Crack initiation, propagation and saturation of TiO2 nanotube film

Vertically orientated TiO2 nanotube array with diameters ranging from 60 up to 80 nm and length of 4 mu m was grown on titanium by anodization. Crack initiation, propagation and saturation were studied using the substrate straining test. The results show that annealing obviously modifies the interfaces. With the increase of tensile strain, cracks in TiO2 nanotube films propagate rapidly and reach the saturation within a narrow strain gap. Interfacial shear strengths of TiO2 nanotube films without annealing, with 250 degrees C annealing and with 400 degrees C annealing can be estimated as 163.3, 370.2 and 684.5 MPa, respectively. The critical energy release rates of TiO2 nanotube films are calculated as 49.6, 102.6 and 392.7 J/m(2), respectively. The fracture toughnesses of TiO2 nanotube films are estimated as 0.996, 1.433 and 2.803 MPa.m(1/2), respectively. The interfacial bonding mechanism of TiO2 nanotube film is chemical bonding.