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 1.0 wt% nano-Y₂O₃ dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5 min and a 70-kA pulse current at 3 Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize 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/nano-indenter and 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 other oxide dispersion-strengthened ferritic steels (<1200 MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y₂Ti₂O₇ or Y₂O₃ particles in a high-alloy ferritic matrix.

Keywords:

• nano-Y₂O₃ dispersed ferritic steel
• mechanical alloying
• microstructure
• mechanical property
• pulse plasma sintering

Acknowledgements

The authors gratefully acknowledge partial financial support provided for this research work by CSIR, New Delhi (project no. OLP 0280 at CSIR-CGCRI) and INAE (Visvesvarya Chair Professorship).