Microstructure and mechanical properties of nano-Y _2O _3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

摘要

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-Y _2O _3 dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000C using a 75-MPa uniaxial pressure applied for 5min and a 70-kA pulse current at 3Hz 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 microano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850-2850MPa), yield strength (500-1556MPa), Young's modulus (175-250GPa) and nanoindentation hardness (9.5-15.5GPa), with up to 1-1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10-20-nm Y _2Ti _2O _7 or Y _2O _3 particles in a high-alloy ferritic matrix.