The physical metallurgy of cast and wrought alloy 718

TLDR: The physical metallurgy of cast and wrought alloy 718 is discussed in this paper in terms of the importance of Nb on the phase reactions found in Alloy 718, and the role or influence of nb is first noted during the solidification of alloy 7 18 as the large atoms Nb, MO, and Ti segregate to the interdendritic regions where the Nb rich Laves phase forms.

Abstract: The physical metallurgy of cast and wrought alloy 718 is discussed in terms of the importance of Nb on the phase reactions found in alloy 718. The role or influence of Nb is first noted during the solidification of alloy 7 18 as the large atoms Nb, MO, and Ti segregate to the interdendritic regions where the Nb rich Laves phase forms. The Laves phase must be solutioned at high temperatures and the Nb must be distributed throughout the dendrite areas. The normal phases found in alloy 718 are the MC, TiN, delta, Laves, ?/’ and ?/. The y and ?/ are the main strengthening phases and their precipitation behavior is determined primarily by the amount of Nb, the temperature and time of exposure. Any incomplete homogenization of the cast or wrought material will produce non-uniform precipitation of the delta, 1/’ and f phases during working or aging heat treatments. The longtime stability of alloy 718 is related to the stability of the 1/’ phase which transforms to delta and ?/ with increasing time and temperatures. Eventually the f phase will solution and the delta phase becomes the terminal phase in the 718 system. An aCr phase is found in the grain boundaries in long time exposures in the 1100°-13500F temperature range. The Mzs C6 carbide phase normally found in Ni base alloys is not found in alloy 7 18.