Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Abstract

Ferritic steel with compositions 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) (all in wt%) each with a 1.0wt% nano-Y2O3 dispersion were synthesized by mechanical alloying andconsolidated by pulse plasma sintering at 600, 800 and 1000C using a 75-MPa uniaxial pressure applied for 5 min and a 70-kA pulse current at3Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used tocharacterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation.Mechanical properties in terms of hardness, compressive strength, yield strength and Young’s modulus were determined using a micro/nanoindenterand universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850 MPa), yield strength(500–1556 MPa), Young’s modulus (175–250 GPa) and nanoindentation hardness (9.5–15.5 GPa), with up to 1–1.5 times greater strength than otheroxide dispersion-strengthened ferritic steels (51200 MPa). These extraordinary levels of mechanical properties can be attributed to thetypical microstructure of uniform dispersion of 10–20-nm Y2Ti2O7 or Y2O3 particles in a high-alloy ferritic matrix.