PNNL

Abstract

Nanocrystalline (NC) metals are stronger and more radiation-tolerant than their coarse-grained (CG) counterparts, but they often suffer from poor thermal stability, i.e., nanograins coarsen significantly when heated to 0.3 to 0.5 of their melting temperature (Tm). Here we report an NC austenitic stainless steel (NC-SS) containing 1 at% lanthanum with an average grain size of 45 nm and an ultrahigh yield strength of ~ 2.5 GPa that exhibits exceptional thermal stability up to 1000 oC (0.75 Tm). In-situ irradiation to 40 dpa at 450 oC and ex-situ irradiation to 108 dpa at 600 oC produce neither significant grain growth nor void swelling, in contrast to significant void swelling of CG-SS at similar doses. This thermal stability is due to segregation of elemental lanthanum and (La, O, Si)-rich nanoprecipitates at grain boundaries. Microstructure dependent cluster dynamics show grain boundary sinks effectively reduce steady-state vacancy concentrations to suppress void swelling upon irradiation.