خواص نانومکانیکی

Nowadays, suitable protective properties of tantalum nitride coatings, such as hardness, abrasion resistance and high corrosion resistance lead to increasing its application in medical engineering and improving the biological behavior of titanium and its alloys. In this research, nanostructured tantalum nitride coating was applied on the NiTi alloy by magnetron sputtering method. Then, the phase, structural and morphological properties of coating were investigated by using XPS, FESEM, AFM, respectively, as well as the nanomechanical properties of the coating were evaluated by using Nano-scanning and nano-scratch methods in different loads.
The results indicate that applying the uniform, homogeneous and crack free tantalum nitride coating with a thickness of 1050 nm. The hardness and elastic modulus of coating is 12.6 and 87.4 GPa under the applied force of 1000 μm and the penetration depth of 91 nm, respectively, which resulted in enhancing the hardness of NiTi alloy surface, about 34%. The coefficient of friction is 0.28 and the dominated wear mechanism of nanostructured tantalum nitride coating is abrasive wear with shearing mechanism.

Due to ultra-high flexural flexibility, shape memory effect, high damping properties, corrosion resistance and good biocompatibility, the nitinol alloys (NiTi) are widely used in the manufacture of medical and biocompatible materials, such as stent, orthopedic implants and surgical instruments. But one of the most important problems of NiTi alloy is the release of nickel ions due to the destruction of the surface, which these ions can interfere with the enzymatic processes involved in protein synthesis and cell proliferation. The applied coating and ion implantation is one of the most important methods for improving the surface and behavior of the NiTi alloy. In this study, surface of NiTi alloy was modified by carbon plasma immersion ion implantations (CPIII). Then nanomechanical properties of coating were surveyed by atomic force microscopy (AFM) with nano-indentation, nano-scratch methods, and also corrosion behavior was investigated by polarization test in 0.5 M NaCl solution. The results indicate a completely homogeneous, uniform and free surface imperfection with a carbon ion implantation depth of about 50 nm, and decreased average surface roughness from 34to 25 nm. The ion implantation process resulted in increasing the hardness and elastic modulus of 80.7% and 21.8%, respectively, and reducing the average friction coefficient from 0.21 to 0.16, and also making dominant the shear wearing mechanism, with a 85% increase in corrosion resistance efficiency.