Study On The Corrosion Behavior Of 312 Ti-Si/Al-C MAX Phase In NaCl And B-Li Solution

Self-sintered ternary layered titanium silicon carbide (Ti3SiC2) with aluminum dopant or not and titanium aluminum carbide (Ti3AlC2) with TiC impurities or not were fabricated and the electrochemical corrosion behavior in 3.5% NaCl and B-Li neutral buffer solution were investigated via traditional electrochemical corrosion test techniques including potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy (EIS). TA2 pure titanium and Zr4 alloy were chosen for comparation respectively in those two solutions.XRD, Metallomicroscopy, XPS, SEM and EDS were employed for texture, composition and topograph characterization. The passivation behavior, corrosion mechanism were clarified from the perspective of Point Defect Model (PDM) and galvanic corrosion between the M-X and A layer. M and A atoms in MAX phase were selectively extracted during corrosion,resulting in the formation of the corresponding oxides, hydroxides/oxyhydroxides and sp2/sp3 hybrid carbons.Aluminum dopant promoted the corrosion resistance of Ti3SiC2 in both self corrosion potential and electrochemical oxidation conditions by improving texture uniformity and enhanced surface oxidation film while the passivation capability weaked due to aluminum accelerated diffusion of silicon, so did the slightly decreasing breakdown potential. Titanium atoms in 1-site corroded prior to silicon in the galvanic microcell for Ti3SiC2 whereas aluminum atoms in Ti3AIC2 which lead to a poor corrosion resistance of Ti3AIC2 in NaCl solution, TiC impurities could improve the corrosion resistance significantly.The stable existence of Al2O3 in B-Li neutral buffer solution increased the passivation ability of Ti3AIC2 leading to a better corrosion resistance compared with Ti3SiC2 in open current potential.Lamellar microstructure and the difference of chemical bonds between M-X and M-A made a different passivation mechanism from valve metals such as Titanium and Zirconium,which lead to a poor corrosion resistance when compared with TA2 pure titanium in NaCl solution and Zr4 alloy in B-Li neutral buffer solution.