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However, the elongation under shear manifested a reduction when the number of ARB passes increased.
A reduction in individual layer thickness was detected with increasing the number of ARB passes.
Furthermore, the number of layers and interface lines are related to the number of cycles and can be calculated with the relationships of 2n and 2n–1 , respectively [14,15].
Notwithstanding that the microstructural evolution in 2024 indicates elongated grains with high aspect ratio, Creation of fine structures was not detected for 6061 with an average grain size of 5 microns.
Both reasons contribute to achieving finer grain size in Al 2024 [16,17].

The effects of process conditions (grain size, acid species and concentration, leaching time and temperature) are discussed.
Optimal operating conditions are suggested: 75μm of grain size, 80 min of leaching time, 0.28 mol/l of concentration of HF, 80  C of leaching temperature.
The effects of process conditions (grain size, acid species and concentration, leaching time and temperature) are discussed.
Particles with sizes of 150μm, 75μm, 48μm and 38μm, that is 100, 200, 300 and 400 mesh numbers, respectively, were leached in turn under the same conditions.
Optimal operating conditions are suggested: 75μm of grain size, 80 min of leaching time, 0.28 mol/l of HF concentration, 80  C of leaching temperature.

The grain size was measured using Image Pro Plus® software.
This sample shows both well-delineated and undefined grains.
The recrystallized grain sizes grow exponentially, but remain small, i.e., ~3 mm, even after 7200 s of annealing at 700ºC; most of the grains have a high-angle grain-boundary, as shown in Fig. 4(d).
Mean austenite grain size as a function of Fig. 7.
Acknowledgments The authors thank FAPEMIG (process number TEC PPM-00373/11), CNPq (process number 471128/2011-2), and CAPES (scholarship of SSFD) for the financial support of this research.

A small number of laser shots and a low temperature of substrates (series 1) probably slowed or stopped the processes of diffusion and coalescence of the already grown grains, which caused the situation that substrates were not uniformly covered with BN.
Registered grains have similar, small sizes (Fig. 1).
The morphology and phase maps of boron nitride coatings An increase in the number of laser shots, the energy of laser and the power of the RF discharge generator (series 4) cause that the substrate is completely coated by boron nitride; moreover, a larger variety of the size and shape of grains can be observed, as a number of quite large grains with an elongated shape have appeared.
On the surface of large grains and among them, a significant amount of small grains can be observed.
Such variation in conditions resulted in the noticeable growth of the grain size.

Nevertheless, a previous study [3] describes the contribution of the delta phase in the grain size control, working as a barrier to the grain sliding.
The aging treatment promotes the precipitation of g’ and g” and grain size growth.
This work aims to analyze qualitatively the effect of each step of double aging heat treatment, using images obtained by optical and scanning electron microscope, Vickers hardness and ASTM grain size number.
Grain size was calculated for each step of heat treatment and the values are represented in table 3.
Inconel 718 ASTM grain size As received 8.20 Solid solution at 1095ºC 7.50 After the first aging step at 955ºC 7.23 Double aged 7.23 Discussion The results obtained for grain size after full double aging heat treatment are coherent with those described by Kuo et al [5] which is an increase of grain size of 9% in the solid solution step.

The average grain sizes is reduced to 80-150μm under the spiral magnetic field.
The average grain size and the numbers of the dendrites was gradually decreased with the increasing stirring time when the time was not more than 20min.
In contrary, if the stirring time is too much (more than 20min), the primary phase grains aggregate again and the size of grains will become larger.
However, with the further increasing of the exciting current, the grains became larger in size and grew from equiaxed grains to columnar ones.
If the stirring time is too longer or the current intensity is too higher, the primary phase grains aggregate more easily and the size of grains will become larger.

Due to the limited number of slip systems in magnesium, elevated ECAP processing temperatures are necessary to allow plastic deformation, while on the other hand a decreasing process temperature results in a finer microstructure.
Grain size distribution shows an inhomogeneous microstructure with a mixture of coarse and fine grains.
The widest spread in grain size is found for AZ31 alloy with grain sizes from 100 μm down to 5 μm.
The finer grains form band shaped structures.
The ECAPed alloys have finer grains with average grain sizes of 4 μm, 3.2 μm and 2.3 μm for AZ31, AZ61 and AZ91, respectively.

The α-lamellae cluster and the original β grain precipitate in the form of 30°/60° and form the original β - grain boundary.
The average number of grain boundary Angle is 45° in the horizontal plane specimens, which maximum grain degrees recorded is 61° constitutes 36.9% of the number fraction.
The average number of grain boundary Angle is 54° in the horizontal plane specimens, which maximum grain degrees recorded is 61° constitutes 46% of the number fraction.
The grains are α grains with the axis of [α.
The original β-grains grow along the deposition direction, and α-lamellae precipitate at 30°/60° along the β-grain boundary There are cross arranged α-lamellae in the original β-grains

The instron machine is used to find out the number of cycles to failure of the material.
When the number of cycles is more, S-N curve is used for the fatigue analysis.
The media consists of semisolid carrier and abrasive grains.
Table 1 shows the number of cycles before the failure of the specimen and their averages.
Design of experiments A statistically design of experiments (DOE) technique, two-levels three variable full factorial design of experiments is used here [14].The three design factors considered in the design of the experiments are extrusion pressure (A), grain size(B) (or mesh number) and abrasive concentration (C).

A number of toughening mechanisms, including fine grain, crack deflection and grain pull-out, were observed during microstructural analysis of the composite.
With increasing the TiB2 content, the grain became smaller which might improve both the flexural strength and fracture toughness of the composite as shown in Figs. 2 (c) and (d).
Both the fine grain and the difference in thermal expansion coefficients between the B4C matrix and TiB2 particle could effectively improve the fracture toughness of the composite.
The grain pull-out was observed on the fracture surface of the composite with 43 % TiB2, which proved the fracture toughness improvement of the composite with the increasing TiB2 content.
The increase of toughness was mainly resulted from both the fine grain and the crack deflection caused by the difference in thermal expansion coefficients between the B4C matrix and the TiB2 particle.