THE GROWTH OF CELLULAR DELTA-PHASE IN A 69NI-15CR-8FE-6NB ALLOY

The growth behavior of cellular delta phase in Ni-base alloy, modified Inconel X-750 type alloy (X-750 M), was investigated mainly using opt ical and transmission electron microscopy. The values of n in the John son-Mehl equation for the growth of the cellular delta phase in X-750 M which was aged in various conditions after a solution heat treatment were estimated to be 1.69-1.84. The values of n in the case of X-750 M which was pre-aged at 943 K for 253 ks after a solution heat treatme nt followed by aging in various conditions were estimated to be 1.44-1 .67. The obtained value of n suggested that the growth of the cellular delta phase in X-750 M after the pre-aging treatment obeyed a volume diffusion rate control with zero nucleation rate. Transformation curve s of gamma + gamma '' phases to the cellular delta + gamma phases in t he specimens aged after the pre-aging treatment were consistent with a theoretical one. The apparent activation energy for the growth of the cellular delta phase in X-750 M aged after the pre-aging treatment wa s estimated to be 232 kJ/mol, which is nearly equal to that for diffus ion of solute atoms in the alloy.