ECAP

ECAP, or Equal Channel Angular Pressing, is a severe plastic deformation technique used to produce bulk metallic materials with ultrafine or nanocrystalline grains. The method enables large strains to be imposed on a billet while preserving its cross-sectional area, which simplifies post-processing and handling compared with other deformation methods.

In the process, a billet is forced to flow through a die that consists of two channels of equal cross-section that intersect at an angle. The material experiences intense shear at the intersection, yet the overall cross-section remains the same. After each pass, the billet is rotated in a predefined way to accumulate additional shear. Common route patterns include A (no rotation between passes), Bc (90-degree rotation in the plane), and C (180-degree rotation), among others. The combination of passes and routes determines the total accumulated strain and the final microstructure.

ECAP can be performed at room temperature (cold ECAP) or at elevated temperatures (hot or warm ECAP) to optimize formability for different materials. It has been applied to a wide range of metals and alloys, including aluminum, copper, magnesium, titanium, steels, and nickel-based superalloys. The technique typically yields significant grain refinement, with grain sizes reduced to the submicron or even nanometer scale, leading to higher yield strength and hardness. In some cases ductility is retained or enhanced, though this depends on material and processing conditions.

Limitations include non-uniform property distribution along the billet, tooling wear from the die channels, frictional heating, and challenges in scaling up for large-scale production. ECAP remains an area of active research for optimizing grain structure, texture development, and mechanical performance in various alloys.