Compacted Oxide Layer Formation Under Conditions Of Limited Debris Retention At The Wear Interface During High Temperature Sliding Wear Of Superalloys

For many applications, including power generation, aerospace and the automobile industry, high temperature wear provides serious difficulties where two or more surfaces move or slide relative to one another. In aerospace, for example, demands for more powerful, efficient engines operating at ever higher temperatures, mean that conventional lubrication is no longer sufficient to prevent direct contact between metallic sliding surfaces, accelerating wear. However, one high temperature phenomenon observed to reduce metallic contact, and thus wear and friction, is the formation of 'glazes', essentially compacted oxide wear debris layers that sinter together to form wear resistant surfaces. This thesis studies the nature of wear encountered with four different combinations of Superalloys, slid together using a 'block-on-cylinder' configuration (Nimonic 80A and Incoloy MA956 as block / sample materials; Stellite 6 and Incoloy 800HT as cylinder / counterface materials) simulating car (automobile) engine 'valve-on-valve-seat' wear. Initially this study concentrates on the combined effects of sliding speed (either 0.314 m/s or 0.905 m/s, supplementing previous testing at 0.654 m/s) and temperature (between room temperature and 750°C) - by altering either or both of these variables, the nature of the wear process can be radically altered, encouraging or suppressing wear protective oxide or 'glaze' layer formation. Extensive characterisation is conducted of the 'glaze' layers during this study, using a wide range of tools including optical microscopy, SEM, EDX (spot, mapping and Autopoint), XRD (including Glancing Angle) and micro-hardness. On selected samples, TEM and STM show these 'glaze' layers to be nano-structured (nano-crystalline), with an estimated grain size of as little as 2 to 10 nm.

Superalloys are unique high-temperature materials used in gas turbine engines, which display excellent resistance to mechanical and chemical degradation. This book introduces the metallurgical principles which have guided their development. Suitable for graduate students and researchers, it includes exercises and additional resources at www.cambridge.org/9780521859042.

Corrosion, Volume 1: Metal/Environment Reactions is concerned with the subject of corrosion, with emphasis on the control of the environmental interactions of metals and alloys used as materials of construction. Corrosion is treated as a synthesis of corrosion science and corrosion engineering. This volume is comprised of nine chapters; the first of which provides an overview of the principles of corrosion and oxidation, with emphasis on the electrochemical mechanism of corrosion and how the kinetics of cathodic and anodic partial reactions control the rate of overall corrosion reaction. Attention then turns to the effects of environmental factors such as concentration, velocity, and temperature based on the assumption that either the anodic or cathodic reaction, but not both, is rate-controlling. The corrosion of ferrous and non-ferrous metals and alloys, as well as rarer and noble metals, is considered. The reader is also introduced to high-temperature corrosion and mechanical factors that affect corrosion. This book concludes with topics of electrochemistry and metallurgy relevant to corrosion, including the nature of the electrified interface between the metal and the solution; charge transfer across the interface under equilibrium and non-equilibrium conditions; overpotential and the rate of an electrode reaction; and the hydrogen evolution reaction and hydrogen absorption by ferrous alloys. This book will be of value to students as well as workers and engineers in the field of corrosion.

High temperature corrosion is a phenomenon that occurs in components that operate at very high temperatures, such as gas turbines, jet engines and industrial plants. Engineers are constantly striving to understand and prevent this type of corrosion. This book examines the latest developments in the understanding of high temperature corrosion processes and protective oxide scales and coatings. Part one looks at high temperature corrosion. Chapters cover diffusion and solid state reactions, external and internal oxidation of alloys, metal dusting corrosion, tribological degradation, hot corrosion, and oxide scales on hot-rolled steel strips. Modern techniques for analysing high temperature oxidation and corrosion are also discussed. Part two discusses methods of protection using ceramics, composites, protective oxide scales and coatings. Chapters focus on layered ternary ceramics, alumina scales, Ti-Al intermetallic compounds, metal matrix composites, chemical vapour deposited silicon carbide, nanocrystalline coatings and thermal barrier coatings. Part three provides case studies illustrating some of the challenges of high temperature corrosion to industry and how they can be overcome. Case studies include the petrochemical industry, modern incinerators and oxidation processing of electronic materials. This book is a valuable reference tool for engineers who develop heat resistant materials, mechanical engineers who design and maintain high temperature equipment and plant, and research scientists and students who study high temperature corrosion and protection of materials. Describes the latest developments in understanding high temperature corrosion Presents the latest research by the leading innovators from around the globe Case studies are provided to illustrate key points

This book presents a general view on thin surface coatings used for tribological applications and it is based on the current state of understanding. The mechanisms of friction and wear in sliding and rolling contacts of coated surfaces are described. Basic information on coating techniques, tribology and surface mechanisms is given. Based on collected experimental works information is given on the properties of thin soft coatings, such as polymer, lamellar solid and soft metal coatings; thin hard coatings, such as nitride, carbide, oxide, boride and diamond and diamond-like coatings; and multi-component and multi-layer coatings. The influence of interface layers and lubricants is highlighted. The methods available for characterization of coated surfaces and for mechanical and chemical evaluation of their tribological properties are described. Tribological evaluation methods for accelerated and field testing and the need for standardization of quality assurance procedures are discussed. A methodology for the selection of thin coatings for tribological applications is presented and knowledge based expert system approaches for coating selection are reviewed. For different application examples, the basic tribological contact mechanisms are described and the possibilities for improving their tribological properties by using surface coatings are discussed. The application examples include sliding and rolling bearings, gears, tools for cutting and forming, erosion resistant applications, magnetic recording systems and bio-medical implants.

Today's shortages of resources make the search for wear and corrosion resistant materials one of the most important tasks of the next century. Since the surface of a material is the location where any interaction occurs, it is that there the hardest requirements on the material are imposed: to be wear resistant for tools and bearings; to be corrosion resistant for turbine blades and tubes in the petrochemical industry; to be antireflecting for solar cells; to be decorative for architectural panels and to combine several of these properties in other applications. Surface engineering is the general term that incorporates all the techniques by which a surface modification can be accomplished. These techniques include both coating and modification of the surface by ion implantation and laser beam melting. In recent years a continuously growing number of these techniques were developed to the extent that it became more and more difficult to maintain an overlook and to understand which of these highly differentiated techniques might be applied to resolve a given surface engineering problem. A similar development is also occuring for surface characterization techniques. This volume contains contributions from renowned scientists and engineers to the Eurocourse the aim of which was to inform about the various techniques and to give a comprehensive survey of the latest development on this subject.