In the 9th Edition of Metals Handbook, the title of this Volume was Surface Cleaning, Finishing, and Coating; for the new ASM Handbook edition, the title has been changed to Surface Engineering. A useful working definition of the term surface engineering is “treatment of the surface and near-surface regions of a material to allow the surface to perform functions that are distinct from those functions demanded from the bulk of the material.” These surface-specific functions include protecting the bulk material from hostile environments, providing low- or high-friction contacts with other materials, serving as electronic circuit elements, and providing a particular desired appearance.
Although the surface normally cannot be made totally independent from the bulk, the demands on surface and bulk properties are often quite different. For example, in the case of a turbine blade for a high-performance jet engine, the bulk of the material must have sufficient creep resistance and fatigue strength at the service temperature to provide an acceptably safe service life. The surface of the material, on the other hand, must possess sufficient resistance to oxidation and hot corrosion under the conditions of service to achieve that same component life. In many instances, it is either more economical or absolutely necessary to select a material with the required bulk properties and specifically engineer the surface to create the required interface with the environment, rather than to find one material that has both the bulk and surface properties required to do the job. It is the purpose of this Volume to guide engineers and scientists in the selection and application of surface treatments that address a wide range of requirements.
Scope of Coverage
This Volume describes surface modifications for applications such as structural components, in which the bulk material properties are the primary consideration and the surface properties must be modified for aesthetics, oxidation resistance, hardness, or other considerations. It also provides some limited information on surface modifications for applications such as microelectronic components, in which the near-surface properties are paramount and the bulk serves mainly as a substrate for the surface material.
The techniques covered may be divided broadly into three categories:
Techniques to prepare a surface for subsequent treatment (e.g., cleaning and descaling)
Techniques to cover a surface with a material of different composition or structure (e.g., plating, painting, and coating)
Techniques to modify an existing surface topographically, chemically, or microstructurally to enhance its properties (e.g., glazing, abrasive finishing, and ion implantation)
Two significant surface-modification techniques that are not covered extensively in this Volume are conventional carburizing and nitriding. Detailed information on these processes is available in Heat Treating, Volume 4 of the ASM Handbook.
The materials that are suitable for surface engineering by the techniques addressed in this Volume include metals, semiconductors, ceramics, and polymers. Coverage of the classes of surfaces to be engineered has been broadened in this edition, reflecting the trend toward the use of new materials in many applications. Hence, this Volume provides information on topics such as high-temperature superconducting ceramics, organic-matrix composites that are substituted for metals in many automotive parts, diamond coatings that are used for either their hardness or their electronic properties, and surfaces that are implanted on medical prostheses for use in the human body. While a number of new materials and processes have been added to the coverage of this Volume, every attempt has been made to update, expand, and improve the coverage of the established surface treatments and coatings for ferrous and nonferrous metals.
In this edition, a section has been added that specifically addresses the environmental protection issues associated with the surface treatment of materials. These issues recently have become extremely important for surface treatment technology, because many surface modification processes have the potential to create major environmental problems. For some technologies, such as cadmium and chromium plating, environmental concerns have prompted intensive research efforts to devise economical alternative surface treatments to replace the more traditional but environmentally hostile methods. This Volume presents the current status of these environmental protection concerns and the efforts underway to address them. This is a rapidly developing subject, however, and many legal and technological changes can be expected during the publication life of this Volume.
Depending on the specific problem confronting an engineer or scientist, the most useful organization of a handbook on surface engineering can be by technique, by material being applied to the surface, or by substrate material being treated. The choice of an appropriate technique may be limited by such factors as chemical or thermal stability, geometrical constraints, and cost. The choice of material applied to a surface is typically dictated by the service environment in which the material will be used, the desired physical appearance of the surface, or, in the case of materials for microelectronic devices, the electrical or magnetic properties of the material. The substrate material being treated is usually chosen for its mechanical properties. Although the surface modification technique and the material being applied to the surface can be changed, in many cases, to take advantage of benefits provided by alternative techniques or coatings, the choice of a substrate material is generally inflexible. For example, if the problem confronting the materials engineer is the corrosion protection of a steel component, the most direct approach is to survey the processes that have been successfully applied to that particular base material. Once candidate processes have been identified, they can be examined in more detail to determine their suitability for the particular problem.
To serve as wide a range of needs as possible, this Volume is organized by both treatment technique and base material. Wherever possible, efforts have been made to cross-reference the technique and material sections to provide the reader with a comprehensive treatment of the subject.
The first several sections are organized by technique, covering surface cleaning, finishing, plating, chemical coating, vapor deposition, ion implantation, and diffusion treatment. The first of the process-oriented sections, “Surface Cleaning,” covers techniques for removing various types of foreign substances. In addition to the mature technologies that have been applied routinely for decades, this section describes a number of processes and innovations that have been developed recently, prompted by both technological demands and environmental concerns. The section “Finishing Methods” addresses processes used to modify the physical topography of existing surfaces. These processes also have a lengthy history, but they continue to evolve with the development of new materials and applications. New information has been added to this section on methods used to assess the characteristics of finished surfaces.
The section “Plating and Electroplating” describes processes used for electrolytic and nonelectrolytic deposition of metallic coatings. Coverage of these techniques has been significantly expanded in this edition to include a larger number of metals and alloys that can be plated onto substrate materials. This section also contains an article on electroforming, a topic that spans surface and bulk material production. The next section, “Dip, Barrier, and Chemical Conversion Coatings,” contains articles on physically applied coatings, such as paints and enamels, as well as on coatings applied by chemical reactions, which are similar in many cases to plating reactions. The final technique-related section, “Vacuum and Controlled-Atmosphere Coating and Surface Modification Processes,” covers techniques that apply coatings from the vapor and liquid phases, plus ion implantation, which modifies the composition near the surface of materials by injecting energetic atoms directly into the substrate. Several new technologies involving deposition of energetic atoms have been added to this section. Reflecting the rapid development of electronic materials applications since the last edition was published, articles have been added on processes specifically applicable to semiconductors, superconductors, metallization contacts, and dielectrics.
Following the technique-oriented sections, a new section has been added for this edition specifically to address methods for the testing and characterization of modified surfaces. This information is similar to that provided in Materials Characterization, Volume 10 of ASM Handbook, but it is extrapolated to surface-specific applications. Because of the functions performed by engineered surfaces and the limited thickness of many coatings, materials characterization techniques must be specifically tailored to obtain information relevant to these problems.
The next four sections of the book focus on then selection and application of surface modification processes for specific bulk or substrate materials. The section “Surface Engineering of Irons and Steels” is new to this edition and provides a convenient overview of applicable processes for these key materials. The articles in the section “Surface Engineering of Nonferrous Metals” provide updated information on the selection and use of surface treatments for widely used nonferrous metals. Reflecting the increased importance of a variety of materials to engineers and scientists and the integration of different classes of materials into devices, a section entitled “Surface Engineering of Selected Nonmetallic Materials” has been added to this edition.
The final section of this Volume, “Environmental Protection Issues,” deals with regulatory and compliance issues related to surface engineering of materials. In recent years, concerns about the impact of many industrial processes on local environments and the global environment have joined economic and technological questions as significant drivers of manufacturing decisions. The surface engineering industry, with its traditional reliance on toxic liquids and vapors for many processes, has been especially affected by these concerns. Environmental protection in surface engineering of materials is a rapidly developing field, and this final section attempts to assess the current status of these issues and give some bases for predicting future trends.