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.

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.

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 explains how to prepare nickel-base alloys for metallographic examination and identifies related processing and imaging challenges. It describes sectioning, mounting, grinding, and polishing procedures along with alternative electropolishing processes. It also provides information on etching and examines the microstructure of Nickel 200, Nickel 270, Duranickel 301, Monel 400, Monel R-405, Monel K-500, and other nickel alloys.

This article explains how to prepare precious metal test samples for metallographic examination. It discusses cutting, mounting, grinding, polishing, and etching and addresses some of the challenges of working with small, relatively soft specimens. It includes dozens of example micrographs, comparing and contrasting the microstructural features of gold, platinum, iridium, palladium, and ruthenium-base alloys. It examines pure gold, intermetallic gold compounds, gold and platinum jewelry alloys, platinum-containing shape memory alloys, and alloys consisting of platinum, aluminum, and copper.

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.

This article illustrates how objective experiments and comparisons can be used to develop surface preparation procedures for metallographic examination of structural features of metals. These procedures are classified as machining, grinding and abrasion, or polishing. The article describes the abrasion artifacts in austenitic steels, zinc, ferritic steels, and pearlitic steels, and other effects of abrasion damages, including flatness of abraded surfaces and embedding of abrasive. Different polishing damages, such as degradation of etching contrast and scratch traces, are reviewed. The article explains the final-polishing processes such as skid polishing, vibratory polishing methods, etch-attack and electromechanical polishing, and polishing with special abrasives. An overview of special polishing techniques for unusual materials such as very hard and very soft materials is provided. The article concludes with a discussion on semiautomatic preparation procedures, providing information on procedures based on the use of diamond abrasives charged in a carrier paste and in a suspension.

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.

Tool steels are prepared for metallographic examination in the same way as carbon steels with a few variations owing to hardness and alloying differences. This article explains what makes tool steels different and how to compensate for it when sectioning, mounting, grinding, polishing, and etching. It provides information and data on composition, hot working, austenitizing, tempering, and powder metal manufacturing and explains how it affects tool steel microstructure, using more than 100 detailed images.

Heat treatment of aluminum alloys is assessed by various quality-assurance methods that include metallographic examination, hardness measurements, mechanical property tests, corrosion-resistance tests, and electrical conductivity testing. The use of hardness measurements in the quality assurance of heat treated aluminum products is effectively used in conjunction with the measurement of surface electrical conductivity. This article provides a detailed discussion of the error sources in eddy-current conductivity measurements. It also presents useful information on the variation of electrical conductivity of alloy 2024 samples as a function of aging time at different isothermal holding temperatures.

This article presents the structural attributes and internal characteristics of spot welds as well as the commonly inspected imperfections in resistance welds. It describes the industrial requirements for weld quality. Commonly performed destructive evaluations, namely, manual testing, quasi-static mechanical tests, dynamic mechanical tests, and metallographic examination, are reviewed. The article reviews weld-quality monitoring using various process signals and provides a discussion on the on-line and off-line nondestructive evaluation methods of spot weld quality.

This article begins with a discussion on the advantages and limitation of ultrasonic welding (USW). It describes variations of the USW process which can produce different weld geometries. These variations are helpful in producing spot welds, line welds, continuous seam welds, ring welds, and microelectronic welds. The article provides information on the functions of USW personnel and describes the special conditions in USW which include the condition of the surface, the use of an interlayer, and the control of resonance. It concludes with a description on the weld quality, the influencing factors, surface appearance and deformation, and metallographic examination.