Corrosion Behavior of Titanium Alloy in Hydroxylammonium Nitrate (HAN)Based Propellant Using Electrochemical Noise Technology

Hydroxylammonium nitrate (HAN)-based propellant is a new type of green propellant.The compatibility of HAN-based propellants with traditional aerospace structural materials， such as titanium alloys， requires further investigation.The corrosion behavior of TC4 titanium alloy in HAN-based propellant was studied over long periods using electrochemical noise (EN) methods， along with scanning electron microscopy (SEM)， X-ray photoelectron spectroscopy (XPS)， and other analytical techniques.Results showed that， with the extension of immersion time， the average values of potential noise and current noise reflected the process of active corrosion-oxide film formation-corrosion equilibrium occurring in both the base material and welded material samples.Moreover， the standard deviation of potential noise in both base material and welded material reached its maximum on the first day of immersion，at values of 5.92 and 6.02，respectively.The standard deviation of potential noise in the welded material was slightly higher than that in the base material， indicating a slightly higher corrosion activity in the welded material.During the 65 d immersion of TC4 in alkaline HAN-based propellant， the slope of the power spectral density (PSD) curve in the highfrequency region remained at approximately－1 dB/dec， far greater than－20 dB/dec， which was consistent with the strong localized corrosion behavior of TC4 alloy in alkaline HAN-based propellant.The alloy element Al in TC4 formed Al2O3 and Al(OH)3 on the surface during the corrosion process in HAN-based propellant， while the oxide of the alloy element Ti reacted with the alkaline HAN medium to form soluble salts， preventing the formation of a stable and dense passivation film on TC4 titanium alloy in alkaline HAN-based propellant.