Development of Nano-Y2O3 Dispersed Ferritic Alloys for Nuclear Reactors

Abstract

In this present work, an attempt has been made to synthesize of elemental powder blend of 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti(alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti(alloy C), and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D), alloys with 1.0 nano-Y2O3 (all in wt %) dispersion by solid state mechanical alloying route and consolidate milled powder by different sintering methods high pressure sintering (HPS), hot isostatic pressing (HIP)[1, 2], pulse plasma sintering (PPS)[3],and hydrostatic extrusion (HE) etc). Following this mechano-chemical synthesis and consolidation, extensive effort has been undertaken to characterize the microstructural evolution by X-ray diffraction, scanning and transmission electron microscopy, scanning tunneling electron microscopy, energy disperse spectroscopy and asses mechanical properties including hardness, compressive strength, Young’s modulus, fracture toughness. The details synthesis and characterization was reported recently in Karak et al. [1,2, 3].The present ferritic alloys record extraordinary levels of compressive strength (summarized at Table-1) (2012-3325 MPa), yield strength (525-1626 MPa), Young’s modulus (240-290 GPa), and hardness (15.5-19.7 GPa) and measure up to 2-3 times greater strength than other oxide dispersion strengthen ferritic steel (ODS steel) (< 1200 MPa) and higher than tungsten based alloys (< 2200 MPa) in strength but at a lower density (~ 7.4 Mg/m3). The novelty of these alloys lies in the unique microstructure and uniform distribution (shown in Figs. 1(a-b)) of either nanomertic (10-20 nm) oxide (Y2Ti2O7 or Y2O3) or intermetallic (Fe11TiY and Al9.22Cr2.78Y phase aggregates (Figs. 1(a-c)) along the grain boundary (Fig. 2a) which causes the grain boundary pinning, resulting high hardness and high compressive strength by annealing after mechanical alloying (MA) under ambient condition using high energy planetary ball milling. Thus, the above results suggest that mechanical alloying followed by high pressure sintering (HPS), pulse plasma sintering (PPS),hot isostatic pressing (HIP) and hydostatic extrusion (HE) etc are a flexible, convenient and promising route for synthesizing ferritic alloys with nano-oxide dispersed matrix offering attractive mechanical properties.