Coherency strain induced hardening in bulk polycrystalline ceramics: A case study with MgO‐based “ceramic alloys”

Abstract

AbstractThe role of coherency strain at the matrix/precipitate interface toward hardening of bulk polycrystalline “ceramic alloys” has been established here. Formation of “near ideal” bulk polycrystalline ceramic microstructure characterized by the presence of uniformly distributed coherent “ultra‐fine” MgCr2O4 particles (size: ~25 nm) within matrix (MgO) grains was achieved via solid‐state precipitation during aging treatment of bulk supersaturated MgO–Cr2O3 solid solutions (formed during pressureless sintering in air, followed by fast cooling). The as‐aged MgO–MgCr2O4 “ceramic alloys” exhibited hardness increment by ~73% over that of phase pure bulk MgO upon aging for just 10 hours at 1000°C in air. Evidences toward the presence of significant coherency strains across the MgO/MgCr2O4 coherent interfaces were obtained with transmission electron microscopy. Analysis based on hardening mechanisms and comparisons with MgO–MgFe2O4 system, having lesser hardening due to lower misfit strain at MgO/MgFe2O4 coherent interfaces (despite greater content of second‐phase particles), confirm the dominant role of coherency strains toward hardness enhancement in “ceramic alloys.”