In situ determination of aging precipitation in deformed Fe-Cu and Fe-Cu-B-N alloys by time-resolved small-angle neutron scattering

We performed in situ time-resolved small-angle neutron scattering (SANS) measurements on high-purity Fe-Cu and Fe-Cu-B-N alloys during isothermal aging at 550 degrees C in order to study the potential self-healing of deformation-induced defects by nanosized Cu precipitation. Three different samples with 0%, 8%, and 24% prestrain were used to study the influence of variable defect levels on the Cu precipitation kinetics. The time-resolved SANS measurements show the presence of two contributions corresponding to spherical precipitates and precipitation at dislocations and/or interfaces, as confirmed by complementary transmission electron microscopy experiments. For the Fe-Cu alloy, prestrain was found to accelerate the formation of spherical precipitates in initial aging stage and lead to a significant enhancement of copper precipitation at dislocations and/or interfaces. For the Fe-Cu-B-N alloy, the addition of boron and nitrogen accelerates the formation of spherical precipitates but suppresses the precipitation along dislocations in the prestrained samples.