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 Ringer's solution at 37 °C. The results were complemented with analysis of the alloy's 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.

Formation of Nitrogen Doped Titanium Dioxide Surface Layer on NiTi Shape Memory Alloy

“…From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12]. It should be noted that in plasma oxidation of NiTi alloy, high chemical affinity of the oxygen particles (i.e., atoms in statu nascendi) is not the only factor that plays a key role during formation of an oxide layer, but also prior cathodic sputtering.…”

“…In the case of cathodic sputtering application, a thicker layer of titanium oxide was obtained (about 80 nm), while without sputtering, the layer's thickness was about 40 nm (Figure 4), despite the application of less chemically active air (instead of oxygen) in the reactive atmosphere during plasma oxidation. From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12].…”

“…It should be noted that during heating of the NiTi alloy in glow discharge conditions, the cathodic sputtering phenomenon was less intense due to higher pressure in the reaction chamber (2.0 hPa). The surface layer of titanium oxide-rutile, as shown in our earlier studies [ 12 , 19 , 21 ], significantly changed the properties of the NiTi, including its corrosion resistance and mechanical properties. TiO 2 is characterized by good biological properties [ 19 , 21 , 28 , 29 ], including antibacterial properties [ 30 ].…”

Formation of Nitrogen Doped Titanium Dioxide Surface Layer on NiTi Shape Memory Alloy

“…From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12]. It should be noted that in plasma oxidation of NiTi alloy, high chemical affinity of the oxygen particles (i.e., atoms in statu nascendi) is not the only factor that plays a key role during formation of an oxide layer, but also prior cathodic sputtering.…”

“…In the case of cathodic sputtering application, a thicker layer of titanium oxide was obtained (about 80 nm), while without sputtering, the layer's thickness was about 40 nm (Figure 4), despite the application of less chemically active air (instead of oxygen) in the reactive atmosphere during plasma oxidation. From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12].…”

“…It should be noted that during heating of the NiTi alloy in glow discharge conditions, the cathodic sputtering phenomenon was less intense due to higher pressure in the reaction chamber (2.0 hPa). The surface layer of titanium oxide-rutile, as shown in our earlier studies [ 12 , 19 , 21 ], significantly changed the properties of the NiTi, including its corrosion resistance and mechanical properties. TiO 2 is characterized by good biological properties [ 19 , 21 , 28 , 29 ], including antibacterial properties [ 30 ].…”

Microstructural and corrosion resistance characterisation of NiTi shape memory alloy modified at low-temperature plasma with carbon coatings produced via RFCVD and IBAD methods

“…The Raman spectra of both the layers revealed the structure of amorphous carbon on the surface that was presented and described in the earlier publications [25,26]. In the coating produced by the RFCVD method, the concentration ratio of sp3 to sp2 bonds was about 50% [24], and in the IBAD coating – about 40% [25].…”

“…Amorphous carbon coatings produced by the RFCVD method on NiTi alloy previously subjected to the oxynitriding process (a-C:N:H + TiO 2 + TiN) are characterised by high corrosion resistance. The electrochemical parameters of the carbon coating ( n = 0.51) indicate that electrochemical processes within the coating are under diffusion control, probably due to surface development [26], which is typical for non-metallic coatings.…”

Formation of Nitrogen Doped Titanium Dioxide Surface Layer on NiTi Shape Memory Alloy

“…From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12]. It should be noted that in plasma oxidation of NiTi alloy, high chemical affinity of the oxygen particles (i.e., atoms in statu nascendi) is not the only factor that plays a key role during formation of an oxide layer, but also prior cathodic sputtering.…”

“…In the case of cathodic sputtering application, a thicker layer of titanium oxide was obtained (about 80 nm), while without sputtering, the layer's thickness was about 40 nm (Figure 4), despite the application of less chemically active air (instead of oxygen) in the reactive atmosphere during plasma oxidation. From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12].…”

“…It should be noted that during heating of the NiTi alloy in glow discharge conditions, the cathodic sputtering phenomenon was less intense due to higher pressure in the reaction chamber (2.0 hPa). The surface layer of titanium oxide-rutile, as shown in our earlier studies [ 12 , 19 , 21 ], significantly changed the properties of the NiTi, including its corrosion resistance and mechanical properties. TiO 2 is characterized by good biological properties [ 19 , 21 , 28 , 29 ], including antibacterial properties [ 30 ].…”

Microstructural and corrosion resistance characterisation of NiTi shape memory alloy modified at low-temperature plasma with carbon coatings produced via RFCVD and IBAD methods

“…The Raman spectra of both the layers revealed the structure of amorphous carbon on the surface that was presented and described in the earlier publications [25,26]. In the coating produced by the RFCVD method, the concentration ratio of sp3 to sp2 bonds was about 50% [24], and in the IBAD coating – about 40% [25].…”

“…Amorphous carbon coatings produced by the RFCVD method on NiTi alloy previously subjected to the oxynitriding process (a-C:N:H + TiO 2 + TiN) are characterised by high corrosion resistance. The electrochemical parameters of the carbon coating ( n = 0.51) indicate that electrochemical processes within the coating are under diffusion control, probably due to surface development [26], which is typical for non-metallic coatings.…”

Formation of Nitrogen Doped Titanium Dioxide Surface Layer on NiTi Shape Memory Alloy

“…From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12]. It should be noted that in plasma oxidation of NiTi alloy, high chemical affinity of the oxygen particles (i.e., atoms in statu nascendi) is not the only factor that plays a key role during formation of an oxide layer, but also prior cathodic sputtering.…”

“…In the case of cathodic sputtering application, a thicker layer of titanium oxide was obtained (about 80 nm), while without sputtering, the layer's thickness was about 40 nm (Figure 4), despite the application of less chemically active air (instead of oxygen) in the reactive atmosphere during plasma oxidation. From the thermodynamic point of view, the Gibbs free energy (about 800 kJ/mol for a 300 • C temperature) favored formation of the most thermodynamically stable (in comparison to other titanium oxides) TiO 2 oxide [26], which was confirmed in our previous studies [12,27]. It has been shown that in lowtemperature plasma, TiO 2 oxide can also be produced during the oxidation of titanium nitride during the oxynitriding process [12].…”

“…It should be noted that during heating of the NiTi alloy in glow discharge conditions, the cathodic sputtering phenomenon was less intense due to higher pressure in the reaction chamber (2.0 hPa). The surface layer of titanium oxide-rutile, as shown in our earlier studies [ 12 , 19 , 21 ], significantly changed the properties of the NiTi, including its corrosion resistance and mechanical properties. TiO 2 is characterized by good biological properties [ 19 , 21 , 28 , 29 ], including antibacterial properties [ 30 ].…”

Microstructural and corrosion resistance characterisation of NiTi shape memory alloy modified at low-temperature plasma with carbon coatings produced via RFCVD and IBAD methods

“…The Raman spectra of both the layers revealed the structure of amorphous carbon on the surface that was presented and described in the earlier publications [25,26]. In the coating produced by the RFCVD method, the concentration ratio of sp3 to sp2 bonds was about 50% [24], and in the IBAD coating – about 40% [25].…”

“…Amorphous carbon coatings produced by the RFCVD method on NiTi alloy previously subjected to the oxynitriding process (a-C:N:H + TiO 2 + TiN) are characterised by high corrosion resistance. The electrochemical parameters of the carbon coating ( n = 0.51) indicate that electrochemical processes within the coating are under diffusion control, probably due to surface development [26], which is typical for non-metallic coatings.…”