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It is based on extruding material through specially designed entry and exit channel dies to produce an ultrafine grained microstructure.
Introduction To date severe plastic deformation (SPD) processing is regarded as a new promising method of manufacturing bulk specimens having ultrafine grained (typically defined as an average grain size less than 1 µm) microstructure of superior mechanical properties in achieving strength, ductility and superplasticity [1-5] at the same time.
The SPD processed materials show not only the unique physical and mechanical properties inherent in various ultrafine grained and nanostructured materials but also a number of advantages over nanostructured materials manufactured by other methods through powder and thin film processing.
In order to optimise the control variables and obtain the ultrafine grained materials with a good quality from coarse grained materials using ECAP, it is essential to combine experimental research with a theoretical analysis of inhomogeneous deformation behaviour of the workpiece during the process.
Geometry channel angle, corner angle, workpiece (shape, length, width, thickness, radius), dies Material elasticity, yield stress, strain hardening, strain rate sensitivity, anisotropy, ductility, history, microstructure Control Variables Processing speed, friction, back pressure, temperature, pass route, number of passes, ejection Internal Parameters stress σ, strain ε, strain rate ε& , dislocation density ρ, cell size d , cell wall volume fraction f , misorientation angle θ Success geometry, microstructure, mechanical properties, homogeneity Results Failure fracture, size inaccuracy, residual stress, grain growth, low strength, low ductility, high pressing load, dies problems (wear, fracture, deformation) Fig. 2 Examples of failures in workpiece and tool.

XRD, FESEM and EDS results showed that TiC-TiB2 ceramic coating was composed of fine TiB2 platelets, TiC irregular grains, Cr metallic phase and a few Al2O3 inclusions.
As a result, at initial stage of solidification a number of TiB2 solids as the primary phases precipitate from TiC-TiB2 liquid, follwed by peritectic reaction (TiB2 + Ti → TiB) due to the presence of liquid Ti alloy, finally, a number of ultrafine TiB platelets (diameter of 0.5 to 1.5 μm and length of 2 to 5 μm) come to existence around the joint of ceramic to Ti alloy, resulting in the achievement of the ultralfine-grained microstructure in joint region and the ceramic coating nearby the joint, as shown in Fig. 4(c) and Fig. 6.
The Ti-6Al-4V substrate consists of equiaxed α and intergranular β phases; however, the heat-affected zone of Ti-6Al-4V substrate nearby the joint area shows the presaence of a number of needle-shaped grains, as shown in Fig. 4(c) and Fig. 7.
The maximum microhardness measured 25.8 ± 3.5 GPa at TiC-TiB2 coating, and high hardness of TiC-TiB2 coating is considered to benefit from the achievement of fine-grained microstructure in near-full-density ceramic coating.
The TiC-TiB2 ceramic coating was composed of a number of fine TiB2 platelets, irregular TiC grains and a few of Cr metallic binder and Al2O3 inclusions, and physical, mechanical properites showed the density, relative density, microhardness and fracture toughness of TiC-TiB2 ceramic coating reached 4.20 g · cm-3, 98.5%, 25.8 ± 3.5 GPa and 16.5 ± 2.5 MPa · m0.5, respectively, and high fracture toughness of the ceramic coating benefited mainly from a coupled toughening mechanism of crack deflection, crack bridging and pull-out by fine TiB2 platelets.

There were a lot of discontinuous grain boundaries in the as-extruded alloy GH720.
Uniform, fine and equiaxial grains were obtained during heat treatment process because the grain boundaries of GH720 were pinned by γ ' phases and growth of recrystallized grain was limited effectively.
A few small dynamically recrystallized grains had been developed along the grain boundaries in extrusion process.
A large number of dislocations got tangled up each other and the cellular substructures were formed by the dislocations glide and climb in extrusion process of GH720.
The recrystallized grains grew by grain boundary migration.

Table 1 Information of two commercial α-Al2O3 powders available from suppliers Series number Average grain size/nm Purity/wt% Supplier 1 150 99.99 TM-D,Taimei Chemicals Co.
The average grain size is determined by linear intercept method using equation 1 according to reference [10]: (1) where C, M and N is length of line, magnification and the number of intercept point, respectively.
Influence of sintering temperature on grain size of Al2O3 ceramic.
At a sintering temperature of 1250 °C, the average grain size is 1.25 µm.
The average grain size is 4.65 µm for a sintering temperature of 1400°C.

The numbers of runs for the experiments were selected using Taguchi Method considering tool rotational speed and dwell time as factors three levels for each factor.
Table.1 shows the number experiments to be carried out for the combination of three tool rotational speeds and three dwell time.
The average grain sizes of refined grains are measured by calculating the sum of grain size at random areas for grains of all parameters and finding the average of it.
Grain size measurement The areas which are subjected to grain size measurement are encircled and shown in Fig. 8.
The minimum average grain size range of 4.54 µm and maximum average grain size range of 17.59 µm was obtained 4.

An addition of BLT generally decreased grain size of the ceramics.
High purity PZT - BLT ceramics with systematic microstructural changes from equiaxed PZT-rich grains to plate-like BLT-rich grains were observed.
BLT ceramic contained plate-like grains while PZT had more equiaxed grains [3].
This was a reason the ceramic with smallest grain size (0.97PZT - 0.03BLT) showed the highest hardness value compared to those with larger grains.
Not only the number of grain boundary played an important role on hardness changes, but also the density of ceramics, i.e. 0.97PZT - 0.03BLT ceramic had the highest density.

Fig. 1 XRD pattern of TiC-TiB2 composite prepared in the experiment FESEM images and EDS results showed that a large number of randomly-orientated, fine TiB2 platelets were uniformly embedded in the irregular TiC grains, and Cr metallic phases located between TiC crystals and TiB2 crystals, moreover, a few of α-Al2O3 inclusions were also observed, as shown by the isolated black particles in Fig. 2, and some largeα-Al2O3 inclusions measured about 5 μm in diameter at surface area of the samples were observed in Fig. 3 especially.
Owing to the face-centered cubic structure, a lot of slip system exist in TiC crystal in room temperature, so the crack develop easily when the crack contact the TiC grain [5].
The compressive stress will release near the crack tip as soon as the crack contact the TiB2 grain.
However, when the crack meets the coarsened TiC grains and Al2O3 inclusions, transgranular fracture is presented, as shown by the arrow C and arrow D in Fig. 8.
XRD, FESEM results showed that the TiC-TiB2 ceramic was mainly composed of a large number of fine TiB2 platelets, irregular TiC grains, a few Cr-Al metallic phases and a few of isolated irregular α-Al2O3 inclusions.

In the given paper results of X-ray study as applied to a number of cladding tubes from Zr-based alloys, worked for several years in reactor, are presented and inhomogeneity of neutron irradiation influence on material of the tube depending on the position of considered fragment relative to lower part of tube is demonstrated.
Reasons of such inhomogeneity consist in different passing of deformation processes in α-Zr grains depending on their initial orientation, controlling operating mechanisms of grain plastic deformation, the attained degree of strain hardening and the final position of grain relative to maxima and minima in the deformation texture of tube material.
Fig. 5 shows, how parameters of X-ray reflection (0002) change for a number of α-Zr grains, responding to sections R–L and R–T in PF(0001) for samples from 2 cladding tubes.
And, when β/β0≈1, the substructure condition of grain under neutron irradiation practically does not change.
Thus, under influence of neutron irradiation initially more distorted grains, located in texture minima, become more perfect, while grains, initially less distorted, localized in texture maxima, acquire additional distortions.

A large number of theoretical works and practical studies are devoted to wear assessment issues.
Some results of studies on the wear of coated abrasives of various grain sizes and manufacturers are presented in the article. 1.
In this case, the mechanism of the coated abrasive wear will also differ from that of abrasive wheels, since there are different values of contact pressure, as well as the total number of abrasive grains in the machining interface.
The machining time (cycle) was 1 min; the number of cycles being 10.
This is due to the fact that at the time of the start of work, not all abrasive grains are grinding, but only the most protruding ones, which are the first to become dull or break out. 4.

The prior austenite grains of DQ steel remains as deformed and elongated along the rolling direction, whereas the RQ steel reveals equiaxed grain morphology due to the complete recrystallization during reheating process at 900˚C.
The effective austenite grain size of DQ-T steel is found to be slightly finer compare to RQ steel.
The prior austenite grains of DQ steel are elongated in parallel to the rolling direction, within which a large amount of deformation is present, whereas equiaxed grains morphology is observed in RQ steel.
In RQ steel, a prior austenite grain has been divided into several martensite packets, which had separated by high-angle grain boundaries (Fig. 2(b)).
For two steels after tempering, there are a large number of precipitation in the prior austenite grain boundaries and martensite lath boundaries (Fig. 2(c), (d)).