Characterisation and oxidation of LVOF sprayed Al₂O₃–40TiO₂ coating on superalloys

Abstract

High temperature oxidation occurs in many equipments ranging from gas turbines, boilers, heat treating retorts to heat exchangers. Superalloys are used for such applications due to their excellent mechanical properties and creep resistance, but lack resistance to oxidation. In the present investigation, Al₂O₃–40TiO₂ coating has been deposited on nickel and cobalt based superalloys by low velocity oxyfuel (LVOF) process. The coating has been characterised for scanning electron microscopy (SEM), X-ray diffraction (XRD) and surface roughness. The high temperature oxidation behaviour of coated and uncoated superalloys has been evaluated at 800°C for 50 cycles of one hour duration. The LVOF coating has shown good adherence to the substrate. AE 435 superalloy has shown the highest weight gain amongst the tested materials, whereas Al₂O₃–40TiO₂ coated Superco 605 superalloy has shown the lowest weight gain. The better oxidation resistance of Al₂O₃–40TiO₂ coating might be attributed to the presence of protective Al₂O₃ phase along with TiO₂ phase in it.

Keywords:

• Superalloys
• Low velocity oxyfuel coating
• Al₂O₃–TiO₂
• Oxidation
• Parabolic rate constant