It is important to inhibit the precipitation ofη phases in precipitation strengthened Fe-Ni based alloys,as they will deteriorate not only the mechanical property but also the hydrogen resistance.The present investigation shows that grain boundary engineering (GBE) can retard the formation and growth of η phase in J75 alloy.After GBE treatment with 5％ cold rolling followed by annealing at 1000 ℃ for 1 h,the fraction of special boundaries (SBs) increases from 38.4％ in conventional alloy to 77.2％ and the fraction of special triple junctions increases from 10％ to 74％.During 800℃ aging treatment,quite amount of cellular η phases adjacent to random grain boundary (RGB) will be found in conventional alloy,and only a few small η phases have been observed in GBE treatment alloy subjected to the same aging treatment for long time.The reason for GBE in inhibiting precipitation of η phase can be attributed to not only introducing high fraction of SBs but also breaking the connectivity of RGB networks.As nucleation and growth of η phases on SBs are difficult due to their lower Ti concentration and diffusion rate,and the disruption of RGB networks reduces supply of Ti atoms to the η phases significantly,which impedes their growth at RGB.