In-situ study on factors impeding dislocation motion in Fe9Cr1.5W0.4Si F/ M steel during high temperature heating

Ferritic/martensitic (F/M) steels are promised candidate materials for the lead-cooled fast neutron reactor. However, their poor high temperature performance limits the highest in-core temperature, decreasing the reactor economics. High dislocation mobility directly related to the low strength of F/M steels but the underlying mechanisms remain unexplored. Here, in-situ heating was performed on irradiated Fe9Cr1.5W0.4Si ferritic martensitic steel in the temperature range of 873-923 K, and the interaction between dislocation lines and obstacles was investigated to reveal the mechanism that led to easier dislocation gliding. Dislocations tended to glide in several planes at the same time and only glided as a whole in one plane occasionally. It was discovered that dislocations usually glided in high index planes such as {123} planes. When moving dislocations intersected with forest dislocations, a new mechanism was found where the segments for different dislocations with the same Burgers vector could exchange, which was important for the moving dislocation to cut through the forest dislocations without decreasing their mobility. The reactions between dislocations and <100> loops included absorption, break away and rebound. Meanwhile, statistical results indicated that the highest ratio was about 48% for the case where <100> loops were restored and dislocations broke away, demonstrating that the <100> loops were not strong obstacles when interacting with moving dislocations at high temperature.