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Aging of the Inconel 718 alloy between 500 and 750 °C

Published online by Cambridge University Press:  31 January 2011

C. Slama ,
C. Servant  and
G. Cizeron
C. Slama
Affiliation:
Laboratoire de Structure des Matériaux Métalliques, Université de Paris-Sud, Bâtiment 414, 91405 Orsay Cedex, France
C. Servant
Affiliation:
Laboratoire de Métallurgie Structurale, URA CNRS 1107, Université de Paris-Sud, Bâtiment 414, 91405 Orsay Cedex, France
G. Cizeron
Affiliation:
Laboratoire de Structure des Matériaux Métalliques, Université de Paris-Sud, Bâtiment 414, 91405 Orsay Cedex, France
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Abstract

The aging of the NC 19 Fe Nb alloy (Inconel 718), previously quenched from 990 °C, is characterized by a hardness peak at 650 °C, then a maximum in hardness at about 750 °C. Over this temperature, the hardness progressively decreases. In the 550–650 °C temperature range, TEM observations have revealed that β (Ni3Nb) precipitates are formed as long platelets parallel between them within the same grain, as well as extremely fine γ′[Ni3(Ti, Al)] particles responsible for the observed improvement in hardness. For a tempering temperature higher than 650 °C, a first hardening occurs after a 4 h treatment, which has been associated with the γ′ phase precipitation, with a more or less spherical shape. Beyond this time, a second hardening takes place linked to the γ″ phase precipitation (Ni3Nb, bct D022 structure), as thin platelet shaped, perfectly coherent with the matrix. The misfit between the γ and γ″ phases is about 3% in the 〈001〉γ″ direction and lower than 1% in the 〈100〉γ″ and 〈010〉γ″ directions. During a longer aging at 750 °C, the γ″ platelets progressively dissolve while β precipitates grow.

Type
Articles
Information
Journal of Materials Research , Volume 12 , Issue 9 , September 1997 , pp. 2298 - 2316
Copyright
Copyright © Materials Research Society 1997

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