Precipitates in INCONEL alloy 617 aged at high temperature

The precipitates of the aged alloys were investigated by means of scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that M23C6 and M6C particles with face-centered cubic(FCC)structure precipitate at grain boundaries,inside grains and the γ′ phase particles with order FCC structure were situated at intragranular sites in the process of aging up to 10 000 h at 760 ℃.During aging up to 10 000 h,the precipitates inside grains remained basically stable.Precipitates discontinuously dispersed at grain boundaries for the alloy aged for 300~3 000 h,then aggregated and distributed continuously after 5 000 h aging.At the same time,the quantity of M6C carbides increased substantially for the alloy aged for 5 000 h.The hardness of the alloy aged for 300 h increased substantially,then a maximum hardness value for the alloy aged for 1 000 h was achieved accompanying by a decrease of the hardness of the alloy aged at 5 000 h.