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ECAP concept:

Equal Channel Angular Pressing (ECAP) is one of the discontinuous processes of Severe Plastic Deformation (SPD). A sketch of such a tool is depicted in Fig. 2.1. Included in Fig. 2.1 is the mathematical terms that describe the development of ??, the Shear strain.

Figure2.1: Typical ECAP tooling apparatus. [1]

The concept behind the tooling consists of two intersecting channels of the same cross section that meet at an angle 2? (see Fig.2.1). The geometry of the tooling allows for material deformation by simple shear. The cross section of the specimen remains equal before and after a processing step, thus it is possible to subject one specimen several times to ECAP in order to reach high levels of plastic deformation. A circular or squared cross section of the channel provides the possibility of a materials processing at different routes that are distinguished by their different combinations of sample rotation around the channel axes between consecutive processing steps. The processed sample will undergo some changes, mainly a distortion of grain size. Repeated processing to form smaller grain sizes breaks down the deformed grains. In addition, the unique deformation path (shearing) changes the structure of the material to make the metal respond in a unique fashion to recrystallization. It has been observed that the grain structure in ECAP material after heat treatment has been refined and is much more uniform. Grain refinement and uniformity of grain size are desirable characteristics in controlling mechanical properties of metals.”