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Most of the materials in nature are polycrystalline materials, which contain a large number of grain boundaries and phase interfaces.
Nevertheless, as far as we know, the influence of grain boundary on the irradiation damage of iron-chromium alloy has not been reported.
It is mixed by a large number of vacancies and small number of interstitials.
Primary radiation damage near grain boundary in bcc tungsten by molecular dynamics simulations[J].
Efficient annealing of radiation damage near grain boundaries via interstitial emission[J].

GRAIN BOUNDARY PINNING BY PARTICLES Paulo R.
The free energy decrease driving grain growth is equal the decrease in grain boundary area per unit of volume, SV , times the grain boundary energy per unit of area, γ, or , γ∆SV .
No grain growth can take place if this extra free energy required to move the grain boundaries is equal or higher than the free energy change driving the grain growth.
The limiting grain radius is sometimes called the critical grain radius.
In order to see if the model expression is being used correctly one can calculate the number of particles that touch the boundary of a grain that possesses a radius equal to the limiting grain radius[3], RL Np (RL) = 1 6f . (9) Eq. 9 was derived assuming that RL = r 6f .

The grinding coefficient of cutting discs with tangential orientation of abrasive grains is 25-29% higher, than at usual discs with non-oriented grains.
The specified methods of production of abrasive tools possess a number of shortcomings.
Methodology for evaluating of the exploitation characterizations of the cutting discs It is known that the number of important operating characteristics of cutting discs include cutting ability (grinding productivity), wear (expense), effective power of cutting, surface quality of cut workpieces, their hardness and texture, maximal work speed, etc.
Radially oriented abrasive grains have sharper front angles in comparison with tangentially oriented grains.
Effective power of cutting discs with tangentially oriented abrasive grains is 4,8-4,9% lower, than at usual discs with non-oriented grains.

It is now recognized that processing by equal-channel angular pressing (ECAP) leads to very significant grain refinement in polycrystalline materials with the as-pressed grains typically having sizes within the submicrometer range.
However, despite the large numbers of experimental investigations of ECAP conducted to date, very little information is currently available on the mechanism of grain refinement.
Samples were annealed prior to pressing to give an initial grain size of ~1 mm.
For each map, the contour lines enclose areas having similar values of microhardness to within a value of 5 on the scale for Hv and the numbers on the lines represent the contours for specific values of Hv.
Ultimately, the appearance of the microstructure remains essentially unchanged with higher numbers of passes.

b) FIB notch in front of a grain boundary with a crack emitted from the notch tip passing the grain boundary.
For example the overall crack length in respect to the number of load cycles is shown in figure 4a.
Fig.4 a) Crack length as function of the number of cycles as measured and as calculated for a specimen without grain boundary.
It has to be pointed out that for the notch positioned closer to the grain boundary the crack arrested over a period of 7,500 cycles at the grain boundary until the crack overcame the grain boundary.
The crack length in respect to the number of load cycles for both cracks was used to calculate the crack growth velocity by a 5-point polynominal fit.

An elevated number of publications have shown the influence of microstructure on the wear of alumina-based ceramics, most of them focused on the role of the grain size [10-16].
Due to the large number of publications related to the doping of alumina and the influence that this factor have, it is essential an approach of this subject.
This causes a spontaneous fracture in the grain boundary for higher grains [22].
Moreover, the higher the ZrO2 amount the higher the Grain size of ZrO2 and the smaller the grain size of alumina, due to the power of drag exerted by the ZrO2 grains over the Al2O3 grains [23].
The small grains were β-Al2TiO5 particles and the higher grains were α-Al2O3 particles.

From the literature it is known that with increasing number of ECAP passes, after an initial formation of ultrafine cell boundaries, the grain size nearly remains constant, but the misorientation between the grains increases, see e.g. [15].
After ECAP deformation, irrespectively of the number of ECAP passes, the microstructure contains areas with nearly equiaxed ultrafine grains and shear bands with ultrafine elongated grains.
However, the SAD patterns show a more pronounced ring-like structure with a higher number of ECAP passes, indicating that the misorientation between the grains and therefore the fraction of high angle grain boundaries has increased.
With a higher number of ECAP passes the fraction of high angle grain boundaries increases and consequently, the cyclic stability of the UFG microstructure also increases.
TEM investigations have shown that after 4, 8 and 12 ECAP passes the grain size nearly remains unchanged, but from SAD patterns it has been concluded that the misorientation increases with a higher number of ECAP passes.

By increasing the numbers of turns in HPT, the hardness values increase to a saturation level and the gradient is removed.
As the microstructure develops from the centre to the half-radius and the peripheral areas, Figs 1(c) and (d), a small number of coarser grains was detected and generally there was a very small grain structure.
Accordingly, a uniform ultrafine-grained structure was achieved with increasing displacement from the centre of the discs and with rising numbers of HPT turns up to 5.
Furthermore, it is observed that the hardness increases as a result of increasing the numbers of HPT revolutions.
Fig. 2 Vickers microhardness across diameters of discs of ZK60 processed by for various numbers of turns of HPT.

Then, grain distribution was observed using a microscope, grain size was determined by the Jeffries and the Heyn methods, and strengthening was investigated by micro-Vickers hardness test.
The number of measurement points was more than 400. 3.
Table. 1 Average value of grain size [µm] Initial Without torsion With torsion Number of grains 81 (41) 85 (46) 126 (45) Jeffries method 59.6 57.7 49.2 Heyn method 47.3 43.3 38.3 3-2.
Table. 1 shows the average grain sizes of the specimens, which were measured by the Jeffries method and the Heyn method, and the number of grains measured was more than 100.
Here, the values in ( ) show the number of grains which are located at the boundary of the measurement area.

RESULTS AND DISCUSSION Fig. 1 shows the relation between stress (σ) and the number of cycles to fracture N for samples exposed to various aging times (tA).
At tA= 6ks, precipitates of average size 78 nm form at the grain boundary.
These dislocations increase in number as the number of repeated loading cycles increases.
Therefore, at aging times that cause the formation of many grain boundary precipitates, repeated loading results in a dramatic accumulation of dislocations in the grain boundary and grain boundary precipitates.
As tA increases to above 6ks, large scale grain boundary precipitates of around 100nm in size are formed along the grain boundary, together with a PFZ of width approximately 0.4 (µm).