This article provides a discussion on the metallographic techniques used for failure analysis, and on fracture examination in materials, with illustrations. It discusses various metallographic specimen preparation techniques, namely, sectioning, mounting, grinding, polishing, and electrolytic polishing. The article also describes the microstructure examination of various materials, with emphasis on failure analysis, and concludes with information on the examination of replicas with light microscopy.

Metallographic examination is one of the most important procedures used by metallurgists in failure analysis. Typically, the light microscope (LM) is used to assess the nature of the material microstructure and its influence on the failure mechanism. Microstructural examination can be performed with the scanning electron microscope (SEM) over the same magnification range as the LM, but examination with the latter is more efficient. This article describes the major operations in the preparation of metallographic specimens, namely sectioning, mounting, grinding, polishing, and etching. The influence of microstructures on the failure of a material is discussed and examples of such work are given to illustrate the value of light microscopy. In addition, information on heat-treatment-related failures, fabrication-/machining-related failures, and service failures is provided, with examples created using light microscopy.

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.

This article commences with a discussion on the characteristics of stress-corrosion cracking (SCC) and describes crack initiation and propagation during SCC. It reviews the various mechanisms of SCC and addresses electrochemical and stress-sorption theories. The article explains the SCC, which occurs due to welding, metalworking process, and stress concentration, including options for investigation and corrective measures. It describes the sources of stresses in service and the effect of composition and metal structure on the susceptibility of SCC. The article provides information on specific ions and substances, service environments, and preservice environments responsible for SCC. It details the analysis of SCC failures, which include on-site examination, sampling, observation of fracture surface characteristics, macroscopic examination, microscopic examination, chemical analysis, metallographic analysis, and simulated-service tests. It provides case studies for the analysis of SCC service failures and their occurrence in steels, stainless steels, and commercial alloys of aluminum, copper, magnesium, and titanium.

Powder forging is an extension of the conventional press and sinter powder metallurgy process, which is recognized as an effective technology for producing a variety of parts to net or near-net shape. This article focuses on the material considerations, such as powder characteristics, alloy development, and inclusion assessment; and process considerations, such as process stages, tool design, and secondary operations; of ferrous alloy powder forging. The mechanical properties of powder forged materials are also reviewed. The article discusses the quality assurance tests for powder forged materials: the part dimensions and surface finish measurement, magnetic particle inspection, metallographic analysis, and nondestructive testing. It concludes with a discussion on the applications of powder forged parts with examples.

This article describes the sectioning process, some general practices, common tools, and guidelines on how to select a cutting tool for a given metallographic sectioning operation. It provides a discussion on the consumable-abrasive cutting and nonconsumable-abrasive cutting methods for metallographic sectioning. Other methods, including the use of hacksaws, shears, burning torches, wire saws, and electrical discharge machining, are also reviewed. The article reviews the issues related to the specimen test location for certification work as well as process troubleshooting and component failure analysis.

Metallographic examination is a critical step in the assessment of thermal spray coating characteristics. This article discusses the major steps involved in metallographic examination: sectioning, mounting, grinding, polishing, optical microscopy, and image analysis. It provides a discussion on etching to reveal grain structure. The article also provides recommendations for metallographic examination of some standard coatings.

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.

Examination of a damaged component involves a chain of activities that, first and foremost, requires good observation and documentation. Following receipt and documentation, the features of damage can be recorded and their cause(s) investigated, as this article briefly describes, for typical types of damage experienced for metallic components. This article discusses the processes involved in visual or macroscopic examination of damaged material; the interpretation of fracture features, corrosion, and wear damage features; and the analysis of base material composition. It covers the processes involved in the selection of metallurgical samples, the preparation and examination of metallographic specimens in failure analysis, and the analysis and interpretation of microstructures. Examination and evaluation of polymers and ceramic materials in failure analysis are also briefly discussed.

This article outlines the basic steps to be followed and the range of techniques available for failure analysis, namely, background data assembling, visual examination, microfractography, chemical analysis, metallographic examination, electron microscopy, electron microprobe analysis, X-ray techniques, and simulations. It also describes the steps for analyzing the data, preparing the report, preservation of evidence, and follow-up on recommendations.

This article focuses on the visual or macroscopic examination of damaged materials and interpretation of damage and fracture features. Analytical tools available for evaluations of corrosion and wear damage features include energy dispersive spectroscopy, electron probe microanalysis, Auger electron spectroscopy, secondary ion mass spectroscopy, and X-ray powder diffraction. The article discusses the analysis and interpretation of base material composition and microstructures. Preparation and examination of metallographic specimens in failure analysis are also discussed. The article concludes with a review of the evaluation of polymers and ceramic materials in failure analysis.

Microstructural analysis of specialized types of magnetic materials is centered on the examination of optical, electron, and scanning probe metallographic techniques unique to magnetic materials. This article provides a comprehensive overview of magnetic materials, their characteristics and sample preparation procedures. It reviews the methods pertaining to the microstructural examination of bulk magnetic materials, including microscopy techniques specified to magnetic materials characterization, with specific examples. The techniques used in the study of magnetic domain structures (microstructure) include the magneto-optical Kerr method, the Faraday method, the Bitter technique, scanning electron microscopy (magnetic contrast Types I and II), scanning electron microscopy with polarization analysis, Lorentz transmission electron microscopy, and magnetic force microscopy. The article also illustrates the microstructure of different types of soft magnetic material and permanent magnets.

This article describes the methods and equipments involved in the preparation of specimens for examination by light optical microscopy, scanning electron microscopy, electron microprobe analysis for microindentation hardness testing, and for quantification of microstructural parameters, either manually or by the use of image analyzers. Preparation of metallographic specimens generally requires five major operations: sectioning, mounting, grinding, chemical polishing, and etching. The article provides information on the principles of technique selection in mechanical polishing, and describes the procedures, advantages, and disadvantages of electrolytic and chemical polishing. It also provides a detailed account of procedures, precautions, and composition for preparation and handling of etchants.

Proper sectioning of the surface to be examined is a very important step in preparing steel specimens. The first step in preventing damage to the metallurgical structure is to minimize the amount of sectioning that is done. This article discusses the various metallographic techniques, namely mounting, grinding, polishing, and etching involved in the microstructural analysis of carbon and alloy steels, case hardening steels, cast iron, ferrous powder metallurgy alloys, wrought and cast stainless steels, tool materials, steel castings, iron-chromium-nickel heat-resistant casting alloys and different product forms of steels.

This article describes the methods and equipments involved in the preparation of specimens for examination by light optical microscopy, scanning electron microscopy, electron microprobe analysis for microindentation hardness testing, and for quantification of microstructural parameters, either manually or by the use of image analyzers. Preparation of metallographic specimens generally requires five major operations: sectioning, mounting, grinding, chemical polishing, and etching. The article provides information on the principles of technique selection in mechanical polishing, and describes the procedures, advantages, and disadvantages of electrolytic and chemical polishing. It also provides a detailed account of procedures, precautions, and composition for preparation and handling of etchants.

Proper sectioning of the surface to be examined is a very important step in preparing steel specimens. The first step in preventing damage to the metallurgical structure is to minimize the amount of sectioning that is done. This article discusses the various metallographic techniques, namely mounting, grinding, polishing, and etching involved in the microstructural analysis of carbon and alloy steels, case hardening steels, cast iron, ferrous powder metallurgy alloys, wrought and cast stainless steels, tool materials, steel castings, iron-chromium-nickel heat-resistant casting alloys and different product forms of steels.

Pitting is a form of localized corrosion that is often a concern in applications involving passivating metals and alloys in aggressive environments. This article describes the test methods for pitting corrosion. These methods include ASTM G 48, ASTM F 746, ASTM G 61, ASTM G 100, and electrochemical noise measurements. The visual examination, metallographic examination, and nondestructive inspection of pits are discussed. The article reviews the procedures for the use of standard charts, metal penetration, statistical analysis, and loss in mechanical properties to quantify the severity of pitting damage.

Plastic deformation of one or both metals is required to obtain bonding in cold welding. This article presents a theoretical model, to explain the bond strength, based on metallographic studies and continuum mechanical analysis of the local plastic deformation in the weld interface. It describes the bonding mechanisms, with illustrations. The article discusses the alternative methods of surface preparation and quality control of the weld interface of a cold weld. It concludes with a description of a variety of metal-forming processes suitable for production of cold welds, namely, rolling, indentation, butt welding, extrusion, and shear welding.

This article discusses the advantages and disadvantages of field metallography and describes the important material characteristics and other aspects to be considered before performing any metallographic procedure. It investigates the various stages of sample preparation in the metallographic laboratory: grinding, polishing, etching, preparing a replica, and obtaining a small sample. The article also illustrates the applications of field metallography with case studies.

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.