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Along with the elevated temperature, further factor which lowers yield stress is the strength decrease due to diminishing number of dislocations during annealing (recovery).
During recrystallization, new dislocations-free grains form at the expense of deformed grains which have had high dislocation density.
The yield stress lowering can be further assisted by previous recovery which gradually diminished the number of dislocations in the temperature region 300-540°C.
The fine grained hcp matrix phase transforms to fcc at high temperatures and the grains quickly coarsen.
Acknowledgment The research was funded by Czech Science Foundation, grant number 19-15479S.

The stored energy was measured as a function of the total number of passes using DSC.
Microstructural evolution of ECAP processed and naturally aged ultrafine grained (UFG) and coarse grained (CG) Al-7075 alloys (Al-5.60%Zn-2.50% Mg1.60%Cu-0.50%Fe-0.40%Si-0.30%Mn0.23%Cr-0.20%Ti) were investigated by DSC [9].
This effect is confirmed by the shift of the recrystallization peaks toward lower temperatures by increasing the number of ECAP passes of the samples.
Fig. 3 DSC scans of ultrafine grained (UFG) and coarse grained (CG) samples of Al-7075 alloys [9].
Zehetbauer, in: Ultrafine grained Materials IV, edited by Y.T.

A number of the constitutive models developed have included the evolution of microstructure during superplastic deformation [3-6].
Contract number G4RD-CT-2000-00217. www.mmfsc.net.
which had a very fine grain, typically 3.4 microns.
The Grain Growth During Deformation.
Contract number G4RD-CT-2000-00217.

Mechanical Properties of Fine-Grained AA1050 after ECAP Stijn Poortmans a, Bert Verlinden b Katholieke Universiteit Leuven, Dept.
This grain refinement towards submicron-grained (SMG) material can be obtained using ECAP ([1],[2]).
Fig. 1 True stress-true strain curves of compression tests for ECAP material with and without annealing; (a) influence of ECAP routes and number of passes on the flow stress (b) influence of post-ECAP annealing.
Annealing for a short time allows the grains and subgrains to coarsen ([4],[5]).
After the initial coarsening, a discontinuous or abnormal grain growth occurs, starting after about 15min at 300°C [4].

Fig.3 Impact toughness values of different process oil cooling Comparison on grain size in different process oil cooling Can be seen from Fig. 4 that circulation heating make grain get refinement, thus improve toughness and fine grains are important method of controlling toughness and avoiding brittleness [13].
Grain finer, grain boundaries more twists and turns, resistance of crack propagation is greater, crack initiation and propagation become harder[14], the number of grain in a certain volume is even more ,then in the same deformation, the deformation is scattered in more grain, because deformation is evener, stress concentration decreases, therefore it is not easy to produce cleavage cracks[15], ductile to brittle transition temperature is lower with grain refinement .
Material of grain refinement is not easy to crack initiation and propagation, thus inhibiting l the brittle fracture of the material.
Because the actual tempering temperature of steel EA4T is 650 ℃, circulation heat and fine grains can improve impact toughness values of steel EA4T. 1. 880 ℃ * 1.5 h 2. 880 ℃ *15min ,circulation heat for 3 times Fig.4 Grain size comparison in different process oil cooling (200 times) Summary Circulation quenching render grain refinement, restrain the temper brittleness of steel EA4T.
References [1] Li Xuefeng study of the grain size of Railway vehicle axle LZW steel[J]. iron and steel, 2001, (8): 36-38

However, it is difficult to control the sintering process because of the relatively large number of influencing parameters.
As can be seen in side-view images of micro gear, in case of 300μm gear, large grain growth occurred and grain boundaries were thermal etched (Fig. 3(b)).
These results inferred that the size of micro part is predomoinant factor over the micro feature size for grain growth.
The grain size of substrate and micro gear in each sample is summarized in Table 1.
Table 1 Grain size of substrate and gear in micro gear parts sintered at different temperature. 300μm gear 500μm gear Sintering substrate gear substrate gear temperature Grain Size [μm] 39.0 75~100 35.4 33~50 1250oC 23.5 30~45 23.5 33~50 1200oC Fig. 4(a) shows the 500μm gear sintered at 1200oC and the degree of grain growth and thermal etching of grain boundary were not altered comparing those of 500μm gear sintered at 1250oC.

Maxwell-Wagner relaxation which occurred at the interfaces of semiconducting grains and insulating grain boundaries was pointed as the well explanation [5,6].
The grains are much smaller in BYT than in BT.
Generally speaking, semiconducting grains and insulating grain boundaries were accounted as the main organization structure in many CCTO-based materials.
As a result, the semiconducting grains would be obtained.
But differs from the CP mechanism in CCTO, the temperature independence of high permittivity is related to an interfacial polarization and is only achieved at nanosize by the activation of a high number of carriers and their trapping at the interfaces (nano-CP ) [8,9].

In all samples with spheroidal grains no textures were observed.
Fig. 7: The numbers give the positions of the measured textures on the sample rings .
It is evident that the grain shape is the all-dominant influence on texture.
The all dominant influence has the grain shape.
Spheroidal grains are not able to orientate during the filling of the mold.

One group of alloys, which are numbered from 1 to 6, are constant Al content of about 6% and various Zn content from 0 to 3%.
Another group of alloys, which are numbered from 7 to 10, are constant Zn content of about 0.4% and various Al content from 0 to 6%.
Fig.3(a) shows the alloy without Al has large α-Mg grain and little precipitates.
The morphology is typical dendritic and β-phase precipitate is at grain boundaries.
The grain size increases significantly.

The results showed that, under the optimal laser parameters condition, a dense layer was found on the surface of specimen and the columnar grains were refined, which results in increasing the total fatigue life of the specimen.
Fig. 6 (a) presents the fracture surface of original specimen, which shows evenly distributed elongated grains indicated by SEM.
It is obviously found that the effect of grain fining of copper film by laser irradiation is evidenced by different levels of stages along thickness direction on the fracture surface.
The surface fracture morphology (a) The original specimen (b) Energy density 5 KJ/m2,Pulse number 1,D=0.5 (c) Energy density 13.9 KJ/m2,Pulse number 30,D=0.5.
A dense layer and grain refinement were found after the specimens were irradiated by excimer laser with the energy density of 5KJ/m2, and the pulse numbers of 1.