No abstract

The 8 phase precipitation behavior of cold drawn alloy 718 has been investigated at l 116 K as a function of cold drawn ratio and aging time. The planar markings formed by cold drawing were identified as deformation twins and developed more clearly as cold drawing ratio increases. The grain boundaries and twins were played as nucleation site of 8 precipitation, therefore, cold drawing enhanced the precipitation of 8 particles. As the cold drawing ratio and aging time increased the amount of round-shaped 8 also increased. In a specimen which was 50% cold drawn and aged for 4 hrs, the finely dispersed 8 phase precipitated throughout the material. As aging time increased, The round-shaped 8 phase changed to plate-like morphology, and the morphology transformation time was increased with cold drawing ratio. With a 50% cold drawn specimen, the transformation time was 7 hrs. On the other hand, for the 50% cold drawn specimen aged for one hour at I 116 K, nucleation of the strain free grain was observed.