Influence of oxynitriding on the wear resistance of VT14 titanium alloy

We investigate the wear resistance of VT14 titanium alloy after oxynitriding realized by modifying nonstoichiometric titanium nitride by oxygen. It is shown that the oxide component in an oxynitride coating improves the wear resistance of the alloy in a friction pair with BrAZh9-4l brass. It is established that the wear rate of a “VT14 titanium alloy with oxynitride coating–U8 steel” tribopair is an order smaller than that of a “VT14 titanium alloy with oxynitride coating–BrAZh9-4l brass” tribopair. It is also established that the tribologic behavior of the former tribopair improves after replacing AMH-10 lubricant by I-40A lubricant.     

Influence of the nonstoichiometry of titanium nitride TiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> on the degree of its modification with oxygen

We investigate the influence of the nonstoichiometry (the degree of completeness) of titanium nitride TiN on the degree of its modification with oxygen. The completeness of titanium nitride was controlled by changing the nitriding temperature, nitriding time, and partial nitrogen pressure. It is shown that as the completeness of titanium nitride decreases, which leads to an increase in the intensity of oxynitriding, and as the nitrogen content in the ternary compound TiN _x O_{1 – x} decreases, the level of surface hardening of titanium alloys after oxynitriding diminishes.     

Influence of the parameters of nitriding on the subsurface hardening of VT6 titanium alloy

We study the influence of the parameters of nitriding (temperature, time of holding, and pressure of the active gas) on the formation of nitride coatings based on VT16 titanium alloy. We give recommendations concerning the possibility of combination of the prescribed thermal treatment with the thermochemical (nitriding) treatment of the alloy aimed at guaranteeing the required level of subsurface hardening. It is shown that the decrease in the partial pressure of nitrogen to 1–10 Pa increases the depth of the hardened zone and ensures the required level of subsurface hardening. The procedure of heating in a vacuum (1 mPa) performed prior to the action of nitrogen improves the surface quality of the alloy. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 49–54, November–December, 2007.     

Substrate temperature and water vapour effects on structural and mechanical properties of TiO x N y coatings

Dc reactive sputtering was successfully implemented to deposit titanium oxynitride thin films using a titanium metallic target, argon, nitrogen and water vapour as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas that of the water vapour was systematically changed from 0 to 0.1 Pa. The study aims at comparing the structural and mechanical properties of the coatings deposited at room temperature (293 K) and at 673 K. Surface morphology of the film was examined by atomic force microscopy and showed different aspects according to the growth temperature. Topography mainly depends on the amount of water vapour introduced during the deposition process. Some significant changes of the crystallographic structure, due to the high substrate temperature were correlated with the evolution of the surface aspect and roughness parameters. Determination of the phase occurrence by X-ray diffraction was also carried out and appeared to be a significant parameter in understanding the evolution of mechanical properties like nanohardness (H _n) and Young’s modulus (E). H _n and E values obtained by nanoindentation ranged from 16.5 to 7 GPa and from 240 to 100 GPa, respectively. For both temperatures, mechanical properties of titanium oxynitride thin films were notably reduced as a function of the water vapour supply, especially for partial pressures higher than 4 × 10⁻² Pa. These mechanical behaviours were correlated and discussed with the phase occurrence and the amorphous structure of titanium oxynitride thin films.     

Dependence of luminescence properties on composition of rare-earth activated (oxy)nitrides phosphors for white-LEDs applications

Rare-earth-activated nitride and oxynitride phosphors are attractive converter materials for white-LEDs applications due to their efficient luminescent characteristics, high thermal and chemical stabilities because their basic crystal structure is built on rigid tetrahedral networks, either of the Si–(O,N) or Al–(O,N) type. Recent progress in fluorescence properties of silicon–aluminum–(oxy)nitride-based luminescent materials with broad excitation bands activated by Eu²⁺, Ce³⁺, and Yb²⁺ for phosphor-converted white-LEDs are reviewed in this article, with the emphasis on the dependence of luminescence properties on composition. We elaborate on these composition-dependent properties in three sections: (i) Eu²⁺-activated nitride and oxynitride phosphors; (ii) Ce³⁺-activated nitride and oxynitride phosphors; and (iii) Yb²⁺-doped α-SiAlON phosphor. Eu²⁺- or Ce³⁺-activated nitride and oxynitride phosphors are categorized into four parts following the structural and/or composition characteristics, i.e., α-SiAlON, β-SiAlON, oxonitridosilicates, nitridoalumosilicates, and nitridosilicates. Some involving aspects for designing and the trends of research and development of these phosphors are addressed at the end of this article.     

Dynamic nitrogen and titanium plasma ion implantation/deposition at different bias voltages

Titanium oxynitride films were prepared on AISI 304 stainless steel samples employing dual titanium and nitrogen plasmas in an immersion configuration. The vacuum arc source provided the titanium plasma and the nitrogen plasma was sustained by hot filament glow discharge. A 30 μs implantation duration and 270 μs titanium arc duration were used in our plasma ion implantation and deposition (PIID) process. The impact of the implantation voltages (8 kV, 16 kV and 23 kV) on the film was investigated. The treated samples were characterized using Auger electron spectroscopy (AES) and atomic force microscopy (AFM). Our results reveal that the thickness of the coating is not changed significantly by the applied voltage. However, the surface morphology varies substantially with the implantation voltage. The 8-kV sample shows the highest titanium content and a smooth island-shaped surface whereas the 23-kV sample features peaks with sharper edges.     

Nitridation of the sol-gel derived TiO2 coating films and the infrared ray reflection

The titanium nitride coating film was prepared on the SiO₂ glass substrate by ammonolysis of titanium dioxide coating film formed by sol-gel method. The X-ray diffraction (XRD) pattern indicated that it is cubic titanium nitride with a lattice parameter,a _o, of 0.4231 nm. The obtained titanium nitride is non-stoichiometric (TiN _x x≤ 1) because the value, 0.4231 nm, is smaller than the stoichiometric one (0.4240 nm). The coating film show very high infrared (i.r.) reflectance in the wavelength region of 2–8 μm.     

Effect of thin carbonate-containing apatite (CA) coating of titanium fiber mesh on trabecular bone response

The influence of thin carbonate-containing apatite (CA) coating on trabecular bone response to cylindrical titanium fiber mesh (porosity of 85%, pore size of 200–300 μm, 2.8 mm diameter × 6 mm length) implants was investigated. Thin CA coatings were deposited by the so-called molecular precursor method. Molecular precursor solution was obtained by adding dibutylammonium diphosphate salt to Ca–EDTA/amine ethanol solution by adjusting Ca/P = 1.67. Sintered cylindrical titanium fiber mesh was immersed into molecular precursor solution and then tempered at 600 °C for 2 h. The immersion and tempering process was repeated three times. An adherent thin CA film could be deposited on the inside of titanium fiber mesh. After the immersion of a CA-coated titanium fiber mesh in simulated body fluid, apatite crystals precipitated on the titanium fiber mesh. Uncoated and CA-coated titanium fiber mesh was inserted into the trabecular bone of the left and right femoral condyles of rabbits. Histological and histomorphometrical evaluation revealed a significantly greater amount of bone formation inside the porous area of the CA-coated titanium fiber mesh after 12 weeks of implantation. The present results suggested that a thin CA-coated titanium mesh has better osteoconductivity and will be useful for a three-dimensional scaffold.     

Effects of the integrity of silicon thin films on the electrical characteristics of thin dielectric ONO film

Capacitors with two kinds of lower electrodes were fabricated and their effects evaluated on the electrical characteristics of oxide–nitride–oxide (ONO) film. One of the electrodes was made of amorphous silicon film chemically deposited using a gas mixture of Si2H6–PH3; the other was made of poly-Si film deposited by SiH4 decomposition and doped by As+ ion implantation. The ONO thin dielectric layer was composed of natural oxide, CVD silicon nitride and thermal oxide formed on the silicon nitride. The capacitance, the leakage current, the dielectric breakdown field and the time-dependent dielectric breakdown (TDDB) were tested to evaluate the electrical properties of the capacitors. The leakage current and the dielectric breakdown voltage showed similar values between the two capacitors, whereas the TDDB under negative bias showed a great difference. This indicates that, with respect to electrical properties, the integrity of the oxide grown on the in situ P-doped amorphous silicon is better than the oxide grown on the As+ ion-implanted poly-Si. What is more, phosphorus in the amorphous silicon did not lead to any problems with junction depth, even after post heat treatment at 950°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ways of intensification of thermodiffusive saturation of titanium alloys in molecular nitrogen

We analyze the results of using the partial pressure of nitrogen, thermokinetic parameters of saturation, elements of vacuum technology (vacuum annealing, heating in vacuum), and the initial structure and texture of material as factors for the intensification of nitriding in molecular nitrogen. We show that the processes of nitride formation and gas saturation are activated both by thermocycling and an increase in the temperature of isothermal soaking. When the partial pressure of nitrogen decreases, the nitride formation is retarded, but the gas saturation is accelerated. A similar effect is observed if one uses elements of vacuum technology. Conditions of high-speed heating make it possible to activate the nitride formation by inhibiting the appearance of the zone of α-solid solution of nitrogen in titanium. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 1, pp. 61–70, January–February, 1999.     

Influence of the ion implantation of nitrogen and boron and TiN coatings on the corrosion of VT-6 titanium alloy

We study the corrosion-electrochemical properties of VT-6 titanium (α + β)-alloy in solutions of hydrochloric and sulfuric acids after high-energy ion implantation with nitrogen (E = 30 keV) for a dose of 2 · 10¹⁷ ion/cm² with subsequent annealing in a vacuum, with boron (E = 100 keV) for a dose of 1 · 10¹⁵ ion/cm², and with nitrogen and boron, as well as in the presence of ion-plasma titanium-nitride coating. It is shown that the modification of the surface increases the corrosion resistance of titanium in highly concentrated solutions of the acids. Note that the corrosion resistance of the titanium-nitride coating whose thickness does not exceed 10μm is somewhat lower than the corrosion resistance of the implanted alloy. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 89–94, May–June, 2008.     

Kinetics of the formation of titanium oxynitride and nitride under the action of VUV, studied by means of ellipsometry

Preparation of thin nanolayers (approximately 10 nm) with the required stoichiometry and minimal grain size is important for the development of nanostructures. The kinetics of the formation of titanium nitride and titanium oxynitride layers through nitridation of the titanium matrix was investigated in the present work. It was shown that the UV radiation causes an increase in nitridation rate, depending on radiation energy, within the studied range 4 to 21 eV. The investigation was carried out with the help of ellipsometry and independent methods: atomic force microscopy, electron microscopy, and X-ray photoelectron spectroscopy. The mechanism of titanium interaction with nitrogen resulting in the formation of nitride and oxynitride layers at the Si/Ti and SiO2/Ti interfaces was investigated, the role of the UV radiation in solid-state reactions was revealed, and the mechanism of the process was proposed on the basis of the experimental data and results of quantum chemical simulation. The use of UV radiation allowed us to obtain the layers at low temperatures (0-5 degrees C) and to achieve a short reaction time due to an increase in reaction rate. The resulting layers have good masking properties (minimal density of pores and defects, high smoothness of the surface). This allows one to use these layers for chemical and electronic passivation and stabilization of the surface of semiconductor nano-objects (quantum dots, quantum wires, nanowhiskers etc.) for electronic and photon nanodevices.     

New plasma surface-treated memory alloys: Towards a new generation of “smart” orthopaedic materials

This paper describes the corrosion resistance, surface mechanical properties, cyto-compatibility, and in-vivo performance of plasma-treated and untreated NiTi samples. Nickel–titanium discs containing 50.8% Ni were treated by nitrogen and carbon plasma immersion ion implantation (PIII). After nitrogen plasma treatment, a layer of stable titanium nitride is formed on the NiTi surface. Titanium carbide is also found at the surface after carbon plasma implantation. Compared to the untreated samples, the corrosion resistances of the plasma PIII samples are better by a factor of five and the surface hardness and elastic modulus are better by a factor of two. The concentration of Ni leached into the simulated body fluids from the untreated samples is 30 ppm, whereas that from the plasma-treated PIII are undetectable. Although there is no significant difference in the ability of cells to grow on either surface, bone formation is found to be better on the nitrogen and carbon PIII sample surfaces at post-operation 2 weeks. All these improvements can be attributed to the formation of titanium nitride and titanium carbide on the surface.     

Surface hardening of titanium during thermocycling in nitrogen

Interaction of titanium with molecular nitrogen under the thermocycling conditions has been studied. It has been shown that cyclic variation of the temperature affects on the saturation intensity, inhibiting (low-temperature nitriding) or intensifying (nitriding at high temperatures or in the region of α ⇔ β-transition) the process. The temperature range of cycling determines the character of near-surface hardening. Deviation from the stoichiometry to the side of nitrogen shortage is typical for nitride films. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 6, pp. 39–43, November–December, 1997.     

Physicochemical properties of electric-spark coatings based on VT6 titanium alloy

We establish regularities of the process of formation and physicomechanical and physicochemical properties of the surface of VT6 titanium alloy subjected to electric-spark alloying with electrode materials based on refractory compounds of titanium and zirconium. It is shown that, in the process of electricspark alloying, the maximum hardness and electrochemical resistance of the alloyed layer in natural corrosive environments are attained for materials based on carbide and titanium carbonitride and the highest resistance to high-temperature oxidation is attained for materials based on zirconium nitride and titanium carbonitride. Frantsevich Institute of Problems in Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 5, pp. 55–59, September–October, 1996.     

Effect of the rarefaction of an oxygen-containing medium on the formation of titanium oxynitrides

We study the effect of the rarefaction of an oxygen-containing medium (0.001 to 10 Pa) on the formation of oxynitrides on the surface of VT1-0 titanium and its OT4, PT-7M, VT20, and VT6s alloys in the course of modification of nitrides formed in molecular nitrogen at a temperature of 850°C. The initiation of titanium oxynitrides becomes more intense as the rarefaction increases from 10 to 0.001 Pa. We also show that the surface microhardness increases after oxynitriding as compared with nitriding, and the depth of the hardened layer is determined by isothermal holding in nitrogen. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 1, pp. 56–60, January–February, 2008.     

Formation of oxynitrides on titanium alloys by gas diffusion treatment

The regularities formation of oxynitride layers on titanium with diffusion treatment has been investigated. Commercially pure titanium, α-, pseudo-α-(Ti-Al-V-Mo-Zr) and (α + β)-(Ti-Al-V) alloys were used. Oxynitrides were formed by the modifying of titanium nitride with oxygen according to the following scheme: TiN_x + O₂ → TiN_xO_1-x. The oxynitriding process was carried out by introducing the controlled oxygen-containing medium into the system at finish stage of nitriding (during cooling). The influence of nitriding parameters (temperature, nitriding time, nitrogen partial pressure) and oxynitriding parameters (temperature, oxynitriding time, oxygen partial pressure) on phase composition as well as mechanical and corrosion properties of the oxynitride coatings were studied. It was determined that the intensity of oxynitriding is more efficient when TiN_x is near its lower limit of homogeneity and increases with lowering of oxygen partial pressure in range 0.0001…0.01 Pa and temperature of oxynitriding in range 1223…923 K. The corrosion properties of oxynitride coatings were improved at higher nitrogen contents in the oxynitride compounds.     

Enhancement of the corrosion resistance of titanium alloys of the Ti-Al-Mo-V system by carbonitriding

We study the regularities of formation of coatings on titanium alloys of the Ti-Al-Mo-V system in the process of saturation in carbon-and-nitrogen-containing media (with an oxygen content of at most 0.01–0.0005 vol.%) and their corrosion-electrochemical behavior in an 80% aqueous solution of sulfuric acid. The difference between the phase compositions of the coatings formed in different temperature ranges of saturation is revealed. Thus, nitride coatings are formed on the surface at temperatures below 1100°C and carbonitride coatings are formed above 1100°C. It is shown that the physicochemical characteristics of nitride coatings formed in carbon-and-nitrogen-containing media are better than the corresponding characteristics of nitride coatings obtained by nitriding for the same temperature, time, and gas-dynamic parameters of saturation. As the content of cubic δ-nitride in the coating increases, the corrosion characteristics of the surface after saturation in carbon-and-nitrogen-containing media increase. Despite a significant surface roughness of carbonitride coatings, their corrosion resistance is high. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 78–83, July–August, 2006.     

Investigation of profiles of implanted Ti atoms over the depth of boron nitride nanocrystalline ceramic exposed to high radiation doses and fluxes with subsequent annealing

Results are presented of an investigation of distribution profiles of implanted Ti atoms at high implantation doses (fluence around 10¹⁷ cm⁻²) over the depth of boron nitride (BN) nanocrystalline ceramic. It is observed that the concentration maxima of implanted impurities are shifted into the substrate under post-implantation annealing in vacuum at 950 °C. This behavior of the implanted impurities in BN is directly the opposite of that observed in earlier studies of polycrystalline aluminum oxide ceramic exposed to similar ion thermal treatment. The effective diffusion coefficient of titanium atoms in BN under thermal annealing is estimated. The Ti/O concentration ratio in the layer modified as a result of implantation and subsequent annealing at 950 °C is close to stoichiometric TiO₂. A simultaneous increase in the concentration of carbon and nitrogen atoms in the surface layers of BN samples was observed as a result of annealing at 830 and 950 °C. Pis’ma Zh. Tekh. Fiz. 25, 53–57 (August 12, 1999)     

Surface modifications to improve Ti–porcelain bonding

Investigations of surface modifications on cast titanium surfaces and titanium-ceramic adhesion were performed. Cast pure titanium was subjected to surface modification by preoxidation and introduction of an intermediate layer of SnO _x by sol–gel process. Surfaces only sandblasted with alumina were used as controls. Specimen surfaces were characterized by XRD and SEM/EDS. The adhesion between the titanium and porcelain was evaluated by three-point flexure bond test. Failure of the titanium–porcelain with preoxidation treatment predominantly occurred at the titanium-oxide interface. Preoxidation treatment did not affect the fracture mode of the titanium–ceramic system and did not increase the bonding strength of Ti–porcelain. However, a thin and coherent SnO _x film with small spherical pores obtained at 300 °C served as an effective oxygen diffusion barrier and improved titanium–ceramic adhesion. The SnO _x film changed the fracture mode of the titanium–ceramic system and improved the mechanical and chemical bonding between porcelain and titanium, resulting in the increased bonding strength of titanium–porcelain.