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Diamond, DLC and Ultra-Hard Coatings
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Diamond, DLC and Ultra-Hard 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 (28 February 2022) | Viewed by 16002

Special Issue Editor

Dr. Francisco J. G. Silva

E-Mail Website
Guest Editor
Department of Mechanical Engineering, ISEP–School of Engineering, Polytechnic of Porto, 4200-072 Porto, Portugal
Interests: tribology; coatings; manufacturing processes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Ultra-hard coatings constitute a remarkable technical surplus in many areas, with tribology being one of the most important. Concerns about sustainability have grown remarkably, as extreme phenomena are happening around the world. Ultra-hard coatings make it possible to contribute effectively to increased sustainability by creating products with better properties and longer lifespan characteristics without the need to use toxic substances or produce difficult-to-treat effluents. This contribution to sustainability is still felt through the reduction of friction between surfaces, which allows for remarkable energy savings. Processes such as PVD and CVD have allowed a remarkable evolution in this area. The research around this type of coatings has been remarkable, allowing us to adapt coatings to the specific needs of each application. In the last decades, it has become extremely easy to find products with multilayer coatings, or with a differentiated composition throughout their cross-section. Through copious advances due to intense research activity in this area, the performance of numerous products has been significantly improved.

This Special Issue aims to promote the dissemination of the latest advances in this field, namely the development of new coatings and new structures, the characterization of these coatings, the design of coatings for tailored applications, and the tribological characterization of ultra-hard coatings, among others.

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

  • Diamond coating synthesis;
  • DLC coating systhesis/deposition;
  • Ultra-hard coating synthesis/deposition;
  • Ultra-hard multilayered coatings;
  • Nanostructured ultra-hard coatings;
  • Coating synthesis and deposition optimization;
  • Simulation applied to coatings characterization;
  • CVD and PVD techniques for the synthesis and deposition of ultra-hard coatings;
  • Characterization of ultra-hard coatings;
  • Tribological characterization of ultra-hard coatings;
  • Study of coatings adhesion to substrates;
  • Residual stresses studies on ultra-hard coatings;
  • Novel coating characterization techniques;
  • Tailor-made ultra-hard coatings;
  • Coatings for cutting tools;
  • Study of friction in ultra-hard coatings;
  • Lifespan study of ultra-hard coatings;
  • Ultra-hard coating applications;
  • Sustainability of ultra-hard coatings.

Prof. Dr. Francisco J. G. Silva
Guest Editor

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Keywords

  • Diamond coatings
  • DLC coatings
  • Ultra-hard coatings
  • Multilayer coatings
  • Tribological coatings
  • Nanostructured coatings
  • Tribological characterization of coatings
  • Micro-hardness, Ultra-micro-hardness
  • Simulation in coatings science
  • Friction, Cutting tools, Ultra-hard coatings application
  • Sustainable materials

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Published Papers (5 papers)

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Research

23 pages, 5536 KiB  
Article
Friction and Wear Performance Evaluation of Bio-Lubricants and DLC Coatings on Cam/Tappet Interface of Internal Combustion Engines
by Rehan Zahid, Muhammad Usman Bhutta, Riaz Ahmad Mufti, Muhammad Usman Abdullah, Haji Hassan Masjuki, Mahendra Varman, Muhammad Abul Kalam, Mian Ashfaq Ali, Jawad Aslam and Khalid Akhtar
Materials 2021, 14(23), 7206; https://doi.org/10.3390/ma14237206 - 26 Nov 2021
Cited by 7 | Viewed by 2970
Abstract
The environmental concerns associated with artificially formulated engine oils have forced a shift towards bio-based lubricants. The deposition of hard coatings on engine components and migrating to environmentally friendly green lubricants can help in this regard. Chemically modified forms of vegetable oils, with [...] Read more.
The environmental concerns associated with artificially formulated engine oils have forced a shift towards bio-based lubricants. The deposition of hard coatings on engine components and migrating to environmentally friendly green lubricants can help in this regard. Chemically modified forms of vegetable oils, with better low-temperature characteristics and enhanced thermo-oxidative stability, are suitable substitutes to conventional lubricant base oils. The research presented in this manuscript was undertaken to experimentally investigate the wear and friction performance of a possible future generation of an environmentally friendly bio-based lubricant as a potential replacement for conventional engine lubricants. In order to quantify the tribological benefits which can be gained by the deposition of DLC coatings, (an (a-C:H) hydrogenated DLC coating and an (a-C:H:W) tungsten-doped DLC coating) were applied on the cam/tappet interface of a direct acting valve train assembly of an internal combustion engine. The tribological correlation between DLC-coated engine components, lubricant base oils and lubricant additives have been thoroughly investigated in this study using actual engine operating conditions. Two additive-free base oils (polyalphaolefines (PAO) and chemically-modified palm oil (TMP)) and two multi-additive-containing lubricants were used in this investigation. Real-time drive torque was measured to determine the friction force, detailed post-test analysis was performed, which involved the use of a specialized jig to measure camlobe wear. An optical profilometer was used to measure the wear on the tappet, high-resolution scanning electron microscopy was employed to study the wear mechanism and energy-dispersive X-ray spectroscopy was performed on the tested samples to qualitatively access the degradation of the coating. When using additive-free TMP, a low friction coefficient was observed for the cam/tappet interface. The presence of additives further improved the friction characteristics of TMP, resulting in reduced average friction torque values. A tremendous enhancement in wear performance was recorded with a-C:H-coated parts and the coating was able to withstand the test conditions with little or no delamination. Full article
(This article belongs to the Special Issue Diamond, DLC and Ultra-Hard Coatings)
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12 pages, 56615 KiB  
Article
Multilayer Diamond Coatings Applied to Micro-End-Milling of Cemented Carbide
by Eduardo L. Silva, Sérgio Pratas, Miguel A. Neto, Cristina M. Fernandes, Daniel Figueiredo and Rui F. Silva
Materials 2021, 14(12), 3333; https://doi.org/10.3390/ma14123333 - 16 Jun 2021
Cited by 12 | Viewed by 2762
Abstract
Cobalt-cemented carbide micro-end mills were coated with diamond grown by chemical vapor deposition (CVD), with the purpose of micro-machining cemented carbides. The diamond coatings were designed with a multilayer architecture, alternating between sub-microcrystalline and nanocrystalline diamond layers. The structure of the coatings was [...] Read more.
Cobalt-cemented carbide micro-end mills were coated with diamond grown by chemical vapor deposition (CVD), with the purpose of micro-machining cemented carbides. The diamond coatings were designed with a multilayer architecture, alternating between sub-microcrystalline and nanocrystalline diamond layers. The structure of the coatings was studied by transmission electron microscopy. High adhesion to the chemically pre-treated WC-7Co tool substrates was observed by Rockwell C indentation, with the diamond coatings withstanding a critical load of 1250 N. The coated tools were tested for micro-end-milling of WC-15Co under air-cooling conditions, being able to cut more than 6500 m over a period of 120 min, after which a flank wear of 47.8 μm was attained. The machining performance and wear behavior of the micro-cutters was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Crystallographic analysis through cross-sectional selected area electron diffraction patterns, along with characterization in dark-field and HRTEM modes, provided a possible correlation between interfacial stress relaxation and wear properties of the coatings. Overall, this work demonstrates that high adhesion of diamond coatings can be achieved by proper combination of chemical attack and coating architecture. By preventing catastrophic delamination, multilayer CVD diamond coatings are central towards the enhancement of the wear properties and mechanical robustness of carbide tools used for micro-machining of ultra-hard materials. Full article
(This article belongs to the Special Issue Diamond, DLC and Ultra-Hard Coatings)
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29 pages, 17382 KiB  
Article
Study on the Influence of the Ball Material on Abrasive Particles’ Dynamics in Ball-Cratering Thin Coatings Wear Tests
by Gustavo Pinto, Andresa Baptista, Francisco Silva, Jacobo Porteiro, José Míguez and Ricardo Alexandre
Materials 2021, 14(3), 668; https://doi.org/10.3390/ma14030668 - 1 Feb 2021
Cited by 10 | Viewed by 2597
Abstract
Micro-abrasion remains a test configuration hugely used, mainly for thin coatings. Several studies have been carried out investigating the parameters around this configuration. Recently, a new study was launched studying the behavior of different ball materials in abrasive particles’ dynamics in the contact [...] Read more.
Micro-abrasion remains a test configuration hugely used, mainly for thin coatings. Several studies have been carried out investigating the parameters around this configuration. Recently, a new study was launched studying the behavior of different ball materials in abrasive particles’ dynamics in the contact area. This study intends to extend that study, investigating new ball materials never used so far in this test configuration. Thus, commercial balls of American Iron and Steel Institute (AISI) 52100 steel, Stainless Steel (SS) (AISI) 304 steel and Polytetrafluoroethylene (PTFE) were used under different test conditions and abrasive particles, using always the same coating for reference. Craters generated on the coated samples’ surface and tracks on the balls’ surface were carefully observed by Scanning Electron Microscopy (SEM) and 3D microscopy in order to understand the abrasive particles’ dynamics. As a softer material, more abrasive particles were entrapped on the PTFE ball’s surface, generating grooving wear on the samples. SS AISI 304 balls, being softer than the abrasive particles (diamond), also allowed particle entrapment, originating from grooving wear. AISI 52100 steel balls presented particle dynamics that are already known. Thus, this study extends the knowledge already existing, allowing to better select the ball material to be used in ball-cratering tests. Full article
(This article belongs to the Special Issue Diamond, DLC and Ultra-Hard Coatings)
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14 pages, 5114 KiB  
Article
Influence of Adhesive Strength, Fatigue Strength and Contact Mechanics on the Drilling Performance of Diamond Coating
by Naichao Chen, Musen Liu and Ping He
Materials 2020, 13(6), 1402; https://doi.org/10.3390/ma13061402 - 19 Mar 2020
Cited by 8 | Viewed by 2950
Abstract
Adhesive strength of the coating significantly affects the lifetime of the coating. However, it is still inevitable for the coating, even with strong adhesive strength, to peel off from the substrate after working for a while. In this work, fatigue and wear behaviors [...] Read more.
Adhesive strength of the coating significantly affects the lifetime of the coating. However, it is still inevitable for the coating, even with strong adhesive strength, to peel off from the substrate after working for a while. In this work, fatigue and wear behaviors were employed to analyze the effect on the mechanics of coating and contribute to a fundamental understanding of peeling of the coating. A small-size Co-cemented tungsten carbide drill bit was selected as the examined substrate to fabricate the diamond coating. Roughening pretreatment with a diamond slurry combined with ultrasonic vibration was performed for the substrate surface to enhance adhesive strength. Meanwhile, a diamond coating without roughening pretreatment was also fabricated for comparison. The lifetime and quality of the coating were evaluated by the drilling test. Although the diamond coating could grow on the substrates with and without roughening pretreatment, the diamond coating with roughening pretreatment possessed a higher lifetime and stronger wear resistance than that without roughening pretreatment. We found that both substrates with and without roughening pretreatment exhibited a coarse surface, whereas the roughening pretreatment could remove the original machined surface of the substrate and thus make the near surface with numerous integrated crystalline grains become the new topmost surface. This increased the contact area and surface energy of the interface, leading to the improvement of adhesive strength. Finally, fatigue strength and contact mechanics were studied to trace the changes in the stress of the diamond coating in the whole process of drilling from a theoretical point of view. We suggest that fatigue strength and contact mechanics may play vital roles on the durability and peeling of the coating. Full article
(This article belongs to the Special Issue Diamond, DLC and Ultra-Hard Coatings)
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9 pages, 2929 KiB  
Article
Microstructures Manufactured in Diamond by Use of Laser Micromachining
by Mariusz Dudek, Adam Rosowski, Marcin Kozanecki, Malwina Jaszczak, Witold Szymański, Martin Sharp and Anna Karczemska
Materials 2020, 13(5), 1199; https://doi.org/10.3390/ma13051199 - 6 Mar 2020
Cited by 9 | Viewed by 3251
Abstract
Different microstructures were created on the surface of a polycrystalline diamond plate (obtained by microwave plasma-enhanced chemical vapor deposition—MW PECVD process) by use of a nanosecond pulsed DPSS (diode pumped solid state) laser with a 355 nm wavelength and a galvanometer scanning system. [...] Read more.
Different microstructures were created on the surface of a polycrystalline diamond plate (obtained by microwave plasma-enhanced chemical vapor deposition—MW PECVD process) by use of a nanosecond pulsed DPSS (diode pumped solid state) laser with a 355 nm wavelength and a galvanometer scanning system. Different average powers (5 to 11 W), scanning speeds (50 to 400 mm/s) and scan line spacings (“hatch spacing”) (5 to 20 µm) were applied. The microstructures were then examined using scanning electron microscopy, confocal microscopy and Raman spectroscopy techniques. Microstructures exhibiting excellent geometry were obtained. The precise geometries of the microstructures, exhibiting good perpendicularity, deep channels and smooth surfaces show that the laser microprocessing can be applied in manufacturing diamond microfluidic devices. Raman spectra show small differences depending on the process parameters used. In some cases, the diamond band (at 1332 cm−1) after laser modification of material is only slightly wider and shifted, but with no additional peaks, indicating that the diamond is almost not changed after laser interaction. Some parameters did show that the modification of material had occurred and additional peaks in Raman spectra (typical for low-quality chemical vapor deposition CVD diamond) appeared, indicating the growing disorder of material or manufacturing of the new carbon phase. Full article
(This article belongs to the Special Issue Diamond, DLC and Ultra-Hard Coatings)
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