The process of grain refinement in equal-channel angular pressing

An investigation of microstructural stability in an Al-Mg alloy with submicrometer grain size

High-purity aluminum (99.99 pct) 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 BC). 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 ECA passes, the grain size was reduced further to about 1.0 µm. The populations of high-angle boundaries (≥15 deg) increased in the disorientation distribution. A texture characteristic of shear deformation of fcc 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.

An investigation of microstructure and grain-boundary evolution during ECA pressing of pure aluminum

The influence of pressing speed in equal-channel angular (ECA) pressing was investigated using samples of pure Al and an Al-1 pct Mg alloy and a range of pressing speeds from ∼10−2 to ∼10 mm s−1. The results show that the speed of pressing has no significant influence on the equilibrium grain size, at least over the range used in these experiments. Thus, the equilibrium grain sizes were ∼1.2 µm for pure Al and ∼0.5 µm for the Al-1 pct Mg alloy for all pressing conditions. However, it is shown that the nature of the microstructure is dependent on the pressing speed, because recovery occurs more easily at the slower speeds, so that the microstructure is then more equilibrated. There is also indirect evidence for the advent of frictional effects when the cross-sectional dimensions of the samples are at or below ∼5 mm.

Influence of pressing speed on microstructural development in equal-channel angular pressing

The review summarises the main methods for the preparation of nanostructured metals, alloys, semiconductors and ceramics. The formation mechanisms of nanostructures based on two different principles, viz. the assembly principle (bottom-up) and the disintegration principle (top-down), are analysed. Isolated nanoparticles, nanopowders and compact nanomaterials produced by these methods possess different properties. The scope of application of various classes of nanostructured materials is considered and the topicality of the development of nanoindustry is emphasised.

http://iopscience.iop.org/article/10.1070/RC2007v076n05ABEH003674/pdf

Nanotechnologies. Properties and applications of nanostructured materials

Mössbauer analysis of submicrometer grained iron

Deformation-induced nonequilibrium grain-boundary phase in submicrocrystalline iron

The shapes of Mossbauer spectra of coarse-grained annealed armco iron and submicrocrystalline (SMC) iron with a grain size of 0.22 μm were compared. The SMC structure was obtained from armco iron by shear under pressure and subsequent annealing at 420°C. An additional sub spectrum attributed to an interfacial component or grain-boundary phase (GBP) [1] was resolved in the spectrum of the SMC iron. The volume fraction of the GBP was estimated. It was suggested that the lattice parameter of the GBP was 1% larger (on average) than that of the crystalline component or grain phase (GP) and that substantial compressive stresses were present in the GBP. The appearance of a satellite subspectrum in fine-grained iron is associated with a jumplike change in the fundamental characteristics of a solid at a certain critical value of the lattice parameter, which continuously changes when going from the geometrical boundary toward the center of a grain.

V.A. Shabashov

Papers

Mössbauer analysis of submicrometer grained iron

Deformation-induced nonequilibrium grain-boundary phase in submicrocrystalline iron

Determination of the grain-boundary phase in submicrocrystalline iron by Mössbauer spectroscopy