This article is a compilation of color etchants that have been developed for a limited number of metals and alloys. It describes the optical methods for producing color, such as polarized light and differential interference contrast, with illustrations. The article discusses film formation and interference techniques such as anodizing, chemical etching, and tint etching. It provides a description of reagents that deposit sulfide films and molybdate films. The article concludes with a discussion on the thermal and vapor deposition methods to produce color.

The metallographic specimen preparation process for microstructural investigations of cast iron specimens usually consists of five stages: sampling, cold or hot mounting, grinding, polishing, and etching with a suitable etchant to reveal the microstructure. This article describes the general preparation of metallographic specimens and the methods of macroscopic and microscopic examination. Usually, gray-scale (black-and-white) metallography is sufficient for microstructural analysis of cast irons. The article discusses the use of color metallography of gray irons and ductile irons. It also presents application examples of color metallography.

This article describes two contemporary approaches for preparing cast iron specimens with a wide range of phases and constituents as well as different graphite morphologies. It introduces concepts and preparation materials that enable metallographers to shorten the process while producing better, more consistent results. Recommended procedures to prepare cast irons and examples of high-alloy cast iron microstructures revealed using a variety of etchants are presented. Several etchants are used to reveal the matrix microstructure, depending on the alloy content. The article discusses the use of black and white etchants and lists the compositions of abrasion-resistant cast irons according to ASTM A532/A532M in a table.

Metallographic techniques for ductile irons are similar to those for other cast irons but more difficult than for steels, because graphite retention is a challenging task. This article presents recommended procedures to prepare ductile irons. It discusses three contemporary approaches for preparing ductile cast iron specimens with a wide range of phases and constituents as well as variations in graphite morphologies. A wide variety of matrix microstructures can be obtained in ductile irons. Examples are presented using a variety of etchants. Control of the nodularity of graphite in ductile irons is critical to their performance. The article presents details concerning the characterization of the graphite nodules.

The reflected light microscope is the most commonly used tool to study the microstructure of metals, composites, ceramics, minerals, and polymers. For the study of the microstructure of metals and alloys, light microscopy is employed in the reflected-light mode using either bright-field illumination, dark-field illumination, polarized light illumination, or differential interference contract, generally by the Nomarski technique. This article concentrates on how to reveal microstructure properly to enable the proper identification of the phases and constituents and, if needed, measuring the amount, size, and spacing of constituents, using the light optical microscope. The discussion covers the examination of microstructures using different illumination methods and includes a comparison between light optical images and scanning electron microscopy images of microstructure.

This article discusses the characterization of gray iron structures, following the sequence of structure formation, as it applies to unalloyed or low-alloyed gray iron. Austenite grains are the basic crystallographic entities of the metallic matrix in gray cast iron precipitated from the liquid melt. The article describes the macrostructure and dendrite morphology of primary austenite. Eutectoid transformation in the solid state causes the transformation of austenite to pearlite and/or ferrite, producing the as-cast structure. The article discusses the observations of the graphite and ferritic/pearlitic structure in as-cast gray iron.

Metallographic contrasting methods include various electrochemical, optical, and physical etching techniques, which in turn are enhanced by the formation of a thin transparent film on the specimen surface. This article primarily discusses etching in conjunction with light microscopy and describes several methods for film formation, namely, heat tinting, color etching, anodizing, potentiostatic etching, vapor deposition, and film deposition by sputtering. It provides information on the general procedures and precautions for etchants and reagents used in metallographic microetching, macroetching, electropolishing, chemical polishing, and other similar operations.

Metallographic analysis is primarily a collection of visual and imaging techniques that provide an insight into the background of a material or part and its behavior. Metallic specimens, both porous and pore-free, are opaque, and as a result, an optical examination must be performed on carefully prepared planar (two-dimensional) surfaces. This article discusses the preparation sequence of ferrous powders, which is normally separated into several well-defined steps: sample selection, sectioning, mounting, grinding, polishing, drying, and chemical etching and/or coating. It provides several suggestions to promote and encourage the safety of those performing metallographic preparation and analysis.

Zirconium and hafnium surfaces require cleaning and finishing for reasons such as preparation for joining, heat treatment, plating, forming, and producing final surface finishes. This article provides information on various surface treatment processes, surface soil removal, blast cleaning, chemical descaling, pickling or etching, anodizing, autoclaving, polishing, buffing, vapor phase nitriding, and electroplating. Applications of these surface treatment processes are also reviewed.

Optical metallography, one of the most common materials characterization techniques, uses visible light to magnify structural features of interest. This article discusses the use of optical methods to evaluate micro and macrostructure and relate it to process conditions and material behavior. It covers the steps involved in sample preparation, including sectioning, mounting, grinding, polishing, and etching, and presents several examples of macro and microanalysis on various metals and alloys.

This article provides information on the basic components of a light microscope, including the illumination system, collector lens, and optical and mechanical components. It describes optical performance in terms of image aberrations, resolution, and depth of field. The article discusses the examination of specimen surfaces using polarized light, phase contrast, oblique illumination, dark-field illumination, bright-field illumination, interference-contrast illumination, and phase contrast illumination. Special techniques and devices that may be used with the optical microscope, to obtain additional information, are also described. The article concludes with information on photomicroscopy and macrophotography.

This article describes the microstructure and metallographic practices used for medium- to high-carbon steels as well as for low-alloy steels. It explains the microstructural constituents of plain carbon and low-alloy steels, including ferrite, pearlite, and cementite. The article provides information on how to reveal the various constituents using proven metallographic procedures for both macrostructural and microstructural examination. Emphasis is placed on the specimen preparation procedures such as sectioning, mounting, grinding, and polishing. The article illustrates the use of proven etching techniques for plain carbon and low-alloy steels.

This article describes metallographic preparation and examination techniques for stainless steels and maraging steels. It presents a series of micrographs demonstrating microstructural features of these alloys. Procedures used to prepare stainless steels for macroscopic and microscopic examination are similar to those used for carbon, alloy, and tool steels. Cutting and grinding must be carefully executed to minimize deformation because the austenitic grades work harden readily. The high-hardness martensitic grades that contain substantial undissolved chromium carbide are difficult to polish while fully retaining the carbides. Unlike carbon, alloy, and tool steels, etching techniques are more difficult due to the high corrosion resistance of stainless steels and the various second phases that may be encountered. The microstructures of stainless steels can be quite complex. Matrix structures vary according to the type of steel, such as ferritic, austenitic, martensitic, precipitation hardenable, or duplex.

Failure analysis is an investigative process that uses visual observations of features present on a failed component fracture surface combined with component and environmental conditions to determine the root cause of a failure. The primary means of recording the conditions and features observed during a failure analysis investigation is photography. Failure analysis photographic imaging is a combination of both science and art; experience and proper imaging techniques are required to produce an accurate and meaningful fracture surface photograph. This article reviews photographic principles and techniques as applied to failure analysis, both in the field and in the laboratory. The discussion covers the processes involved in field and laboratory photographic documentations, provides a description of professional digital cameras, and gives information on photographic lighting and microscopic photography. Special techniques can be employed to deal with highly reflective conditions and are also described in this article.

This article reviews photographic principles, namely, visual examination, field photographic documentation, and laboratory photographic documentation, as applied to failure analysis and the specific techniques employed in both the field and laboratory. It provides information on the photographic equipment used in failure analysis and on film and digital photography. The article describes the basics of photography and the uses of different types of lighting in photography of a fractured surface. The article also addresses the techniques involved in macrophotography and microscopic photography as well as other special techniques.

Magnesium and its alloys are among the most difficult metals to prepare for metallographic examination. This article describes specimen preparation processes, including sectioning, mounting, grinding, and polishing. It discusses macro and microexamination techniques as well as related etching processes, including macroetching and color etching based on polarized light enhancement. The article concludes with an overview of the effects of alloying elements, including aluminum, beryllium, calcium, copper, iron, lithium, manganese, rare earth metals, silicon, silver, strontium, thorium, tin, zinc, and zirconium.

Zirconium, hafnium, and their alloys are reactive metals used in a variety of nuclear and chemical processing applications. This article describes various specimen preparation procedures for these materials, including sectioning, mounting, grinding, polishing, and etching. It reviews some examples of the microstructure and examination for zircaloy alloys, hafnium, zirconium, and bimetallic forms.

This article discusses the specimen preparation of three types of cast and wrought heat-resistant alloys: iron-base, nickel-base, and cobalt-base. Specimen preparation involves sectioning, mounting, grinding, polishing, and etching. The article illustrates the microstructural constituents of cast and wrought heat-resistant alloys. It describes the identification of ferrite by magnetic etching. The transmission electron microscopy examination of the fine strengthening phases in wrought alloys and bulk extraction in heat-resistant alloys are included. The article also reviews the gamma prime phase, gamma double prime phase, eta phase, laves phase, sigma phase, mu phase, and chi phase in wrought heat-resistant alloys.

This article focuses on the metallography and microstructures of wrought and cast aluminum and aluminum alloys. It describes the role of major alloying elements and their effect on phase formation and the morphologies of constituents formed by liquid-solid and/or solid-state transformations. The article also describes specimen preparation procedures and examines the microstructure of several alloy samples.

This article describes the various steps involved in image analysis, including sample selection and preparation, image preprocessing, measurement, and data analysis and output. It reviews various types of image analyzers and explains how operator bias and poor sample selection and preparation practices can lead to measurement error. It also examines several applications, illustrating how microstructural measurements can be used to assess quality control and better understand how processing changes affect microstructure and, in turn, material properties and behavior.