High temperature cyclic oxidation resistance of 50Cr-50Al coatings mechanically alloyed on low carbon steel

Highlights: • 50Cr-50Al coatings were deposited on ST41 steel by a mechanical alloying technique. • The cyclic oxidation resistance of coatings with and without annealing was studied. • The coatings formed an Al₂O₃ scale after oxidation test at 800 °C for 8 cycles. • The diffusion of Fe atoms through coating defects led to Fe-oxides nodule formation. • After cyclic oxidation test, cracks were formed close to the substrate surface. In the present study, the 50Cr-50Al coatings were mechanically alloyed on low carbon steel at two different milling times of 1 h and 4 h, and subsequently annealed in vacuum at 800 °C for 2 h. The resistances of coatings with and without annealing against high temperature cyclic oxidation were studied at 800 °C for up to 8 cycles. The phase compositions and structures of oxidized samples were analyzed by X-ray diffractometer and SEM-EDX analyzer. The results showed that carbon steel is susceptible to oxidation. The resistance of low carbon steel towards oxidation at high temperature was improved by applying 50Cr-50Al coatings due to the formation of Al₂O₃. However, Fe atoms from the substrate had a tendency to diffuse outwards through defects in the coating layer, resulting into the formation of Fe-oxides nodules. The coated sample that was prepared for 4 h showed a better oxidation resistance than that of 1 h. Then, the annealing treatment significantly enhanced the coating's oxidation resistance. Based on the results of present work, the annealed 50Cr-50Al coating prepared for 4 h exhibited the lowest mass gain. The details are presented in this paper.