Thermal stability and mechanical properties of Fe-Cr-Zr alloys developed by mechanical alloying followed by spark plasma sintering

Highlights: • Bulk size stable nc Fe-Cr-Zr alloys synthesized through MA followed by SPS. • TEM study of the SPSed samples confirmed that the matrix grains is < 100 nm. • Attractive hardness (>9 GPa) & superior compressive strength (UCS-2.2 GPa, YS-1.8 GPa). • Segregation of Zr & evolution of Fe₂Zr played pivotal role in high thermal stability. -- Abstract: The present work aims to investigate (i) the feasibility of formation of Fe-7Cr-xZr and Fe-15Cr-xZr (x = 0.25, 0.5 and 1 at%) disordered solid solutions by mechanical alloying (MA) and (ii) their thermal stability and mechanical properties of spark plasma sintered (SPSed) samples. Effect of Zr addition on phase evolution in Fe-Cr-Zr alloy and its influence on their thermal stability and mechanical properties (microhardness and compression strength) have been studied in detail. Transmission electron microscopy-selected area diffraction pattern (TEM-SAED) and X-ray diffraction (XRD) phase analysis confirm the formation of complete solid solution after 25 h of MA. Grain size was observed to stabilize significantly within nanometer range after annealing at 600–1200 °C. The SPSed (at 1000 °C) samples showed the best combination of hardness (9.4 GPa) and compressive strength (ultimate compressive strength-2200 MPa and yield strength-1800 MPa) corresponding to an average grain size of < 100 nm. This is due to the strengthening mechanisms of grain boundary strengthening (owing to solute segregation and solute drag effect), precipitation hardening (Zener pinning) by Fe₂Zr phase and excellent densification achieved by SPS.