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Hence, microcracks were evaluated regarding their propagation capabilities according to grain orientation and barrier function of grain boundaries.
Coarse-grain annealing resulted in an average grain size of ~ 410 mm in contrast to the as-received condition with an average grain size less than ~ 120 mm.
In order to reach very high numbers of cycles and hence very low crack growth rates, an ultrasonic fatigue testing system was used.
In case of the coarse-grained condition of Ni201 crack started from a grain boundary triple junction (Fig. 2b).
Red ellipses denote the crack initiation grain boundaries.

It was restricted in one-dimensional statistical wheel characterizations such as surface roughness of wheels and number of cutting edges.
Their centers along the tool surface are: ; .x0 and y0 are grain center position coordinates, rx and ry are random numbers equably distributed in [-0.5, 0.5] generated by the computer.
Conic Grain.
The height of grain tip for each grain can be recognized by the color of the grain.
Acknowledgements This work is supported by National Science Foundation of China (NSFC, Grant number 50975198).

After 50% reduction and above, an equiaxed, fine grained structure mainly surrounded by high-angle boundaries was uniformly formed with dislocation substructures, where the dislocation density in the grains is relatively low.
Introduction Decreasing a grain size is a promising strategy to increase both strength and toughness of metals.
A large number of low-angle boundaries are also present within the blocks.
With increasing applied strain, a martensite lath structure was gradually changed into an equiaxed fine grained structure containing dislocation substructures.
A quite uniform fine grained structure with a large amount of high-angle boundaries was obtained only after 50% compression and above.

The following equation is realized up to 0.2µm grain size in the relation between yield strength σy and grain size d: σy [MPa]= 100+600×d[µm]-1/2.
In the photograph (a), it is found that dislocations nucleate at grain boundary and a fairly large number of dislocations move even though the applied stress is less than yield strength.
The grain refinement below 1µm is not so easy but ultra fine grained (UFG) iron has been fabricated by consolidation of mechanically milled iron powder.
The grain size of commercial low carbon steels is around 10µm, thus the contribution to grain refinement strengthening can be estimated at 140MPa (white arrow).
Fig. 13 schematically illustrates the grain boundary.

While, due to its high melting point and high sintering temperature needed, the ultra-fine grain sized tungsten is not easy to be fabricated.
The ultra-fine grained W or W composites have been researched for many years, however, due to its sintering temperature is much high (more than 2000 oC), and the grain is much apt to grow in such high temperature, thus it is difficult to obtain ultra-fine grained W by conventional powder sintering method, so alternative processing routes deserve to be attempted.
The formation of cracks is one of the gravest problems of this technique used to fabricate ultra-fine grained W or W composites, and two methods were proposed to solve this problem in this paper.
The material in front of the propagating wave is preheated by the heat generated by the combustion, the rapid auto combustion-like wave preheating has a number of significant advantages over traditional processing methods, such as complete or partial elimination of external energy supply by the utilization of the internal heat released in the chemical reactions, and convenient control of the process rate, temperature, degree of heating by variation in the rates of heat release and transfer.
Conclusions The characteristics of high pressure and high heating rate make explosive consolidation a promising method to fabricate ultra-fine grained Tungsten, by hindering the undesirable grain growth associated to conventional sintering processes.

a horita@zaiko.kyushu-u.ac.jp, blangdon@usc.edu Keywords: Aluminum alloy, Grain refinement, High-pressure torsion, Severe plastic deformation, Ultrafine grains.
It is convenient in practice to express the total strain in terms of the total number of rotations applied.
Figure 4 shows a montage of the internal microstructure on the longer plane of this specimen after N = 1, where N is the number of turns: the plane of sectioning is illustrated at the upper right in Fig. 4.
To evaluate the significance of continuing processing to a larger number of turns, Fig. 7 shows a montage of the microstructures on a longitudinal section after a total of 2 turns.
(3) After two turns, the microstructure at the edge in the mid-section was uniform with equiaxed grains, high angle boundaries and an average grain size of ~130 nm.

AFM images manifest that, with the increase of deposition time, the grain size becomes larger accompanied by the decrease of the number density.
In addition, AFM images manifest that the grain size becomes larger accompanied by the decrease of the number density with increasing the deposition time.
For the film deposited in 40 minutes, large Si grains with about 35 nm in diameter is distributed among the small Si grains.
Compared Fig. 4(a) with Fig. 4(b), it is clear that, with the increase of deposition time, the grain size becomes larger accompanied by the decrease of the number density.
AFM images manifest that, with increasing the deposition time, the grain size becomes larger accompanied by the decrease of the number density.

It was ensured that the lines were roughly equidistant and did not intercept the same grain twice; the number of lines per image varied between 5 and 9.
The length of each line, in μm, was divided by the number of interception points along it to give the average grain size for that line,.
The mean of the average grain sizes, , was then calculated to give the approximate grain size for the specimen, as shown in Eq. 2 (where n is the number of horizontal lines on the image).According to ASTM E112-13, which illustrates the standard test methods for determining average grain size, a 95 % confidence interval should be calculated to determine the relative accuracy of the mean grain size value.
The 95 % confidence interval is calculated as shown in Eq. 4, where s is the standard deviation, n is the number of values for each image (3), and t is the value of Student’s t distribution (for p=0.025 and n-1 degrees of freedom).
Image (f) is of the specimen produced at 1000°C with a 30 minute dwell time At 800°C, although the number of primary alpha grains does not increase, the initial alpha grains grow as the dwell time increases, implying that the primary alpha volume fraction increases for increasing dwell time.

The more cycle times, the grain is smaller.
Experimental results Fig. 1 shows the relationship of alloy plasticity and cycle number. (1) Elongation: without making any treatment, the extension rate is 35%.
With the increasing of cycle number, the elongation increased.
The more cycles, the grain is finer [14].
In addition, it is significantly, the number of second phase particles that gotten after the five cycles is more than that after three cycles.

Grain refinement remains the only option to increase strength without introducing harmful side effects.
Numbers indicate applied pass strain.
Partial austenite recrystallization after each finishing pass was expected to provide only limited austenite grain refinement and a relatively coarse final ferrite grain size.
The depth of the X trough correlated with the final ferrite grain size.
Influence of Al on grain refinement in as-rolled V-microalloyed steels.