EFFECT OF AGING TIME ON PHASE TRANSFORMATION, MICROSTRUCTURE AND HARDNESS OF Co-Cr-Mo ALLOYS

Yıl 2019, Cilt: 7 Sayı: 1, 146 - 153, 01.03.2019

Mehmet Yıldırım , Ali Keleş

https://doi.org/10.15317/Scitech.2019.188

Öz

The effect of heat-treatment on phase
relationships, microstructures and hardness of Co-Cr-Mo alloys were
investigated in detail. The samples were produced by investment casting
technique and subsequently solutionized (1240 °C for 4 h) and aged (720 °C for
2, 4, 8 and 16 h). Phase analysis of the samples were performed via X-ray
diffraction analysis, microstructural examination were done by light optical
and scanning electron microscopy. The microstructures of as-cast and short-time
(2 and 4 h) aged samples were composed of FCC γ-Co matrix phase and fine M₂₃C₆
(where M= Co, Cr and Mo) precipitates. Increasing the aging time to 8 and 16 h
led to partial transformation of FCC γ-Co matrix phase into HCP ε-Co phase. The
volume fraction of ε-Co phase increased with increasing aging time. Moreover,
hardness of the Co-Cr-Mo samples were significantly enhanced with formation of
ε-Co phase.

Anahtar Kelimeler

Co-Cr-Mo alloys, Hardness, Microstructure

Yaşlandırma Süresinin Co-Cr-Mo Alaşımlarının Faz Dönüşümleri, Mikroyapıları ve Sertliğine Etkisi

Öz

Bu
çalışmada, ısıl işlemin Co-Cr-Mo
alaşımlarının faz ilişkileri, mikroyapıları ve sertliklerine etkisi detaylı
biçimde incelenmiştir. Alaşım
hassas döküm yöntemiyle üretilmiş, takiben çözeltiye alma (1240 °C’de 4 saat) ve
yaşlandırma (720 °C’de 2, 4, 8 ve 16 saat) ısıl işlemi uygulanmıştır. Numunelerin faz
analizleri X-ışınları kırınım yöntemiyle, mikroyapıları ise optik ve taramalı
elektron mikrokobisi yöntemleriyle incelenmiştir. Dökülmüş haldeki ve kısa süre
(2 ve 4 saat) yaşlandırılmış numunelerin mikroyapıları YMK kristal yapısına
sahip γ-Co matris fazı ve M₂₃C₆ (M= Co, Cr ve Mo) tipi
ince karbür çökeltilerinden meydana gelmektedir. Artan yaşlandırma süresi ile
birlikte γ-Co matris fazı kısmen ε-Co fazına dönüşmüştür. ε-Co fazının miktarı
artan yaşlandırma süresi ile artmıştır. Ayrıca, ε-Co fazının oluşumu alaşımın
sertliğini önemli ölçüde arttırmıştır.

Anahtar Kelimeler

Co-Cr-Mo alaşımları, Mikroyapı, Sertlik

Kaynakça

• ASTM F75-12 Standard, 2012, “Co-28Cr-6Mo Alloy castings and casting alloy for surgical implants”.
• Bates, J. F., Knapton, A. G., 1977, “Metals and alloys in dentistry”, International Metals Review, Vol. 22, No 1, pp. 39-60.
• Davis, J. R., 2003, Handbook of materials for medical devices, ASM International, Materials Park, OH, USA.
• Disegi, J. A., Kennedy, R. L., Pilliar, R., 1999, Cobalt based alloys for biomedical applications, ASTM, West Conshohocken, PA, USA.
• Escobedo, J., Mendez, J., Cortes, D., Gomez, J., Mendez, M., Mancha, H., 1996, “Effect of nitrogen on the microstructure and mechanical properties of a CoCrMo alloy”, Materials and Design, Vol. 17, pp. 79-83.
• Garcia, A. J. S., Medrano, A. M., Rodriguez A.S., 1999, “Formation of HCP martensite during the isothermal aging of an FCC Co-27Cr-5Mo-0.05C orthopedic implant alloy”, Metallurgical and Materials Transactions A, Vol. 30A, pp. 1177-1184.
• Giacchi, J. V., Morando, C. N., Fornaro, O., Palacio, H. A., 2011, “Microstructural characterization of as-cast biocompatible Co-Cr-Mo alloys”, Materials Characterization, Vol. 62, pp. 53-61.
• Kilner, T., Pilliar, R. M., Weatherly, G. C., Alibert, C., 1982, “Phase identification and incipient melting in a cast CoCr surgical implant alloy”, Journal of Biomedical Materials Research, Vol. 16, pp. 63–79.
• Lee, S. H., Takahashi, E., Nomura, N., Chiba, A., 2005, “Effect of heat treatment on microstructure and mechanical properties of Ni- and C-Free Co-Cr-Mo alloys for medical applications”, Materials Transactions, Vol. 46, No 8, pp. 1790-1793.
• Lee, S. H., Takahashi, E., Nomura, N., Chiba, A., 2006, “Effect of carbon addition on microstructure and mechanical properties of a wrought Co-Cr-Mo implant alloy”, Materials Transactions, Vol. 47, No 2, pp. 287-290.
• Lopez, H. F., Garcia, A. J. S., 2008, “Martensitic transformation in a cast Co-Cr-Mo-C alloy”, Metallurgical and Materials Transactions A, Vol. 39A, pp. 8-18. Massalski, T.B., Okamoto, H., 1990, Binary Alloy Phase Diagrams, ASM International, Materials Park, OH.
• Matkovic, T., Matkovic, P., Malina, J., 2004, “Effects of Ni and Mo on the microstructure and some other properties of Co-Cr dental alloys”, Journal of Alloys and Compounds, Vol. 366, pp. 293-297.
• Mendes, P. S. N., Lins, J. F. C., Mendes, P. S. N., Prudente, W. R., Siqueira, R. P., Pereira, R. E., Rocha, S. M. S., Leoni, A. R., 2017, “Microstructural Characterization of Co-Cr-Mo-W Alloy as Casting for Odonatological Application”, International Journal of Engineering Research and Application, Vol. 7, No 3, pp. 34-37.
• Northwood, D. O., 1985, “The development and applications of zirconium alloys”, Materials and Design, Vol. 6, No 2, pp. 58-70.
• Olson, G. B., Cohen, M., 1976, “A general mechanism of martensitic nucleation: Part I. General concepts and the FCC → HCP transformation”, Metallurgical Transactions A, Vol. 7, No 12, pp. 1915-1923.
• Pickering, F. B., 1978, Physical metallurgy and design of steels, Applied Science, Essex, UK.
• Ramirez, V. L. E., Castro, R. M., Herrera, T. M, García, L. C. V., Almanza, C. E., 2009, “Cooling rate and carbon content effect on the fraction of secondary phases precipitate in as-cast microstructure of ASTM F75 alloy”, Journal of Material Processing Technology, Vol. 209, pp. 1681–1687.
• Sage, M., Gillaud, C., 1950, “Méthode d'analyse quantitative des variétés allotropiques du cobalt par les rayons X”, Review Metallurgy, Vol. 47, No 2, pp. 139-145.
• Shi, L., Northwood, O. D., Zhengwang, C., 1994, “The properties of a wrought biomedical cobalt-chromium alloy”, Journal of Materials Science, Vol. 29, No 5, pp. 1233-1238.
• Sims, C. T., Hagel, W., Stoloff, N., 1987, The superalloys II: High temperature materials for aerospace and industrial power, Wiley & Sons, Hoboken, NJ, USA.
• Yıldırım, M., Keleş, A., 2018, “Production of Co-Cr-Mo Biomedical Alloys via Investment Casting Technique”, Turkish Journal of Electromechanics & Energy, Vol. 3, No 1, pp. 12-16.
• Zhuang, L. Z., Wagner, E. W., 1989, “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, Vol. 24, No 2, pp. 381-388.