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To identify the aged specimens, three-digital numbers were attached to capital A, e.g., the A482 specimen represented the specimen that was aged at 482°C for 8 hr.
In the A593 specimen, the coarsening of α precipitates as well as the decreased number and density of the lath-like α account for the lowered strength and hardness of the specimen (Fig. 1(c)).
Besides, the prior β grain boundaries were profiled with α precipitates.
The faceted appearance is attributed to the restricted number of slip systems available when the plastic zone size is less than grain size, thereby favoring fracture along specific planes [11].
It was deduced as the crack advance approached grain boundaries the relative weak nature of the grain boundaries caused intergranular separations therein.

When a visible TBC spallation area reached to about 20 % of the total surface area, the test was stopped and the number of thermal cycles was recorded.
Tree-like sub-grains grew around the main columnar grains, as shown in Fig. 1b.
Gaps and pores are abundant for the sub-grains.
As a result, pores between sub-grains disappeared.
Pores between sub-grains disappeared during sintering due to joining of those sub-grains.

The grain structure of the as-received AZ80 alloy showed dislocations, twins and second-phase particles and-/or precipitates distributed uniformly within grains.
The heat treatment significantly changed the grain structure of the AZ80 alloy, but did not affect the ZE10 alloy apart from grain enlargement.
Grain enlargement (Fig. 4b) as well as clean grain structure was observed on the heat treated ZE10 (Figs. 4b and 5b).
The grain structures were also similar (between the as-received and heat treated conditions) except for an increase in grain size at various locations.
This is supported by the higher elongation (hence, higher ductility) after heat treatment caused by the dissolution of precipitates, decreasing the number of twins and dislocations.

The specimens with Yb2O3 had high aspect ratio β-Si3N4 grains, and formed the high melting crystalline Yb4Si2N2O7.
However, the sintering of silicon nitride is very difficult because of a large number of covalent bond Si-N.
Microstructures with elongated β- Si3N4 grains interlocked and superimposed on each other can be observed with increasing sintering temperature.
However, the grain size and aspect ratio of SN2 samples was obviously larger than that of SN1 ones.
Increasing atomic number of lanthanide, the viscosity of the liquid phase is expected to elevate [16].

In Mn-Zn ferrites, the grain boundaries exhibit different chemical and physical properties than the ferrite grains.
The segregation of impurities and the partial re-oxidation of the Fe2+ on the grain boundaries during cooling make the Mn-Zn ferrite grain boundaries highly insulating in comparison to the grain interior.
For example, high initial magnetic permeability can be achieved only in samples with large grain size and residual porosity located at grain boundaries.
The number of turns in the coil are limited to Np + Ns = 60.
The grain size is measured from SEM and is given in Table 1.

Material FCC morphology Phase fractions FCC / BCC [%] Grain morphology Grain circular equivalent diameter (CED) [µm] Average grain major axis [µm] Average grain minor axis [µm] Average grain aspect ratio AlCrFe2Ni2 Widmannstätten and vermicular 62 / 38 Columnar 340 +/- 293 756 +/- 807 215 +/- 202 3.6 +/-2.34 AlCrFe2Ni2Mo0.1 Mainly vermicular 57 / 43 equiaxed 339 +/- 239 468 +/- 326 270 +/- 202 1.96 +/- 0.86 Reference 1.4517 Coarse Widmanstätten 47 / 53 equiaxed 1476 +/- 875 1937 +/- 1132 1151 +/- 758 1.79 +/- 0.55 Note, the rather large variation (i.e. standard deviation) in the measured grain sizes and grain morphologies of the materials analyzed in the present study, introducing a significant error to the further estimation of fatigue notch factors, based on grain size analysis.
With respect to the fatigue properties of the MEAs, no grain refinement was investigated, which could be another interesting aspect to improve their fatigue properties, since a smaller grain size corresponds to a larger number of microstructural barriers encountered by a potential crack growing due to fatigue and to a reduced slip band length ahead of the crack tip and therefore, a lower crack growth rate [67].
Furthermore, a higher number of grain boundaries tends to block dislocation slip and dislocation pile-up, resulting in less build-up of stress concentrations in a component and a potentially enhanced fatigue endurance limit, due to the so-called “Hall-Petch-Effect” [68, 69], as a result of different orientations of adjacent grains, requiring more energy for dislocations to change their direction and move into the next grain.
A finite element method (FEM) numerical modelling approach of fatigue initiation life was performed by Mlikota et al. [70] for notched samples with different grain sizes and results showed that by decreasing the grain size or the slip band length, the total number of cycles for the fatigue crack initiation and the total fatigue life increased and the material performed higher fatigue resistance.
Navarro, Grain size effects on notch sensitivity, Int.

Near prior austenite grain boundaries, the laths with single K-S variant existed.
The number of small packets per Fig. 2: OM images with nital etching of step-quenched lath martensite in maraging steel.
White broken lines are the initial blocks and black broken lines show prior austenite grain boundaries.
The blocks emerge from austenite grain boundaries with single K-S variant.
The red, blue and green in the maps indicate Bain correspondence numbers, B1, B2 and B3, respectively.

The shape of Silicon grain in Fig. 1(b) is regular and its granularity is uniform.
On one hand, the size of grains among the powders becomes small in the process of high-energy ball milling.
The growing number of tiny diffuse oxide can fill the internal micro hole of Al-50Si alloy, and reduce the internal porosity of the alloy are reduced.
The small particle means the size of grains become small.
As we know, the tensile strength of materials are decided by the size of the grains.

In the next part of the work the deformation of the alloy at lower temperatures will be considered in order to reach a finer grain microstructure and to determine the ductility of material (defined by the number of rotations to its destruction).
The grain size of α phase was about 700 µm.
The microstructure after deformation of the alloy showed a significant grain refinement almost to the tensile axis of the sample.
As a result of such deformation, a weak gradient microstructure with the axial symmetry appeared with a minimum grain size in the surface layer of the material.
According to the EBSD measurements, changing the temperature from 800 to 850 °С brought about only negligible increase of grains size.

When the Al-10RE addition continues to increase, a large number of RE elements will be rich at the grain boundary, resulting in the coarse grain.
Some micro-particle will precipitate from the grain boundaries as the network-shape, and thus it will effectively prevent the growth of grains.
A large number of RE will enrich at the grain boundaries, which makes grain coarsen and dendrite arm spacing widen.
A large number of RE enrich at the grain boundaries.
So, they will be rich at grain boundaries, which will separate from the grain boundary.