Biomedical Engineering Reference
In-Depth Information
that subject the work-piece to high-accumulated strains [30]. With
increasing straining of the material, the size of both microstructural
levels decreases in size. At the same time, the disorientation —
difference in crystallographic orientation — is increasing. In order to
obtain the smallest microstructural sizes, plastic strains more than
600-800% are necessary. A number of severe plastic deformation
(SPD) methods for producing bulk ultra ine grain metals/alloys have
been developed [30, 50]. The signiicant feature of these processes
is that the external dimensions of the work-piece do not change
signiicantly during the processing.
Examples of these methods include equal channel angular
extrusion or pressing (ECAE or ECAP) [40, 50-52, 57], cyclic
extrusion compression method (CEC) [38], high pressure torsion
(HPT) [27], twist extrusion (TE) [5], friction stir processing (FSP)
[47], and multi directional forging (MDF), also known as multiaxial
compression/forging (MAC/F) [12]. In addition, there are several
methods of producing ultra ine grain sheet metals, such as
accumulative roll bonding (ARB) [48], and repeated corrugation
and straightening (RCS) [21]. From different variants of SPD
techniques, only a few have industrial potential.
4.3.1
Equal Channel Angular Pressing
Equal Channel Angular Pressing (ECAP) is one of the discontinuous
processes of severe plastic deformation. In principal, the tool consists
of two intersecting channels of the same cross section that meet at
an angle 2
α
(Fig. 4.7).
Figure 4.7
Schematic ECAE/P process.
