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High-purity aluminum (99.99 pet) was processed by equal-channel angular pressing (ECAP) at room temperature through a die with a 90 deg angle between the die channels. Samples were examined by transmission electron microscopy (TEM) and orientation imaging microscopy (OIM) methods after one, four, and 12 passes through the die. Repetitively pressed samples were rotated by 90 deg in the same sense between successive pressing operations (route Be). After one pressing, TEM showed a subgrain structure which was elongated in the shearing direction. Corresponding OIM data illustrated an inhomogeneous microstructure in which bandlike features were also aligned with the shearing direction. The lattice orientation varied from location to location in the material. The boundary disorientation distribution determined from the OIM data exhibited a peak at 2 to 5 deg, in agreement with a predominance of subgrains in the microstructure. After four pressings, the microstructure data obtained by TEM and OIM were mutually consistent. The disorientation data revealed a decrease in the population of 2 to 5 deg boundaries accompanied by an overall upward shift in the distribution. Two orientations were generally apparent in the texture, although specific orientations varied with location. Often, a (111) orientation tended to align with the shear direction. Following 12 EGA passes, the grain size was reduced further to about 1.0 fim. The populations of high-angle boundaries (^15 deg) increased in the disorientation distribution. A texture characteristic of shear deformation of fee metals became apparent, although the orientations and particular components varied with location. Microstructural refinement during severe straining includes the development of large fractions of high-angle boundaries.

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This study reports that solid-state reactions occur by the application of high-pressure torsion (HPT) to the Al-Cu system even at low homologous temperature. A bulk form of disc consisting of two separate half-discs of pure Al and pure Cu are processed by HPT at ambient temperature under a pressure of 6 GPa. X-ray diffraction analysis and high-resolution transmission electron microscopy confirm the formation of different intermetallic phases such as Al 2 Cu, AlCu and Al 4 Cu 9 , as well as the dissolution and supersaturation of Al and Cu in each matrix. It is shown that the diffusion coefficient is enhanced by 10 12-10 22 times during the HPT processing in comparison with the lattice diffusion and becomes comparable to the surface diffusion. The enhanced diffusion is attributed to the presence of a high density of lattice defects such as vacancies, dislocations and grain boundaries produced by HPT processing.

The application of friction stir processing (FSP) to a cast NiAl bronze (NAB) material is presented as a means for selective modification of the near-surface layers by converting as-cast microstructures to a wrought condition in the absence of macroscopic shape change. This may enable selective surface hardening of cast components. The complex physical metallurgy of the NAB is reviewed, and microstructure changes associated with FSP for a selected set of processing parameters are examined by optical microscopy (OM) and transmission electron microscopy (TEM) methods. Direct temperature measurement in the stir zone is infeasible and, so, these microstructure changes are used to estimate peak temperatures in the stir zone. The persistence of a Fe 3 Al phase ( ii ) indicates that peak temperatures are below the solvus for this phase, while the presence of transformation products of the ␤ phase, including fine Widmanstätten ␣, bainite, and martensite, indicates that peak temperatures exceed the eutectoid temperature for the reaction throughout the stir zone. b S a ϩ k i i i

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