Preferential nucleation of (O, Y/La/Ce/Hf)-core nano-clusters in multi-element micro-alloyed ferritic alloys: A first-principles study

Abstract

The high creep strength and high radiation resistance of nanostructured ferritic alloys (NFAs) have been generally attributed to the high-density precipitation of (O, Y)-core nano-clusters and nano-oxides. In this work, the early-stage nucleation of (O, X)-core (X = La, Ce, and Hf) nano-clusters (NCs) with respect to (O, Y)-core NCs in multi-element micro-alloyed NFAs was investigated using first-principles calculations. Their competitive precipitation preference and possible growth sequence were predicted. The (O–O) pair was suggested as the most fundamental core of all types of NCs. Yttrium always has the strongest affinity with the (O–O) pairs to initiate the nucleation of NCs during the early-stage nucleation. Under the absence or depletion of yttrium, other types of (O, X)-core (X = La, Ce, Hf) structures could form, leading to different nucleation paths with the preference ordering of (O, La)-core > (O, Ce)-core > (O, Hf)-core. NC nucleation and composition in NFAs would, thus, strongly depend on the number availabilities of micro-alloying solute species in the neighborhood of the (O–O) pairs.