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Many fine particles were observed at the grain boundary fracture surface.
The maximum hardness number (near 640 HV) of the different specimens was observed to be similar, regardless of the aging temperature, but the time required to reach peak hardness increased with decreasing temperature.
Discussion Embrittlement and De-Embrittlement of the Grain Boundary.
The fracture surface showed typical grain boundary facets.
This grain boundary embrittlement is due to the precipitation of η-Ni3Ti phase at the prior austenite grain boundaries.

In [38] the segregation effect for the grain boundary impurity diffusion problem was investigated for the case of an open grain model where the grains are represented by parallel slabs.
In the present paper, we analyse the GB impurity diffusion problem for the closed grain model where the grains are assumed to have a cubic shape.
The segregation effect in the cubic grain model is analysed and compared with the simple parallel slab grain model.
(14) This critical value is the same for both parallel slab grain boundaries and closed grains models.
There have been a number of attempts to develop suitable closed grain models, such as the cubic grain model introduced by Suzuoka [45], the spherical grain model developed by Bokstein and colleagues in [43], the Levine-MacCallum model for polycrystals [46].

The temperature of ECAP not only governs the grain size and misorientation angles of grain boundaries but also the volume fraction of precipitates, thus affecting the probability of twinning and grain growth after fatigue treatment.
Misorientation Number of Misorientations Angle (deg) 0 100 200 300 400 5.4 10.9 16.4 21.9 27.4 32.9 38.4 43.9 49.4 54.9 60.4 65.9 71.4 76.9 82.4 87.9 Misorientation Number of Misorientations Angle (deg) 0 100 200 300 400 5.4 10.9 16.4 21.9 27.4 32.9 38.4 43.9 49.4 54.9 60.4 65.9 71.4 76.9 82.4 87.9 Misorientation Number of Misorientations Angle (deg) 0 100 200 300 400 5.4 10.9 16.4 21.9 27.4 32.9 38.4 43.9 49.4 54.9 60.4 65.9 71.4 76.9 82.4 87.9 (a) (b) (c) (d) Fig.2.
The stress amplitude as function of the number of cycles for the АМ60 alloy ECAPed at different temperatures For the sake of comparison, Fig. 4 shows in addition the published data of the fatigue endurance limit of an Mg alloy with a similar composition (Al 3.8-5.0, Zn 0.8-1.5, Mn 0.3-0.7) and with mean grain sizes of 7 µm and 15 µm [8].
It should be noted that a considerable increase in the dislocation density and the number of twins is observed after the fatigue tests.
Misorientation Number of Misorientations Angle (deg) 0 100 200 300 400 500 5.7 11.3 16.9 22.5 28.1 33.7 39.3 44.9 50.4 56.0 61.6 67.2 72.8 78.4 84.0 89.6 Misorientation Number of Misorientations Angle (deg) 0 100 200 300 400 500 5.4 11.0 16.6 22.2 27.8 33.4 39.0 44.6 50.3 55.9 61.5 67.1 72.7 78.3 83.9 89.5 Misorientation Number of Misorientations Angle (deg) 0 100 200 300 400 500 3.9 9.6 15.3 21.0 26.7 32.4 38.1 43.8 49.5 55.2 60.9 66.6 72.3 78.0 83.7 89.4 (a) σmax= 80 MPa (b) σmax= 90 MPa (c) σmax= 110 MPa (d) σmax= 120 MPa Fig.7.

According to the results, the original <10 1 0> fiber texture of the extruded AZ61 alloy became disintegrated and a new texture progressively developed with increase in number of ECAP pressing.
The effect of grain size strengthening was examined in the ECAPed Mg alloys with different grain size but with a very similar texture.
An image analysis program of Matrox Inspector 2.2 was used to determine the grain size distribution and mean grain size from optical micrographs.
This ineffectiveness of grain-size reduction on strength agrees well with Mukai et.
Summary Texture modification during ECAP has a great influence on the strength of Mg alloys because HCP metals have limited number of slip systems.

The influence of the variation of different parameters on calculated grain structure is shown.
They determine the number of possible generated nucleuses in the surface and bulk areas.
Increasing the range of ∆Tmax parameter for the bulk the distribution range is wide and the numbers of new grains drastically arise.
The smaller values of surface nucleation parameters as well as the thickness of surface area bring smaller number of grains generated at the borders and finally thinner chill zone.
It results in a smaller central zone, because a lower number of grains arose.

The grain size on the rolling surface after cold rolling slightly increases, accompanied a certain stretch, but microstructure on the cross section formed fibrous feature, and the greater of the deformation implemented, the fuzzier of the grain boundaries and more slender of the grain become.
However, a large number of lath martensite appeared after the heating temperature went to 850°C, and the microstructure was found to be fully martensite after the sample was quenched from 950℃.
However, the austenitic grain size decreases when the sample was reheated after double cold rolling, and the austenitic grain size decreases with the increase of deformation degree, but the austenite grain refinement comes to be indistinctive when the deformation amount increases to a certain extent.
Ultra-refinement of austenitic grains in low-carbon structural steel [J].
Method of Prior Austenite Grain Refining Using Induction Hardening[J].

In a number of cases literature data for pure copper and magnesium alloys are cited.
Superplasticity It is known that coarse-grained materials with the grain size over 10 μm do not exhibit characteristics of superplasticity [22].
The view of the samples of the magnesium alloy ZK 60 processed by ECAP with the number of passes n equal to 1, 2, 3, 4, 6, shown after tension to failure to 1500, 3050, 2130, 2100, 930 %, correspondingly (Т= 473 К, ε =10-4s-1).
In spite of a significant number of publications on the properties of NSM, the tribological behaviour, the mechanisms of friction and wear for such materials have been studied poorly.
Until very recently, they have been inconsiderable in number due to difficulties in synthesis of macroscopic samples suitable for testing.

Control of the prior austenite grain size by the dispersion of inclusions has been optimized only by experiments thus far, and no quantitative analysis has been offered on the effects of the kind, number and size of the dispersed particles for pinning austenite grains.
The two lattices are superposed, so that each FD cell contains the same number of MC cells.
The correlation between MCS and real time is defined in each FD cell by its temperature, and thereby the number of MC steps in a given FD time increment is given to each FD cell, while the correlation is the same throughout the FD cell of interest.
Grain size D during grain growth simulation using MC !!
The grain growth near the fusion boundary simulated well in the model result and the decrease in grain size with increasing distance from the fusion boundary as well, although the twins in austenite grains seen in Fig. 3(a) makes it rather difficult to compare the exact grain size between the two figures.

Composition of the investigated steel a) b) c) Figure 1. a) Image quality map of the grain investigated, b) phase map of the same grain, c) Phase map of the same grain but at higher magnification showing the formation of α’ martensite at the intersection between ε bands For the sake of brevity, the results of this study will be illustrated with reference to one representative grain, illustrated in Fig. 1.
The observations made on this grain are generally representative of the results found for the 10 grains analyzed from this sample.
One way to reduce the number of arbitrary cut-offs in this method is to turn to experimental results that support the fact that not all 6 α’ variants are equally likely to form in a single ε-martensite plate.
We have found this to be true for all the grains analyzed in this sample.
This direction is readily known when the two intersecting epsilon variants are known and reduces the total number of α’ variants from 6 per ε-plate to only 2 per ε-plate.

During annealing at temperatures from 800 to 1000 °C, a large number of equiaxed grains as fine as few hundreds of microns were found embedding in the matrix; the recrystallized grains stay quite stable and show minor dependence on annealing temperature and time.
After being heated to 1200 °C for extended time, abnormal grain growth took place and resulted in bimodal grained structure.
There are still a large number of dislocations tangled with second particles even after being heat treated at a high temperature for hours.
The nano-crystalline grains (54nm) in as-milled powder grow to ultra-fine (about 500 nm, Fig. 4b) equiaxed grains.
After annealing from 800 to 1000 °C, a large number of equiaxed grains with few hundreds of microns are found to recrystallize in the matrix and preferentially to located on interfaces.