Janusz Kamiński

Hybrid a-CNH+TiO2+TiN-type surface layers produced on NiTi shape memory alloy for cardiovascular applications

AIM The goal was to improve the properties of NiTi shape memory alloy to make it suitable for cardiac applications. For this purpose, a hybrid a-CNH+TiO2+TiN-type surface layer was produced on NiTi alloy and characterized. MATERIALS & METHODS The NiTi alloy subjected to hybrid process combining low-temperature oxynitriding under glow discharge conditions and radio frequency chemical vapor deposition process was examined for microstructure, surface topography, corrosion resistance, wettability and surface-free energy, Ni ion release and platelets adhesion, aggregation and activation. RESULTS The hybrid surface layers showed slightly increased surface roughness, better corrosion resistance, a more hydrophobic nature, decreased surface free energy, smaller release of nickel ions and reduced platelets activation. CONCLUSION The produced layers could expand the range of NiTi medical applications.

Porous Titanium Scaffolds for Biomedical Applications: Corrosion Resistance and Structure Investigation

Due to its suitable physical properties and good biocompatibility, the titanium (Ti) can be used for development of porous structures for biomedical applications. The state of art in the field of corrosion resistance showed problems with corrosion analysis of porous metals. Therefore, it is essential to understand the influence of porosity of metals on corrosion parameters. The aim of this study was to investigate the corrosion resistance of highly porous titanium scaffolds for biomedical application. The Ti scaffolds were fabricated by powder metallurgy technique. The total porosity of the scaffolds ranged from 45 to 75%. The cast Ti sample was also tested for comparison. The electrochemical behavior of the Ti samples was monitored by electrochemical impedance spectroscopy (EIS) and potentiodynamic method at the room temperature. All electrochemical experiments were performed by a three-electrode technique in a cell containing a 0.9% NaCl electrolyte solution. With use of AAF, the active area of porous Ti was estimated. The porous Ti with porosity of 75% shows a better resistance to corrosion than the other porous Ti scaffolds. However, the corrosion resistance of Ti scaffolds was lower than cast Ti.

Structure and corrosion resistance of titanium oxide layers produced on NiTi alloy in low-temperature plasma

Abstract The paper presents comparative results of NiTi corrosion resistance tests of the alloy in initial state and after oxidizing and oxynitriding in low temperature plasma. These processes allow obtaining TiO2 or composite TiO2 + TiN layers with a titanium nitride (TiN) interlayer. Corrosion resistance tests of diffusion layers produced on NiTi were carried out via electrochemical impedance spectroscopy and the potentiodynamic method in Ringers solution at 37 °C. The results were complemented with analysis of the alloys structure, surface topography, and elemental distribution in the layers. The results showed an increase in corrosion resistance of NiTi alloy both after glow-discharge oxidation and oxynitriding. Significant shortening of the passive range of oxynitrided layers may result both from differences in surface topography and the thickness of the oxide layers.

Corrosion Resistance of Titanium Aluminide Layers on Two Phase (α+β) Ti6Al4V Titanium Alloy

The paper presents results of investigations into the structure and corrosion resistance of Ti-Al diffusion layers produced on two phase (a+b) Ti6Al4V alloy by Chemical Vapour Deposition (CVD). The process was carried out in aluminium chloride (AlCl3) mixed with argon atmosphere. Surface topography and microstructure characterization of the coatings were examined by scanning electron microscopy (SEM). The local chemical composition witch 1 μm lateral resolution was measured via EDS. The phase content was investigated by X-ray diffraction and analysis of the chemical composition of the surface by XPS. Corrosion resistance was tested using the potentiodynamic method in 0.1M Na2SO4 and 0.1M H2SO4 solutions at the room temperature. Their resistance to high temperature at atmospheric pressure was tested by 24-hours cycling to 700°C. The results indicate that the layers produced on the Ti6Al4V titanium alloy exhibit a very good adhesion combined with exceptional corrosion resistance, especially high at high temperatures.

Corrosion Resistance of NiTi Shape Memory Alloy after Nitriding and Oxynitriding Processes under Glow Discharge Conditions for Medical Applications

NiTi alloy is being increasingly used in medicine due to its unique properties, i.e. shape memory and superelasticity. As a self-passivating material it is characterized by relatively high biocompatibility, however its use for long-term medical implants is questionable due to the nickel content of ≥ 50%. Therefore, the investigations on the surface modification of NiTi alloy are carried out to improve its corrosion resistance and thus reduce the metalosis effect, i.e. the migration of the alloy constituents, especially nickel, into the surrounding tissue.In this paper, the surface topography and corrosion resistance of NiTi alloy (50,8%Ni) both before and after low-temperature nitriding and oxynitriding processes under glow discharge conditions, are presented.The study of surface topography showed a slight increase in roughness parameters after nitriding process and a significant increase in these parameters after the oxynitriding process. A similar trend was observed in the study of corrosion resistance. Both processes increase the corrosion resistance of NiTi alloy, as shown by both the impedance spectroscopy results, the values of corrosion potential (-65 mV for the alloy in the initial state, - 45 mV for the alloy with the nitrided layer, + 18 mV for the alloy with the oxynitrided layer) and the values corrosion current (respectively 0.047 μA/cm2, 0.043 μA/cm2, 0.015 μA/cm2).These comparative studies present an improvement of corrosion resistance of NiTi after the processes under glow discharge. The best results were obtained for the oxynitrided layer.

Hydrostatic Extrusion and Nano-Hardness of Nanocrystalline Grade 2 Titanium.

The structure and corrosion resistance of Grade 2 titanium subjected to the hydroextrusion processes were examined. The microstructure was characterized using optical microscopy and transmission electron microscopy. The corrosion resistance was determined using the impedance and potentiodynamic methods, in 0.1 M H2SO4 solutions and an acidified 0.1 M NaCl solution with a pH of 4.2, at ambient temperature. Nanohardness tests were performed under a load of 100 mN. It has been demonstrated that the hydroextrusion method makes it possible to obtain relatively homogeneous nanocrystalline titanium Grade 2 with an increased hardness, the elastic modulus almost unchanged with respect to that of the initial structure and a lower corrosion resistance.

Microstructure and properties of ultrafine grain nickel 200 after hydrostatic extrusion processes

This paper presents the results of the studies of the structure and properties of ultrafine grained nickel 200 obtained by hydrostatic extrusion processes. Microstructure was characterized by means of optical microscopy and electron transmission microscopy. Corrosion resistance was studied by impedance and potentiodynamic methods using an AutoLab PGSTAT 100 potentiostat in 0.1 M Na2SO4 solution and in acidified (by addition of H2SO4) 0.1 M NaCl solution at pH = 4.2 at room temperature. Microhardness tests were also performed. The results showed that hydrostatic extrusion produces a heterogeneous, ultrafine-grained microstructure in nickel 200. The corrosive resistance tests showed that the grain refinement by hydrostatic extrusion is accompanied by a decreased corrosive resistance of nickel 200.