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.     

Fatigue of VT20 titanium alloy with vacuum-plasma coatings at high temperatures

We study the influence of vacuum–plasma TiN, (TiAl)N, and (TiC)N coatings on the high-cycle fatigue of VT20 titanium alloy in the temperature range 350–640°C for a loading frequency of 10 kHz. It is shown that, in this temperature range, the fatigue limits of VT20 alloy with the indicated coatings 6 μm in thickness become 15–25% higher than for the material without coating. The possibility of replacement of steel blades with titanium blades with vacuum-plasma coatings is demonstrated. Translated from Problemy Prochnosti, No. 4, pp. 101–107, July–August, 2009.     

Production of conversion oxide-ceramic coatings on zirconium and titanium alloys

We consider the possibilities of surface hardening of zirconium and titanium alloys with conversion oxide-ceramic coatings. These coatings have been produced by the method of plasma-electrolytic treatment in alkaline solutions. We have established that the plasma temperature in discharge spark channels reaches (6–9) · 10³ K. The thickness of the coatings is 100 to 120 and 30 to 40 μm, and their microhardness is ∼ 800 and ∼ 1000 MPa for zirconium and titanium alloys, respectively. The functional properties of the coatings depend on the synthesis conditions, including the electrolyte composition, the cathode and anode current densities, and also the treatment time. We have evaluated the thickness, microhardness, and wear resistance of the coatings under conditions of dry friction and cavitation as well as their fatigue strength and corrosion resistance. We have established that this treatment provides a high wear and corrosion resistance of the alloys under study with insignificant decrease in their fatigue strength. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 2, pp. 117–124, March–April, 2006.     

Influence of hydrogen on the long-term strength of tire steels

We establish that the time to fracture of specimens made of 8Mn−8Ni−4Cr steel decreases in tap water at high stresses by a factor of 2.5 and, in the course of electrolytic hydrogenation, by a factor of 35–50 as compared with that obtained in tests in twice-distilled water. The use of a hardening surface treatment and protective coatings under the same conditions increases the long-term strength by a factor of 1.5–2. A combined plasma Al+V₂O₅ coating with subsequent soaking with epoxy compound preserves the plastic characteristics of steel and, hence, increases the time to fracture in the best way. The application of plasma nitride (TiN+CrN+NbN) coatings on the thread and mounting surfaces of elements of a rotor shroud unit gives them a high hardness and resistance to dripping and scoring and prevents the penetration of hydrogen-containing media into the base. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 4, pp. 37–42, July–August, 1999.     

Distribution of temperature in a plate with a single-layer coating subjected to intense heating

We establish the distribution of temperature formed under conditions of abrupt changes in the surface temperature near the adhesional contact between the base and the coating in a plate of infinite length made of molybdenum or niobium both sides of which are covered with silicide coatings. The problem of heat conduction for a multilayer plate subjected to thermal cycling is solved by the method of finite integral transformations. It is shown that a silicide coating with a thickness of 60–100 μm leads to the formation of a significant temperature gradient in the base material under conditions of cyclic variation of temperature. This work was partially supported by the Soros International Program in the Field of Exact Sciences (ISSEP), Grant No. PSU 062034. Translated from Problemy Prochnosti, No. 3, pp. 128–133, May–June, 1998.     

Influence of the structure on the regularities of cavitation wear of eutectic coatings

We analyze the influence of the structure and the main physicomechanical characteristics of eutectic coatings obtained using concentrated sources of energy on the mechanism and kinetics of their cavitation wear. We establish a correlation between the rate of cavitation wear, the size of the structural components, and the mechanical characteristics of the coating. Ukrainian National Technical University “Kiev Polytechnic Institute,” Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 69–74, March–April, 1998.     

An electrodeposition method of calcium phosphate coatings on titanium alloy

Calcium phosphates coatings were deposited onto titanium alloy discs via en electrodeposition method. Titanium alloy discs were blasted with calcium phosphate particles, then etched in a mixture of nitric and fluoric acids and rinsed in demineralized water. The titanium alloy disc (cathode) and platinum mesh (anode) were immersed in a supersaturated calcium phosphate electrolyte buffered at pH 7.4 and connected to a current generator. The microstructure, chemical composition and crystallinity of the electrodeposited coatings were studied as function of time 10–120 min, temperature 25–80°C, current density 8–120 mA/cm², magnesium and hydrogen carbonate amounts (0.1–1 mM). Uniform calcium phosphate coatings were obtained in 30 min but coating thickness increased with deposition time. Raising the temperature of electrolyte resulted in more uniform coatings as ionic mobility increased. Low current density was preferable due to hydrogen gas evolving at the cathode, which disturbed the deposition of calcium phosphate crystals on titanium. The amounts of magnesium and hydrogen carbonate ions affected both the homogeneity and morphology of the coatings. This study showed that the electrodeposition method is efficient for coating titanium with osteoconductive calcium phosphate layers.     

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.     

Evolution of the phase composition of coatings in the course of thermodiffusion noncontact carbonitriding of titanium

We have studied the evolution of the phase composition of coatings on titanium formed by thermodiffusion noncontact carbonitriding. We show that the use of this method enables one to decrease the saturation temperature to 800–850°C. The temperature-time and gas-dynamic parameters of the process determine the phase composition of surface layers. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 4, pp. 114–120, July–August, 2008.     

Influence of Surface-Modified Conducting Fillers on the Properties of Epoxy Coatings

We have developed a new epoxy composition for antistatic coatings on metallic surfaces, filled with technical carbon and talc, which had been surface-modified by paranitroaniline and phosphoric acid. It has been shown that, with the introduction of modified fillers, the content of gel fraction in an epoxy coating increases by 5–6%, its adhesion becomes 2.5–2.7 times higher, and the amount of organic solvents decreases. We have also established that the electric resistance of the coating is more stable in time as compared with the commercial antistatic ground-coat enamel, and the frequency dependence of the resistance is more clearly pronounced after exposure to a chloride-containing medium, which corroborates the better protective properties of antistatic coatings with modified current conductive fillers. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 4, pp. 53–58, July–August, 2005.     

Surface hardening of titanium by noncontact thermodiffusion carbonitriding

We have studied the influence of the parameters of noncontact carbonitriding on the properties of coatings and surface layers. We have shown that this method enables one to decrease the saturation temperature to 800–850°C. The temperature-time and gas-dynamic parameters of this process determine the phase and structural features of surface layers. Regulating the technological parameters of saturation, one can affect the properties of coatings. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 63–68, September–October, 2008.     

Effect of coatings on the distribution of heat in bar-disk tribosystems

We develop an analytic method for the evaluation of the surface temperature and the coefficient of distribution of heat in a tribosystem formed by an immobile bar and a rapidly rotating disk with coating. The analysis of numerical results demonstrates that surface temperature increases with the thickness of the coatings if the thermal conductivity of the coating is lower than the thermal conductivity of the disk. For coatings of fixed thickness, surface temperature decreases as the angular velocity increases. We also study the dependences of the coefficient of distribution of heat between the bodies on their geometric parameters and thermal properties. Franko L'viv University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 43–49, May–June, 1997.     

Physicochemical properties of tungsten-carbide and zirconium-diboride galvanic coatings on steel

We study the physicochemical and mechanical properties of galvanic coatings based on tungsten carbide and zirconium diboride and obtained as a result of electrolysis of ionic melts on steels. The thickness of the coatings does not exceed 100 μm. The application of these coatings makes the wear resistance of steel specimens 6–9 and 8–9 times higher and their abrasion resistance 7–8 and 8–10 times higher, respectively. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 68–72, January–February, 2007.     

Electrophoretic deposition of porous CaO–MgO–SiO<Subscript>2</Subscript> glass–ceramic coatings with B<Subscript>2</Subscript>O<Subscript>3</Subscript> as additive on Ti–6Al–4V alloy

The sub-micron glass–ceramic powders in CaO–MgO–SiO₂ system with 10 wt% B₂O₃ additive were synthesized by sol–gel process. Then bioactive porous CaO–MgO–SiO₂ glass–ceramic coatings on Ti–6Al–4V alloy substrates were fabricated using electrophoretic deposition (EPD) technique. After being calcined at 850°C, the above coatings with thickness of 10–150 μm were uniform and crack-free, possessing porous structure with sub-micron and micron size connected pores. Ethanol was employed as the most suitable solvent to prepare the suspension for EPD. The coating porous appearance and porosity distribution could be controlled by adjusting the suspension concentration, applied voltage and deposition time. The heat-treated coatings possessed high crystalline and was mainly composed of diopside, akermanite, merwinite, calcium silicate and calcium borate silicate. Bonelike apatite was formed on the coatings after 7 days of soaking in simulated body fluid (SBF). The bonding strength of the coatings was needed to be further improved.     

Radiation characteristics of heat protective materials of the buran orbital spacecraft

Some features of investigations of the temperature dependence of the integrated and spectral emissivity of erosion-resistant coatings on a low-thermal conductivity fibrous heat insulation are discussed. Results are provided for the standard ‘black’ and ‘white’ coatings. A study is made of the influence of repeated attacks of the high-temperature dissociated air on the integrated emissivity of the ‘black’ coating. Data are obtained on the radiation characteristics of this coating after full-scale tests during the Buran orbital spacecraft flight. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 1, pp. 26–30, January–February, 2000.     

Effect of Carbon-Containing Conducting Fillers on the Properties of Epoxy Coatings

We have established that antistatic coatings based on EP-0010 putty and graphite have low adhesion to metal and breaking strength but are resistant to the action of an operating environment. The use of carbon black as a conducting additive increases 1.5–3 times the strength of free films obtained on the basis of the given epoxy composition as compared with graphite and decreases their mass losses in an operating environment. The adhesion of epoxy coatings based on the EP-0010 composition modified by carbon black is 2–2.5 times as great as that of coatings with a graphite filler. The use of a plasticizer based on epoxidated vegetable oil instead of an inert phthalate plasticizer in a carbon-containing epoxy composition is promising and, in the case of optimal content of the components, enables one to enhance significantly the physicomechanical characteristics of antistatic epoxy coatings and their resistance to the action of the operating environment. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 2, pp. 109–113, March–April, 2005.     

On the connection between the adhesive strength and temperature drops in heat-protective coatings

We propose a procedure and results of experimental determination of the dependence of adhesive strength of a ZrO₂ plasma-sprayed heat-protective coating with NiCr sublayer on the value of the stationary temperature drop in it. The dependences of the adhesive strength on the temperature of the surface of adhesive contact are compared for homogeneous and inhomogeneous temperature fields. The results obtained enable us to substantiate the choice of temperature drop in heat-protective coatings with regard for the adhesion safety factor. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 126–130, July–August, 1998.     

Influence of technological factors on the formation of amorphous plasma-sprayed coatings

We investigate the influence of technological factors of the process of pulsed plasma spraying (in particular, of the composition of plasma-forming gases and magnetic fields) on the formation of amorphous coatings. It is experimentally established that the formation of coatings in the presence of a magnetic field applied in the region of spraying favors the formation of amorphous coatings and, thus, increases their adhesion to the base. The application of argon-hydrogen mixtures as plasma-forming gases make it possible to obtain homogeneous coatings with elevated contents of the amorphous component. “L'vivs'ka Politeknika” State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 77–81. May–June, 1997.     

Antifriction properties of heat-resistant alloys in hydrogen

We investigate the influence of hydrogen on friction properties of heat-resistant KhN55MBYu alloy and establish the main regularities of variation in the sliding friction coefficient in the process of operation of a shaft-bush couple depending on the temperature and pressure of hydrogen as well as on the rate and type of loading. Some recommendations concerning the efficient use of certain plasma and self-lubricating coatings for the operation of valve hydrogen engines are given. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 2, pp. 108–112, March-April, 2000.     

Interaction between amorphous boron and titanium alloys in a gaseous oxygen-containing medium

We study the influence of oxygen partial pressure in the course of diffusion saturation of titanium with the formation of boride phases (TiB, TiB₂) at 900°C. We establish the dependence of the reactivity of saturating medium, consisting of powdered amorphous boron and a vacuum atmosphere, on the oxygen partial pressure. We also present some physical characteristics of boride coatings. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 30–34, September–October, 2006.