Studies On The Structure And Performance Of Ti32Mo Alloy Passive Film Formed In HCl Solution

The corrosion performance of Ti32Mo alloy in HCI solution of two different temperatures (18℃ and 70 ℃) and two concentrations (1 mol/L and 4 mol/L) is studied, while the composition and structure of passive films formed on the Ti32Mo alloy at different anodic polarization potential (0.2V and 0.9V (vs. SCE)) in 70 ℃, 4mol/l HCI have been studied by XPS.Anodic polarization curves and EIS prove that the Ti32Mo alloy is self-passive in HCI solutions used in the experiment. The EIS of Ti32Mo alloy is capacitive in all solutions used in experiments at corrosion potential (* c). With the concentration of HCI solution, temperature and anodic potential increasing, the inductive character of the EIS become more predominant. The EIS of Ti32Mo alloy in 18℃, 4mol/L HCI solution and anodic potential 0.9V or 1.5V is characterized by the capacitive resistance at high frequency part and the inductive resistance at low frequency part. A proper mathematics mode is applied to the impedance of the passive films, and the simulating results in accordance with the equivalent circuit indicate that the mathematics mode is correct.The EIS of Ti32Moalloyin70℃, 4mol/L HCI solution and anodic potential 0.9V or 1.5V is capacitive at the high frequency part and inductive at low frequency part, and at the extremely low frequency part ofthe Nyquist curve, the impedance increase greatly with the frequencydecreasing. An explanation combining the XPS is given for this phenomenon.The XPS simulating results of elements in different sputtering depths are obtained through the XPSPEAK program. The concentrations of different elements and the concentrations of elements for different valence are calculated in accordance with the XPS simulating results. It was found that the passive films were composed of an outer layer and an inner layer and the outer layer is 8nm deep. For the sample passived at +0.2 V, the Mo enrichment (f(Mo)) is varied from 1.75 for the outermost layer to 1.40 at 8nm deep, and for the sample passived at +0.9V, the factor of Mo enrichment (fl[Mo)) is varied between 1.42-1.32. The outer layer can be divided into two fine sub-layers. The sub-layer I is from Onm to 3nm deep and the sub-layer II include the passive film from 3nm to 8nm deep. The passive films are consisted of a series of different valence titanium-molybdenum compound containing oxide, hydroxide and chloride.