DC plasma-polymerized hexamethyldisilazane coatings of an equiatomic TiNi shape memory alloy

The TiNi corrosion resistance of Ti50Ni50 shape memory alloy can be substantially improved by DC plasma-polymerized hexamethyldisilazane (PHMDSN) coatings. The initial PHMDSN deposition rate increases with increasing DC voltage. The deposition rate decreases gradually with time until the glow discharge is extinguished. The higher DC voltage used in plasma polymerization will develop a film with a more inorganic nature from the IR spectrum analysis and water contact angle measurements. The PHMDSN coatings for DC voltage ≥1000 V are protection against the corrosion in Ringer’s solution and can be deformed up to a 2% strain. The corrosion current density of the TiNi alloy can be lowered by as many as four orders of magnitude. The pitting potential and re-passivation potential can also be enhanced to nobler potential after PHMDSN coatings. The widely scattered pitting potential of the as-homogenized TiNi can also be improved by the PHMDSN coatings.