Cobalt–chromium–molybdenum (CoCrMo) alloys are known for medical use due to their biocompatibility, corrosion and  wear resistance. The chemical and phase composition, as well as microstructure of the alloy directly affect the mechanical  properties. In this investigation, CoCrMo alloy samples were obtained by vacuum precise casting. The procedure of  melting and casting process as well as their parameters are given. Molds fabricated of copper, gray iron, steel, ceramics  and graphite were used during the casting process. In this way, the cooling rate influence on the obtained microstructure  was examined. Besides, different casting temperatures (1400°C, 1450°C and 1500°C) were applied for each kind of mold.  After metallographic preparation, the microstructure was examined on the cross section of samples by optical microscopy.  The obtained results show that by increasing the cooling rate, the microstructure of samples become finer and more  homogeneous

Marković, Gordana

Mihailović, Marija

Mihajlović, Slavica

Patarić, Aleksandra

Đorđević, Nataša G.

Central Repository of the Institute of Chemistry, Technology and Metallurgy (CER)

Main Organizer The Association of Metallurgical Engineers of Serbia Co-organizers Institute for Technology of Nuclear and Other Mineral Raw Materials in Belgrade, Serbia; The Faculty of Technology and Metallurgy at the University of Belgrade, Serbia; The Faculty of Technology at the University of Banja Luka, Bosnia and Herzegovina; The Faculty of Metallurgy at the University of Zagreb in Sisak, Croatia; The Faculty of Natural Sciences and Engineering at the University of Ljubljana, Slovenia; The Faculty of metallurgy and technology at the University of Podgorica, Montenegro. CONGRESS PROCEEDINGS - MME SEE 2023 5th Metallurgical & Materials Engineering Congress of South-East Europe Editors: Dr. Miroslav Sokić,Institute for Technology of Nuclear and Other Mineral Raw Materials Dr. Branislav MarkovićInstitute for Technology of Nuclear and Other Mineral Raw Materials prof. Dr. Vaso ManojlovićFaculty of Technology and Metallurgy, University of Belgrade Technical editor: M. Sc. Gvozden JovanovićInstitute for Technology of Nuclear and Other Mineral Raw MaterialsPublished and printed by: Association of Metallurgical Engineers of Serbia (AMES) Kneza Miloša 9/IV,  11000 Belgrade Serbia For the publisher: AMES president Dr. Miroslav SokićCirculation: 120 copiesISBN 978-86-87183-32-2 GOLD SPONSOR SILVER SPONSOR 5th Metallurgical & Materials Engineering Congress of South-East Europe 2023 – Trebinje, BIH  Scientific Committee   Miroslav Sokić, Serbia, president  Marija Korać, Serbia, vice president  Sanja Martinović, Serbia, vice president  Aleksandra Daković, Serbia  Ana Kostov, Serbia  Bernd Friedrich, Germany  Borislav Malinović,  Bosnia and Herzegovina  Boštjan Markoli, Slovenia  Branislav Marković, Serbia  Corby Anderson, USA  Dragomir Glišić, Serbia  Duško Minić, Serbia  Efthymios Balomenos, Greece  Hakan Atapek, Turkey  Hasan Avdušinović,  Bosnia and Herzegovina  Jarmila Trpčevska, Slovakia  Jasna Stajić-Trošić, Serbia  Jovana Ružić, Serbia  Karlo Raić, Serbia  Kemal Delijić, Montenegro  Lijun Zhang, China  Ljubica Radović, Serbia  Martin Debelak, Slovenia  Mile Đurđević, Austria  Miljana Popović, Serbia  Mirjam Jan Blažić, Slovenia  Miroslav Ignjatović, Serbia  Nada Štrbac, Serbia  Natalija Dolić, Croatia  Nebojša Tadić, Montenegro  Nenad Radović, Serbia  Pasquale Daniele Cavaliere, Italy  Petar Uskoković, Serbia  Rossita Paunova, Bulgaria  Srećko Manasijević, Serbia  Srećko Stopić, Germany  Tatjana Volkov-Husović, Serbia  Vaso Manojlović, Serbia  Veljko Đokić, Serbia  Vesna Maksimović, Serbia  Vladan Ćosović, Serbia  Zdenka Zovko-Brodarac, Croatia  Željko Kamberović, SerbiaOrganizing Committee  Branislav Marković, Serbia, president  Vaso Manojlović, Serbia, vice president  Aleksandar Jovanović, Serbia  Gvozden Jovanović, Serbia  Milena Obradović, Serbia  Mladen Bugarčić, Serbia  Nela Vujović, Serbia  Nikola Kanas, Serbia  Stefan Dikić, Serbia5th Metallurgical & Materials Engineering Congress of South-East Europe 2023 – Trebinje, BIH Reviewer Committee • Aleksandar Jovanović, Serbia• Aleksandar Savić, Serbia• Aleksandra Daković, Serbia• Blažo Lalević, Serbia• Bojan Međo, Serbia• Boštjan Makroli, Slovenia• Branislav Marković, Serbia• Branko Matović, Serbia• Dragana Živoinović, Serbia• Dragana Radovanović, Serbia• Dragomir Glišić, Serbia• Dušica Pešević, Bosnia and Herzegovina• Gvozden Jovanović, Serbia• Ivana Cvijović-Alagić, Serbia• Jelena Avdalović, Serbia• Jelena Lović, Serbia• Jovana Perendija, Serbia• Karlo Raić, Serbia• Kemal Delijić, Montenegro• Ksenija Nešić, Serbia• Maja Đolić, Serbia• Maja Obradović, Serbia• Marija Ercegović, Serbia• Marija Korać, Serbia• Marina Jovanović, Bosnia and Herzegovina• Milica Pošarac Marković, Serbia• Milisav Ranitović, Serbia• Miljana Popović, Serbia• Miroslav Sokić, Serbia• Mladen Bugarčić, Serbia• Nebojša Nikolić, Serbia• Nenad Radović, Serbia• Rada Petrović, Serbia• Silvana Dimitrijevic, Serbia• Srđan Matijašević, Serbia• Srećko Stopić, Germany• Stevan Dimitrijević, Serbia• Suzana Filipović, Serbia• Tatjana Volkov-Husović, Serbia• Vaso Manojlović, Serbia• Vladan Ćosović, Serbia• Zoran Anđić, Serbia• Zoran Stević, Serbia• Željko Kamberović, Serbia 5th Metallurgical & Materials Engineering Congress of South-East Europe 2023 – Trebinje, BIH 221  MICROSTRUCTURE ASSESSMENT OF Co ALLOY  INTENDED FOR DENTISTRY Aleksandra Patarić1, Gordana Marković1, Nataša Đorđević1, Slavica Mihajlović1, Marija Mihailović2  e-mail: a.pataric@itnms.ac.rs 1-Institute for Technology of Nuclear and other Mineral Raw Materials, Franchet d’Eperey St.86, 11000 Belgrade, Serbia 2-University of Belgrade - Institute оf Chemistry, Technology and Metallurgy - National Institute of the Republic of Serbia, Njegoševa 12, Belgrade, Serbia Cobalt–chromium–molybdenum (CoCrMo) alloys are known for medical use due to their biocompatibility, corrosion and wear resistance. The chemical and phase composition, as well as microstructure of the alloy directly affect the mechanical properties. In this investigation, CoCrMo alloy samples were obtained by vacuum precise casting. The procedure of melting and casting process as well as their parameters are given. Molds fabricated of copper, gray iron, steel, ceramics and graphite were used during the casting process. In this way, the cooling rate influence on the obtained microstructure was examined. Besides, different casting temperatures (1400°C, 1450°C and 1500°C) were applied for each kind of mold. After metallographic preparation, the microstructure was examined on the cross section of samples by optical microscopy. The obtained results show that by increasing the cooling rate, the microstructure of samples become finer and more homogeneous. Keywords: CoCrMo alloy, vacuum precise casting, cooling rate Introduction Co-Cr-Mo alloys are distinguished by their high strength, biocompatibility, non-corrosiveness, and exceptional wear resistance [1, 2]. These alloys exhibit high fluidity and low viscosity at elevated temperatures, which allows for the casting of complex shapes [3]. These properties make them well-suited for use in dentistry for the manufacture of various dental components, including prostheses, bridges, dental crowns, and orthodontic appliances. Additionally, their resistance to tarnishing also makes them ideal for dental applications [4, 5]. Being in the aggressive environment of the oral cavity, Co-Cr-Mo alloys must be biocompatible [6]. Cobalt, chromium, and molybdenum are microelements in the human body, and these alloys are recognized as hypoallergenic [2]. They exhibit excellent corrosion resistance, owing to the formation of a passivating layer that inhibits the release of metal ions into the oral cavity [2, 7]. The microstructural characteristics of a material have a profound effect on its mechanical properties, thus defining its suitability for a given application [8]. A heterogeneous and coarse-grained microstructure usually results in low strength and increased brittleness, while a fine-grained, uniform morphology is a good indicator of superior strength. The final obtained structure largely depends on the processing temperature and cooling rate. Elevated processing temperatures are more likely to yield a homogeneous and coarse-grained structure, with a higher density of dislocations, compared to lower cooling temperatures [9]. Rapid cooling leads to the formation of fine crystals, which contributes to increased strength and ductility [10]. Different molds have different coefficients of thermal conductivity, with higher values corresponding to faster cooling [11]. Materials and methods Alloy was prepared from the following elements Co (99.99 wt.%), Cr (99%), Mn (99.9%), Mo (99,8%), Si (98%) by vacuum precise casting in a vacuum induction furnace. Cobalt chromium and manganese are integral components of alloys, while manganese and silicon are important for detoxification and cleaning of alloys during melting. Granulation of raw materials is 0.5-5 mm.   In order to prevent the oxidation of the alloy and to obtain its appropriate chemical composition, the  Congress Proceedings  Characterisation and structure of materials 222  casting process was carried out in a vacuum induction furnace. Melting and casting process was performed under the vacuum of 0.04 mbar Five different kinds of molds with dissimilar thermal conductivity coefficients were prepared for casting alloys, from the following materials: copper (386 W/m.K), gray iron (52.5 W/m.K), ceramic (1.38 W/m.K), steel (50 W/m.K) and graphite (4180 W/m.K) [12, 13, 14, 15]. The molds should be preheated to the temperature of about 1000 ºC while the casting temperatures were in range of 1450-1550 ºC. After melting, casting and cooling, five series of samples cast in five different molds were made. The microstructure of samples (cast in five different molds) was examined after the usual metallographic preparation. The samples were ground and polished. Polishing was carried out using alumina suspension (Al203) that was applied on a rotating self-adhesive disc. A mixture of potassium ferrocyanide, potassium hydroxide and water was used for samples etching. For the qualitative microstructure analysis the image analysis device Leica Q500MC was used. Results and discussion The characteristic microstructure appearance at the cross section of samples casted in five different molds is shown in Figures 1, 2, 3, 4 and 5. Sample 1 was cast in graphite-base mold, sample 2  in copper mold, sample 3 in gray iron mold, sample 4 in steel mold and sample 5 in ceramic mold.      (a)          (b) Figure 1 Microstructure of sample 1 cross section, (graphite-base mold), surface area (a) center (b)     (a)          (b) Figure 2 Microstructure of sample 2 cross section, (copper mold), surface area (a) center (b)  5th Metallurgical & Materials Engineering Congress of South-East Europe 2023 – Trebinje, BIH 223      (a)          (b) Figure 3 Microstructure of sample 3 cross section, (gray iron mold), surface area (a) center (b)         (a)         (b)   Figure 4 Microstructure of sample 4 cross section, (steel mold), surface area (a) center (b)     (a)         (b) Figure 5 Microstructure of sample 5 cross section, (ceramic mold ),surface area (a) center (b) As it can be seen, the cellular/dendritic morphology is the result of Co segregation from the solid solution during the solidification process. However, the morphology of the samples differs from one another. This is a consequence of the different cooling rate, because each material (five kinds of molds) has various thermal conductivity coefficients. If the thermal conductivity coefficient is higher, the cooling rate is also higher. The finest and the most homogenous is microstructure of the sample 1 and 2, cast in graphite-base mold and copper mold, because of the high cooling rate. With cooling rate decrease, the microstructure became less fine and more dendritic (samples 3 and 4).    Congress Proceedings  Characterisation and structure of materials 224  Due to the small difference in thermal conductivity coefficients, the microstructure of samples 3 and 4, does not differ significantly. Sample 5 has the roughest microstructure with pronounced dendrites and a lot of porosity, because of the lowest cooling rate.  In all samples, a slightly larger grain can be observed in the center compared to the surface area. This is also a consequence of the cooling rate decreasing from the surface area to the center of samples. Conclusion Results of microstructure assessment of the samples reveal a difference in the morphology, size and shape of the grains. The cooling rate directly affects the obtained microstructure of the alloy.  The higher cooling rate results in a finer and more homogeneous microstructure, which is the case with the samples 1 and 2 cast in graphite base mold and copper mold. Some less fine and less homogeneous microstructure has samples 3 and 4 cast in gray iron mold and steel mold.  The poorest microstructure with porosity appears, has sample 5 cast in ceramic mold. It is clear that the cooling rate directly affects the microstructure and that the appropriate structure can be achieved by properly choosing the material from which the mold is made. This is very important because  the mechanical properties depend on the microstructure, which will be the subject of study in our following researches. Acknowledgement This work was supported by the Ministry of Science, Technological Development and Innovations, Grant No. 451-03- 47/2023-01/200026 (IHTM) and Grant No.451-03-47/2023-01/200023 (ITNMS). References [1] Ren, Zhe, Steven Eppell, Sunniva Collins, and Frank Ernst. "Co–Cr–Mo alloys: Improved wear resistance through low-temperature gas-phase nitro-carburization." Surface and Coatings Technology 378 (2019): 124943. [2] Łukaszczyk, A., and J. Augustyn-Pieniążek. "Corrosion resistance of Co-Cr-Mo alloy used in dentistry." Archives of metallurgy and Materials 60, no. 1 (2015): 523-528. [3] Liu, R., S. Q. Xi, S. Kapoor, and X. J. Wu. "Investigation of solidification behavior and associate microstructures of Co–Cr–W and Co–Cr–Mo alloy systems using DSC technique." Journal of materials science 45 (2010): 6225-6234. [4] Averyanova, Maria, Philippe Bertrand, and Benoît Verquin. "Manufacture of Co-Cr dental crowns and bridges by selective laser Melting technology: This paper presents the successful application of the selective laser melting technology in dental frameworks manufacturing from Co-Cr alloy using Phenix PM 100T Dental Machine over a production period of 14 months." Virtual and Physical Prototyping 6, no. 3 (2011): 179-185. [5] De Aguiar, S. R. M. M., M. Nicolai, M. Almeida, and A. Gomes. "Electrochemical behaviour of a cobalt–chromium–molybdenum dental alloy in artificial salivas." Bio-medical materials and engineering 25, no. 1 (2015): 53-66. [6] Giacchi, J. V., C. N. Morando, O. Fornaro, and H. A. Palacio. "Microstructural characterization of as-cast biocompatible Co–Cr–Mo alloys." Materials characterization 62, no. 1 (2011): 53-61.    5th Metallurgical & Materials Engineering Congress of South-East Europe 2023 – Trebinje, BIH 225  [7] Moslehifard, Elnaz, Tahereh Ghaffari, Samineh Mohammadian-Navid, Mina Ghafari-Nia, Amirali Farmani, and Farzad Nasirpouri. "Effect of chemical passivation on corrosion behavior and ion release of a commercial chromium-cobalt alloy." Journal of Dental Research, Dental Clinics, Dental Prospects 14, no. 3 (2020): 171. [8] Bakkaloğlu, Adem. "Effect of processing parameters on the microstructure and properties of an Nb microalloyed steel." Materials letters 56, no. 3 (2002): 200-209. [9] Ko, Kyung-Ho, Hyeon-Goo Kang, Yoon-Hyuk Huh, Chan-Jin Park, and Lee-Ra Cho. "Effects of heat treatment on the microstructure, residual stress, and mechanical properties of Co–Cr alloy fabricated by selective laser melting." Journal of the Mechanical Behavior of Biomedical Materials 126 (2022): 105051. [10] Zhuang, L. Z., and E. W. Langer. "Effects of cooling rate control during the solidification process on the microstructure and mechanical properties of cast Co-Cr-Mo alloy used for surgical implants." Journal of materials science 24 (1989): 381-388. [11] Ahmadein, M., Ammar H. Elsheikh, and Naser A. Alsaleh. "Modeling of cooling and heat conduction in permanent mold casting process." Alexandria Engineering Journal 61, no. 2 (2022): 1757-1768. [12] Fuchs, Hans U. The dynamics of heat: a unified approach to thermodynamics and heat transfer. New York, NY, USA:: Springer, 2010. [13] Fundições, Tupy. "Thermal conductivity of gray iron and compacted graphite iron used for cylinder heads." Revista Matéria 10, no. 2 (2005): 265-272. [14] Langenberg, E., E. Ferreiro-Vila, V. Leborán, A. O. Fumega, V. Pardo, and F. Rivadulla. "Analysis of the temperature dependence of the thermal conductivity of insulating single crystal oxides." APL Materials 4, no. 10 (2016): 104815. [15] Dong, Kaijun, Xiaobin Gu, Lihua Peng, Peng Liu, Shuai Jiang, and Liang Bian. "Recent advancements in typical mineral-encapsulated form-stable phase change materials for thermal energy storage." Journal of Energy Storage 52 (2022): 104931.   CIP - Каталогизација у публикацији   Народна библиотека Србије, Београд  669(082)(0.034.2) 66.017/.018(082)(0.034.2) 621.7/.9(082)(0.034.2)  METALLURGICAL & Materials Engineering Congress of South-East Europe (5 ; 2023 ; Beograd)     Congress Proceedings [Електронски извор] / 5th Metallurgical & Materials Engineering Congress of South-East Europe MME SEE Congress 2023, Trebinje, Bosnia and Herzegovina 7-10th June 2023 ; [[organized by] The Association of Matallurgical Engineers of Serbia [AMES] ... [et al.]] ; [editors Miroslav Sokić, Branislav Marković, Vaso Manojlović]. - Belgrade : Association of Metallurgical Engineers of Serbia (AMES), 2023 (Belgrade : Association of Metallurgical Engineers of Serbia (AMES)). - 1 USB fleš memorija ; 1 x 6 x 9 cm  Sistemski zahtevi: Nisu navedeni. - Nasl. sa naslovne strane dokumenta. - Tiraž 120. - Preface / Miroslav Sokić. - Bibliografija uz svaki rad.  ISBN 978-86-87183-32-2  а) Металургија -- Апстракти б) Технички материјали -- Зборници в) Наука о материјалима -- Зборници г) Металопрерађивачка индустрија -- Зборници  COBISS.SR-ID 117307657 

Microstructure assessment of Co alloy intended for dentistry

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Microstructure assessment of Co alloy intended for dentistry

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