Enhanced corrosion resistance and surface bioactivity of AZ31B Mg alloy by high pressure cold sprayed monolayer Ti and bilayer Ta/Ti coatings in simulated body fluid

Abstract

Ti and Ta/Ti coatings were successfully applied on AZ31B Mg alloy using high pressure cold spray process. These coatings (particularly Ta/Ti coating) with high hardness lowered the wear rate of AZ31BMg alloy. In-vitro bioactivity test, infinite focus 3D measurement and EDS results revealed that the calcium-phosphate (Ca–P) compounds nucleation and growth capabilities on both the coatings surface are higher than AZ31B Mg alloy surface due to the highly passivating nature and rough surface (island-like) of the high pressure cold sprayed Ti and Ta/Ti coatings, which are further conducive to the biological fixation. Electrochemical corrosion and immersion tests disclosed that a dense layer of Ta on Ti coating was able to enhance the corrosion resistance of Ti/AZ31B Mg system in the Hank's balanced salt solution. Rct (charge transfer resistance) and │Z│f=0.01Hz values for Ta/Ti coated Mg alloy have remained slightly stable. This imparted that the rate of electrochemical processes at the electrode/electrolyte interface could remain very slow in the course of immersion time. Likewise, the OCP (open circuit potential) values of Ta/Ti coating remained constant during long term electrochemical corrosion test. This behavior could originate from fairly dense structure of the high pressure cold sprayed Ta layer which considerably impeded the penetration of corrosive solution into the coating interiors. Ta/Ti coating presented the most positive potential, highest Rct, and highest│Z│f=0.01Hz values, suggesting that it is the most thermodynamically stable/least to be corroded in Hank's balanced salt solution over time. In general, cold sprayed Ta/Ti coating might open a new way to broaden the utilization of Mg alloys in the field of biomaterials.