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.     

Structure and properties of electric-spark alloyed TiN,TiB<Subscript>2</Subscript>, and Mo coatings on VT22 titanium alloy and their transformation under light-thermal treatment

We have established that electric-spark alloyed TiN, TiB₂, and Mo coatings improve substantially the tribotechnical characteristics of VT22 titanium alloy. It has been shown that an increase in the slip velocity from 1.0 to 10 m/sec increases the wear intensity and friction coefficient by a factor of 1.5–2 and 1.3, respectively. A significant amount of oxides in the coatings and their additional alloying with titanium after treatment by concentrated solar radiation favor a 3–4 times increase in the layer thickness but lower its tribotechnical properties.     

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.     

Fatigue characteristics of VT22 titanium alloy with wear-resistant coatings

We study the influence of wear-resistant gas-thermal plasma and ion-plasma nitride coatings, diffusive electrochemical treatment, and vacuum nitriding on the fatigue resistance of specimens made of VT22 titanium alloy. The experimental results demonstrate that the wear-resistant hard coatings decrease the fatigue limit, whereas the procedure of sand-blasting increases the fatigue resistance of the alloy. Unlike diffusive coatings, plasma coatings suffer cracking and exfoliate from the surface of titanium alloy, which reveals their insufficient adhesion and high stiffness. The obtained results are quite urgent for the aircraft industry, where the VT22 alloy is extensively used. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 119–122, November–December, 2006.     

Processing and properties of titanium–titanium boride (TiB<Subscript>w</Subscript>) matrix composites—a review

Although titanium (Ti) alloys possess desirable properties such as specific strength, corrosion resistance and low density, their low specific stiffness and wear resistance have restricted their widespread application. Recently, composite strategies have provided means for overcoming these limitations. Titanium boride (TiB_w) in-situ whisker reinforcements are currently recognized as one of the most compatible and effective reinforcements for Ti. This paper provides an overview of recent activities in this evolving area of Ti–TiB composites, covering processing, properties and potential applications.     

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.     

Tribological properties of carbonitride coatings formed on titanium by thermodiffusion carbonitriding

We have studied the tribological properties of VT14 titanium alloy with carbonitride coatings formed by the contact and noncontact method and binary (oxide and nitride) coatings. In the case of the contact method, specimens are saturated in a graphite backfill, and in the case of the noncontact method, specimens are located above it. We have investigated the wear resistance of a “titanium disk–bronze block” friction pair in AMH-10 hydraulic fluid under a load to 3 MPa on a friction path to 15 km. It has been established that coatings based on ternary interstitial compounds (titanium carbonitrides) provide a higher wear resistance than that of coatings based on binary interstitial compounds (titanium nitrides and oxides).     

Studies on the properties of high-velocity oxy-fuel thermal spray coatings for higher temperature applications

Materials operating at high temperatures in corrosive media suffer erosion-corrosion wear, oxidation, and hot corrosion. Among various methods used for the protection of the surfaces against degradation, we can especially mention the technology of application of coatings by high-velocity oxy-fuel spraying, which gives coatings which high strength and hardness, low (less than 1%) porosity, and high erosion-corrosion and wear resistances. The characteristics of the coatings and their protective properties are presented. The role of some high-velocity oxy-fuel coatings in the protection of metals and alloys against degradation at high temperatures in various media is demonstrated. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 6, pp. 80–95, November–December, 2005.     

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.     

钛合金激光熔覆的研究现状与发展趋势

钛合金具有高比强、良好的耐蚀性能等优点,但其耐磨性差,限制了它在摩擦机构的应用.激光熔覆技术是近年来发展起来的一种新型表面改性工艺.在钛合金表面进行激光熔覆,可提高钛合金的表面性能,获得高硬度、耐磨性能好、低摩擦系数的熔覆层.简要阐述了钛合金表面激光熔覆的研究现状,包括激光熔覆工艺、熔覆层的组织与性能,指出了存在的问题,并展望了钛合金激光熔覆的发展方向.     

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.     

Effect of yttrium additions on the properties of grain-refined Mg–3%Nd alloy

A systematic study was carried out to evaluate the effect of up to 2.5% yttrium additions on the properties of Mg–3%Nd alloy designated for high-temperature gravity casting applications. All the tested alloys were grain-refined by zirconium. The results show that additions of yttrium significantly improved the tensile yield strength, fatigue strength, and creep resistance while reducing the ductility. However, other properties such as the ultimate tensile strength and corrosion resistance in 5% NaCl solution were nearly not affected. The strengthening effect obtained by the yttrium additions is explained in terms of solid-solution strengthening and due to formation of a ternary phase of Mg–Nd–Y. The improved creep resistance was due to the large solubility of yttrium in solid-solution magnesium matrix and to the effective creep deformation barriers created by the ternary phase. The casting performance of the tested alloys in terms of fluidity was similar and no significant effect of the yttrium was evident     

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.     

微弧氧化处理对多孔Ti-15Mo合金显微结构、耐磨性和耐蚀性的影响

在铝酸盐电解液中对多孔Ti-15Mo合金进行微弧氧化表面改性。利用SEM和XRD研究多孔合金微弧氧化涂层的显微结构和相组成。采用显微硬度计、动电位极化曲线和球-盘摩擦磨损仪分析微弧氧化处理对多孔Ti-15Mo合金硬度、耐蚀性和耐磨性的影响。结果表明,微弧氧化处理未改变多孔Ti-15Mo合金原有的孔隙率和孔径,在合金表面和孔隙内壁呈现典型的粗糙多孔微弧氧化形貌。微弧氧化涂层主要由金红石TiO_2和Al_2TiO_5相组成。经微弧氧化处理后,多孔Ti-15Mo合金的表面显微硬度提高了32%,摩擦系数降低了近50%,磨损率大幅度下降,磨损机制由磨粒磨损转变为粘着磨损。微弧氧化处理后多孔Ti-15Mo合金的耐蚀性较基体提高了近1个数量级,微弧氧化陶瓷涂层的保护效率高达90.78%。     

Study of nanocrystalline plasma electrolytic carbonitriding for CP-Ti

Commercially pure titanium is subjected to carbonitriding according to a new procedure called plasma electrolytic carbonitriding. The influence of voltage and time on the thickness of carbonitrided layers is investigated. The kinetics of growth of the layers is analyzed according to their thickness and microhardness. The coatings formed on the titanium substrate are multilayer. They are formed by a combination of TiN, TiO₂, and the α-phase in the form of inclusions of high concentrations of nitrogen and carbon in a close-packed hexagonal crystal lattice of titanium. All layers are very hard with hardnesses varying from 1100 (Vickers-Knoop hardness) for the TiN layer and 900 for the α-phase to 250 for the nonmodified surface. There exist strong metallic bonds between the layers of the coating. The time dependence of the form t ^1/2 is established for the diffusion of nitrogen and carbon in the outer layers. The results of wear tests reveal that the mass losses of carbonitrided samples become 4–17 times lower than for the intact samples. Thus, the procedure of plasma electrolytic carbonitriding enables one to get highly efficient stable coatings on titanium. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 36–42, November–December, 2007.     

Effect of laser microalloying with niobium on the wear resistance of stainless steels

We have studied the effect of laser alloying of 20Kh13 and 12Kh18N10T steels with niobium on their physicochemical properties. Microalloyed surface layers of thickness more than 350 μm, enriched with niobium, carbon, and oxygen in the solid solution and separate oxycarbide inclusions, were formed by means of laser treatment. The microhardness of the external layers of steels becomes 2–3 times higher (up to 7.1–7.7 GPa). Laser alloying reduces the wear of 20Kh13 steel by a factor of 5–6 under a contact pressure of 0.29 MPa and cuts it in half under 0.42 MPa. The wear of 12Kh18N10T steel is reduced by a factor of 2–3. We have also proposed a scheme of the wear of steels, according to which their wear resistance increases owing to the formation of hardened surface layers, where the oxycarbide inclusions exert a reinforcing action on the more plastic solid solution of niobium, carbon, and oxygen in iron.     

Hydrogen content in titanium and a titanium–zirconium alloy after acid etching

Dental implant alloys made from titanium and zirconium are known for their high mechanical strength, fracture toughness and corrosion resistance in comparison with commercially pure titanium. The aim of the study was to investigate possible differences in the surface chemistry and/or surface topography of titanium and titanium–zirconium surfaces after sand blasting and acid etching. The two surfaces were compared by X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, scanning electron microscopy and profilometry.The 1.9 times greater surface hydrogen concentration of titanium zirconium compared to titanium was found to be the major difference between the two materials. Zirconium appeared to enhance hydride formation on titanium alloys when etched in acid. Surface topography revealed significant differences on the micro and nanoscale. Surface roughness was increased significantly (p < 0.01) on the titanium–zirconium alloy. High-resolution images showed nanostructures only present on titanium zirconium.     

Mechanical characterization of anti-infectious,anti-allergic,and bioactive coatings on orthopedic implant surfaces

In total joint replacement much effort has been made to reduce implant loosening. We investigated different implant coatings (copper integrated titanium dioxide (TiO₂–Cu), titanium nitride (TiN), plasma polymerized allylamine (PPAAm), and calcium phosphate (CaP)) regarding the adhesion strength and wear resistance. Standardized scratch and adhesive tests were applied. Abrasive wear was measured with artificial bone and bone cement using a special testing machine. All tested coatings have higher bonding strengths than the 22 N/mm² required for medical implant surface coatings by ASTM standard 4711-F. Using bone cement, wear testing revealed higher wear rates in most cases. Polished surfaces reduce the amount of wear, whereas rough surfaces highly increase the wear rate due to three-body wear, especially ceramic surfaces. In general, the application of bone cement in conjunction with modified implant surfaces can lead to an increase in wear rate.     

微弧氧化处理对多孔Ti-15Mo合金显微结构、耐磨性和耐蚀性的影响

在铝酸盐电解液中对多孔Ti-15Mo舍金进行微弧氧化表面改性.利用SEM和XRD研究多孔舍金微弧氧化涂层的显微结构和相组成.采用显微硬度计、动电位极化曲线和球-盘摩擦磨损仪分析微弧氧化处理对多孔Ti-15Mo合金硬度、耐蚀性和耐磨性的影响.结果表明,微弧氧化处理未改变多孔Ti-15Mo合金原有的孔隙率和孔径,在合金表面和孔隙内壁呈现典型的粗糙多孔微弧氧化形貌.微弧氧化涂层主要由金红石TiO2和Al2TiO5相组成.经微弧氧化处理后,多孔Ti-15Mo合金的表面显微硬度提高了32％,摩擦系数降低了近50％,磨损率大幅度下降,磨损机制由磨粒磨损转变为粘着磨损.微弧氧化处理后多孔Ti-15Mo合金的耐蚀性较基体提高了近1个数量级,微弧氧化陶瓷涂层的保护效率高达90.78％.     

FACTORS CONTROLLING THE FATIGUE STRENGTH OF NITRIDED TITANIUM

Abstract— The factors affecting the fatigue strength of nitrided titanium were clarified. The fatigue strength depended strongly on the fracture strength of the compound layer formed on the surface by nitriding. We found a Hall-Petch relationship between the fatigue strength of nitrided titanium and the grain size. The findings indicated that the reduction in the fatigue strength by nitriding results from both the formation of the compound layer possessing low fracture strength and grain growth occurring from ordinary nitriding. Furthermore, low-temperature nitriding (620°C, 24 h) was proposed to suppress grain growth. This treatment method improved not only the wear resistance and the corrosion resistance but also the fatigue strength of titanium.