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The NiAl coating was prepared on the surface of NiCrW-based superalloy by pack cementation method with CaCl₂ as an activator. The surface and cross-section of the coated specimens were analyzed via X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. Results show that CaCl₂ can replace NH₄Cl as an effective activator. The NiAl coating with an almost single phase structure and a thickness of 30 μm can be obtained after pack cementation at 950 °C for 4 h. A chromium-rich interlayer can be observed between the NiAl coating and the substrate. When the filling ratio of the pack powder is less than 100%, the needle-like θ-Al₂O₃ phase is formed on the NiAl layer surface. During the constant temperature air oxidation test at 1000 °C, the NiAl coating suffers from high speed oxidation to slow speed oxidation, which is in agreement with the phase transformation from needle-like metastable θ-Al₂O₃ to irregular granular stable α-Al₂O₃. The final stable α-Al₂O₃ provides a good oxidation resistance for the substrate.