Effect of Si addition on the microstructure and mechanical property of nanostructured oxide dispersion strengthened ferritic steel synthesized via mechanical alloying and spark plasma sintering

Abstract

Nanostructured oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steel powders of two different nominal compositions, Fe-14Cr-2W-0.3Ti-0.3Y2O3 and Fe-14Cr-2W-0.3Ti-1Si-0.3Y2O3, wt.%, were synthesized by mechanical alloying and consolidated via spark plasma (SPS) sintering at different sintering temperatures (900, 1000 and 1050 °C). The effect of Si addition on the sinterability, phase composition, microstructure, and mechanical properties viz. microhardness, nanoscale hardness, and elastic modulus were investigated. The addition of 1 wt.% Si caused reduction in milling time and resulted in finer (5 ± 1.2 μm) and uniform particles. The addition of Si also led to faster reduction in crystallite size as compared to the Si-free sample. TEM analysis revealed formation of Y2Ti2O7 and Cr2O3 nano-sized particles in the Si-free ODS steel. However, formation of Cr2TiO4 and SiO2 along with Y2Ti2O7 particles were observed in Si-containing ODS steel. Hardness and Elastic modulus of Si-containing ODS steel sample sintered at 900 °C was higher than that of the samples sintered at higher sintering temperature because of fine microstructure and absence of α-Fe to γ-Fe phase transformation in 900 °C sintered sample.