Study On The Preparation And Oxidation/Hot Corrosion Resistance Properties For The Zr-Doped(Ni,Pt) Al Coating

Due to its excellent high-temperature oxidation resistance,β-（Ni,Pt）Al coating has been widely used as a high-temperature protective coating for key hot components such as turbine blades of aeroengines.However,the hot corrosion resistance ofβ-（Ni,Pt）Al coating is insufficient,and the cost of the Pt is too high,as well as the oxide scale on the coating surface is prone to failure due to spallation in service environments.The low-cost reactive element Zr can not only promote the formation of oxide scale with high adhesion and low growth rate,but also reduce the harmful effects of sulfur.Therefore,in this paper,Zr was used to partially replace Pt in（Ni,Pt）Al coatings to improve the service performance of the coating and simultaneously reduce the cost of Pt to some extent.Pure（Ni,Pt）Al coating and low,medium,high Zr-doped（Ni,Pt）Al coatings were prepared on DD5 Ni-based single crystal superalloy by pulse electroplating combined with“above-pack”aluminization treatment,and the hot corrosion behavior and cyclic oxidation behavior of these four coatings were investigated.The main results are as follows:（1）The thickness of the four as-deposited coatings was similar（40.8±0.9μm）,and the Al content was the same（～33 at.%）.The contents of Zr and Pt in pure（Ni,Pt）Al coating,Low-Zr coating,Medium-Zr coating,and High-Zr coating were（at.%）:0Zr-7.95Pt,0.54Zr-7.53Pt,1.41Zr-6.99Pt,and 2.05Zr-6.54Pt,respectively.Therefore,the substitution amounts of Zr for Pt,i.e.Zr/（Zr+Pt）,were 0%,7%,17%,and 24%,respectively.（2）Hot corrosion test of（Ni,Pt）Al coatings with different substitutions in75 wt.%Na₂SO₄+25 wt.%K₂SO₄ mixed salts at 900℃showed that replacing Pt partially with Zr improved the hot corrosion resistance of（Ni,Pt）Al coating.After 200 h hot corrosion,the mass gain of pure（Ni,Pt）Al coating and Low-Zr coating was large（1.32 mg/cm² and 1.30 mg/cm²,respectively）,while that of Medium-Zr coating and High-Zr coating was smaller（1.03 mg/cm² and 1.10mg/cm²,respectively）.The oxide scale thickness（4.94μm and 4.98μm,respectively）and degree of oxide scale spallation of the Medium-Zr coating and High-Zr coating were significantly lower than those of the Low-Zr coating and pure（Ni,Pt）Al coating（5.90μm and 6.29μm,respectively）.That means Zr partially replacing Pt can reduce the growth rate of the oxide scale and improve its spallation resistance ability.The amount of the Al₂O₃ intrusions and corrosion depth（5.86μm and 9.44μm,respectively）of Medium-Zr coating and High-Zr coating were significantly smaller than those of Low-Zr coating and pure（Ni,Pt）Al coating（14.36μm and 14.53μm,respectively）.That means Zr partially replacing Pt can inhibit the development of Al₂O₃ intrusions.The growth of more Zr O₂ particles in the oxide scale of High-Zr coating led to local scale spallation.The hot corrosion resistance increased in the order of Medium-Zr coating>High-Zr coating>Low-Zr coating>pure（Ni,Pt）Al coating.（3）The cyclic oxidation test of（Ni,Pt）Al coatings with different substitutions at 1100℃showed that replacing Pt partially with Zr improved the spallation resistance of oxide scale of（Ni,Pt）Al coating.After 300 cycles,the oxidation mass gain of pure（Ni,Pt）Al coating was the smallest（0.30 mg/cm²）,but its oxide scale spallation was the most serious.The mass gain of Low-Zr coating was slightly larger（0.46 mg/cm²）,and its oxide scale spallation was relatively less.While Medium-Zr coating and High-Zr coating showed larger weight gain（0.65 mg/cm² and 0.96 mg/cm²）,but their oxide scale remained intact.There were many interface voids in the oxide scale spalling area of pure（Ni,Pt）Al coating,while fewer interface voids were observed in the oxide scale spalling area of Low-Zr coating.Thus Zr partially replacing Pt can reduce the formation of oxide scale/coating interface voids.Moreover,there were many oxide pegs at the oxide scale/coating interface of the High-Zr coating,which increased the adhesion of the oxide scale.However,the largest amount of Zr O₂particles were formed in the oxide scale,resulting in the thickest oxide scale and more severe cracking of the oxide scale than Medium-Zr coating.The surface roughness of pure（Ni,Pt）Al coating was the highest（2.048μm）,followed by that of High-Zr coating and Low-Zr coating（1.966μm and 1.718μm）,while that of Medium-Zr coating was the least（1.479μm）and its surface rumpling extent was minimal.