Two‐step reactive flash sintering of high entropy pyrochlore: Densification, grain growth, and microstructural homogeneity

Abstract Two‐step reactive flash sintering (TSRFS) was employed to achieve fast densification of high entropy pyrochlore (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 ) 2 Zr 2 O 7 with suppressed grain growth and improved microstructural homogeneity. Theoretical density of ∼98.15% with a grain size of ∼684 nm was achieved by TSRFS, representing only half the grain size compared with conventional one‐step reactive flash sintering (RFS), while the total holding time of TSRFS was only 1.5 times that of RFS. Although longer duration in step 1 benefited faster densification, it was demonstrated that the shorter time in step 1 not only resulted in smaller grain size in TSRFS samples with identical densities but also helps mitigate the grain size heterogeneity between sample cores and surfaces. Therefore, the art of efficiently using TSRFS lies in the reasonable manipulation of the time and power in step 1 and 2, achieving a balance between densification, grain growth, and microstructural homogeneity.