The Effects of Ball Milling Parameters on the Homogeneity of Y-Ti-O Nano-Feature Distribution in Nano-Structured Ferritic Alloys

摘要

Successful development of advanced fission and future fusion reactors requires high performance structural materials that can provide long-term service in extremely hostile environments. Nano-structured ferritic alloys (NFA) show great promise of meeting these challenges. NFA have high tensile and creep strengths permitting operation up to 800℃. They also show remarkable resistance to radiation damage, and can manage a high concentration of He (1). The outstanding properties of NFA derive from an ultrahigh density of nano-scale Y-Ti-O enriched features (NF) that provide dispersion strengthening, stabilize dislocation and fine grain structures, reduce excess concentrations of displacement defects, and trap He in fine bubbles. The first NFA processing step is mechanical alloying (MA) Fe-12 to 14Cr-0.3 to 0.6Ti-l to 3W alloy powder with Y_2O_3 by ball milling. The MA dissolves the Y and O in the ferrite matrix, which subsequently precipitate as NF during hot consolidation by extrusion or hot isostatic pressing. [1]. Ball milling, however, does not always produce uniform concentrations of dissolved Y and O, or corresponding homogeneous distributions of NF. Regions of lower NF concentrations are softer and experience dislocation recovery and grain growth leading to bimodal grain size distributions, reducing the NFA fracture toughness and strength. The atom probe map of Ti in Fig. la shows a non-uniform NF distribution resulting in a bimodal grain structure shown in Fig. lb. The objective of this research is to develop improved milling methods that produce homogeneous distributions of NF. The research approach uses systematic variations of milling parameters, combined with a rapid screening method to characterize their relative successes.