This invention provides a method, replica film, and application for directly detecting
silicon nitride grain boundary phases. The method includes the following steps: S1,
etching a polished
silicon nitride ceramic sample with
hydrofluoric acid solution; S2, replicating the etched polished surface with a first
solvent and a
cellulose acetate film to obtain a primary replica; S3, vacuum-depositing a
carbon film onto the primary replica to obtain a secondary replica; S4,
cutting and attaching the secondary replica film to low-temperature
paraffin wax, then dissolving the
cellulose acetate in a second
solvent; S5, transferring the dissolved secondary replica film to a third
solvent, and after the secondary replica film has fully expanded, retrieving it with a
copper mesh,
drying it, and observing it under an
electron microscope. The method provided by this invention can separate the
grain boundary phase from the
silicon nitride main phase, obtaining the
solid grain boundary phase while retaining the morphological outline of the
silicon nitride main phase. This method is simple to operate, low in cost, and provides great convenience for studying the influence of grain boundary phases on the mechanical and optical properties of
silicon nitride separately.