High-temperature nanoindentation creep studies on castable and sintered nanostructured low-activation ferritic-martensitic alloys

• Creep properties of CNA & SNA are similar due to MX and M23C6 precipitates. • Nanoindentation creep tests reveal similar properties due to microstructure. • Stress exponent (n) of 8–33 indicates dislocation-dominated creep in both alloys. • SNA by DCS replicates CNA's microstructure & creep properties for rapid production. • Findings aid high-stress, high-temperature materials for nuclear applications. In this article, we present the creep characteristics of two reduced activation ferritic-martensitic steels of identical starting compositions formed by different fabrication routes: a nanostructured ferritic alloy commonly referred to as a castable nanostructured alloy (CNA) and a sintered nanostructured alloy (SNA) variant. Through a series of nanoindentation experiments spanning a temperature range of 25 °C to 650 °C, with a maximum load of 100 mN, we find creep behaviors in the cast and sintered materials to be remarkably similar. The creep stress exponent ( n ) for CNA and SNA were found to be in the range of 8–35 and the activation volume was ∼14–42 b 3 , underscoring a dominance of dislocation-mediated mechanisms in both alloys. Notably, we observed a decline in the creep stress exponent with increasing temperature, attributable to the heightened influence of thermally activated dislocations. This phenomenon suggests a potential transition in the deformation mechanism towards a thermally activated dislocation climb process, significantly impacting the observed creep behavior.