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3 pages, 161 KiB

Open AccessEditorial

Metal Surfaces

by Saulius Kaciulis and Roberto Montanari

Coatings 2021, 11(2), 255; https://doi.org/10.3390/coatings11020255 - 22 Feb 2021

Viewed by 1312

Abstract

Surface phenomena such as corrosion, wear, heterogeneous catalysis, segregation, etc [...] Full article

(This article belongs to the Special Issue Metal Surfaces)

Research

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18 pages, 4579 KiB

Open AccessFeature PaperArticle

Cr Segregation and Impact Fracture in a Martensitic Stainless Steel

by Eleonora Bolli, Alessandra Fava, Paolo Ferro, Saulius Kaciulis, Alessio Mezzi, Roberto Montanari and Alessandra Varone

Coatings 2020, 10(9), 843; https://doi.org/10.3390/coatings10090843 - 29 Aug 2020

Cited by 14 | Viewed by 2704

Abstract

The fracture surfaces of a 10.5 wt.% Cr martensitic stainless steel broken in Charpy tests have been investigated through X-ray photoelectron spectroscopy (XPS). The specimens have been examined in two different conditions: as-quenched and heat treated for 10 h at 700 °C. The [...] Read more.

The fracture surfaces of a 10.5 wt.% Cr martensitic stainless steel broken in Charpy tests have been investigated through X-ray photoelectron spectroscopy (XPS). The specimens have been examined in two different conditions: as-quenched and heat treated for 10 h at 700 °C. The trends of Fe/Cr ratio vs. test temperature are similar to the sigmoidal curves of absorbed energy and, after both ductile and quasi-cleavage brittle fractures, such ratio is always significantly lower than the nominal value of the steel chemical composition. Cr segregation does not occur on a macroscopic scale but takes place in microscopic zones which represent weaker spots in the steel matrix and a preferred path for moving cracks. Small area (diameter 300 µm) XPS measurements evidenced a higher density of such microscopic zones in the inner part of probes; this is explained by the different diffusion length of Cr atoms in the external and inner parts during quenching from austenitic field which has been calculated through FEM simulations. No significant differences of Cr concentration were observed in fracture surfaces of probes with and without heat treatment. The results highlight how Cr segregation plays a role not only in the intergranular mode of fracture but also in the quasi-cleavage and ductile ones. Full article

(This article belongs to the Special Issue Metal Surfaces)

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12 pages, 10532 KiB

Open AccessArticle

Repetitive Impact Wear Behaviors of the Tempered 25Cr3Mo2NiWV Fe-Based Steel

by Cheng Zhang, Pu Li, Hui Dong, Dongliang Jin, Jinfeng Huang, Feng Mao and Chong Chen

Coatings 2020, 10(2), 107; https://doi.org/10.3390/coatings10020107 - 26 Jan 2020

Cited by 5 | Viewed by 3066

Abstract

This study aimed to reveal the impact wear behaviors of tempered 25Cr3Mo2NiWV steel. The specimens were subject to various heat treatment processes for generating different mechanical and wear properties. The impact wear tests were performed with an MLD-10 dynamic abrasive wear tester. Worn [...] Read more.

This study aimed to reveal the impact wear behaviors of tempered 25Cr3Mo2NiWV steel. The specimens were subject to various heat treatment processes for generating different mechanical and wear properties. The impact wear tests were performed with an MLD-10 dynamic abrasive wear tester. Worn surface morphologies and micro-cracks of the cross-sections were analyzed by optical microscope and scanning electron microscope. The Vickers hardness of the sample and the impact wear mechanism were also analyzed. The steel with the best combination of hardness and toughness had the lowest wear. With the increase of wear time, the dominant wear mechanism varied from slight plastic deformation to micro-cutting and adhesive wear. Finally, micro fatigue peeling occurred. After impact wear, the cracks could initiate from the surface or the sub-surface. Micrographs of the crack in the cross-section demonstrated two different propagation modes of fatigue fractures. The results showed that the strength and toughness of steel affected the crack propagation, surface spalling, and wear failure mechanism during impact wear. Full article

(This article belongs to the Special Issue Metal Surfaces)

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11 pages, 3583 KiB

Open AccessArticle

An Erosion-Corrosion Investigation of Coated Steel for Applications in the Oil and Gas Field, Based on Bipolar Electrochemistry

by Claudio Mele, Francesca Lionetto and Benedetto Bozzini

Coatings 2020, 10(2), 92; https://doi.org/10.3390/coatings10020092 - 21 Jan 2020

Cited by 13 | Viewed by 4095

Abstract

In this research, a simple experimental apparatus based on a bipolar electrode (BPE) configuration was set up, in order to tackle erosion-corrosion problems of materials of interest in the oil and gas field. As a case study, the resistance to erosion and corrosion [...] Read more.

In this research, a simple experimental apparatus based on a bipolar electrode (BPE) configuration was set up, in order to tackle erosion-corrosion problems of materials of interest in the oil and gas field. As a case study, the resistance to erosion and corrosion of carbon steel samples coated by Electroless Nickel Plating and by thermo-sprayed coating with the high velocity oxy fuel (HVOF) process was investigated. The main objective was to demonstrate if this simple, contactless technique could be applied to effectively discriminate the erosion-corrosion behavior of different materials in a vast range of experimental conditions. In fact, by means of polarization curves, visual inspection and morphological analysis by scanning electron microscope (SEM), the effects due to erosion-corrosion by solid particles, by fluid and those due to simple erosion were evaluated. Full article

(This article belongs to the Special Issue Metal Surfaces)

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12 pages, 15574 KiB

Open AccessArticle

Surface Morphological Features of Molybdenum Irradiated by a Single Laser Pulse

by Roberto Montanari, Ekaterina Pakhomova, Riccardo Rossi, Maria Richetta and Alessandra Varone

Coatings 2020, 10(1), 67; https://doi.org/10.3390/coatings10010067 - 11 Jan 2020

Cited by 11 | Viewed by 3057

Abstract

Molybdenum (Mo) is considered a plasma facing material alternative to tungsten (W) for manufacturing the divertor armours of International Thermonuclear Experimental Reactor (ITER). Transient thermal loads of high energy occurring in a tokamak during the service life have been simulated through a single [...] Read more.

Molybdenum (Mo) is considered a plasma facing material alternative to tungsten (W) for manufacturing the divertor armours of International Thermonuclear Experimental Reactor (ITER). Transient thermal loads of high energy occurring in a tokamak during the service life have been simulated through a single laser pulse delivered by a Nd:YAG/Glass laser, and the effects have then been examined through scanning electron microscopy (SEM) observations. An erosion crater forms in correspondence with the laser spot due to the vaporization and melting of the metal, while all around a network of cracks induced by thermal stresses is observed. The findings have been compared to results of similar experiments on W and literature data. The morphology of the crater and the surrounding area is different from that of W: the crater is larger and shallower in the case of Mo, while its walls are characterized by long filaments, not observed in W, because the lower viscosity and surface tension of Mo allow an easier flow of the liquid metal. Most importantly, the volume of Mo ablated from the surface by the single laser pulse is about ten times that of W. This critical aspect is of particular relevance and leads us to conclude that W remains the best solution for manufacturing the armours of the ITER divertor. Full article

(This article belongs to the Special Issue Metal Surfaces)

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16 pages, 5132 KiB

Open AccessArticle

Effect of 0.8 at.% H on the Mechanical Properties and Microstructure Evolution of a Ti–45Al–9Nb Alloy Under Uniaxial Tension at High Temperature

by Qiqi Yu, Daosheng Wen, Shouren Wang, Beibei Kong, Shuxu Wu and Teng Xiao

Coatings 2020, 10(1), 52; https://doi.org/10.3390/coatings10010052 - 07 Jan 2020

Cited by 5 | Viewed by 2061

Abstract

To investigate the effect of hydrogen on the high-temperature deformation behaviors of TiAl-based alloys, the high-temperature tensile experiment was carried out on a Ti–45Al–9Nb (at.%) alloy with the H content of 0 and 0.8 at.%, respectively. Then, the effect of hydrogen on the [...] Read more.

To investigate the effect of hydrogen on the high-temperature deformation behaviors of TiAl-based alloys, the high-temperature tensile experiment was carried out on a Ti–45Al–9Nb (at.%) alloy with the H content of 0 and 0.8 at.%, respectively. Then, the effect of hydrogen on the high-temperature mechanical properties of the as-cast alloy was studied, the constitutive relations among stress, temperature, and strain rate were established, and the microstructure was analyzed. The results indicated that, compared with the unhydrogenated alloy, the flow stress of the hydrogenated alloy was significantly reduced, and the peak stress of the hydrogenated alloy decreased by (16.28 ± 0.17)% deformed at 1150 °C/0.0004 s⁻¹. Due to the presence of hydride (TiAl)H_x in the alloy, the elongation showed a decline trend with increasing strain rate at the same deformation temperature. Compared with the unhydrogenated alloy, the elongation of the hydrogenated alloy reduced by (26.05 ± 0.45)% (0.0004 s⁻¹), (23.49 ± 0.38)% (0.001 s⁻¹), and (14.23 ± 0.19)% (0.0025 s⁻¹), respectively, indicating that 0.8 at.% H softened the Ti–45Al–9Nb alloy and reduced the high-temperature plastic deformability. Under the same deformation condition, the deformation extent of the hydrogenated alloy was less than that of the unhydrogenated alloy. There were more residual lamellae in the hydrogenated alloy, and the extent of dynamic recrystallization was lower than that of the unhydrogenated alloy. Full article

(This article belongs to the Special Issue Metal Surfaces)

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18 pages, 4246 KiB

Open AccessArticle

Microstructural and Corrosion Characteristics of Al-Fe Alloys Produced by High-Frequency Induction-Sintering Process

by Asiful H. Seikh, Muneer Baig, Jitendra Kumar Singh, Jabair A. Mohammed, Monis Luqman, Hany S. Abdo, Amir Rahman Khan and Nabeel H. Alharthi

Coatings 2019, 9(10), 686; https://doi.org/10.3390/coatings9100686 - 21 Oct 2019

Cited by 16 | Viewed by 3705

Abstract

Al-x wt.% Fe bulk alloys were fabricated from a powder mixture of pure Al and x wt.% of Fe, where x = 2 wt.%, 5 wt.% and 10 wt.%. Initially, as-mixed mixtures were processed using a mechanical-alloying (MA) technique in an attritor [...] Read more.

Al-x wt.% Fe bulk alloys were fabricated from a powder mixture of pure Al and x wt.% of Fe, where x = 2 wt.%, 5 wt.% and 10 wt.%. Initially, as-mixed mixtures were processed using a mechanical-alloying (MA) technique in an attritor for 4 h. The milling was performed in an argon atmosphere at room temperature followed by the sintering of the milled powders in a high-frequency induction furnace to produce bulk samples. Scanning electron microscopy (SEM) was used to study the morphology of the produced alloys, and X-ray diffraction (XRD) to determine the phases formed after the sintering process and their crystallite size. The corrosion behavior of the fabricated samples was studied by immerging them in a 3.5% sodium chloride (NaCl) solution at room temperature using cyclic-polarization (CP) and electrochemical-impedance-spectroscopy (EIS) techniques. The SEM results showed that Fe was uniformly distributed in the Al matrix, and XRD revealed the formation of Al and intermetallic, i.e., Al₆Fe and Al₁₃Fe₄, phases in the Al-Fe alloys after sintering. The hardness of the Al-Fe alloys was increased with the addition of Fe due to the formation of intermetallic compounds. Electrochemical results showed that there was a proportional relationship between the percentage of Fe additives and corrosion potential (E_corr) where it shifted toward a nobler direction, while corrosion current density (i_corr) and corrosion rate decreased with an increasing Fe%. This observation indicates that the addition of Fe into an Al matrix leads to an improvement in the corrosion resistance of the alloys. Full article

(This article belongs to the Special Issue Metal Surfaces)

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Review

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15 pages, 2751 KiB

Open AccessReview

Laser Surface Texturing for Biomedical Applications: A Review

by Ishwer Shivakoti, Golam Kibria, Robert Cep, Bal Bahadur Pradhan and Ashis Sharma

Coatings 2021, 11(2), 124; https://doi.org/10.3390/coatings11020124 - 22 Jan 2021

Cited by 66 | Viewed by 6938

Abstract

For generating a texture or pattern on a work surface, one of the emerging processes is laser surface texturing (LST). It is an effective method for producing texture on a work surface. Literature shows that various lasers have been applied to generate textures [...] Read more.

For generating a texture or pattern on a work surface, one of the emerging processes is laser surface texturing (LST). It is an effective method for producing texture on a work surface. Literature shows that various lasers have been applied to generate textures on the surface of work materials. Recently, LST has shown tremendous potential in the field of biomedical applications. Applying the LST process, the efficacy of the biomaterial has been drastically improved. This paper presents an in-depth review of laser surface texturing for biomedical applications. The effect of LST on important biomaterial has been thoroughly studied; it was found that LST has extreme potential for surface modification of biomaterial and can be utilized for biomedical applications. Full article

(This article belongs to the Special Issue Metal Surfaces)

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27 pages, 12425 KiB

Open AccessReview

ESCA as a Tool for Exploration of Metals’ Surface

by Eleonora Bolli, Saulius Kaciulis and Alessio Mezzi

Coatings 2020, 10(12), 1182; https://doi.org/10.3390/coatings10121182 - 03 Dec 2020

Cited by 10 | Viewed by 2918

Abstract

The main principles and development of electron spectroscopy for chemical analysis (ESCA) are briefly reviewed. The role of ESCA techniques (X-ray photoelectron spectroscopy and Auger electron spectroscopy) in the investigation of metallic surfaces is discussed, evidencing their importance and analytical potentiality. An overview [...] Read more.

The main principles and development of electron spectroscopy for chemical analysis (ESCA) are briefly reviewed. The role of ESCA techniques (X-ray photoelectron spectroscopy and Auger electron spectroscopy) in the investigation of metallic surfaces is discussed, evidencing their importance and analytical potentiality. An overview is given of a series of recent experimental cases of ESCA application for the characterization of different metals and metallic alloys, illustrating the main results and various phenomena, such as the formation of impurity defects, corrosion, migration of constituent elements in various alloys, clustering in liquid alloy, etc., that can occur on the surface and the interface of investigated materials. These materials comprise the collection coins of noble metals, some metal alloys and Ni-based superalloys, nitride coatings on stainless steel, composite material with TiAlV alloy, treated austenitic steels, and graphene interface with polycrystalline metal foils. The present review could be particularly recommended for the newcomers to the research field of surface analysis and its application for various metals, their treatments, and possible modifications in operating conditions. Full article

(This article belongs to the Special Issue Metal Surfaces)

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