

Open AccessFeature PaperArticle

Tribological Behaviour of Ti or Ti Alloy vs. Zirconia in Presence of Artificial Saliva

by Fabio Alemanno, Veronica Peretti, Angela Tortora and Silvia Spriano

Coatings 2020, 10(9), 851; https://doi.org/10.3390/coatings10090851 - 31 Aug 2020

Cited by 6 | Viewed by 2365

Abstract

Abutment is the transmucosal component in a dental implant system and its eventual appearance has a major impact on aesthetics: use of zirconia abutments can be greatly advantageous in avoiding this problem. Both in the case of one and two-piece zirconia abutments, a critical issue is severe wear between the zirconia and titanium components. High friction at this interface can induce loosening of the abutment connection, production of titanium wear debris, and finally, peri-implant gingivitis, gingival discoloration, or marginal bone adsorption can occur. As in vivo wear measurements are highly complex and time-consuming, wear analysis is usually performed in simulators in the presence of artificial saliva. Different commercial products and recipes for artificial saliva are available and the effects of the different mixtures on the tribological behaviour is not widely explored. The specific purpose of this research was to compare two types of artificial saliva as a lubricant in titanium–zirconia contact by using the ball on disc test as a standard tribological test for materials characterisation. Moreover, a new methodology is suggested by using electrokinetic zeta potential titration and contact angle measurements to investigate the chemical stability at the titanium–lubricant interface. This investigation is of relevance both in the case of using zirconia abutments and artificial saliva against chronic dry mouth. Results suggest that an artificial saliva containing organic corrosion inhibitors is able to be firmly mechanically and chemically adsorb on the surface of the Ti c.p. or Ti6Al4V alloy and form a protective film with high wettability. This type of artificial saliva can significantly reduce the friction coefficient and wear of both the titanium and zirconia surfaces. The use of this type of artificial saliva in standard wear tests has to be carefully considered because the wear resistance of the materials can be overestimated while it can be useful in some specific clinical applications. When saliva is free from organic corrosion inhibitors, wear occurs with a galling mechanism. The occurrence of a super-hydrophilic saliva film that is not firmly adsorbed on the surface is not efficient in order to reduce wear. The results give both suggestions about the experimental conditions for lab testing and in vivo performance of components of dental implants when artificial saliva is used. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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16 pages, 3364 KiB

Open AccessArticle

Influence of Conditions for Production and Thermo-Chemical Treatment of Al₂O₃ Coatings on Wettability and Energy State of Their Surface

by Mateusz Niedźwiedź, Władysław Skoneczny and Marek Bara

Coatings 2020, 10(7), 681; https://doi.org/10.3390/coatings10070681 - 15 Jul 2020

Cited by 4 | Viewed by 2652

Abstract

This article presents the influence of the anodizing parameters and thermo-chemical treatment of Al₂O₃ coatings made on aluminum alloy EN AW-5251 on the surface free energy. The oxide coating was produced by DC (Direct Current) anodizing in a ternary electrolyte. The thermo-chemical treatment of the oxide coatings was carried out using distilled water, sodium dichromate and sodium sulphate. Micrographs of the surface of the Al₂O₃ coatings were characterized using a scanning microscope (SEM). The chemical composition of the oxide coatings was identified using EDS (Energy Dispersive X-ray Spectroscopy) microanalysis. Surface free energy (SFE) calculations were performed by the Owens–Wendt method, based on wetting angle measurements made using the sessile drop technique. The highest value of surface free energy for the only anodized coatings was 46.57 mJ/m², and the lowest was 37.66 mJ/m². The contact angle measurement with glycerine was 98.06° ± 2.62°, suggesting a hydrophobic surface. The thermo-chemical treatment of the oxide coatings for most samples contributed to a significant increase in SFE, while reducing the contact angle with water. The highest value of surface free energy for the coatings after thermo-chemical treatment was 77.94 mJ/m², while the lowest was 34.98 mJ/m². Taking into account the contact angle measurement with glycerine, it was possible to obtain hydrophobic layers with the highest angle of 109.82° ± 4.79° for the sample after thermal treatment in sodium sulphate. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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9 pages, 10956 KiB

Open AccessArticle

The Influence of Anodic Alumina Coating Nanostructure Produced on EN AW-5251 Alloy on Type of Tribological Wear Process

by Mateusz Niedźwiedź, Władysław Skoneczny and Marek Bara

Coatings 2020, 10(2), 105; https://doi.org/10.3390/coatings10020105 - 24 Jan 2020

Cited by 9 | Viewed by 2638

Abstract

The article presents the influence of the anodic alumina coating nanostructure produced on aluminum alloy EN AW-5251 on the type of tribological wear process of the coating. Oxide coatings were produced electrochemically in a ternary electrolyte by the DC method. Analysis of the nanostructure of the coating was performed using ImageJ 1.50i software on micrographs taken with a scanning electron microscope (SEM). Scratch tests of the coatings were carried out using a Micron-Gamma microhardness tester. The scratch marks were subjected to surface geometric structure studies with a Form TalySurf 2 50i contact profiler. Based on the studies, it was found that changes in the manufacturing process conditions (current density, electrolyte temperature) affect changes in the coating thickness and changes in the anodic alumina coating nanostructure (quantity and diameter of nanofibers), which in turn has a significant impact on the type of tribological wear. An increase in the density of the anodizing current from 1 to 4 A/dm² causes an increase in the diameter of the nanofibers from 75.99 ± 7.7 to 124.59 ± 6.53 nm while reducing amount of fibers from 6.6 ± 0.61 to 3.8 ± 0.48 on length 1 × 10³ nm. This affects on a change in the type of tribological wear from grooving to micro-cutting. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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13 pages, 5854 KiB

Open AccessArticle

Investigation of the Oxidation Mechanism of Dopamine Functionalization in an AZ31 Magnesium Alloy for Biomedical Applications

by Arezoo Ghanbari, Fernando Warchomicka, Christof Sommitsch and Ali Zamanian

Coatings 2019, 9(9), 584; https://doi.org/10.3390/coatings9090584 - 16 Sep 2019

Cited by 31 | Viewed by 3651

Abstract

Implant design and functionalization are under significant investigation for their ability to enhance bone-implant grafting and, thus, to provide mechanical stability for the device during the healing process. In this area, biomimetic functionalizing polymers like dopamine have been proven to be able to improve the biocompatibility of the material. In this work, the dip coating of dopamine on the surface of the magnesium alloy AZ31 is investigated to determine the effects of oxygen on the functionalization of the material. Two different conditions are applied during the dip coating process: (1) The absence of oxygen in the solution and (2) continuous oxygenation of the solution. Energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) are used to analyze the composition of the formed layers, and the deposition rate on the substrate is determined by molecular dynamic simulation. Electrochemical analysis and cell cultivation are performed to determine the corrosion resistance and cell’s behavior, respectively. The high oxygen concentration in the dopamine solution promotes a homogeneous and smooth coating with a drastic increase of the deposition rate. Also, the addition of oxygen into the dip coating process increases the corrosion resistance of the material. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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16 pages, 7476 KiB

Open AccessFeature PaperArticle

Tri-Functional Calcium-Deficient Calcium Titanate Coating on Titanium Metal by Chemical and Heat Treatment

by Seiji Yamaguchi, Phuc Thi Minh Le, Morihiro Ito, Seine A. Shintani and Hiroaki Takadama

Coatings 2019, 9(9), 561; https://doi.org/10.3390/coatings9090561 - 3 Sep 2019

Cited by 15 | Viewed by 3834

Abstract

The main problem of orthopedic and dental titanium (Ti) implants has been poor bone-bonding to the metal. Various coatings to improve the bone-bonding, including the hydroxyapatite and titania, have been developed, and some of them have been to successfully applied clinical use. On the other hand, there are still challenges to provide antibacterial activity and promotion of bone growth on Ti. It was shown that a calcium-deficient calcium titanate coating on Ti and its alloys exhibits high bone-bonding owing to its apatite formation. In this study, Sr and Ag ions, known for their promotion of bone growth and antibacterial activity, were introduced into the calcium-deficient calcium titanate by a three-step aqueous solution treatment combined with heat. The treated metal formed apatite within 3 days in a simulated body fluid and exhibited antibacterial activity to Escherichia coli without showing any cytotoxicity in MC3T3-E1 preosteoblast cells. Furthermore, the metal slowly released 1.29 ppm of Sr ions. The Ti with calcium-deficient calcium titanate doped with Sr and Ag will be useful for orthopedic and dental implants, since it should bond to bone because of its apatite formation, promote bone growth due to Sr ion release, and prevent infection owing to its antibacterial activity. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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9 pages, 3646 KiB

Open AccessArticle

The Formation of Microcrystal in Helium Ion Irradiated Aluminum Alloy

by Hao Wan, Shuai Zhao, Qi Jin, Tingyi Yang and Naichao Si

Coatings 2019, 9(8), 516; https://doi.org/10.3390/coatings9080516 - 15 Aug 2019

Cited by 1 | Viewed by 3138

Abstract

A microstructure variation in Al-1060 alloy after helium ion irradiation was revealed by a transmission electron microscope (TEM). The result shows that ion irradiation produced dislocations, dislocation loops, cavities and microcrystals in the irradiated layer. Dislocation-defect interactions were portrayed, especially the pinning effect of a dislocation loop and cavity on moving dislocation. Irradiation-induced stress was recognized as the main factor which impacted on the interaction of defect. Based on the dislocation inhibited with irradiation defects, the mechanism of microcrystal formation was proposed. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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9 pages, 3615 KiB

Open AccessArticle

The Effect of Heat Treatment on Properties of Ni–P Coatings Deposited on a AZ91 Magnesium Alloy

by Martin Buchtík, Michaela Krystýnová, Jiří Másilko and Jaromír Wasserbauer

Coatings 2019, 9(7), 461; https://doi.org/10.3390/coatings9070461 - 23 Jul 2019

Cited by 49 | Viewed by 4721

Abstract

The present study reports the effect of phosphorus content in deposited electroless nickel (Ni–P) coatings, the heat treatment on the microhardness and its microstructural characteristics, and the influence of the temperature on the microstructure of the Mg alloy substrate during the heat treatment. The deposition of Ni–P coatings was carried out in the electroless nickel bath, and the resulting P content ranged from 5.2 to 10.8 wt.%. Prepared samples were heat-treated in the muffle furnace at 400 °C for 1 h after the coating deposition. The cooling of the samples to room temperature was proceeded in the air. For as-deposited and heat-treated samples, it was determined that with the increasing P content, the microhardness was decreasing. This may be caused by the changes in the structure of the Ni–P coating. The X-ray diffraction patterns of the as-deposited Ni–P coatings showed that the microstructure changed their nature from crystalline to amorphous with the increasing P content. The heat treatment of prepared samples led to the significant increase of microhardness of Ni–P coatings. All the heat-treated samples showed the crystalline character, regardless of the P content and the presence of hard Ni₃P phase, which can have a positive effect on the increase of microhardness. The metallographic analysis showed changes of substrate microstructure after the heat treatment. The prepared coatings were uniform and with no visible defects. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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14 pages, 5643 KiB

Open AccessFeature PaperArticle

Surface Activation and Characterization of Aluminum Alloys for Brazing Optimization

by Sara Ferraris, Sergio Perero and Graziano Ubertalli

Coatings 2019, 9(7), 459; https://doi.org/10.3390/coatings9070459 - 23 Jul 2019

Cited by 8 | Viewed by 5323

Abstract

Brazing of Al-alloys is of interest in many application fields (e.g., mechanical and automotive). The surface preparation of substrates and the in depth investigation of the interface reaction between aluminum substrates and brazing materials is fundamental for a proper understanding of the process and for its optimization. The interaction between two aluminum based substrates (Al5182 and Al6016) and two studied brazing materials (pure Zn and for the first time ZAMA alloy) has been studied in simulated brazing condition in order to define the best surface preparation conditions and combination substrate-brazing material to be used in real joining experiments. Three different surface preparations were considered: polishing and cleaning, application of flux and vacuum plasma etching (Ar) followed by sputtering coating with Zn. Macroscopic observation of the samples surface after “brazing”, optical microscopy, and microhardness measurements on the cross-section and XRD measurements on the top surface gave a comprehensive description of the phenomena occurring at the interface between the substrate and the brazing alloy which are of interest to understand the brazing process and for the detection of the best conditions to be used in brazing. Plasma etching (Ar) followed by sputtering coating with Zn resulted a promising solution in case of Al5182 brazed with Zn, while the addition of flux was more effective in case of Al6016 substrate. ZAMA alloy demonstrated good interface reactivity with both Al6016 and Al5182 alloys, particularly on only cleaned surfaces. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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17 pages, 3001 KiB

Open AccessFeature PaperArticle

Grafting of Gallic Acid onto a Bioactive Ti6Al4V Alloy: A Physico-Chemical Characterization

by Martina Cazzola, Sara Ferraris, Enrico Prenesti, Valentina Casalegno and Silvia Spriano

Coatings 2019, 9(5), 302; https://doi.org/10.3390/coatings9050302 - 3 May 2019

Cited by 17 | Viewed by 4559

Abstract

Despite increasing interest in the use of natural biomolecules for different applications, few attempts of coupling them to inorganic biomaterials are reported in literature. Functionalization of metal implants with natural biomolecules could allow a local action, overcoming the issue of low bioavailability through systemic administration. In the present work, gallic acid was grafted to a pre-treated Ti6Al4V in order to improve its biological response in bone contact applications. The grafting procedure was optimized by choosing the concentration of gallic acid (1 mg/mL) and the solvent of the solution, which was used as a source for functionalization, in order to maximize the amount of the grafted molecule on the titanium substrate. The functionalized surfaces were characterized. The results showed that functionalization with Simulated Body Fluid (SBF) as solvent medium was the most effective in terms of the amount and activity of the grafted biomolecule. A key role of calcium ions in the grafting mechanism is suggested, involving the formation of coordination compounds formed by way of gallic acid carboxylate and Ti–O⁻ as oxygenated donor groups. Bioactive behavior and surface charge of the pre-treated Ti6Al4V surface were conserved after functionalization. The functionalized surface exposed a greater amount of OH groups and showed higher wettability. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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10 pages, 3398 KiB

Open AccessArticle

Hydrothermal Synthesis of Protective Coating on Mg Alloy for Degradable Implant Applications

by Jinshu Xie, Jinghuai Zhang, Shujuan Liu, Zehua Li, Li Zhang, Ruizhi Wu, Legan Hou and Milin Zhang

Coatings 2019, 9(3), 160; https://doi.org/10.3390/coatings9030160 - 28 Feb 2019

Cited by 12 | Viewed by 3652

Abstract

Biodegradable magnesium (Mg) alloys are known as “the new generation of biomedical metal materials”. However, high degradation rates restrict their clinical application. To overcome this issue, a new and simple method for producing of protective coating based on hydrothermal synthesis at 200 °C in 0.5 M NaHCO₃ was elaborated. The microstructure, elemental and phase composition of the produced films were examined by scanning electron microscope (SEM), X-ray energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD). The mechanical strength of the protective coating was evaluated by grid scribing method. The corrosion protection effect was evaluated using linear sweep voltammogram (LSV) and electrochemical impedance spectroscopy (EIS) methods in the simulated body fluid (SBF). Since the corrosion process is accompanied by stoichiometric evolution of hydrogen, the amount of the latter was measured to quantify the overall corrosion rate. Both the coatings morphology and phase composition were sensitive to the treatment duration. The coating formed after 0.5 h was loose and mainly consisted of spherical flower-like Mg₅(CO₃)₄(OH)₂·4H₂O accompanied by small amounts of Mg(OH)₂. The treatment duration of 3 h resulted in a thicker compact coating composed mainly of irregular granular MgCO₃ as well as Mg(OH)₂. The coating providing the most effective protection and uniform corrosion was achieved by 2 h treatment at 200 °C. Full article

(This article belongs to the Special Issue Surface Engineering of Light Alloys)

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