Investigation of the oxidation behavior of aluminum coated Ti6Al4V alloy by pack cementation method

Titanium-based alloys are a material frequently used in areas such as aviation, medicine, and defense industries due to their superior mechanical properties, such as lightweight, and high corrosion resistance. Ti6Al4V alloy, which is one of these titanium alloys, is an α+β alloy. Although Ti6Al4V alloy exhibits good mechanical properties, hovewer its strength decreases after 400°C. Therefore, some surface treatments are required to ensure its use in areas where material life is very important, such as aviation.In this study, the oxidation behavior of the coating layer was investigated by aluminizing the Ti6Al4V titanium alloy with the pack cementation method. The coating process was carried out at 600, 800°C for 4, 6, and at 700°C for 4, 6 and 8. Hardness measurements of aluminised samples showed that the hardness values increased from 320 to 600 HV for the coating layer compared to the bare Ti6Al4V alloy. The homogeneous and continuous aluminum-rich coating layer on the surface was obtained for 700°C and 6 hours process time.Aluminized and untreated samples were subjected to oxidation tests at different temperatures and times. These tests were carried out at 800, 850, and 900°C for 4, 20, and 40 hours. Weights of the samples were determined before and after oxidation tests, and weight gains were compared. It was observed that the highest weight gain were obtained for the untreated sample.Al2O3 oxide layer was observed on the surface of the Al-coated samples after oxidation, while an TiO2 oxide layer was formed on the untreated sample. It was observed that the oxide layer formed in both of the samples, which were coated for 4 and 6 hours, was dramatically increased with the oxidation time. As a result of the characterization processes performed on the oxidized samples, it was observed that the oxidation resistance of the sample aluminized for 6 hours was higher than that of 4 hours. After oxidation process, calculated activation energies are 181,13kJ/mol for the bare sample, 464,79 kJ/mol for 4 hours aluminum coated at 700°C, 530,93 kJ/mol for 6 hours aluminum coated at 700°C respectively.