Effect of SiC film on tensile properties of nanostructured Ti produced by compressive deformation at liquid-nitrogen temperature

The effect of silicon carbide (SiC) film on tensile properties of nanostructured titanium (nanostructured Ti) was investigated. The nanostructured Ti was produced by a multi-step severe compressive plastic deformation at liquid-nitrogen temperature, and presents a microstructure with high densities of nano-scale (from a few to tens nanometers) domains along with high dislocation density inside. The SiC film (a few micron-meters thickness) was deposited on the nanostructured Ti (substrate) using a radio-frequency magnetron sputtering technique at room temperature, and presents a structure with amorphous/crystalline mixture and an impressive plastic deformation capacity. The film-substrate interface displays a good bonding, with a considerably high adhesion force together with evident film-substrate element diffusions. Relative to the nanostructured Ti without SiC film, the nanostructured Ti with SiC film exhibits a much higher tensile ductility while without an obvious change in earlier stress-strain behaviors. The enhanced tensile ductility is believed to be due to the great improvement in force stability that can be attributed to three identified factors, i.e. the increase of strain hardening capacity originated from the obstruction of surface film to deformation defects of inner substrate, the decrease of actual stress in substrate surface layer due to the stress transfer from surface layer to surface film, and the increased difficulty of shear band generation due to the microstructure coarsening in substrate surface layer induced by the film processing. The present investigation demonstrates the possibility that an appropriate surface film modification may be an effective approach for nanostructured materials to improve their ductility while without a degradation of strength. (C) 2007 Elsevier B.V. All rights reserved.