Fracture toughness and adhesion of thermally grown titanium oxide on medical grade pure titanium

The mechanical properties and adhesion characteristics of a thin thermally grown titanium oxide film on commercially pure titanium were examined. Tensile tests were used to introduce controlled strains in the thermally grown oxide (TGO), through the titanium substrate, to study the damage evolution and to quantitatively evaluate the intrinsic strength and fracture toughness of the TGO layer. Details of the TGO adhesion behaviour were explored. Nanoindentation was used to determine the Young's modulus and hardness of the TGO. Tensile loading resulted in multiple cracking to occur in the TGO layer along with distinctive inclined cracking driven by shear band deformation in the titanium substrate. The fracture toughness of the TGO was determined to be 1.8 ± 0.6 MPa m1/2. Localised delamination of the TGO was observed but only when the titanium substrate was strained well within the plastic deformation region by more than about 2.5%.