Effect Of Temperature On Residual Stress And Mechanical Properties Of Ti Films Prepared By Both Ion Implantation And Ion Beam Assisted Deposition

Ti thin films have been extensively studied for their potential applications in micro-electro-mechanical systems (MEMS), medical implants, and intelligent materials. However, residual tensile stress in the deposited films will become one critical problem for their wide application, as it influences not only adhesion between film and substrate, but also deformation of MEMS structure, mechanics and thermodynamics of dislocation transformation, and super elasticity effect, etc.Ti films with a thickness of 1.6μm (group A) and 4.6μm (group B) were prepared on the surface of silicon crystals by metal vapor vacuum arc (MEVVA) ion implantation combined with ion beam assisted deposition (IBAD) technique. Anneal temperatures ranging from 100°C to 500°C were used to investigate the effect of temperature on residual stress and mechanical properties of the Ti films. X-ray diffraction (XRD) was used to measure residual stress of the Ti films. The morphology, elemental analysis, roughness, nanohardness, and modulus of the Ti films were measured by scanning electron microscopy (SEM), scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindentation, respectively. It is showed that the residual stress values in the MEVVA-IBAD deposited films change significantly with Ti film thickness and anneal temperatures due to the stress relaxation behaviors. The residual tensile stress values of sample groups A and B at 500°C annealing reach 0.6 GPa and 4.5 GPa, respectively. The critical temperature values of sample groups A and B when residual stress changes from compressive to tensile are 404°C and 428°C, respectively. The experimental results suggest that residual stress values are sensitive to anneal temperature and film thickness. The mechanism of stress relaxation of the Ti films has been discussed. The stress variation is attributed to re-crystallization under high temperature in Ti film. The experimental results suggest that the temperature effect on thicker films (group B and C) is much stronger than that on thinner films (group A) attributed to more effective re-crystallization. The effect of temperature on film mechanical properties was scrutinized. The grain size and mean surface roughness of annealed films increase with annealing temperature. The maximum values of grain size of sample group A and C are 46.7 nm and 134.9 nm, respectively. The values of nanohardness and modulus of the Ti films reach their maximum values at very thin depth near the surface, then, reach consistent values with increasing depth of the indentation. It is clear that the heat effect on film nanohardness and modulus depends on temperature, however, the temperature effect on film mechanical properties is relatively slight than that on residual stress.