Effects of Zr, Al, and Al+Zr Addition on Phase Evolution Characteristics and Strengthening Mechanisms of Fe‐42Ni‐2Y₂O₃ Oxide Dispersion Strengthening Steels Developed by Mechanical Alloying and Spark Plasma Sintering

In the present study, Fe‐42 wt% Ni‐2 wt% Y₂O₃ super‐invar‐based steels have been explored to study the effects of Zr, Al, and Zr+Al addition on phase evolution, strengthening mechanisms, and mechanical behavior. Three different compositions, such as Fe‐42Ni‐2Y₂O₃‐2Zr (2YZr), Fe‐42Ni‐2Y₂O₃‐2Al (2YAl), and Fe‐42Ni‐2Y₂O₃‐2Zr‐2Al (2YAlZr), are developed by mechanical alloying (MA) followed by spark plasma sintering (SPS) at 1100 °C with an applied pressure of 60 MPa. The 2YZr alloy after SPS shows the evolution of a uniform grain size of ≈1.7 μm, whereas 2YAl reveals the formation of bimodal grain structure sintered under the same condition. Conversely, the combined effect of Al and Zr addition results in the evolution of ultrafine grained structure (≈380 nm) after SPS at the same condition (i.e., at 1100 °C). The superior mechanical strength of the 2YAlZr alloy (5.3 GPa/1415 MPa) is attributed to the evolution of uniformly dispersed extremely fine (60 nm) high‐density Al‐ and Zr‐rich oxide complexes in the ultrafine grained matrix. The analysis of strengthening contributions to the yield strength is found to be correlated well with the experimental results and attributed to the morphology of microstructural constituents, their stability, and volume fraction of dispersoids in the matrix.