PRECIPITATION AND GROWTH OF DELTA-PHASE IN NI-15CR-8FE-6NB ALLOY

The Precipitation and growth behaviors of delta phase in Ni-base superalloy, modified Inconel X-750 type alloy (X-750 M), have been investigated mainly by optical and transmission electron microscopy. The morphology, the crystallography and equilibrium transformation temperatures of the cellular and the Widmanstatten precipitation of gamma phase to delta + gamma phases have been discussed. The obtained results are as follows (1) The hardness of X-750M aged in various conditions closely related to the size and the quantity of gamma" and delta precipitates. (2) The orientation relationship between gamma and delta phase in the cellular and the Widmanstatten precipitates was : {111}gamma//{010}delta [110]gamma//[100]delta. (3) The interlamellar spacing in each precipitation mode was inversely proportional to the degree of undercooling below the equilibrium transformation temperature of gamma phase to delta + gamma phases. (4) According to the theory of diffusion controlled eutectoidal growth, the equilibrium transformation temperatures of the cellular and the Widmanstatten precipitation were estimated to be 1 279 and 1 313 K, respectively. These temperatures were consistent with the experimental tendency.