Research On The Properties Of Ta₂O₅ And TaON Nanocrystalinecoatingsin Simulated Physiological Solution Environment

In recent years, titanium and its alloys have been widely used in manufacture of aerospace, automotive industries and medical devices owing to its favorable properties, such as low density, high strength-to-weight ratio, superior biocompatibility, etc. However, many problems have been found in the application of titanium alloys. For instance, as long-term use biomaterial in human body, the alloy element ions may release into the blood or thrombus format on the surface of material, which can cause heavily harm to their users;titanium alloys also suffer from serious disadvantages of poor tribological properties and they also exhibitpoor corrosion resistance in some aggressive environment, all of these inherent shortcomings of titanium alloy have been greatly hindered them from being extensively applied. As is well known to all of us, both wear and corrosion are surface-controlled degradation processes. Therefore, surface modification technology could be one of the most effective means to improve the surface-relative performances of titanium alloy.Tantalum-based materials possess biological nontoxic, excellent wear and corrosion performance characteristics, tantalum and its oxide（Ta-O）, nitride（Ta-N） and other compound thin films or coatings have been gained much attention in biomedicine, machinery and some other industries. In this paper, Ta₂O₅ coating and TaON coating were deposited onto the polished surface of Ti-6A1-4V alloy by double cathode glow discharge technique. The cross-section SEM images show that both of the coatings, with a uniform thickness of ²5 μm, exhibits an extremely dense and homogeneousmicrostructure, and appears to be well adhered to the Ti–6Al–4V substratewithout any visible defects. TEM images indicate both of the coatings have the similarmicrostructural characteristics, composed of equiaxed grains with an average grain size of ¹5 nm.Nanoindentation tests show that the coatings can greatly improve the hardness and elastic modulus of Ti–6Al–4V alloy. Scratch tests show the adhesion strength between the coatings and the substrate is enough for engineering application. Under dry sliding wear conditions, the specific wear rates of the coatings were of the order of 10-6 mm3 N-1 m-1 under applied loads ranging from 2.3N to 5.3N and are two orders of magnitude smaller compared to uncoate Ti-6Al-4V alloy. Electrochemical tests were employed to analysis the corrosion behavior of the two coatings in simulatedbody fluids（0.9 wt.% NaCl solution and Ringer’s solution） and 3.5 wt.% NaCl solution.The electrochemical experiment results show that: both in simulatedbody fluids and in 3.5 wt.% NaCl solution, the two as-deposited coatings can remarkly enhance the corrosion resistance of the Ti-6Al-4V alloy, andthetheir corrosion resistanceappear almost independent with the soaking time. Mott–Schottky analysis and potential of zero charge（PZC） measurements indicate that both the Ta₂O₅ and TaON coating exhibited a lower carrier density and a larger capability to inhibit the adsorption of aggressive chloride ions than uncoated Ti–6Al–4V.At last, the two nanocrystalline coatingswere soaked in Hank’s solution for 15 days and the results showed that the apatite layer was formed on both of the surfaces, which is beneffical to the coating materials’ rapid osseointegration in the living body.