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

The effect of heat-treatment on phase relationships, microstructures and hardness of CoCr-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.

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

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.

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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 ascast 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 cobaltchromium 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.