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.     

Corrosion of titanium alloys in aqueous solutions of hydrochloric acid

We investigate the kinetics of corrosion of α-, (α+β)-, and β-titanium alloys in aqueous solutions of hydrochloric acid. It is shown that the process of dissolution obeys a parabolic law and is accompanied by the formation of an oxide (TiO₂ rutile) film on the metal surface. We demonstrate that corrosion processes are intensified as the amount of the β-phase in titanium alloy increases. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 112–115, May–June, 1997.     

Influence of arsenic, antimony and phosphorous on the microstructure and corrosion behavior of brasses

The effect of minor additions of As, Sb and P on phase distribution and corrosion behavior has been studied in brasses. The alloys investigated were 60Cu–39Zn–1Pb, 48.95Cu–45Zn–5Pb–1Sn–0.05As, 48.90Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb and 48.85Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb–0.05P. Immersion tests in 1% CuCl₂ solution indicated that the addition of As improved corrosion resistance while the combined addition of As + Sb and As + Sb + P was not beneficial. The hardness increased significantly with the addition of As, Sb and P. Microstructural observations indicated an increase in β phase fraction in the As, Sb and P containing alloys. X-ray diffraction studies confirmed the formation of intermetallic compounds in As, Sb and P containing alloys. Based on the microstructural observations, the intermetallic compounds appear to be primarily precipitated in the β phase with As + Sb and As + Sb + P additions. The lower corrosion resistance of the alloys 48.90Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb and 48.85Cu–45Zn–5Pb–1Sn–0.05As–0.05Sb–0.05P has been related to increase in β phase volume fraction and precipitation of intermetallic compounds in the β phase.     

The effects of calcium and yttrium additions on the microstructure,mechanical properties and biocompatibility of biodegradable magnesium alloys

In this study, the effects of calcium (Ca) and yttrium (Y) on the microstructure, mechanical properties, corrosion behaviour and biocompatibility of magnesium (Mg) alloys, i.e. Mg–xCa (x = 0.5, 1.0, 2.0, 5.0, 10.0, 15.0 and 20.0%, wt%, hereafter) and Mg–1Ca–1Y, were investigated. Optical microscopy, X-ray diffractometry (XRD), compressive and Vickers hardness testing were used for the characterisation and evaluation of the microstructure and mechanical properties. The in vitro cytotoxicity of the alloys was assessed using osteoblast-like SaOS2 cells. The corrosion behaviour of these alloys was evaluated by soaking the alloys in simulated body fluid (SBF) and modified minimum essential medium (MMEM) at 37 °C in a humidified atmosphere with 5% CO₂. Results indicated that the increase of the Ca content enhances the compressive strength, elastic modulus and hardness of the Mg–Ca alloys, but deteriorates the ductility, corrosion resistance and biocompatibility of the Mg–Ca alloys. The Y addition leads to an increase in the ductility; but a decrease in the compressive strength, hardness, corrosion resistance and biocompatibility of the Mg–1Ca–1Y alloy when compared to the Mg–1Ca alloy. Solutions of SBF and MMEM with the immersion of Mg–xCa and Mg–1Ca–1Y alloys show strong alkalisation. Our research results indicate that Mg–xCa alloys with Ca additions less than 1.0 wt% exhibited good biocompatibility, low corrosion rate as well as appropriate elastic modulus and strength; whilst the Y is not a proper element for Mg alloys for biomedical application due to its negative effects to the corrosion resistance and biocompatibility.     

Development of titanium alloys by the method of complex alloying

We study the effect of alloying on the mechanical properties of welded joints and base metal of titanium alloys of the system Ti-Al-Mo-V-Cr-Fe. We also formulate the theoretical aspects and principles of complex alloying of titanium alloys and the theory of alloying of additive materials for the welding of α-, (α + β), and β-alloys. It has been shown that (α + β)-(VT23) and β-(VT19) structural titanium alloys, developed on the basis of the proposed theory of complex alloying, provide high weight efficiency of construction of present-day flying vehicles. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 45–50, September–October, 2006.     

Structure and Properties of Aluminum Alloys Modified with Silicon Carbide by Laser Surface Treatment

We study the structure and properties of AA6082 and AA7075 aluminum alloys modified with particles of SiC with the help of a laser. It is shown that the wear resistance of alloys laser reinforced with SiC in the case of friction against an abrasive wheel is 30–75 times higher than for nonmodified alloys. On the basis of the data of electrochemical investigations, it is shown that, for AA7075 alloy, the influence of its structural heterogeneity on the variation of corrosion potentials decreases as the corrosion activity of the medium increases. We measured the values of corrosion currents of the surfaces of alloys in various corrosive solutions. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 3, pp. 34–40, May–June, 2005.     

Corrosion and electrochemical properties of binary cobalt and nickel alloys

The influence of pH of electrolyte on the tungsten content and current efficiency of a Co–W coating is determined. We determine the corrosion rates of Co–W and Ni–Pd alloys by the polarization resistance method and show that the coatings are classified as belonging to highly corrosion-resistant coatings. The catalytic reactivity of coatings in a model reaction of hydrogen release is assessed. Dependences of the corrosion resistance and catalytic reactivity of Co–W and Ni–Pd alloys on the contents of the components are obtained, and their character is justified. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 6, pp. 89–92, November–December, 2008.     

Influence of oxalic acid on the corrosion of VT1-0 titanium in a water-ethylene-glycol heat carrier

We present the regression-analytic and regression models aimed at the evaluation of the corrosion losses of VT1-0 titanium as a function of time and the coefficients of acceleration of corrosion depending on the concentration of oxalic acid and temperature. It is shown that, in a 66% solution of ethylene glycol, oxalic acid intensifies the process of corrosion of VT1-0 titanium for concentrations higher than 0.1% due to the formation of complexes of the products of oxidation of titanium with oxalate anions, especially at elevated temperatures. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 103–107, September–October, 2006.     

Corrosion and stress-corrosion resistance of deposited metals in hydrogen-sulfide solutions

We study the corrosion, electrochemical, and corrosion–mechanical properties of deposited KKh30N6VSR cobalt-based, NKh15SR3 nickel-based, and Kh16N8S5 iron-based alloys in a standard NACE hydrogen-sulfide solution. It is shown that the deposited Kh16N8S5 iron-based alloy is unsuitable for these conditions due to its low corrosion resistance and susceptibility to hydrogen-induced cracking. The cobalt- and nickel-based alloys are suitable for the surfacing of the components of shutoff fittings of the oil-and-gas extraction equipment. However, as far as the “operating characteristics–cost” ratio is concerned, the nickel-based alloy outweighs the cobalt- based alloy.     

Investigation of Thermodiffusion Carbonitride Coatings on Titanium Alloys

We study specific features of the processes of phase formation and gas saturation in VT1-0, VT14, OT-4, and VT20 titanium alloys held in a carbon-and-nitrogen-containing medium for 5 h at 1100°C. Depending on the type of alloy, the TiC _x N _y carbonitride phases of different compositions are formed on the metal surface under the indicated conditions. The analysis of the corrosion and electrochemical behavior of alloys shows that the best protective properties are exhibited by the carbonitrides formed on the surface of VT20 alloy (whose composition is close to equiatomic and the surface roughness is minimum). __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 4, pp. 59–65, July–August, 2005.     

Corrosion resistance of nitrided titanium alloys in aqueous solutions of hydrochloric acid

It is shown that vacuum heating prior to nitridation contributes to the formation of nitrided layers on a surface. The layers adequately protect titanium alloys from corrosion in aqueous solutions of hydrochloric acid. Moreover, vacuum heating makes it possible to perform effective nitridation at low temperatures. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 34, No. 1, pp. 108–110, January–February, 1998.     

In vitro corrosion behaviour of Ti–Nb–Sn shape memory alloys in Ringer’s physiological solution

The nearly equiatomic Ni–Ti alloy (Nitinol) has been widely employed in the medical and dental fields owing to its shape memory or superelastic properties. The main concern about the use of this alloy derives form the fact that it contains a large amount of nickel (55% by mass), which is suspected responsible for allergic, toxic and carcinogenic reactions. In this work, the in vitro corrosion behavior of two Ti–Nb–Sn shape memory alloys, Ti–16Nb–5Sn and Ti–18Nb–4Sn (mass%) has been investigated and compared with that of Nitinol. The in vitro corrosion resistance was assessed in naturally aerated Ringer’s physiological solution at 37°C by corrosion potential and electrochemical impedance spectroscopy (EIS) measurements as a function of exposure time, and potentiodynamic polarization curves. Corrosion potential values indicated that both Ni–Ti and Ti–Nb–Sn alloys undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Ti–18Nb–5Sn alloy. Significantly low anodic current density values were obtained from the polarization curves, indicating a typical passive behaviour for all investigated alloys, but Nitinol exhibited breakdown of passivity at potentials above approximately 450 mV(SCE), suggesting lower corrosion protection characteristics of its oxide film compared to the Ti–Nb–Sn alloys. EIS studies showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The obtained EIS spectra were analyzed using an equivalent electrical circuit representing a duplex structure oxide film, composed by an outer and porous layer (low resistance), and an inner barrier layer (high resistance) mainly responsible for the alloys corrosion resistance. The resistance of passive film present on the metals’ surface increases with exposure time displaying the highest values to Ti–18Nb–4Sn alloy. All these electrochemical results suggest that Ti–Nb–Sn alloys are promising materials for biomedical applications.     

Structure and properties of high-modulus alloys of the Ti-B system

We study the influence of alloying with Al, Zr, and Si on the structure and mechanical properties (including the modulus of elasticity) of cast and deformed alloys of the Ti-B system. It is shown that, by optimizing the compositions of titanium alloys subjected to combined silicoboride hardening and additionally alloyed with aluminum, it is possible to get the modulus of elasticity E as high as 160 MPa with a strength σ of 1500 MPa and a level of plasticity δ of 2–5% at room temperature. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 27–32, May–June, 2006.     

High-temperature and cyclic corrosion crack resistance of alloys of the Ti-Si-Al-Zr system

We study new alloys of the Ti-Si-Al-Zr system. It is shown that the high-temperature and cyclic corrosion crack-growth resistances of cast materials remain practically constant up to temperatures of 700–800°C and in a 3% NaCl solution (pH = 7), respectively. Annealing and quenching from the (α + β)-and β-phase regions of Ti-4Si-5Al-5Zr cast alloy lead mainly to changes in the structure of the matrix and do not improve its strength and cyclic crack-growth resistance in the investigated working media, except the increase in the threshold of corrosion fatigue after treatment from the β-region and formation of a lamellar β-matrix. The increase in the strength, plasticity, and cyclic crack-growth resistance of these alloys at room and high temperatures is attained as a result of the formation of a globular structure of the matrix and silicide phase after thermomechanical treatment with deformation of at least 90%. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 45–56, May–June, 2006.     

Corrosion behaviour of aluminium alloys in ethanol fuels

In this study, the corrosion behaviour of several aluminium alloys in ethanol fuels was investigated by immersion and polarization tests. The corrosion properties of cast aluminium alloys (Al–17wt%Si–4wt%Cu–Mg, Al–8wt%Si–3wt%Cu, Al–7wt%Si–Mg and Al–17wt%Si–4wt%Cu–Mg with a chemically deposited nickel layer) in ethanol blended gasoline fuels were examined at various ethanol and water contents and various temperatures. Electrochemical and gravimetric measurements revealed a pronounced acceleration of the corrosion process above the boiling point. Additions of water restrain the corrosion. Increasing the ethanol content and the temperature leads to a higher corrosion sensitivity of the aluminium alloys. Furthermore, the nickel layer is very protective in all tested fuels. For aluminium alloys, a theory of the corrosion process in ethanol blended gasoline fuels is proposed.     

Damages to conic specimens of titanium and aluminum alloys under impact loading

We present the results of experimental determination of the character of damage to specimens having the shape of truncated cones made of titanium VT14 and aluminum AMg6 alloys under impact loading and perform a numerical analysis of longitudinal stresses at the sites of formation of rear cleavage cracks. Translated from Problemy Prochnosti, No. 5, pp. 110–112, September–October, 1997.     

Status of the titanium production,research, and applications in the CIS

We present a survey of the research and development of titanium alloys, mill products, processes, and applications in the CIS between the tenth and eleventh Titanium World Conferences. Driven by an increased world-market demand, the titanium industry of the CIS has become an important contributor to the global expansion of titanium in volume and applications. Unfortunately, the domestic shipments of titanium and, especially of mill products, remain low because of the inadequate consumption of titanium by domestic end-users, such as aerospace, chemical, and marine (shipbuilding) industries. Although the titanium-research activity remains not as extensive as earlier, it is characterized by a certain recovery motivated by both performance-driven and cost-driven applications. In numerous cases, the studies are performed through broad international cooperation. Due to its application-oriented nature, these trends of activities are moving from academic institutions to industrial research groups. Hence, the fundamental studies of the complex nature of titanium-based materials are gradually shifted to the applied research aimed at the development and scaling up of advanced alloys, processes, and new applications. The “Titan” Interstate Association realizes an important mission by keeping the titanium industry and science in the CIS united, coherent, and cooperative despite the disintegrative political and economic trends in the countries of the former Soviet Union. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 7–20, May–June, 2008.     

Plasma coatings and their ability to protect titanium alloys against corrosion fretting-fatigue fracture

We study the influence of plasma-sprayed coatings with various chemical compositions and structures on the serviceability of Ti−5.0 Al−2.0 Zr−3.0 Sn−2.0V titanium alloy under the conditions of fretting-fatigue fracture for console specimens. It was discovered that, under the conditions of fretting fatigue, coatings made of powders of titanium and chromium carbides slightly decrease the fretting fatigue limit. Coatings made of a powder of TS-8 (α+β)-alloy, a mechanical mixture of self-fluxing alloys based on nickel (NiCrBSi), and tungsten carbides (WC) increase the endurance limit by 10–15%. At the same time, spraying with plated (Ni)−(Al₂O₃) powders increases this quantity by 40% and even more. Voltammetric investigations does not reveal any correlation between the corrosion electrochemical properties of coatings (corrosion currents and potentials) at 20°C and fretting fatigue durability in a 3% aqueous solution of sodium chloride. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 72–76, May–June, 1997.     

Spongy titanium alloyed with oxygen for the production of titanium alloys

We study the influence of alloying of spongy titanium with oxygen on the structure, mechanisms of fracture, and mechanical properties of titanium. It is shown that, within the range of concentrations 0.05–0.30%, oxygen insignificantly affects both the structure and the mechanism of fracture of cast titanium but strongly increases its strength with preservation of plasticity within the admissible range specified for standard titanium alloys of this grade. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 78–80, May–June, 2008.     

High-temperature salt and gas corrosion of refractory alloys based on nickel

We present the results of investigations of chloride corrosion and oxidation of refractory éP539 and éP99 nickel-base alloys. We established that the heat-resistance of these alloys is rather high up to a temperature of 1273 K, whereas, at a temperature of 973 K, the chloride corrosion proceeds intensively and has an intercrystalline character. Under the same kinetic conditions, the rate of chloride corrosion is greater than the rate of oxidation by two to three orders of magnitude. éP539 alloy is more resistant against chloride corrosion than éP99 alloy by a factor of 1.1–1.3, but the heat-resistance of the former is less than that of the latter by the same factor. Frantsevich Institute for Problems of Materials Technology, Ukrainian National Academy of Sciences, Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 1, pp. 87–92. January–February, 2000.