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Mechanical and Tribological Properties of Advanced Materials and Coatings
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Mechanical and Tribological Properties of Advanced Materials and Coatings

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Thin Films and Interfaces".

Deadline for manuscript submissions: closed (20 May 2023) | Viewed by 28136

Special Issue Editor

Dr. Chang-Lae Kim

E-Mail Website
Guest Editor
Functional Materials and Tribology Laboratory, Department of Mechanical Engineering, Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju 61452, Republic of Korea
Interests: micro/nanomaterials; functional materials; flexible electrode; micro/nanostructure; micro/nano patterning; surface treatment/coating; friction; wear; lubrication; in situ visualization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Various materials such as metals, ceramics, polymers, and micro/nano materials can be synthesized or mixed into alloys or composites to improve various properties. In addition, the surface of the materials can be protected through various surface treatment/patterning and surface coating techniques. However, the condition in which two objects are in contact is a particularly complex state due to various factors, such as material properties, surface roughness, contact pressure, sliding speed, ambient atmosphere/temperature/humidity, etc. Therefore, it is difficult to cover a complex contact state only by setting one condition of the material itself. A number of studies are being conducted using theoretical, numerical/analytic, and experimental methods to improve mechanical and tribological properties of materials and coatings. Methods for improving the mechanical and tribological properties of materials and coatings include using various materials with excellent mechanical properties, friction and wear properties, or forming micro/nanopatterns, structures, and multilayers. In particular, the durability of the surface can be improved by understanding complex contact conditions and analyzing various mechanisms for friction and wear phenomena. In other words, it means that an extraordinarily strong material is used to protect the part where contact occurs from damage, or conversely, a material that is flexible to deformation is used to reduce the contact pressure. In this Special Issue, we would like to deal with studies on preventing surface damage and improving mechanical and tribological properties using a wide range of materials, surface treatment/patterning, and coating technologies.

We look forward to receiving your contributions to this issue.

Prof. Chang-Lae Kim
Guest Editor

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Keywords

  • micro/nano materials
  • functional materials
  • micro/nano structure
  • micro/nano patterning
  • surface treatment
  • coatings
  • finite element analysis
  • tribological properties
  • mechanical properties

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Published Papers (17 papers)

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13 pages, 3576 KiB  
Article
Characterization of Structural, Optical, Corrosion, and Mechanical Properties of HfO2 Thin Films Deposited Using Pulsed DC Magnetron Sputtering
by Ewa Mańkowska, Michał Mazur, Małgorzata Kalisz, Marcin Grobelny, Jarosław Domaradzki and Damian Wojcieszak
Materials 2023, 16(14), 5005; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16145005 - 14 Jul 2023
Cited by 2 | Viewed by 891
Abstract
Various properties of HfO2, such as hardness, corrosion, or electrical resistance, depend on the method and the conditions of deposition. In this work, a thorough comparison of scarcely investigated mechanical properties of HfO2 thin films deposited with different conditions of [...] Read more.
Various properties of HfO2, such as hardness, corrosion, or electrical resistance, depend on the method and the conditions of deposition. In this work, a thorough comparison of scarcely investigated mechanical properties of HfO2 thin films deposited with different conditions of reactive magnetron sputtering process is presented. Four thin films were sputtered in processes that varied in plasma ignition method (continuous or sequential) and target–substrate distance. The structural characteristics of the HfO2 thin films were examined using Raman spectroscopy and X-ray diffraction measurements. Furthermore, the optoelectronic properties were determined based on transmittance and current–voltage characteristics. The mechanical properties of the HfO2 thin films were determined using nanoindentation and scratch test. In turn, the corrosion properties were determined by analyzing the voltametric curves. The transparent HfO2 thin films deposited in the continuous process are characterized by better corrosion resistance than the same layer formed in the sequential process, regardless of the target–substrate distance (8 cm or 12 cm). Furthermore, these samples are also characterized by the highest value of Young’s modulus and scratch resistance. The combination of good corrosion and scratch resistance could contribute to the new application of HfO2 as a corrosion protective material. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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27 pages, 16391 KiB  
Article
Manufacturing Process, Microstructure and Physico-Mechanical Properties of W-Cr Coatings Reinforced by Cr3C2 Phase Produced on Tool Steel through Laser Processing
by Dariusz Bartkowski and Aneta Bartkowska
Materials 2023, 16(13), 4542; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16134542 - 23 Jun 2023
Viewed by 1043
Abstract
This paper presents study results of laser processing of W-Cr, WCr/Cr3C2 and Cr3C2 pre-coats applied on steel substrate in the form of paste. For this study, production parameters were selected to obtain the greatest possible durability of [...] Read more.
This paper presents study results of laser processing of W-Cr, WCr/Cr3C2 and Cr3C2 pre-coats applied on steel substrate in the form of paste. For this study, production parameters were selected to obtain the greatest possible durability of final coatings. Laser processing was carried out using a diode laser machine with a rated power of 3 kW. The laser beam scanning speed was constant at 3 m/min, but variable laser beam powers were used: 600 W, 900 W and 1200 W. Multiple laser tracks with 60% overlapping were used. After remelting the pre-coat with a steel substrate, new coatings were obtained. Following the experiment, microstructure, microhardness, wear, corrosion resistance and chemical composition were investigated. It was found that it is possible to produce W-Cr/Cr3C2 coatings through laser processing. These coatings do not have the characteristics of a composite coating; however, increasing the reinforcing phase in the pre-coat positively affects the wear resistance and microhardness. The addition of a reinforcing phase was found to lead to a microhardness of about 750–890 HV01 for 25% and 75% Cr3C2, respectively, in comparison to coating without Cr3C2. The wear resistance of coatings reinforced by chromium carbide improved more than twofold in reference to the W-Cr coating. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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16 pages, 10066 KiB  
Article
Novel Ni-P-Tribaloy Composite Protective Coating
by Ahmed Mabrouk and Zoheir Farhat
Materials 2023, 16(11), 3949; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16113949 - 25 May 2023
Cited by 2 | Viewed by 1135
Abstract
Oil and gas pipelines are subject to various forms of damage and degradation during their operation. Electroless Nickel (Ni-P) coatings are widely employed as protective coatings due to their ease of application and unique properties, including high wear and corrosion resistance. However, they [...] Read more.
Oil and gas pipelines are subject to various forms of damage and degradation during their operation. Electroless Nickel (Ni-P) coatings are widely employed as protective coatings due to their ease of application and unique properties, including high wear and corrosion resistance. However, they are not ideal for protecting pipelines due to their brittleness and low toughness. Composite coatings of higher toughness can be developed through the co-deposition of second-phase particles into the Ni-P matrix. Tribaloy (CoMoCrSi) alloy possesses excellent mechanical and tribological properties making it a potential candidate for a high-toughness composite coating. In this study, Ni-P-Tribaloy composite coating consisting of 15.7 vol.% Tribaloy was successfully deposited on low-carbon steel substrates. Both the monolithic and the composite coatings were studied to evaluate the effect of the addition of Tribaloy particles. The micro-hardness of the composite coating was measured to be 6.00 GPa, 12% greater than that of the monolithic coating. Hertzian-type indentation testing was carried out to investigate the coating’s fracture toughness and toughening mechanisms. The 15.7 vol.% Tribaloy coating exhibited remarkably less severe cracking and higher toughness. The following toughening mechanisms were observed: micro-cracking, crack bridging, crack arrest, and crack deflection. The addition of the Tribaloy particles was also estimated to quadruple the fracture toughness. Scratch testing was performed to evaluate the sliding wear resistance under a constant load and a varying number of passes. The Ni-P-Tribaloy coating exhibited more ductile behavior and higher toughness, as the dominant wear mechanism was identified as material removal, as opposed to brittle fracture in the Ni-P coating. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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16 pages, 7722 KiB  
Article
Effect of Polymer Ether Ketone Fibers on the Tribological Properties of Resin-Based Friction Materials
by Lekai Li, Zichao Ma, Guoqin Liu, Jin Tong, Wei Song, Lili Ren, Tianjian Tong and Yunhai Ma
Materials 2023, 16(5), 2094; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16052094 - 03 Mar 2023
Cited by 1 | Viewed by 1353
Abstract
Resin-based friction materials (RBFM) are widely used in the fields of automobiles, agriculture machinery and engineering machinery, and they are vital for safe and stable operation. In this paper, polymer ether ketone (PEEK) fibers were added to RBFM to enhance its tribological properties. [...] Read more.
Resin-based friction materials (RBFM) are widely used in the fields of automobiles, agriculture machinery and engineering machinery, and they are vital for safe and stable operation. In this paper, polymer ether ketone (PEEK) fibers were added to RBFM to enhance its tribological properties. Specimens were fabricated by wet granulation and hot-pressing. The relationship between intelligent reinforcement PEEK fibers and tribological behaviors was investigated by a JF150F-II constant-speed tester according to GB/T 5763-2008, and the worn surface morphology was observed using an EVO-18 scanning electron microscope. The results showed that PEEK fibers can efficiently enhance the tribological properties of RBFM. A specimen with 6 ωt% PEEK fibers obtained the optimal tribological performance, the fade ratio was −6.2%, which was much higher than that of the specimen without the addition of PEEK fibers, the recovery ratio was 108.59% and the wear rate was the lowest, which was 1.497 × 10−7 cm3/(Nm)−1. The reason for the enhancing tribological performance was that, on the one hand, PEEK fibers have a high strength and modulus which can enhance the specimens at lower temperatures; on the other hand, molten PEEK at high temperatures can also promote the formation of secondary plateaus, which are beneficial for friction. The results in this paper can lay a foundation for future studies on intelligent RBFM. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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16 pages, 8553 KiB  
Article
Assessment of Condition Diagnosis System for Axles with Ferrous Particle Sensor
by Sung-Ho Hong and Hong-Gyu Jeon
Materials 2023, 16(4), 1426; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16041426 - 08 Feb 2023
Cited by 3 | Viewed by 961
Abstract
This study presents a condition diagnosis system based on a ferrous particle sensor to estimate the durability of axles in construction equipment. Axles are mechanical devices that play the role of the differential gear in construction equipment that move with wheels and require [...] Read more.
This study presents a condition diagnosis system based on a ferrous particle sensor to estimate the durability of axles in construction equipment. Axles are mechanical devices that play the role of the differential gear in construction equipment that move with wheels and require high reliability. In the durability testing of new axles, failure identification and real-time diagnosis are required. One of the typical failure modes of an axle is increased ferrous-wear particles due to metal-to-metal contact. Therefore, a condition diagnostic program based on the ferrous particle sensor is developed and applied in the bench tests of axles. This program provides information on the amount of wear with respect to ferrous particles using a simple diagnostic algorithm. Additionally, it allows separation and storage of measured data that exceed the reference values; the system provides warnings using color, sound, and pop-up windows to facilitate diagnosis. In the two tests, the first case detected a failure, but in the other case, the sensor did not detect it even though a failure occurred. From the results of bench tests, it is confirmed that the sensor location is a critical factor. Therefore, a multi-physics-based analysis method is suggested for positioning the ferrous particle sensor. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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11 pages, 2991 KiB  
Article
Effect of Wet Granulation on Tribological Behaviors of Cu-Based Friction Materials
by Lekai Li, Jian Zhuang, Tianjian Tong, Jin Tong, Xucheng Zhao, Feipeng Cao, Wei Song, Donghai Wang, Yitong Tian, Yunhai Ma, Dongyu Chen and Qifeng Zhang
Materials 2023, 16(3), 1075; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16031075 - 26 Jan 2023
Cited by 5 | Viewed by 1282
Abstract
Because of the excellent thermal conduction, corrosion resistance, and tribological properties, copper-based friction materials (CBFMs) were widely used in airplanes, high-speed trains, and wind power generation. With operating speed continuously increasing, CBFMs are suffering more complicated and extreme working conditions, which would cause [...] Read more.
Because of the excellent thermal conduction, corrosion resistance, and tribological properties, copper-based friction materials (CBFMs) were widely used in airplanes, high-speed trains, and wind power generation. With operating speed continuously increasing, CBFMs are suffering more complicated and extreme working conditions, which would cause abnormal abrasion. This paper presents an experiment to investigate how the tribological behaviors of CBFMs are regulated by granulation technology. Samples were prepared by the method of granulation and cool-pressed sinter. The tribological properties of specimens with different granule sizes were studied. The results showed that granulation could improve the tribological properties of CBFMs. The friction coefficient (COF) increased first and then decreased with increasing granule size. Specimen fabricated with 5–8 mm granules obtained the lowest COF, which was reduced by 22.49% than that made of powders. Moreover, the wear rate decreased first and then increased as granule size increased. The wear rate of samples prepared by granules 3–5 mm was lower than that of all of the other samples. This is because the structured samples prepared by wet granulation can promote the formation of secondary plateaus, which are beneficial for enhancing tribological properties. This makes granulation a promising method for enhancing the tribological performances of CBFMs. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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12 pages, 4655 KiB  
Article
Tribological Effects of Water-Based Graphene Lubricants on Graphene Coatings
by Sung-Jun Lee, Yoon-Chul Sohn and Chang-Lae Kim
Materials 2023, 16(1), 197; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16010197 - 26 Dec 2022
Cited by 2 | Viewed by 1185
Abstract
In this study, the friction and wear characteristics of graphene coatings were evaluated using lubricants with various ratios of graphene ink to deionized (DI) water. When dry graphene ink and pure DI water were used as lubricants, the graphene coating initially peeled off, [...] Read more.
In this study, the friction and wear characteristics of graphene coatings were evaluated using lubricants with various ratios of graphene ink to deionized (DI) water. When dry graphene ink and pure DI water were used as lubricants, the graphene coating initially peeled off, and the friction coefficient rapidly increased to a large value. However, when a lubricant with graphene ink added to DI water was used, a lubricating film was formed on the graphene coating and the friction coefficient was reduced significantly. Under dry and pure DI water conditions, severe wear morphologies were formed on the graphene coating surface, whereas in the case of the lubricant with graphene inks added to DI water, insignificant wear morphologies were formed. When the mixing ratio between DI water and graphene ink was 100:10 and 100:5, the friction coefficient and wear rate were the lowest, respectively. As a result of a long-term experiment in which the sliding cycle was performed for up to 100,000 cycles under the same experimental conditions, the lubricant with a 100:10 mixing ratio showed excellent lubrication properties, confirming that the friction coefficient and wear rate were significantly reduced compared to that of the dry or pure DI water lubrication conditions. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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14 pages, 7247 KiB  
Article
Friction Property of Hierarchical Micro/Nanopatterned PDMS
by Gang-Min Kim, Jeong-Won Lee, Sung-Jun Lee and Chang-Lae Kim
Materials 2022, 15(24), 8736; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15248736 - 07 Dec 2022
Cited by 2 | Viewed by 1103
Abstract
Polydimethylsiloxane (PDMS) has many advantages, but the friction coefficient generated by contact with the counter material is high. The purpose of this study is to reduce the friction coefficient by forming hierarchical micro/nanopatterns on the PDMS surface using the imprinting method. In addition, [...] Read more.
Polydimethylsiloxane (PDMS) has many advantages, but the friction coefficient generated by contact with the counter material is high. The purpose of this study is to reduce the friction coefficient by forming hierarchical micro/nanopatterns on the PDMS surface using the imprinting method. In addition, the optimum conditions for reducing the friction coefficient by controlling the sliding speed and normal load were determined. After contacting flat bare PDMS and hierarchical micro/nanostructured PDMS with a counter tip made of polyurethane (PU), the change in friction with sliding speed and vertical load was evaluated. Under normal load conditions, the average friction coefficient of the bare PDMS decreased as the sliding speed increased, and that of the patterned PDMS slightly increased. Regardless of the sliding speed, the friction coefficient decreased as the normal load increased for both specimens. At a sliding speed of 4 mm/s under a load of 10 mN, the friction reduction effect of the pattern structure was the largest at 79%. Overall, the greatest friction reduction effect (84%) was confirmed in patterned PDMS with the lowest friction coefficient under the conditions of 4 mm/s, 50 mN, compared to bare PDMS with the highest friction coefficient under the conditions of 4 mm/s, 10 mN. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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13 pages, 5532 KiB  
Article
Effect of Bilayer Thickness and Bias Potential on the Structure and Properties of (TiZr/Nb)N Multilayer Coatings as a Result of Arc-PVD Deposition
by Rakhadilov Bauyrzhan, Pogrebnjak Alexander, Sagdoldina Zhuldyz, Buitkenov Dastan, Beresnev Vyacheslav and Amina Mukhamedova
Materials 2022, 15(21), 7696; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15217696 - 01 Nov 2022
Cited by 4 | Viewed by 1117
Abstract
This work is devoted to the study of the formation of nanostructured multilayer coatings (TiZr/Nb)N on the surface of an AISI 321 steel substrate depending on the deposition parameters of the Arc-PVD method. The results of the X-ray diffraction analysis showed the formation [...] Read more.
This work is devoted to the study of the formation of nanostructured multilayer coatings (TiZr/Nb)N on the surface of an AISI 321 steel substrate depending on the deposition parameters of the Arc-PVD method. The results of the X-ray diffraction analysis showed the formation of solid solution (TiNb)N and ZrN in the multilayer coatings with an FCC structure, ε-NbN with a hexagonal structure, as well as with a small volume fraction of the ε-Ti2N and β-Nb2N phase. On the basis of phase composition data, it is possible to assume that an increase in the number of bilayers leads to a decrease in the nitrogen concentration in the bilayers and, consequently, to a decrease in the volume fraction of ε-NbN and β-Nb2N nitrides. In all investigated systems obtained at −100 V and −200 V bias potentials, ε-NbN is the main phase. The study of the element distribution over the thickness of the (TiZr/Nb)N coating confirms the results of the X-ray diffraction analysis. The use of the structure model in the form of alternating layers allows for significantly improving the adhesion characteristics of the protective coating, as well as ensuring their high hardness. Based on the experimental results, it is possible to analyze changes in the mechanical and tribological properties of multilayer coatings depending on the number of applied bilayers. The results of the study of the elastic modulus and hardness of multilayer coatings (TiZrNb)N with different numbers of bilayers showed that a large number of bilayers (small thickness of each individual layer) shows the lowest value of hardness. It is assumed that as the bilayer thickness decreases, the coating characteristics are closer to the monolayer alloy than to the multilayer structure. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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18 pages, 4381 KiB  
Article
Application of Condition Monitoring for Hydraulic Oil Using Tuning Fork Sensor: A Study Case on Hydraulic System of Earth Moving Machinery
by Hong-Gyu Jeon, Jong-Kyun Kim, Seon-Jun Na, Min-Seok Kim and Sung-Ho Hong
Materials 2022, 15(21), 7657; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15217657 - 31 Oct 2022
Cited by 5 | Viewed by 1573
Abstract
In this study, we focus on the correctness of oil condition monitoring, specifically of a tuning forks sensor in hydraulic systems. We also aim to analyze the correlation between the online monitoring sensor signal and offline oil analysis by periodically sampling the hydraulic [...] Read more.
In this study, we focus on the correctness of oil condition monitoring, specifically of a tuning forks sensor in hydraulic systems. We also aim to analyze the correlation between the online monitoring sensor signal and offline oil analysis by periodically sampling the hydraulic oil. In recent years, condition-based monitoring (CBM) of hydraulic oils has played a key role in extending earthmoving machinery uptime and reducing maintenance costs. We performed rig test and field test to develop a condition monitoring system based on oil analysis for construction equipment. Using the rig test, a reference line for the diagnosis of viscosity and dielectric constant for the new hydraulic oil was derived, and the characteristics of each sensor parameter for artificial contamination and oxidation were confirmed. In order to affirm the validity of oil diagnosis using oil sensors, the oil sensors were applied to four excavators to detect changes in oil conditions over 12 months. It was found that monitoring hydraulic oil with an oil sensor detecting the change in oil properties and contamination can provide reliable information for establishing diagnostic criteria. The finding allows us to predict the remaining oil life and to determine the oil change intervals based on the diagnosis of the oil condition. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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12 pages, 6469 KiB  
Article
Fabrication of TiO2 ̶ KH550 ̶ PEG Super-Hydrophilic Coating on Glass Surface without UV/Plasma Treatment for Self-Cleaning and Anti-Fogging Applications
by Muhammad Nobi Hossain, Sung-Jun Lee and Chang-Lae Kim
Materials 2022, 15(9), 3292; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15093292 - 04 May 2022
Cited by 9 | Viewed by 2980
Abstract
In this study, we have developed a self-cleaning transparent coating on a glass substrate by dip coating a TiO2 ̶ KH550 ̶ PEG mixed solution with super-hydrophilicity and good antifogging properties. The fabrication of the thin-film-coated glass is a one-step solution blending [...] Read more.
In this study, we have developed a self-cleaning transparent coating on a glass substrate by dip coating a TiO2 ̶ KH550 ̶ PEG mixed solution with super-hydrophilicity and good antifogging properties. The fabrication of the thin-film-coated glass is a one-step solution blending method that is performed by depositing only one layer of modified TiO2 nanoparticles at room temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the structure and morphology of the nanoparticles and the thin-film-coated glass. The surface functional groups were investigated using Fourier-transform infrared spectroscopy (FT-IR), and the optical properties of the glass coating were measured using a UV/Vis spectrometer. The results revealed that the KH-500-modified TiO2 film coating was in an anatase crystalline form. The hydrophilicity of the coated and uncoated glass substrates was observed by measuring their water contact angle (WCA) using a contact angle instrument. The maximum transparency of the coated glass measured in the visible region (380–780 nm) was approximately 70%, and it possessed excellent super-hydrophilic properties (WCA ~0°) at an annealing temperature of 350 °C without further need of UV or plasma treatment. These results demonstrate the super-hydrophilic coated glass surface has potential for use in self-cleaning and anti-fogging applications. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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12 pages, 2790 KiB  
Article
Friction and Wear Characteristics of Polydimethylsiloxane under Water-Based Lubrication Conditions
by Sung-Jun Lee, Yoon-Chul Sohn and Chang-Lae Kim
Materials 2022, 15(9), 3262; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15093262 - 02 May 2022
Cited by 9 | Viewed by 1794
Abstract
In this study, the friction and wear characteristics of polydimethylsiloxane (PDMS) were evaluated when using lubricants created by adding surfactants at various ratios to deionized (DI) water. When pure DI water is used as a lubricant, the repulsion of water from the hydrophobic [...] Read more.
In this study, the friction and wear characteristics of polydimethylsiloxane (PDMS) were evaluated when using lubricants created by adding surfactants at various ratios to deionized (DI) water. When pure DI water is used as a lubricant, the repulsion of water from the hydrophobic PDMS surface is large and the interfacial affinity is low; thus, the lubrication properties cannot be significantly improved. However, when a lubricant with a surfactant is added to DI water, the interfacial affinity with the PDMS surface increases to form a lubricating film, and the friction coefficient is greatly reduced. In this study, under dry and pure DI water conditions, severe wear tracks were formed on the PDMS surface after 10,000 cycles of reciprocating sliding motion under a vertical load of 100 mN, whereas in the case of the surfactant-based and water-based lubricant, no severe wear tracks occurred. The friction and wear characteristics of the PDMS were evaluated by increasing the normal loads and sliding cycles with a water-based lubricant containing 1 wt % surfactant. Under normal loads of 300 mN and 500 mN, only minor scratches occurred on the PDMS surface up to 10,000 and 100,000 cycles, respectively, but after 300,000 cycles, very severe pit wear tracks occurred. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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8 pages, 2178 KiB  
Article
Measurement of Shear Strengths of Cu Films Using Precise Chip Forming
by Jeong-Heon Lee and Jae B. Kwak
Materials 2022, 15(3), 948; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15030948 - 26 Jan 2022
Cited by 1 | Viewed by 1662
Abstract
The mechanical properties of thin films are under-researched because of the challenges associated with conventional experimental methods. We demonstrate a technique for determining the intrinsic shear strength and strain of thin films using a nano-cutting technique based on an orthogonal cutting model with [...] Read more.
The mechanical properties of thin films are under-researched because of the challenges associated with conventional experimental methods. We demonstrate a technique for determining the intrinsic shear strength and strain of thin films using a nano-cutting technique based on an orthogonal cutting model with precise control of the cutting system. In this study, electroplated Cu films with thicknesses of 1.5 μm and 5 μm and a sputtered Cu film with a thickness of 130 nm were fabricated to evaluate the mechanical strength. Experiments revealed a shear strength of approximately 310 MPa with a shear strain of 1.57 for the electroplated Cu film and a shear strength of 389 MPa with a shear strain of 2.03 for the sputtered Cu film. In addition, X-ray diffraction analysis was performed to correlate the experimental results. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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17 pages, 4182 KiB  
Article
Characteristics of the Structure, Mechanical, and Tribological Properties of a Mo-Mo2N Nanocomposite Coating Deposited on the Ti6Al4V Alloy by Magnetron Sputtering
by Stanisław Adamiak, Wojciech Bochnowski, Andrzej Dziedzic, Łukasz Szyller and Dominik Adamiak
Materials 2021, 14(22), 6819; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14226819 - 11 Nov 2021
Cited by 5 | Viewed by 1835
Abstract
Mo-Mo2N nanocomposite coating was produced by reactive magnetron sputtering of a molybdenum target, in the atmosphere, of Ar and N2 gases. Coating was deposited on Ti6Al4V titanium alloy. Presented are the results of analysis of the XRD crystal structure, microscopic [...] Read more.
Mo-Mo2N nanocomposite coating was produced by reactive magnetron sputtering of a molybdenum target, in the atmosphere, of Ar and N2 gases. Coating was deposited on Ti6Al4V titanium alloy. Presented are the results of analysis of the XRD crystal structure, microscopic SEM, TEM and AFM analysis, measurements of hardness, Young’s modulus, and adhesion. Coating consisted of α-Mo phase, constituting the matrix, and γ-Mo2N reinforcing phase, which had columnar structure. The size of crystallite phases averaged 20.4 nm for the Mo phase and 14.1 nm for the Mo2N phase. Increasing nitrogen flow rate leads to the fragmentation of the columnar grains and increased hardness from 22.3 GPa to 27.5 GPa. The resulting coating has a low Young’s modulus of 230 GPa to 240 GPa. Measurements of hardness and Young’s modulus were carried out using the nanoindentation method. Friction coefficient and tribological wear of the coatings were determined with a tribometer, using the multi-cycle oscillation method. Among tested coatings, the lowest friction coefficient was 0.3 and wear coefficient was 10 × 10−16 m3/N∙m. In addition, this coating has an average surface roughness of RMS < 2.4 nm, determined using AFM tests, as well as a good adhesion to the substrate. The dominant wear mechanism of the Mo-Mo2N coatings was abrasive wear and wear by oxidation. The Mo-Mo2N coating produced in this work is a prospective material for the elements of machines and devices operating in dry friction conditions. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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13 pages, 3361 KiB  
Article
Assessment of the Physical, Mechanical, and Tribological Properties of PDMS Thin Films Based on Different Curing Conditions
by Gang-Min Kim, Sung-Jun Lee and Chang-Lae Kim
Materials 2021, 14(16), 4489; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14164489 - 10 Aug 2021
Cited by 17 | Viewed by 3188
Abstract
Polydimethylsiloxane (PDMS), a silicone-based elastomeric polymer, is generally cured by applying heat to a mixture of a PDMS base and crosslinking agent, and its material properties differ according to the mixing ratio and heating conditions. In this study, we analyzed the effects of [...] Read more.
Polydimethylsiloxane (PDMS), a silicone-based elastomeric polymer, is generally cured by applying heat to a mixture of a PDMS base and crosslinking agent, and its material properties differ according to the mixing ratio and heating conditions. In this study, we analyzed the effects of different curing processes on the various properties of PDMS thin films prepared by mixing a PDMS solution comprising a PDMS base and a crosslinking agent in a ratio of 10:1. The PDMS thin films were cured using three heat transfer methods: convection heat transfer using an oven, conduction heat transfer using a hotplate, and conduction heat transfer using an ultrasonic device that generates heat internally from ultrasonic vibrations. The physical, chemical, mechanical, and tribological properties of the PDMS thin films were assessed after curing. The polymer chains in the PDMS thin films varied according to the heat transfer method, which resulted in changes in the mechanical and tribological properties. The ultrasonicated PDMS thin film exhibited the highest crystallinity, and hence, the best mechanical, friction, and wear properties. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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9 pages, 1369 KiB  
Article
Effect of Surface Structure Complexity on Interfacial Droplet Behavior of Superhydrophobic Titanium Surfaces for Robust Dropwise Condensation
by Je-Un Jeong, Dae-Yun Ji, Kwon-Yeong Lee, Woonbong Hwang, Chang-Hun Lee, Sung-Jae Kim and Jeong-Won Lee
Materials 2021, 14(15), 4107; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14154107 - 23 Jul 2021
Cited by 3 | Viewed by 1899
Abstract
In general, the dropwise condensation supported by superhydrophobic surfaces results in enhanced heat transfer relative to condensation on normal surfaces. However, in supersaturated environments that exceed a certain supersaturation threshold, moisture penetrates the surface structures and results in attached condensation, which reduces the [...] Read more.
In general, the dropwise condensation supported by superhydrophobic surfaces results in enhanced heat transfer relative to condensation on normal surfaces. However, in supersaturated environments that exceed a certain supersaturation threshold, moisture penetrates the surface structures and results in attached condensation, which reduces the condensation heat transfer efficiency. Therefore, when designing superhydrophobic surfaces for condensers, the surface structure must be resistant to attached condensation in supersaturated conditions. The gap size and complexity of the micro/nanoscale surface structure are the main factors that can be controlled to maintain water repellency in supersaturated environments. In this study, the condensation heat exchange performance was characterized for three different superhydrophobic titanium surface structures via droplet behavior (DB) mapping to evaluate their suitability for power plant condensers. In addition, it was demonstrated that increasing the surface structure complexity increases the versatility of the titanium surfaces by extending the window for improved heat exchange performance. This study demonstrates the usefulness of DB mapping for evaluating the performance of superhydrophobic surfaces regarding their applicability for industrial condenser systems. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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Review

Jump to: Research

18 pages, 4982 KiB  
Review
Varnish Formation and Removal in Lubrication Systems: A Review
by Sung-Ho Hong and Eun Kyung Jang
Materials 2023, 16(10), 3737; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16103737 - 15 May 2023
Cited by 1 | Viewed by 1815
Abstract
This study presents the current literature regarding the investigation of varnish contamination among the various types of lubricant contaminations. As the duration of use of lubricants increases, the lubricant deteriorates and may become contaminated. Varnish has been known to cause filter plugging, sticking [...] Read more.
This study presents the current literature regarding the investigation of varnish contamination among the various types of lubricant contaminations. As the duration of use of lubricants increases, the lubricant deteriorates and may become contaminated. Varnish has been known to cause filter plugging, sticking of the hydraulic valves and fuel injection pumps, flow obstruction, clearance reduction, poor heating and cooling performance, and increased friction and wear in various lubrication systems. These problems may also result in mechanical system failures, performance degradation, and increased maintenance and repair costs. To improve the problems caused by varnish contamination, an adequate understanding of varnish is required. Therefore, in this review, the definitions and characteristics, generating machinery, generating mechanisms, causes, measurement methods, and prevention or removal methods of varnish are summarized. Most of the data presented herein are reports from manufacturers related to lubricants and machine maintenance that are included in published works. We expect that this summary will be helpful to those who are engaged in reducing or preventing varnish-related problems. Full article
(This article belongs to the Special Issue Mechanical and Tribological Properties of Advanced Materials and Coatings)
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