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A number of literature is available dealing with the effect of RRA treatment on SCC behaviour of 7xxx series (7050, 7075, 7020 etc.) alloys [6,7].
The ageing curve displays that the peak hardness (HV10 202) is attained at about 24 h, and this is attributed to the precipitation of primarily large numbers of fine disc shaped η'(MgZn2) precipitates.
Fig. 4a shows the TEM micrograph of T6 temper, consist of a large numbers of fine η' precipitates (~5 nm) within the grains and the distribution of continuous η precipitates (~20 nm) along the grain boundary.
Fig. 4b, the TEM micrograph of the RRA temper, exhibits also fine η' precipitates (~5 nm) within the grains and the η precipitates along the grain boundary.
Fig. 7a shows a number of pits (acted as stress concentration), cracks as well that have been initiated from the base of the pits and the propagation of cracks.

The grain boundaries are well-defined and the grains are reasonably equiaxed suggesting that recrystallization took place during the extrusion at 380 oC.
Only after 1-pass ECAE, large portion of the grains were substantially refined, so that the grains became less resolved to the optical microscope.
Some elongated coarse grains with grain size above 10 µm still remained in the alloy.
A number of twins were observed within these coarse grains.
With increasing ECAE passes, the small grains were further refined, and the area fraction of coarse grains and their average grain size decreased.

Shear strain [9] (r: distance from the disc centre, N: number of turns, h: thickness of disc), was introduced through rotations for either N = 3, 10, 50 or 120 turns with a rotation speed of 1 rpm.
Vickers microhardness plotted against distance from the disc centre for Al-50%Ni sample processed by HPT for various numbers of turns.
The hardness increased with an increasing number of turns and an increasing distance from the disc centre and saturation of the hardness level at 920 Hv was attained after 50 turns.
This behaviour arises because the magnitude of strain created through HPT increases with increasing the number of turns and the distance from the disc centre.
Twinning, dislocation slip and grain boundary sliding mechanisms appear to be active under compression.

These particles are also referred to as dispersoids and are believed to impose a Zener drag on the moving grain boundary and thus reduce the grain size of a recrystallized product.
The number density along any grain boundary, determined by random line intercept measurements, is with 38 particles/100 µm the same as for the grain interior.
Recent analysis in model systems of Al-Zr showed zirconium segregating to grain boundaries and thus reducing grain boundary mobility [5, 6].
Conf. on Recrystallization and Grain Growth, B.
Conf. on Recrystallization and Grain Growth, B.

Fig. 2c demonstrates the distribution of grain boundary misorientations, by which the average grain boundary angle and the fraction of high angle grain boundary (≥15 deg) were measured.
However, the strip-like carbide may play a dominant function, because the number of strip-like carbide is obviously more than that of spherical carbide in each tempered steels.
The residual carbides pin and drag grain boundaries, by which prevent grain growth.
Therefore, it can not be seen that the number of carbide increases obviously as improving V content.
Summary (1) The prior austenite grain is refined owing to different types of carbide pinning grain boundary during austenitization.

An influence of a real structure of a grain-oriented material on a stress-strain state was shown.
According to the radiograph data the degree of the grain-orientedness, i.e. a number of grains with a specific crystallographic orientation was determined.
The festoon height in FEM of the anisotropic grain-oriented by 70% sample is greater than in FEM of the grain-oriented by 40% sample.
a – isotropic; b – anisotropic; c – anisotropic grain-oriented by 40%; d – anisotropic grain-oriented by 70% a b c d Fig. 5.
Graphs of the force value changes on the punch in the drawing process of FEM parts. a – isotropic; b – anisotropic; c – anisotropic grain-oriented by 40%; d – anisotropic grain-oriented by 70% From the shown graphs it follows that the maximum stress in the deformation of the isotropic model is higher than those of the anisotropic, anisotropic grain-oriented by 40% and by 70% models.

EBSD of the steady-state microstructures revealed strong grain refinement.
This is mainly due to the fact that such alloys contain a large number of additional elements, which may act in a complex way during hot deformation.
In particular, the behavior of solidsolution niobium atoms is questionable; in spite of their low bulk diffusion rate, Nb solutes are able to interact with grain boundaries and reduce considerably grain-boundary mobility.
This may be due to the stabilization of dislocation walls by niobium solutes (i.e., decrease of dynamic-recovery kinetics) and/or the decrease of grain-boundary mobility, because substructure is usually swept out by moving grain boundaries.
It may be attributed to the decrease of grain-boundary mobility because thermal twinning during deformation is associated with grain-boundary migration [5].

It can been seen from Fig.2 that the grain size of the web is minimum , the grain size of R -joint is biggest and the grain size of flange is in the middle.
There are coarse grains and the grain orientation confusion in R-joint.At the rolling deformation, because of difficult deformation, the amount of grain crushing is not the same,resulting in abnormal coarse grains appearing in R-joint .
Because of finer grain of web, there is much more grain boundaries than that of flange.
In engineering application of H-beam, a large number of grain boundaries continue to hinder dislocation movement.
Table 3 Average grain size number PA1 PA2 PA3 PB1 PB2 PB3 PC1 PC2 grain size number 9.6 9.3 9.1 9.8 9.6 9.0 9.8 9.2 average diameter （μm） 11.3 12.8 13.5 10.7 11.7 13.9 10.8 13.1 PC3 PD1 PD2 PD3 PE1 PE2 PE3 grain size number 9.6 9.2 9.3 9.6 9.5 9.5 9.3 average diameter （μm） 11.5 13.4 12.7 11.5 11.2 11.4 11.5 In the rolling deformation of H-beam, the deformation of R-joint is the most complex and heat stored in R-joint is the maximum .So the cooling effect of R-joint is worse than that ofthe flange webs, resulting in uneven grain size in R-joint.

With world-wide strict legislation for reduction or removal of lead from industrial waste, development of a large number of lead-free alternative solder materials had been intensively examined.
However, application of this Pb-Sn conventional solder alloy have prompted numbers of problems associated to the restrain of lead-containing substances[3].
The transport processes controlled by Al diffusion along grain boundaries as the dispersed Cr and Al nanoparticles and a great number of grain boundaries promote rapid selective oxidation for Al after oxidation, subsequent to a continuous fine-grained oxide formation.
Striking improvement in the film microstructure, in terms of the compactness, uniformity and refinement of grains was found with the addition of these additives.
(c) Gelatin with thiourea and OPPE:- smoother, more uniform, compact and finer grain, with grain size of about 3–4µm films was observed. [21] Summary Electrodeposition can be used to synthesize a large number of nanocrystalline metals, alloys, and composite materials.

The grains are stretched in the drawing direction.
Measurements and results A number of metallographic studies were carried out which confirmed that after this treatment the wire obtained an ultra-fine grain structure.
But one can see that ferrite grains crush and become smaller (see fig. 3, a).
In some grains the nanostructuring process just begins.
One can see subgrain-grain forming ending at last obtaining of ultrafine grain structure predominantly with largeangle boundaries.