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It could refine the grain and achieve ultra-fine grain materials.
The method could improve the process route effectively and obtain a uniform grain structure.
So it could obtain the grain structure which is more fine and uniform.
It predicts the regions can get more fine grain structure.
(2) The stress and strain of sample is obvious nonuniform for one pass ECAP and the uniformity is improved gradually with the increase number of passes

According to Hall-Petch relationship which is inversely proportional to the strength and grain size, i.e. the finer grains, the higher the intensity of them.
The grain refinement is one of mechanisms of the plasticisation and strengthening [4].
In recent years, ultra-fine grained materials gradually attracted more and more attention.
Among them, ECAE process is one of the research directions with most industrialized promising, the approach can be obtained with sub-micron grain microstructure ultra-fine grained materials.
Simulation parameters were set as follows: the punch stroke 60mm, extrusion speed 1mm/s, 200 simulation steps, the step size 0.3mm, element numbers 8000, boundary friction factor 0.12, the extrusion temperature 20 °C.

There is a large number of annealing twins in the structure.
The grains are equiaxed, and the austenite grain boundary is flat and the grain size is fine.
Although a certain amount of dislocation plug is placed in front of precipitates and grain boundaries and other obstacles, at the same time, the number of dislocation pinned by substituent radicals in local areas is reduced.
There is a large number of precipitates widely distributed in grain boundary and matrix in the sample, which will become the obstacle of dislocation movement and reduce the free path of dislocation movement.
After a long period of high temperature creep, a large number of brittle phases are produced at the grain boundary of heat-resistant steel.

Furthermore, the Al3Sc precipitates are very effective in hindering the grain boundaries and improve the stability of the ultrafine grains at elevated temperatures [13].
During processing by HPT, the strain imposed in the material is directly proportional to the number of turns and the distance to the centre of the disc [3,14-16].
It is also observed that the Vickers microhardness increases with increasing distance from the centre of disc and the number of HPT turns.
Discussion The average Vickers microhardness measurements depicted in Fig. 2 reveal that there is a gradual evolution towards homogeneity with increasing numbers of turns in HPT processing.
Langdon, Twenty-five years of ultrafine-grained materials: Achieving exceptional properties through grain refinement, Acta Mater. 61 (2013) 7035-7059

With increase in cooling rate the grain is obviously refined.
Furthermore, at lower cooling rate vanadium carbonitrides, which can supply large number of nucleation position to bainite, can precipitate adequately.
Grain size of ferrite at different cooling rates was presented in Fig.5.
Grain size of ferrite gets small with the increase in cooling rate.
The finest grain size of core ferrite with 5.3 μm was obtained at 15 ℃/s

The testing procedure based on applying cyclic loading with defined stress amplitude to determine the number of cycles to the fracture is described e.g. in Eurocode 3 standard, part 1-9 [9].
The fatigue crack growth rate for applied loading is defined by the crack length increment for given number of loading cycles.
C and m are material constants, da/dN is the fatigue crack growth rate (da – crack length increment, dN – corresponding number of cycles) and DK is the stress intensity factor range.
Small particles present in the grains and also on the grain boundaries were observed in the case of S355 J0A specimen, while in the case of other specimens only small amount of particles was observed only on the grain boundaries.
The grain size is similar in both cases.

The model considers the number of cycle to crack initiation, the number of cycle of short crack propagation and the number of cycles of long crack propagation.
Parameter n describes the relative position of the crack tip to the grain boundary [13].
Journal Title and Volume Number (to be inserted by the publisher) 9 The material considered is surface hardened 18CrMo4 steel with an approximate grain size of 0.05 mm (UTS=1300 MPa, Yield stress=950 MPa).
As regards the initial dimension of the crack, it was chosen equal to the typical grain size of the material used.
It can be noted that most of the total time of crack propagation is spent to cross the first grains.

The experimental results show that the forced convection caused by the low frequency electromagnetic (LFE) filed can make the melt temperature uniform, promote the evacuation of superheat, make the temperature in the liquid pool lower than the liquidus temperature of 6063 aluminum alloy, increase the number of floating nuclei, make the ingot with fine and homogeneous macrostructure, though there is no addition of any grain refiners.
Additionally, there is no addition of grain refiners, such as Al-Ti-B, Al-Ti-C and Al-Ti master alloys.
For the 6063 aluminum alloy, when the melt temperature is 654 °C, fs is about 0.15, there are a number of floating nuclei in the sump.
As shown in Fig. 3(b) and 4(b), ingot with fine and homogeneous macrostructure can be obtained, although there is no addition of grain refiners.

These dopants can dissolve into ZnO grains and segregate at the ZnO grain boundaries.
The dopants dissolved into ZnO grains may act as a donor, providing electrical carriers to increase the conductivity of the grains, and the dopants segregated at the grain boundaries form interface states, increasing the barrier height.
It should be noted from the EDX results that the doped W atoms exist both in ZnO grains and at grain boundaries.
The resultant Pr6WO12 phase would also segregate at the grain boundaries, inhibiting the growth of ZnO grains.
The varistor voltage of the samples is proportional to the number of grain boundaries between the two applied electrodes, but in opposite proportion with the size of ZnO grains.

The alloy was tested under a number of stress amplitudes ranging from 92 to 202 MPa in as-cast state, 160 to 244 MPa in one-pass and 174 to 244 MPa in two-pass ECAE and the number of cycles to failure was measured for each test.
Three fatigue specimens were used for each stress level, and number of cycles to failure was determined by taking the mean value of three measurements.
In addition, decreasing of grain size during ECAE processing results in an increase of the amount of grain boundaries, which led to improvement in strength values (grain boundary strengthening).
Mechanical properties and deformation behavior of ECAE processed Al-20Zn alloy were affected strongly by the number of passes.
Stress amplitude versus number of cycles to failure (S-N) curves of the as-cast and ECAE processed Al-20Zn alloy.