The role of martensitic transformation in corrosion fatigue failure of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at %) medical alloys

The effect of cyclic dynamic loading on the kinetics of changes in the electrode potentials of Ti-22Nb-6Ta and Ti-22Nb-6Zr (at %) superelastic medical alloys in a model solution simulating the bone tissue environment in a living organism is studied with the use of electrochemical chronopotentiometry. An increase in the applied load from 450 to 780 MPa is found to affect dramatically the character of changes in the electrode potentials of the alloys during exposure. Ti-22Nb-6Ta alloy exhibits higher resistance to corrosion fatigue cracking than does Ti-22Nb-6Zr alloy. It is shown that the superelasticity of the alloys is responsible for the deceleration of the corrosion fatigue cracking due to the blocking effect of martensite crystals formed in the structure during the loading half-cycle, which is confirmed by the low rate of the potential decrease after the nucleation of corrosion fatigue cracks.