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Ultrafine grained (UFG) metals with grain sizes in the range of 10-1000 nm exhibit favorable mechanical properties including very high strength and ductility[7,8].
After 14h immersion, a number of cracks but no corrosion pits were observed on the surface of the HPT treated sample in Fig. 5c, while it can be seen that the corrosion pits enlarged and the corrosion products were dissolved on the surface of the as-cast samples in Fig. 5d.
Thus higher density of grain boundaries and the uniform redistribution of second-phase nanoparticles in the grain interiors would accelerate corrosion by forming more micro-electrochemical cells at the initial stage of corrosion between the second-phase nanoparticles and the matrix and at the grain boundaries.
However, as the second phase of the as-cast alloy mainly distributed along the grain boundaries, the pitting corrosion mainly occurred at grain boundaries; therefore the second phase came off grain boundaries after immersion for 14h (Fig. 5d). 4.
[9] Balyanov A, et al, Corrosion resistance of ultra fine-grained Ti, Scr.

This goal is still a pending task in spite of the great number of studies that have been carried out since this property was discovered in YTZP materials, and a good example can be found in the following reference [11].
To determine the optimum sintering conditions, a large number of tests were carried out in the SPS, changing either temperature, heating rate, pressure or sintering time.
Density and grain size of the ceramic materials samples.
Grain size of the materials.
In Table 1, average grain size values are included.

With regard to nanotubes and other blocks it was proposed later [7] to extend the nanostructure type number up to 36.
It is clear from (2) that the effective grain growth retardation can be achieved by an increase of the number of inclusions and their radii decreasing.
The abnormal grain growth was studied experimentally for a number of copper, nickel and iron based alloys, as well as hard alloys and diamond (see references in survey [19]).
The number of pittings in the ultra-fine-grained samples was greater but their distribution was more uniform.
From the experimental data it was concluded that the number of pitting defects is decreasing with the increasing number of nano-twinned grains, and the passivating copper sub-oxide Cu2O layer with {111} texture (this layer slows down the corrosion) grows on the top points of the textured copper nanotwins.

When the forging pass is 6, the final forging temperature has an important influence on the grain size in the fine grain zone.
However, high forging temperature is harmful for obtaining ultra-fine grains as grains grow quickly at high temperature.
The number and detail parameters of the samples are shown in Table 1.
Many small grains are distributed on the grain boundary junction (as signed by the arrows).
New recrystal grains are preferentially formed near the grain boundary junctions due to their high energy.

The effects of workpiece hardness, holding time and cooling methods in annealing and the number of grain layer are investigated.
Table 3 Specifications of micro swager Number of dies 3 Die inclusion angle [°] 12.5 Feeding rate of wedge [mm/s] 0.38 Stroke of wedge [mm] 20 Motor power [W] 150 Motor speed [rpm] 200 Results and Discussion Hardness Test.
The number of grain layers was not observed because of the residual work hardening by the prior drawing process.
There are about 2 to 3 grain layers and with carbide precipitated in some grains.
Table 4 Results with swaging tests Holding time 10 minutes 45 minutes 90 minutes 1-6 Hours Furnace -cooling G2: cracks; grain layers: NA G3: breaks; grain layers: NA G2: sound; grain layers: 2 G3: fair; grain layers: 2 (Fig. 6) G2: cracks; grain layers: 2-3 (Fig. 7) G3: breaks; grain layers: 1-2 Water -cooling G1: fair; grain layers: 4 G2: sound; grain layers: 3 G3: breaks; grain layers: 2 G1: fair; grain layers: 4 (Fig. 8) G2: sound; grain layers: 3 (Fig. 9) G3: cracks; grain layers: 2 G1: cracks; grain layers: 2 G2: sound; grain layers: 2 G3: cracks; grain layers: 2 Fig. 6.

By drawing the several lines on the SEM image and the number of intersection was counted to determine average grain size.
The average grain size D can be measured by using equation below.
Experimental Outcome and Discussion Microstructural Evolution and Grain Size.
The grain size sample for 0.5wt% (a) and 0.4 wt% (b) of MnO2.
The spontaneous tetragonal to monoclinic phase transformation of grains takes place if the grain size is higher than critical value.

There are a number of publications addressing the circumstances under which the interaction is more severe.
The original grains of the core changed due to the liquid film passage to large grains.
Recrystallization of aluminium alloys during a thermal treatment follows a number of steps before reaching its final stage [15].
SIBM involves the bulging of a part of a pre-existing grain boundary leaving a dislocation free region behind the moving grain boundary.
The non-homogenised alloy will form a large number of very small dispersoids during the brazing cycle, responsible for recrystallization inhibition or sub grain structure stabilization.

Obviously, accepter dopants Mn2+, Cu2+ and Cu+ ions only distribute near the grain boundaries to form grain-boundary layers.
It plays an important role in the formation of semiconducting grain (n-type)-insulating grain boundary-semiconducting grain (n-type) structure in SrTiO3 ceramics [8].
It made the grain boundary Schottky barrier height increase, the electron depletion layer near the grain boundary thickens, and insulating properties of grain boundary enhance.
CuO doped samples had larger and better homogeneous distribution grain size, higher sintered density, and thinner grain boundary.
Acknowledgements This project is supported by open foundation of Guangxi Key Laboratory for Advanced Materials and Manufacturing Technology (Contact Number: GXKFJ11-12).

The grain size of the two steels was refined to 5-9 μm.
Controlled rolling and cooling can improve the performance of steel by controlling the number and size of martensite/austenite (MA) islands of the microstructure in steel [6-8].
The elongation of steel also increased with grain refinement.
The grains were significantly elongated and distributed in a fibrous shape.
The grain size of the two steels was refined to 5-9 μm.

The solid squares indicate the average grain size.
When all grains are sequenced from large to small, the diameters of grains at of 20% and 80% of all measured grains are marked by an upper and lower short bars at the given frequency.
Two short bars at the extreme of a straight line are the upper and lower average grain sizes at the frequency, where the upper one is obtained by ranking all grains measured from large to small and then determined at grain number fraction of 20% while the lower is achieved at the fraction of 80%.
Therefore, in order to evaluate the uniformity of microstructures, we introduce two new parameters of d(0.8) and d(0.2); the former is defined as the maximum average grain size at which the grain number fraction is 80% when all measured grains are sequenced from small to large and the latter is the minimum average grain size with the grains number fraction of 20% in the same sequencing operation.
The solid squares indicate the average grains size under different levels of B0. 50 60 70 80 0 20 40 60 80 100 120 140 Electronic flux density (A) Average grain size (Micrometer) 90 Average grain size 50 60 70 80 0 20 40 60 80 100 120 140 Electronic flux density (A) Average grain size (Micrometer) 90 Average grain size Fig. 6 The measured grain size in AZ31B alloys as a function of electric current.