Biomedical Engineering Reference
In-Depth Information
Figure 4.9
High-pressure torsion technique.
4.3.4
Other Severe Plastic Deformation Methods
Twist Extrusion (TE) process was developed in 1999 [4]. This process
can change the structure of materials, signiicantly improving some
of their physical and mechanical properties. TE works by extruding
a prism specimen through a matrix whose proile consists of two
prism-like regions separated by a twist passage. The extruded
material undergoes an intense shift, with the property that the inal
cross-section of the specimen is identical to the initial cross-section.
This property allows for a repeated extrusion, that accumulates the
value of deformation.
There are currently three main application areas of TE: obtaining
ultra-ine grained crystalline and nano-crystalline structures in bulk
specimens; increasing the plasticity of secondary non-ferrous metals
and alloys, which allows one to signiicantly broaden the range of
production; and obtaining bulk specimens by consolidating porous
materials which allows one to create substantially different, new
compositions with unique characteristics.
Friction Stir Processing (FSP) provides the ability to thermo-
mechanically process selective locations on the structure's surface
and to some considerable depth (>25 mm) to enhance speciic
properties.
Multi-Axial Compressions/Forgings involves the deformation of
a rectangular cross section samples through a series of compressions
so that the initial dimensions of the billet are retained. The loading
direction is changed through 90° between successive compressions.
MAG/F's are effective in producing ine grain structure, but are
