The compound zone that forms on the surface of nitrided steels is often called the white layer. When the nitrided sample is sectioned through the case, and then polished and etched with a standard solution of nital (2 to 5% nitric acid and alcohol), the immediate surface etches out as white in appearance above the nitrided case. This chapter focuses on the methods to control the compound zone, or white layer. It first provides information on a test to determine the presence of the white layer, and discusses the processes involved in the reduction of the compound zone by the two-stage process. Next, it describes other methods for controlling compound zone formation, and, finally, reviews the factors related to the determination of case depth in nitriding.

Superalloys are susceptible to damage from a variety of surface contaminants. They may also require special surface finishes for subsequent processing steps such as coating applications. This chapter describes some of the cleaning and finishing procedures that have been developed for superalloys and how they work. It discusses the effect of metallic contaminants, tarnish, oxide, and scale and how they can be detected and removed. It also discusses chemical and mechanical surface finishing techniques and where they are used, and presents several application examples.

This chapter discusses the important aspects that a metallographer should understand in order to effectively reveal a microstructure. It begins by exploring etching response and how it can be a tool for revealing various microstructural features. The next part of the chapter discusses methods for revealing microstructure in the as-polished (unetched) specimen, then guidelines for selecting and using etchants when needed. The chapter discusses different types of etchants in terms of their ingredients, etching procedure, and major uses. The etchants discussed include basic etchants (nital and picral and their variations) and tint etchants for carbon and low-alloy steels and cast irons, and basic etchants for stainless steels. Finally, information is provided on different illumination methods (differential interference contrast and dark-field illumination) that can be used to highlight certain features in microstructures.

This appendix provides corrosion rate values for various grades of commercially pure and alloyed titanium. The values were derived from published sources and in-house laboratory tests. These data serve only as a starting point or initial guideline for corrosion performance.