Characterization of the Dendritic Microstructure of Investment Cast Alloy 718

The as-cast alloy 718 shows a multiphasic structure which consists of dendrites, carbides and Laves phases. The amount, size, shape, and dispersion of these phases affect the properties and the processing which follows, This structure was characterized by measurements of volume fraction, size, dispersion, and shape factor of carbide and Laves phases. Secondary arm spacing and Vickers hardness were also measured i.n the as-cast condition. All the above measurements were carried out on two different sized castings which had different cooling conditions, Compositional analysis of the phases in the castings concerned are clearly linked to solidification behavior ofthe alloy. These values were statistically analyzed to distinguish the effects of the casting conditions. Superalloys 718,6;!5,706 and Various Derivatives Edited by E.A. Loria The Minerals, Metals &Materials Society, 1994