Ion beam mixing of B, ZrO2, and Cr layers with sintered α‐SiC, and Y and Cr layers with hot pressed Si3N4 was measured at room temperature. The mixing ion was selected from 1‐MeV Ni+, 2‐MeV Au+, or 1‐MeV O+ ions. The amount of mixing was evaluated from Rutherford backscattering and Auger electron spectroscopies and occasionally from cross‐section transmission electron microscopy. It was found that mixing takes place in the B/SiC, Cr/SiC, and Y/Si3N4 systems. No mixing is observed in the ZrO2/SiC and Cr/Si3N4 systems even after high dose ion bombardment. The enthalpy of mixing rule, which states that metals mix with insulators if the reaction enthalpy is negative and do not mix if it is positive, has been examined and found to hold for these systems.