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Crystals
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Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components
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Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 33832

Special Issue Editors

Dr. Patrice Berthod

E-Mail Website
Guest Editor
Institut Jean Lamour and Faculty of Sciences and Technologies, University of Lorraine, 54000 Nancy, France
Interests: elaboration, microstructures and properties of superalloys and dental alloys (mechanical behavior, oxidation and corrosion)
Special Issues, Collections and Topics in MDPI journals
Dr. Pascal De March

E-Mail Website1 Website2
Guest Editor
1. Faculty of Odontology and Institut Jean Lamour, University of Lorraine, 54000 Nancy, France
2. Luxembourg Institute of Science and Technology, 4362 Esch-sur-Alzette, Luxembourg
Interests: prosthetic dentistry and implantology; dental alloys
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

At present, cobalt-based alloys are used in various applications: as refractory alloys for the hottest parts in aeronautical or power generation turbines, corrosion-resistant alloys for dental prostheses and other biomedical devices, wear-resistant alloys for hardfacing components, amorphous alloys for applications exploiting their magnetic properties, etc. Among the first cobalt-based alloys to appear, there were the conventionally cast chromium-rich ones which emerged about a century ago for responding dentistry needs and, a little later, their cousin cobalt-based superalloys which allowed developing turbines for WWII military aircrafts. From this period, the chemical composition and elaboration techniques were more or less continuously developed and improved. New elaboration ways, metallurgical strengthening principles, or answers for enhanced resistance against corrosion, for instance, are today investigated for crystalline cobalt-based superalloys (e.g., cobalt–rhenium–chromium alloys or gamma/gamma prime Co-based single crystals) as for dental alloys (e.g., new compositions and additive manufacturing).

The purpose of this Special Issue of Crystals, entitled “Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components” is to gather the most recent research results concerning single crystalline or polycrystalline cobalt-based alloys, coming from additional studies on well-known alloys or from works on recently developed metallurgical principles and fabrication processes. In this frame, we are pleased to invite researchers to submit to us their contributions dealing with the following topics (not exhaustive list):

  • Characterization of cobalt-based superalloys and other cobalt alloys for various applications;
  • Study of cast, wrought, and powder metallurgy cobalt alloys;
  • Innovative compositions of alloys based on cobalt or with high content in cobalt (Co–Re–Cr, Co–W–Al, high entropy alloys, etc.);
  • New elaboration ways for cobalt alloys (single-crystalline solidification, additive manufacturing, etc.);
  • Dependence of microstructures and properties on the chemical composition and the process parameters;
  • Characterization and understanding of the mechanical deformation/rupture and wear-phenomena;
  • Characterization of the behaviors in oxidation by various hot gases and in corrosion by liquid/molten medias (aqueous solutions, artificial saliva, molten salts or glasses);
  • Characterization of dental Co–Cr alloys manufactured via conventional casting, milling, selective laser melting (SLM), milling soft metal.

Prof. Dr. Patrice Berthod
Dr. Pascal De March
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Cobalt-based superalloys
  • Wear-resistant cobalt alloys
  • Dental cobalt alloys
  • High temperature components
  • Hardfacing materials
  • Biomedical applications
  • New compositions and elaboration ways
  • Microstructure
  • Mechanical properties
  • Hot or room temperature oxidation and corrosion

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Related Special Issue

Published Papers (6 papers)

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Research

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14 pages, 9484 KiB  
Article
Microstructure and Mechanical Property of a Multi-Scale Carbide Reinforced Co–Cr–W Matrix Composites
by Shiyang Wang, Sheng Zhan, Xingyu Hou, Long Wang, Hongwei Zhang, Hongyu Zhang, Yuan Sun and Lujun Huang
Crystals 2022, 12(2), 198; https://doi.org/10.3390/cryst12020198 - 28 Jan 2022
Cited by 3 | Viewed by 2256
Abstract
In order to meet the demand for high wear-resistant Co-based material used in fields such as aerospace, energy, medical, etc., this study attempts to improve the comprehensive performance of this material by adding some reinforced phases and adjusting the sintering temperature. Results indicate [...] Read more.
In order to meet the demand for high wear-resistant Co-based material used in fields such as aerospace, energy, medical, etc., this study attempts to improve the comprehensive performance of this material by adding some reinforced phases and adjusting the sintering temperature. Results indicate the pure Co–Cr–W alloy is composed of γ-Co, M29C, and M6C (Ni3W3C), and the Co–Cr–W matrix composites are composed of γ-Co, M29C, M6C (Co2W4C), M23C6, and WC. With increasing the hot-pressing sintering temperature, the element diffusion in the material becomes sufficient, and the microstructure of Co–Cr–W alloy and composites materials becomes denser. When the sintering temperature is over 1150 °C, the bending strength and the toughness of the Co–Cr–W matrix composites are higher than that of the pure Co–Cr–W alloys. The added reinforced phases help the composites to gain a multi-scale strengthening effect, which makes the composites have a more comprehensive performance. Our results emphasize the importance of added reinforced phases and help to optimize the preparing process in preparing the Co–Cr–W alloys. Full article
(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)
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21 pages, 44095 KiB  
Article
In-Situ XRD Study of Phase Transformation Kinetics in a Co-Cr-W-Alloy Manufactured by Laser Powder-Bed Fusion
by Patrick Hegele, Jonas von Kobylinski, Leonhard Hitzler, Christian Krempaszky and Ewald Werner
Crystals 2021, 11(2), 176; https://doi.org/10.3390/cryst11020176 - 10 Feb 2021
Cited by 10 | Viewed by 4088
Abstract
The additive manufacturing process of laser powder-bed fusion (L-PBF) is an increasingly popular approach for patient-specific production of dental frameworks made from Co-Cr alloys. Macroscopically, frameworks produced in this way exhibit high anisotropy especially in Young’s modulus, and are missing standardized requirements. Microscopically, [...] Read more.
The additive manufacturing process of laser powder-bed fusion (L-PBF) is an increasingly popular approach for patient-specific production of dental frameworks made from Co-Cr alloys. Macroscopically, frameworks produced in this way exhibit high anisotropy especially in Young’s modulus, and are missing standardized requirements. Microscopically, pronounced texture and high residual stresses are characteristic. To reduce resulting detrimental effects, the as-built (AB) parts are heat treated. Dependent on the treatment temperature, effects like the transformation of the γ-phase matrix in the AB condition to ϵ-phase, precipitation, stress relief, and grain growth were observed. While the existence of these processes was established in the past, little is known about their kinetics. To fill this gap, these effects were studied with in-situ X-ray diffraction (XRD) methods in isothermal heat treatments (HTs) at four different sample surface temperatures TS reaching from 650∘C to 900∘C. Furthermore, room temperature ex situ XRD and SEM/EDS measurements completed the analysis. An evaluation of the datasets, with single peak fitting and QXRD methods, yielded the following results. In the HTs below a certain threshold, a γ-to-ϵ transformation was observed in the sample bulk and close to the sample surface. In the latter case, evidence for a partially strain-induced transformation related to oxide formation was present. Above this threshold and possibly slightly below, σ- and Laves-phase precipitated. Additionally, peak profile evolutions hinted at a drop of inter- and intragranular stresses within the first 30 to 60 min. Therefore, an HT of about 30 to 60 min slightly above the threshold is proposed as optimal for reducing residual stresses while retaining a predominantly single-phased microstructure, possibly superior in corrosion properties and likewise in bio-compatibility. Full article
(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)
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18 pages, 7364 KiB  
Article
Effects of Ni Additions on the High Temperature Expansion, Melting and Oxidation Behaviors of Cobalt-Based Superalloys
by Patrice Berthod, Lionel Aranda and Jean-Paul Gomis
Crystals 2021, 11(2), 173; https://doi.org/10.3390/cryst11020173 - 9 Feb 2021
Cited by 6 | Viewed by 2359
Abstract
Nickel is often added to cobalt-based superalloys to stabilize their austenitic structure. In this work the effects of Ni on several high temperature properties of a chromium-rich cobalt-based alloy reinforced by high fraction of TaC carbides are investigated. Different thermal analysis techniques are [...] Read more.
Nickel is often added to cobalt-based superalloys to stabilize their austenitic structure. In this work the effects of Ni on several high temperature properties of a chromium-rich cobalt-based alloy reinforced by high fraction of TaC carbides are investigated. Different thermal analysis techniques are used: differential scanning calorimetry (DSC), thermo-mechanical analysis (TMA) and thermogravimetry (TG). Results show that the progressive addition of nickel did not induce great modifications of microstructure, refractoriness or thermal expansion. However, minor beneficial effects were noted, including reduction of the melting temperature range and slight decrease in thermal expansion coefficient. The most important improvement induced by Ni addition concerns the hot oxidation behavior. In this way, introducing several tens wt % Ni in this type of cobalt-based alloy may be recommended. Full article
(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)
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12 pages, 3005 KiB  
Communication
Impact of the Co/Ni-Ratio on Microstructure, Thermophysical Properties and Creep Performance of Multi-Component γ′-Strengthened Superalloys
by Christopher H. Zenk, Nicklas Volz, Carolin Zenk, Peter J. Felfer and Steffen Neumeier
Crystals 2020, 10(11), 1058; https://doi.org/10.3390/cryst10111058 - 21 Nov 2020
Cited by 13 | Viewed by 3266
Abstract
The Ni content is a crucial factor for the development of γ′-strengthened Co-based superalloys and some studies have systematically addressed its influence on various properties in model superalloys. In this paper, we report for the first time the influence of the Co/Ni ratio [...] Read more.
The Ni content is a crucial factor for the development of γ′-strengthened Co-based superalloys and some studies have systematically addressed its influence on various properties in model superalloys. In this paper, we report for the first time the influence of the Co/Ni ratio in the more advanced nine-component superalloy ERBOCo-1: exchanging Co and Ni in this Co/Ni-based superalloy while keeping the other alloying elements constants has a big influence on a variety of material properties. The elemental segregation after casting is slightly more pronounced in the alloy with higher Ni-content. Microstructural characterization of this alloy termed ERBOCo-1X after heat-treatment reveals that the precipitates are cuboidal in the Co- and spherical in the Ni-rich alloy, indicating a decrease in the γ/γ′ lattice misfit. Analyzing the elemental partitioning behavior by atom probe tomography suggests that the partitioning behavior of W is responsible for that. Furthermore, it is found that even though Ni exhibits the highest overall concentration, the γ matrix phase is still Co-based, because Ni is strongly enriched in the γ′ precipitates. Creep tests at 900 °C reveal that even though the microstructure looks less favorable, the creep resistance of the Ni-rich alloy is slightly superior to the Co-rich variant. Full article
(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)
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20 pages, 5717 KiB  
Article
High-Entropy FeCoNiB0.5Si0.5 Alloy Synthesized by Mechanical Alloying and Spark Plasma Sintering
by Kaouther Zaara, Mahmoud Chemingui, Sophie Le Gallet, Yves Gaillard, Lluisa Escoda, Joan Saurina, Joan Josep Suñol, Frédéric Bernard, Mohamed Khitouni and Virgil Optasanu
Crystals 2020, 10(10), 929; https://doi.org/10.3390/cryst10100929 - 12 Oct 2020
Cited by 14 | Viewed by 2965
Abstract
A FeCoNi(B0.5Si0.5) high-entropy alloy with the face-centered cubic (FCC) crystal structure was synthesized by mechanical alloying and spark plasma sintering (SPS). Phase evolution, microstructure, morphology and annealing behaviors were investigated. It was found that a single FCC solid solution [...] Read more.
A FeCoNi(B0.5Si0.5) high-entropy alloy with the face-centered cubic (FCC) crystal structure was synthesized by mechanical alloying and spark plasma sintering (SPS). Phase evolution, microstructure, morphology and annealing behaviors were investigated. It was found that a single FCC solid solution appears after 50 h of milling. The grain size was 10 nm after 150 h of milling. Microstructure parameters were calculated by the Rietveld fitting of the X-ray Diffraction patterns. Magnetic characterizations of milled and annealed powders at 650 °C for 1 h were investigated. The heat treatment improves the magnetic properties of the milled powders by enhancing the saturation magnetization value from 94.31 to 127.30 emu/g and decreasing the coercivity from 49.07 to 29.57 Oe. The cohabitation of the FCC phase with the equilibrium crystalline phases observed after annealing is responsible of this magnetic softening. The as-milled powder was also consolidated by spark plasma sintering at 750 and 1000 °C. The obtained specimen consolidated at 750 °C improved the coercivity to 25.06 Oe and exhibited a compressive strength of 1062 Mpa and Vickers hardness of 518 ± 14 HV, with a load of 2 kN. The nanoindentation technique with the Berkovich indentor gave hardness and indentation elastic modulus of 6.3 ± 0.3 Gpa (~640 HV) and 111 ± 4 Gpa for samples consolidated by SPS at 750 °C. Full article
(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)
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Review

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16 pages, 727 KiB  
Review
Cobalt–Chromium Dental Alloys: Metal Exposures, Toxicological Risks, CMR Classification, and EU Regulatory Framework
by Alina Vaicelyte, Christine Janssen, Marc Le Borgne and Brigitte Grosgogeat
Crystals 2020, 10(12), 1151; https://doi.org/10.3390/cryst10121151 - 18 Dec 2020
Cited by 59 | Viewed by 17057
Abstract
During the 20th century, metal alloys have assumed an important role as restorative materials. Among existing examples, cobalt–chromium (Co–Cr) alloys increasingly began to be used in medicine and especially in dentistry. Their success is mainly due to their mechanical properties such as stiffness, [...] Read more.
During the 20th century, metal alloys have assumed an important role as restorative materials. Among existing examples, cobalt–chromium (Co–Cr) alloys increasingly began to be used in medicine and especially in dentistry. Their success is mainly due to their mechanical properties such as stiffness, strength and corrosion resistance, thus allowing a high biocompatibility. There are quite meaningful data on the corrosion and toxicity of Co–Cr alloys for their use in restorative materials such as dental prostheses. Toxicological studies following Co and Cr exposures in the oral cavity are more difficult to conduct because there are many different situations leading to the release of metal ions and wear particles. Furthermore, the links between exposure and the appearance of local or systemic toxicity are not automatic. Since 2017, the European Union (EU) regulatory framework for Co–Cr alloys has been undergoing profound changes. A new EU Medical Devices Regulation (MDR) (2017/745) will be applied in May 2021 with the need to consider that Co metal is a new carcinogenic, mutagenic and toxic to reproduction (CMR) substance. On 18 February 2020, the 14th Adaptation to Technical Progress (ATP14) to the Classification, Labelling and Packaging (CLP) regulation was published, including the harmonised classification for Co metal as a CMR 1B substance. In this context, the use of Co might be forbidden if the medical devices are invasive and as soon as they include more than 0.1% (m/m) Co. This review provides a specific overview on Co–Cr dental alloys in terms of metal ions and wear particles release, toxicological risks, and the actual and new EU regulatory framework. Full article
(This article belongs to the Special Issue Cobalt-Based Alloys: From Prosthetic Dentistry to Hot Turbine Components)
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