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Sigma phase formation and its effect on mechanical properties in the corrosion-resistant superalloy K44

J. S. Hou, J. T. Guo, L. Z. Zhou and H. Q. Ye


The sigma phase (σ) formation in long-term aged polycrystalline K44 superalloy has been studied as a function of aging temperature and time. The σ phase in K44 alloy forms mainly in dendrite cores with a few at interdendritic regions. The kinetics of σ formation can be described by the Johnson–Avrami–Mehl equation that yields activation energies of more than 130 kJ/mol in an early stage and less than 100 kJ/mol in steady state. Tensile experiments at room temperature and 1173 K and endurance experiments at 1173 K and 274 MPa were performed to test the effect of σ phases on these properties and no remarkable harmful effect is found. Moreover, the effect of long-term aging on the mechanical properties is realized mostly through the variation of γ′, not σ phase formation.

2 Correspondence address: Prof. J. T. Guo, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, P.R. China, Tel.: +862423971911, Fax: +862423891320. E-mail: (J.T. Guo)


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Received: 2005-05-09
Accepted: 2005-08-22
Published Online: 2013-03-01
Published in Print: 2006-02-01

© 2006, Carl Hanser Verlag, München