Softening of α-Ti by electrochemically introduced hydrogen

Abstract

The substantial and permanent modification of the elastic and inelastic properties of α-Ti have been achieved by hydrogen charging with cathodic polarization in an alkaline solution at RT, with the effects being dependent on the hydrogen state of the metal. The decrease in the elastic modulus to values close to those characteristic for bones have been caused by the distortion of the Ti lattice due to the supersaturation of the solid solution with hydrogen and (or) due to the formation of hydride precursors and precipitates. The low, but still detectable decrease in the elastic modulus has been observed by the formation of a compact hydride layer. On the basis of a thorough examination of the effect of cathodic polarization on the formation and morphology of the hydride phase and on the state of the α-Ti lattice, the electrochemical parameters provided: (1) the presence of hydrogen in supersaturated solid solution, (2) the formation of hydride precipitates of various stoichiometry and (3) the formation of the compact hydride surface layer have been determined. Taking into account the hydrogen induced metal softening, the easiness of electrochemical alloying the metal with hydrogen and no health hazard produced by this element when dissolved in body liquids, the electrochemical hydrogen treatment of Ti implants can be considered as very promising.