Efficiency of Two-Stage Ion-Plasma Process for Depositing Alloyed Diffusion Aluminide Coatings on High-Temperature Nickel Alloys

Diffusion ion-plasma coatings deposited by two-stage process in a MAP-1 installation with the use of three nickel alloys of the Ni – Cr – Al – Y system with additives of tantalum, tungsten, and rhenium, and two aluminum alloys with additives of nickel, yttrium, and silicon are considered. The structure and the chemical and phase compositions of coatings on high-temperature nickel alloys ZhS6U, ZhS26, and ZhS32 are studied depending on the thickness of the layers of the initial alloys. It is shown that the two-stage process of deposition of coatings considerably improves their service characteristics.     

Condensation and condensation-diffusion coatings for turbine blades made of high-temperature alloys with a directed crystal structure

Results of an investigation of condensation (condensed) and condensation-diffusion coatings for protecting working turbine blades made of high-temperature nickel alloys from high-temperature gas corrosion are presented. The coatings were deposited on specimens of a high-temperature model nickel alloy by the ion-plasma method.Translated from Metallovedenie i Tetmicheskaya Obrabotka Metallov, No. 4, pp. 15 – 18, April, 1996.     

Mathematical Simulation of Phase Formation and Growth in Nickel Aluminizing

A mathematical model is developed for simulating the formation and growth of phases in the diffusion of aluminum through the nickel matrix of high-temperature alloys. The kinetic laws of diffusion processes in multiphase coatings deposited from a gaseous phase by the method of circulation are determined. The suggested mathematical model is tested experimentally.     

TiAl-Nb基合金高温抗氧化研究进展

TiAl-Nb基合金具有优异的综合性能,在先进飞行器及武器等耐高温部件中有巨大的应用潜力,但其高温抗氧化性能无法满足实际使用需求。综述了TiAl-Nb基合金高温抗氧化防护方面的研究进展,包括TiAl-Nb基合金的多元合金化、表面合金化、抗氧化涂层及其抗氧化机理,通过分析不同氧化防护措施的特性,展望了TiAl-Nb基合金高温抗氧化防护的发展趋势。国内外研究结果显示,通过多元合金化方法改善合金组织,并在氧化过程中促进形成保护性Al_2O_3而抑制形成TiO_2,是提高TiAl-Nb基合金高温抗氧化性能的有效手段。利用表面合金化对合金表面的显微组织和成分进行改善,氧化时促进抗氧化性能优良的Al_2O_3或SiO_2保护膜形成,显著提高了TiAl-Nb基合金的抗氧化性能。但高温下合金化层与基体之间的Al、Si、Ti等元素的互扩散会加剧合金化层的退化,进行表面多元合金化,特别是添加微量活性元素,对促进保护性氧化膜的形成及抑制互扩散有良好效果。通过制备表面抗氧化涂层,在氧化时生成保护性氧化膜,阻碍O的内扩散,能够起到良好的高温抗氧化作用,但需要解决涂层/基体合金的结合力较差和反应扩散等问题,制备复合涂层或扩散阻挡层是解决上述问题的有效途径。     

Enhancement of magnetic texture and functional characteristics of iron-based soft magnetic alloys

It has been shown that the formation of nitride-oxide magnetically active electrically insulating coatings on ribbons of iron-based soft magnetic alloys using the method of ion-plasma deposition and subsequent magnetic annealing in an ac magnetic field leads to a substantial improvement of their static and dynamic magnetic properties.     

A Study of Coatings on High-Temperature Nickel Alloys by the Potentiodynamic Method

A potentiodynamic technique is used for studying the corrosion resistance of diffusion aluminized, alumosiliconized, and chromoaluminized condensed ion-plasma coatings and combined coatings obtained by ion-plasma sputtering with subsequent circulation aluminizing and thermovacuum treatment. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 24 – 27, June, 2005.     

Current Thoughts on Reactive Element Effects in Alumina-Forming Systems: In Memory of John Stringer

In memory of John Stringer (1934–2014), one of the leaders in studying the reactive element (RE) effects, this paper reviews the current status of understanding of the effect of RE dopants on high-temperature oxidation behavior, with an emphasis on recent research related to deploying alumina-forming alloys and coatings with optimal performance in commercial systems. In addition to the well-known interaction between indigenous sulfur and RE additions, effects have been observed with C, N, and O found in commercial alloys and coatings. While there are many similarities between alumina-forming alloys and coatings, the latter bring additional complicating factors such as the effects of O incorporation during thermal spraying MCrAlY coatings, coating roughness, and heat treatments that must be considered in optimizing the beneficial dopant addition. Analogies can be seen between RE effects in alloys and in the substrates beneath diffusion M–Al coatings. Recently, there has been more interest in the influence of mixed oxidant environments, since these may modify the manifestation of the RE effect. Finally, some thoughts are provided on optimizing the RE benefit and modeling oxidation of RE-doped alloys.     

Corrosion resistance of aluminum alloys with a titanium nitride coating

The ion-plasma method of depositing refractory coatings makes it possible to treat parts at temperatures of about 200°C. Since these temperatures correspond to aging regimes of heat-treatable high-strength aluminum alloys, it becomes possible to combine the process of deposition of a wear-resistant coating with toughening treatment of them that consists of quenching and aging. The present paper concerns results of a study of the tribotechnical properties and corrosion resistance of titanium nitride coatings deposited by the ion-plasma method on alloys D16, PV90, and 1420. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 30–32, September, 1998.     

Designing oxidation-resistant coatings

This article examines the historical development of high-temperature, oxidation- and corrosion-resistant coatings, demonstrating how diffusion surface treatments, modified diffusion coatings, the design of M-Cr-Al-X corrosion-resistant overlay coatings, and the application of thermal-barrier coatings can be used to reduce the scaling (oxidation) rate of coated components. Future trends in high-temperature coating design are also reviewed, including the custom design of corrosion-resistant alloys, smart overlay coating concepts, diffusion barriers, and the use of layered thermal-barrier coating structures. For more information, contact J.R. Nicholls, Cranfield University, School of Industrial and Manufacturing Science, Cranfield, Bedfordshire MK430AL, United Kingdom     

Development of Ion-Plasma Coatings for Protecting Intermetallic Refractory Alloys VKNA-1V and VKNA-25 in the Temperature Range of 1200 – 1250°C

Metal Science and Heat Treatment - Multilayer heat-resistant ion-plasma coatings for protecting the parts of the hot duct of gas-turbine engines produced from refractory nickel alloys based on VKNA...     

Chromized coatings obtained by spontaneously propagating high-temperature synthesis

The discovery in 1967 of the phenomenon of the propagation of the combustion front of powdered high melting chemical elements, which leads to the formation of high melting compounds, marked the beginning of the application of new technologies of hardening the surface of alloys on the basis of spontaneously propagating high-temperature synthesis (SHS). In dependence on the conditions of realizing SHS processes it is possible to obtain diffusion layers in the regime of combustion or thermal self-ignition. The article reviews these methods on the example of chrornizing of carbon steels. The microstructure, phase and chemical composition of the coatings were investigated. The obtained chrornized layers are very heat-resistant and have great microhardness.Moscow Highway Institute. Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 8–12, March, 1994.     

Formation of segregation inhomogeneity in high-temperature nickel-base alloys

The process of hardening of model high-temperature nickel alloys with additives of Nb, Mo, Ti, W is studied in a range of cooling rates typical for large castings. The rules of the segregation processes and the formation of the structure are described. It is shown that despite the low volume fraction of the eutectic component its morphology and laws of formation have a considerable effect on the structural homogeneity of the alloy. Carbide, intermetallic, and carbide-intermetallic eutectics can form in the alloys depending on the cooling conditions. The diffusion processes in crystallization of the alloys are a sign of active mass exchange between the eutectic liquid and the primary solid phases. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 19–22, February, 1999.     

An X-ray study of residual macrostresses in protective coatings for gas-turbine blades

The x-ray method is used to determine residual macrostresses in the surface layer of protective coatings on high-temperature alloys. Coatings deposited by the high-energy vacuum-plasma (HEVP) method were subjected to diffusion annealing and mechanical treatment. The calculated and experimental values of residual thermal stresses in the coatings are compared. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 30–34, November, 1997.     

Diffusion permeability of yttrium-based heat-resistant ion-plasma coatings

The diffusion permeability of yttrium-containing ion-plasma coatings on substrates made of the low-alloy chromium-based Cr–0.7V–0.17La alloy has been studied. It has been found that protective coatings of this type have a strong barrier effect on diffusion fluxes in the substrate–coating–environment system and that YCr + YCrO₃ coatings ensure the best protection of the substrates against gas saturation.     

High-Temperature Nitriding of Refractory Alloys

Processes of high-temperature internal nitriding of refractory alloys based on nickel and cobalt are described. Thermodynamic backgrounds for formation of zones of internal nitriding with optimum phase compositions in alloys containing alloying elements with different affinity for nitrogen are considered. It is shown experimentally that the structures obtained in zones of internal nitriding with segregations of stable fine nitride phases depend on the ratio of concentrations of the nitride-forming elements, on the nitriding temperature, and on the composition of the saturating atmosphere. The kinetic parameters of the process of internal nitriding and the conditions of formation of through diffusion layers are determined. It is shown experimentally that the refractory characteristics of the nitrided layers are enhanced.     

Oxidation of multicomponent two-phase alloys

The high-temperature corrosion behavior of two-phase alloys presents a number of differences compared to that of single-phase alloys. These differences are mainly a consequence of the limitations that the presence of two phases impose on the diffusion of the alloy components. In this review, it is shown that the exclusive scale formation of the more stable, slow-growing oxide is more difficult on a two-phase alloy, requiring a higher concentration of the more reactive alloy component than for a corresponding single-phase alloy. The main types of corrosion behavior for binary two-phase alloys are also considered, showing that if diffusion in the alloy is slow the scale structure will closely reflect that of the starting material. When diffusion in the alloy is not negligible, the scale structure becomes similar to what forms on single-phase alloys. The oxidation of two-phase ternary alloys is shown to be even more complex than the two-phase binary alloys. The principal added complexity compared to the binary alloys is that diffusion in the ternary alloys may also occur in the presence of two metal phases, as a result of an extra degree of freedom in the ternary system. The oxidation behavior of two-phase ternary alloys is discussed in the context of a number of recent experimental results.     

Oxidation Behavior of a High-Nb-Containing TiAl Alloy with Multilayered Thermal Barrier Coatings

Oxidation of TiAl alloys has been recognized as an obstacle for high-temperature applications such as aero engine and gas turbine. Substantial efforts have been made to improve oxidation resistance of TiAl alloys at elevated temperatures. In this study, multilayered thermal barrier coatings are prepared to protect a high-Nb-containing TiAl alloy from oxidation by air plasma spraying. The combination of Al₂O₃-13wt.%TiO₂ ceramic coatings and NiCoCrAlY metallic coatings can improve thermal stability and increase the service lifetime of coatings. The fully melted TiO₂ particles distribute in ceramic coatings uniformly and act as sealing pores and microcracks, which decrease porosity of the ceramic coatings and reduce diffusion channels of oxygen atoms. The porosity of surface and cross-section morphology are 5.5?±?0.8 and 5.1?±?0.8%, respectively. The results of oxidation experiment carried out at 800 and 900 °C for 100 h indicate that the coatings can effectively protect a high-Nb-containing TiAl alloy from oxidation. The mass gain of the high-Nb-containing TiAl alloys with coatings is lower than that of the one without coatings. The ceramic coatings retard diffusion of large amount of oxygen atoms, and bond coatings avoid to be excessively oxidized. Thus, the multilayered thermal barrier coatings exhibit an excellent long-term stability.     

Boron and phosphorus saturation of nickel coatings on titanium alloys

The use of titanium alloys for parts that operate under contact friction conditions is possible if the alloy's tribological characteristics are substantially improved. This paper concerns the investigation of technological, high-temperature, diffusion saturation with boron and phosphorus coatings on titanium alloy surfaces by the chemical precipitation of nickel.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 13 – 15, February, 1995.     

Diffusion saturation of nickel alloys with aluminum and chromium from the gas phase by the circulation method

Protective coatings on parts made of high-temperature nickel alloys increase substantially their service life and resistance to oxidation and corrosion in a high-temperature gas medium. A promising direction in this respect is the use of a gas circulation method for depositing protective coatings that envisages separated positioning of the saturated alloy and the saturating powder containing chromium, aluminum, cobalt, and other elements. Transfer of these elements to the surface of the saturated alloy occurs by means of forced circulation of the gas phase in the closed volume of the installation at a specified temperature. The present work is devoted to the problem of diffusion saturation of the surface of nickel alloys of the ZhS type with Cr and Al by the gas circulation method. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 21–25, October, 1998.     

Oxidation-resistant coatings for ultra-high-temperature refractory Mo-based alloys

The synthesis of robust coatings that provide protection against environmental attack at ultra-high temperatures is a difficult challenge. In order to achieve this goal for Mo-based alloys the fundamental concepts of reactive diffusion pathway analysis and kinetic biasing are used to design a multilayer coating with a phase sequencing that provides for structural and thermodynamic compatibility and an underlying diffusion barrier to maintain coating integrity. The coating structure evolution during high-temperature exposure facilitates a prolonged lifetime as well as a self-healing capability. Both borosilicide and aluminide coatings that can be synthesized by a pack cementation process are demonstrated to yield superior environmental resistance on Mo-based systems at temperatures up to l,700°C and can be adapted to apply to other refractory metal systems.