Oscillatory Pressure Sintering Enables Low‐Strain Grain Boundaries in High‐Entropy Carbides

High‐entropy carbides (HECs) are promising ultra‐high‐temperature ceramics but suffer from poor sinterability, residual stress, and grain boundary defects. Conventional hot pressing (HP) cannot simultaneously achieve full densification and homogeneous lattice strain. We report a strain‐engineering strategy using oscillatory pressure sintering (OPS) at 1800°C to prepare (Zr,Mo,Ti,Nb,Ta)C with low‐strain grain boundaries. OPS yields near‐full densification (99.64%), uniform elemental distribution, and a strain range of −1.5% to +1.5%, narrower than HP (−9% to +15%), eliminating stress concentration. The microstructure exhibits hardness of 25.18±0.38 GPa and toughness of 3.54±0.23 MPa·m 1/2 . OPS homogenizes lattice strain, stabilizes grain boundaries, and enhances properties, offering a route to high‐performance HECs.