Research on Microstructure and Properties of Co-Si Alloys by Vacuum Suction Casting

Abstract:

Rapid solidification of Co-Si alloys was investigated by using vacuum suction casting in this study. Different microstructures and intermediate phases were obtained. Eutectic εCo phase and eutectoid εCo + αCo₂Si structures were obtained in the first eutectic Co_76.9Si_23.1 alloy. The microstructures of hypereutectic Co₇₀Si₃₀ alloys were composed of primary αCo₂Si phase and interdendritic lamellar eutectoid εCo + αCo₂Si. While for hypoeutectic Co₆₃Si₃₇ alloy at the second eutectic point, CoSi dendrites were the primary phase, and αCo₂Si+CoSi eutectoid structures can be seen at the interdendritic region. Especially, a metastable CoSi₂ phase was found in Co₆₃Si₃₇ alloy. This indicates that eutectoid decomposition βCo₂Si→ CoSi+αCo₂Si is restrained in eutectic Co_60.3Si_39.7 alloy. For rapid solidified Co₅₅Si₄₅ and Co₅₂Si₄₈ alloys, αCo₂Si+CoSi eutectoid structures were not observed, while metastable CoSi₂ were obtained. The higher hardness achieved in Co-Si alloys at the second eutectic point, for the reason of the higher volume fractions of compound phases.

• Periodical: Materials Science Forum (Volume 850)
• Pages: 202-207
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.850.202
• Online since: March 2016
• Authors: Zhen Peng, Peng Hui Wu, Jing Zhang, Ning Liu, Xiao Jing Wang
• Keywords: Co-Si Alloys, Hardness, Metastable Phase, Microstructure, Rapid Solidification

References

[1] Okamoto, H. Co-Si (Cobalt-Silicon). J. Phase Equil. Diff. 29(2008) 295-302.

[2] Zhang, L. J.; Du, Y.; Ouyang. Y. F; Xu, H. H.; Lu, X. G.; Liu, Y. J.; Kong, Y.; Wang J. Atomic mobilities, diffusivities, and simulation of diffusion growths in the Co-Si system. Acta Mater. 56(2008) 3940-3950.

DOI: 10.1016/j.actamat.2008.04.017

[3] Faria, M.I.S.T.; Coelho, G.C.; Nunes, C.A.; Avillez, R.R. Microstructural characterization of as-cast Co–Si alloys. Mater. Charact. 56(2006) 66-72.

DOI: 10.1016/j.matchar.2005.10.001

[4] Baldan, R.; Faria, M. I. S. T.; Nunes, C. A.; Coelho, G. C.; Chad. V. M.; Avillez, R. R. D. Microstructural Evidence of βCo2Si-phase Stability in the Co-Si System. J. Phase Equil. Diff. 29(2008) 477-481.

DOI: 10.1007/s11669-008-9390-0

[5] Dal, M.J.H.V.; Huibers, D.G.G.M.; Kodentsov, A.A.; Loo, F.J.J. V. Formation of Co–Si intermetallics in bulk diffusion couples. Part I. Growth kinetics and mobilities of species in the silicide phases. Intermetallics. 9(2001) 409-421.

DOI: 10.1016/s0966-9795(01)00018-8

[6] Leonhardt, M., Löser, W., Lindenkreuz, H. G. Non-equilibrium solidification of undercooled Co–Si melts. Scripta Materialia. 50(2004) 453-458.

DOI: 10.1016/j.scriptamat.2003.11.003

[7] Yao, W.J.; Wang, N.; Wei, B. Containerless rapid solidification of highly undercooled Co-Si eutectic alloys. Materials Science and Engineering A. 344(2003) 10-19.

DOI: 10.1016/s0921-5093(01)01895-0

[8] Liu, N.; Liu, F.; Lu, L.M.; Gao, X.Y.; Wang, X.J. Nonequilibrium Solidification Behavior of Co-Si Alloys Near the First Eutectic Point. Metal. Mater. Trans. B. 45(2014) 815-820.

DOI: 10.1007/s11663-014-0051-x

[9] Lu, Y.P.; Li, T.J.; Fu, Y.B.; Sun, J.B.; Luo, D.W.; Yang, G.C.; Zhou, Y.H. Phase selection during solidification of undercooled Ni70. 2Si29. 8 eutectic alloy. Progress in Natural Science. 19(2009) 1619-1624.

DOI: 10.1016/j.pnsc.2009.04.011

[10] Lu, Y.P.; Liu, F.; Yang, G.C.; Wang, H.P.; Zhou, Y.H. Grain refinement in solidification of highly undercooled eutectic Ni–Si alloy. Materials Letters. 61(2007) 987-990.

DOI: 10.1016/j.matlet.2006.06.028

[11] Lu, Y.P.; Liu N.; Shi, T.; Luo, D.W.; Xu, W.P.; Li, T.J. Microstructure and hardness of undercooled Ni78. 6Si21. 4 eutectic alloy. Journal of Alloys and Compounds. 490(2010) L1-L4.

DOI: 10.1016/j.jallcom.2009.09.038

[12] Çadırlı, E.; Herlach, D.M.; Davydov, E. Microstructural, mechanical, electrical and thermal characterization of arc-me lted Ni–Si and Co–Si alloys. Journal of Non-Crystalline Solids. 356(2010) 1735-1741.

DOI: 10.1016/j.jnoncrysol.2010.06.005