January 2021 - Blue Etch Anodizing of Titanium
Visual examination for defects is an essential step in evaluating the processing and manufacturing of metal products, as their presence can negatively affect overall properties, such as strength, fatigue resistance, or corrosion resistance. Some defects are identifiable on a macroscale, while others are only visible at higher magnifications after special preparation. In machined and/or polished samples, evaluation is performed in the as-prepared and etched conditions. Etching is a technique involving acids that can be used to visually highlight microstructural features, including segregation defects, that make them easier to defect and document.
Blue Etch Anodizing is an inspection procedure used for the detection of defects in titanium and titanium alloys, such as segregation, inclusions, alpha case, and porosity, among others. This test can be performed on a variety of product forms, including discs, bars, near-net shape forgings, and wire. Blue Etch Anodizing is most commonly used for products intended for aerospace, medical, and energy applications.
Inspection involves immersing the machined or polished surface in the Blue Etch Solution and then anodizing the sample. The combination of chemical treatment procedures a surface of various shades of blues and greys. These colors provide a contrast between the bulk material, appearing as a light grey or blue, versus sharper colors that highlight the defects.
Common specifications that invoke this procedure include:
AMS2642, which governs that structural examination of alpha-beta and certain alpha titanium alloys.
Manufacturer-specific documents and internal procedures