Degradation Mechanism And Protective Coating Design Of Aerospace Titanium Alloy In Marine Environment

With the continuous commissioning of the Liaoning frigate and Shandong frigate,China’s navy is gradually turning from the land to the dark blue.The long-term cruise of the aircraft carrier in the territorial waters of the South China Sea,the frequent take-off and landing of the carrier-borne aircraft,and the harsh environment of high temperature,high humidity,and high salt in the South China Sea are easy to cause premature failure of key components of the carrier-borne aircraft.The middle-end of the engine compressor blade is prone to serious salt-water vapor cooperative corrosion during service.Although the middle end blade is made of Ti6Al4V alloy material with excellent corrosion resistance,it is still difficult to meet the requirements of long-term service in such a harsh environment.In this paper,the thermal salt corrosion test and thermal salt-water vapor corrosion test of Ti6Al4V alloy at 650℃and 25%Na Cl+75%Na₂SO₄ environment were systematically studied.It is found that the oxidation of the Ti element is the main factor in the hot salt corrosion process of Ti6Al4V alloy during 1000h.The corrosion weight gain is high,and the surface oxide layer is gradually thickened,accompanied by the layer by layer peeling off.TC4 titanium alloy is difficult to resist the hot salt corrosion invasion for a long time.During the 400h heat-salt-water corrosion test of Ti6Al4V alloy,the weight loss of titanium alloy was the main factor,and a large number of corrosion holes appeared,the corrosion depth was up to 152μm.The corrosion caused by the decomposition of Na₂SO₄ and the corrosion invasion of Na Cl made the Ti6Al4V alloy suffer more serious corrosion invasion in a shorter corrosion time than the hot-salt test.NiCoCrAlY/AlSiY/AlSi coatings were prepared on Ti6Al4V alloy by multi-arc ion plating.It was found that the coating effectively protected the substrate from the corrosion damage of the mixed salt under 1000h of hot salt corrosion.The corrosion weight gain of the coating is 29%of that of the titanium alloy,and the corrosion rate is low.The formation of the TGO layer effectively prevents the diffusion of elements and the invasion of corrosive materials.In the middle and late period of the experiment,the surface layer of the coating is partially peeling off and longitudinal cracks appear,which are filled with alumina to prevent the further diffusion of elements.In the process of thermal salt-water corrosion test for 400h,the coating gained a very high corrosion weight,and the large amount of YAl O₃ produced played a good protective role.At the later stage of the experiment,the coating surface layer was largely peeled off,the barrier layer was also damaged to a certain extent,and Ni,Cr,Ti,and other elements were diffused upward.Under the cooperative corrosion action of thermal salt and water vapor,the corrosion invasion of the coating was more serious than that of the thermal salt experiment,but the corrosion invasion of the substrate was very little.Therefore,The coating can effectively protect titanium alloy from corrosion under a harsh cooperative corrosive environment.Marine environment saltwater vapor synergistic corrosion mechanism of the present study is less,thus revealing the compressor blades of Marine environment corrosion mechanism is of great significance for the long-term development of China’s navy,this article discussed and designed a new type of coating,to protect the substrate from Marine environment corrosion,and offers a new thought and method for protection of compressor blade.