In oder to improve density and bond strength of atmospheric plasma sprayed Cr3C2-NiCr coatings, chromium diffusion treatments have been carried out in the range of 1073 to 1373 K. In this work, the change of structure and hardness were examined by SEM, EDX, XRD and micro vickers hardness tester. The results obtained are as follows.
(1) Thin Cr23C6 carbide layer which slightly contains Cr2C has been formed on the sprayed coating surface by the chromium diffusion treatment. This carbide layer is extremely high desity and high micro vickers hardness, HV1500.
(2) The thickness of this carbide layer became large (about 20 μm at 1373 K for 57.6 ks), as the temperature and period for chromium diffusion treatment incereased. It is found that at higher temperature than 1203 K this carbide layer covered the sprayed coating surface with nearly unform thickness. The growth rate of this carbide layer goes with a parabolic rule and the activity energy for the growth is 113.9 kJ/mol.
