Al-Si-Cr coating was prepared on the surface of 25Cr35NiNb alloy by pack cementation

and its anti-coking properties were studied by coking experiment using ethylene cracking test apparatus. The microstructure of coating and the morphology of coke were investigated with metallurgic microscope

electronic scanning microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Al-Si-Cr coating with thickness of about 130 mm was obtained by pack cementation. The coating had multiple layers with dense structure

consisting of an outer layer composed of aluminum-silicon-rich compounds and an inner layer composed of chromium- silicon-rich compounds. The Al-Si-Cr coating had excellent coking inhibiting properties. It could inhibit catalytic coking effectively

and the rate of coke inhibition was up to 72.5%.