Oxidation And Hot Corrosion Behaviour Of A Ni-Based Superalloys With Ti And NiCrAlY Coating Deposited By Arc Ion Plating During High Temperature Exposure

A kind of Ni-base superalloy has been studied to meet the requirement of jet-engine turbine vane served in the sea climate. Due to high-temperature oxidation and hot corrosion of turbine vane, both Ni28Crl1A10.5Y coating and Ni19Co27Cr11A10.5Y were prepared respectively by arc ion plating technique to improve the oxidation and corrosion resistance of Ni-base superalloy. Therefore, the high-temperature oxidation and hot corrosion behavior and mechamism of Ni-base superalloy, NiCrAlY coated Ni-base superalloy, were studied with a series of high-temperature and corrosion experiments under different conditions.The results showed the mass gain per unit surface area was faster in the early stage, and then tended to be slower and steady based on oxidation dynamics curves of Ni-base superalloy at850℃,900℃,950℃and1000℃. The internal and external oxidation of Ni-base superalloy took place during high-temperature oxidation and obviously the oxide layers were composed of outside layer, which consisted of Cr2O3, A12O3, TiO2and NiCr2O4, and inside layer, which consisted only of Al2O3. The depth of inside oxide layer related only to temperature, deepening with the increase of temperature. The Ti element of Ni-base superalloy accelerated the internal and external oxidation during high-temperature oxidation.The Ni-base polycrystal superalloy was coated with3-4mg (Na2SO4+K2SO425wt.%salt mixture)/cm2and oxidized at850℃and950℃respectively. The results showed the salt mixture accelerated the corrosion due to oxidation and sulfuration during hot corrosion and the internal oxidation and sulfuration zones were formed and the corrosion and internal sulfuration layers deepened with the increase of temperature. The three layers of corrosion were formed and the outer was Al2O3and NiCr2O4, the intermediate was Al2O3, the inside was CrS and Ti2S.The Ni-base polycrystal superalloy was coated with3-4mg (Na2SO4+NaCl50wt.%salt mixture)/cm2and oxidized at700℃and800℃respectively. The oxidation and sulfuration took place during hot corrosion and the internal oxidmation and sulfuration zones were formed and the corrosion and internal sulfuration layers deepened with the increase of temperature. The corrosion products can be divided into three layers and the outer was AI2O3, Cr2O3and NiCr2O4the intermediate was Al2O3, the inside was CrS and Ti2S. The NaCl accelerated the corrosion process and the corrosion, internal oxidation and internal sulfuration layers deepened as the increase of temperature.The arc ion plated Ni28Crl1A10.5Y coating was coated with3-4mg (Na2SO4+K2SO425wt.%salt mixture)/cm2and oxidized at950℃. The results showed the corroded coating prevents the Ni-base superalloy substrate from obvious corroding and oxidating after120h mainly due to active element Y and Al2O3synergy effect which hindered the internal oxidation and sulfuration of superalloy. An Al2O3scale was formed on the coating surface in the early stage, and then the alkaline dissolution reaction of Al2O3took place during hot corrosion to form Cr2O3. The Y2OS2formed on the coating surface to delay the corrosion of S element.The results showed that the mass gain per unit surface area of both arc ion plated Ni28Crl1A10.5Y coating and Nil9Co27Crl1A10.5Y coating was faster in the early stage, and then tended to be much slower and steady based on oxidation dynamics curves, which approximately obeyed parabola law, at900℃and1000℃. The only Al element oxidation took place on the coating surface and the0-Al2O3to a-Al2O3transformation occurred during high-temperature oxidation. The oxidation resistance of Ni28Cr11A10.5Y coating was superior to that of Ni19Co27Crl1A10.5Y coating at900℃and1000℃.