Hot Corrosion Behavior Of Arc Ion Plated NiCoCrAlYSiHf Coating Via High-Current Pulsed Electron Beam

MCrAlYX high-temperature protective coating technology has been widely used in various gas turbine engines for modern aviation,ships and ground power generation.The hot corrosion behavior of MCrAlYX coating in molten salt environment is directly related to its service life and safety performance.This paper aims to improve the hot corrosion performance of MCrAlYX coating prepared by Arc Ion Plating(AIP)technology.The AIP-MCrAlYX coating was irradiated with the High-Current Pulsed Electron Beam(HCPEB)surface modification technology.The coating structure was purposefully adjusted at the micro level to achieve favorable control of the growth behavior of thermally grown oxide(TGO).The coating's hot resistant corrosion performance in different molten salt corrosion environments can be improved by HCPEB irradiation.In different molten salt environments,the corrosion performance of MCrAlYX coating mainly depended on the growth behavior of TGO,which was closely related to the surface state,phase composition and microstructure of coatings.NiCoCrAlYSiHf coating prepared by AIP technology was mainly composed of?/?'phase,?-Ni Al phase and NiCoCr phase.Surface of the original coating was rather rough and uneven,with fine pores and a large number of large granular clusters structure.After HCPEB irradiation,the?-Ni Al and NiCoCr phases disappeared and the surface of the coating became rather smooth.The remelted layer with uniform thickness had typical solidification texture.After irradiatioan with 30 pulses,the thickness of remelted layer could reach about 7?m,and the surface roughness could be reduced to 1.745?m.TEM results showed that a large number of Al-Y nano particles and high density of dislocation entanglement structure were distributed in the remelted layer.Obviously,the above modification effects played a very important role in promoting the rapid formation of the protective oxide film in the initial stage of hot corrosion.The hot corrosion performance of NiCoCrAlYSiHf coating in Na₂SO₄/K₂SO₄(75:25wt.%/wt.%),Na₂SO₄/NaCl(75:25wt.%/wt.%),Na₂SO₄/V₂O₅(40:60 wt.%/wt.%)was tested by direct brushing method.The growth process of TGO in different molten salt environments before and after HCPEB modification and the hot corrosion kinetic behavior were analyzed.The mechanism of corrosion failure and enhancement of corrosion resistance in different molten salt environments were explained,which provided a reliable theoretical basis and process route for improving the corrosion resistance of MCrAlYX coating.After hot corrosion for 100 h of AIP-NiCoCrAlYSiHf coating in Na₂SO₄/K₂SO₄corrosion salt at 900?,the results showed that the phenomenon of internal oxidation along large particles and spalling in local areas appeared.TGO presented a double layer structure,including the outer layer of mixed oxide and the inner layer of loose Al₂O₃.After hot corrosion for 100 h in Na₂SO₄/NaCl corrosion salt at 900?,TGO was mainly composed of mixed oxides,with large area spalling and penetrating cracks.The spalling area of oxide film was large,and the internal oxidation depth had extended to 25?m away from the coating surface.After hot corrosion for 100 h in Na₂SO₄/V₂O₅corrosion salt at 900?,TGO was not very dense and had penetrating cracks inside.TGO presented a multi-layer structure,including outer layer of a mixture of spinel oxide and Cr₂O₃oxide,and inner layer of Al₂O₃oxide.Microcracks distributed along the depth of the coating appeared in local area under the oxide film.The results of hot corrosion kinetics showed that the original coating had the slowest hot corrosion rate in Na₂SO₄/K₂SO₄and the fastest rate in Na₂SO₄/V₂O₅.For HCPEB treated coatings,after hot corrosion for 100 h in Na₂SO₄/K₂SO₄corrosion salt at 900?,TGO was still composed of a smooth,continuous and dense Al₂O₃oxide film with a thickness of about 2?m.After hot corrosion for 100 h in Na₂SO₄/NaCl corrosion salt at 900?,TGO was mainly composed of Al₂O₃and Cr₂O₃,with a thickness of about 3?m.However,slight cracks and slight pitting internal oxidation appeared in local areas on the surface.After hot corrosion for 100 h in Na₂SO₄/V₂O₅corrosion salt at 900?,there were no obvious defects such as holes and cracks in TGO.The thickness of TGO was about 4?m.At this moment,TGO had a double-layer structure.The outer layer was a mixed oxide composed of spinel and Cr₂O₃,and the inner layer was Al₂O₃.The results of hot corrosion kinetics showed that the hot corrosion rate of HCPEB modified coating was significantly lower than that of the original coating in different molten salt environments.The modification characteristics of HCPEB irradiated coatings could promote the rapid formation of a uniform and continuous Al₂O₃protective oxide film in the early stage of hot corrosion,and improved its chemical stability,and this can greatly improve the hot corrosion resistance of the modified coatings.