Plastic deformation is one of the methods of modifying the structure
and properties of materials . In conventional deformation
techniques, the material loses its cohesion and undergoes destruction.
Torsion applied under high pressure, known as the Bridgmen method,
permits almost unlimitedly large deformation degrees . The
deformation process consists of torsion combined with compression. The
iron samples have the shape of discs. The compressive pressure was
about 5 GPa. After 5 rotations of the compressive punches, the maximum
true strain obtained was e = 10.
The structural inhomogeneity of the material thus deformed was
examined. The microhardness was measured along 10 different radii
(figure below). In the central point of the sample the microhardness
was 268HV and it increases to about 470 HV towards the sample edges.
The microhardness profiles are shown in the figure below. Optical
microscopy shows characteristic concentric circles formed during the
torsion. Electron microscopy has revealed uniaxial crystallites whose
size ranges from 100 to 300nm. The dislocation density distribution is
nonuniform both in the scale of the entire sample and in the
1. V.M.Segal, Mat.Sc.Eng. A197 (1995), p.157;
2. F.Z.Utyashev, F.U.Enikeev, V.V.Latysh, Ann.Chim.Fr. 21 (1996),