Effects of initial microstructure on the grain boundary network during grain boundary engineering in Hastelloy N alloy

Grain boundary engineering (GBE) was carried out on Hastelloy N alloy which is an important structural material used for molten salt reactor. The proportion of low Σ coincidence site lattice (CSL) grain boundaries of the Hastelloy N alloy can be enhanced to more than 70% with the formation of large-size highly-twinned grain-cluster microstructure which was formed through extensive multiple twinning events during recrystallization. The effects of cold deformation amounts and subsequent annealing on the grain boundary character distribution (GBCD) were investigated. The effects of initial grain size and the primary carbide distribution which was affected by the content of silicon on the grain boundary network evolution were discussed. It was determined that the initial grain size and primary carbide distribution will affect the recrystallization kinetics and hence influence the formation of highly twinned grain-cluster microstructure and the GBCD. The particle stimulated nucleation (PSN) caused by the primary carbides has a detrimental effect on the promotion of low Σ CSL grain boundaries.