Corrosion Behavior Of CuAl-NiC Sealing Coating In Simulated Marine Environment

CuAl-NiC seal coating,which is composed of substrate(0Cr₁₇Ni₄Cu₄Nb alloy),bonding layer（Ni Al coating）and surface layer（CuAl-Ni C coating）,has excellent corrosion resistance and abradability.It is mainly used for sealing of the gas pipe of aeroturbine engine compressor.It is a representative medium/low temperature coating.The surface layer of CuAl-Ni C seal coating contains a metal phase（CuAl）,a lubricating phase（Ni C）and pores and thus is a porous multi-phase multilayer structure.It works mostly in the marine climate（high humidity,high salt）.In most cases,the seal coating undergoes electrochemical corrosion,leading to a short service life and even incalculable consequences due to its peeling off.In this paper,CuAl-NiC seal coating was studied on the corrosion of the surface layer by soaking test,neutral salt spray test,galvanic corrosion,salt spray test and electrochemical noise technology;its morphology before and after the corrosion was analyzed by 3D confocal,X-ray diffraction,scanning electron microscopy,etc.;its electrochemical behaviors before and after the corrosion were analyzed by electrochemical testing techniques such as electrokinetic scanning,impedance,etc.,and its corrosion behavior was studied.The results of galvanic corrosion and electrochemical noise test show that when Ni Al coating forms a galvanic couple with the substrate or surface layer in galvanic corrosion test,it always is corroded more quickly as an anode,and CuAl-Ni C coating is protected as a cathode;after 20 h galvanic corrosion test of CuAl-Ni C coating,its self corrosion current density and corrosion resistance decrease and increase,respectively;in the electrochemical noise test,all coatings basically have the pitting index of 1 before and after corrosion in the time domain analysis,indicating that the three materials are locally corroded before and after corrosion.The results of soaking test（28 d）and neutral salt spray test（96 h）show that in the soaking test（28 d）,the CuAl-Ni C seal coating has the lowest self corrosion current density and the biggest corrosion resistance at 21 d,with aluminum oxide as main corrosion product;in the neutral salt spray test,the CuAl-Ni C seal coating has the lowest impedance value and the biggest corrosion resistance at 48 h,with iron oxide as main corrosion product.The corrosion products are different in the two tests partially due to the fact that in the soaking test,the transmission of oxygen content is limited and total reaction rate is controlled by cathodic reaction O₂+2H₂O+2e^-→4OH^-resulting in lower corrosion rate and detection of no element of the substrate on the coating surface.The results of salt spray test（8 d）show that the CuAl-NiC seal coating has the lowest self-corrosion current density,the smallest corrosion rate and the biggest corrosion resistance at 6 d,with copper oxide as main corrosion product.