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Besides thin films, nanocrystalline metals prepared by high energy ball milling also exhibit polymorphic phase transformation below certain grain size.
In polycrystalline thin films, variation of film thickness may lead to the change of microstructure of thin films which primarily involves the following: (i) change of crystallite size (or grain size) in thin films.
(ii) change of film thickness changes defect densities (density of dislocations, grain boundaries etc.) in polycrystalline thin films.
(iii) The interface energy is the energy of the film-substrate interface and also the grain boundary energy (which is typically 1/3rd of the surface energy of the film) of the film.
Taking the inter-planer lattice spacing (d) as 0.24019nm in case of {111} fiber textured fcc Ti, for 288nm thick film the number of atoms in the single atomic column can be calculated as 1199.

As the current increased, Mg and B reacted completely and grains grew gradually, which made the surface denser and denser.
The appearance of MgB2 (002) peaks indicates that the films contain a considerable number of MgB2 c-axis orientation grains.
Combined with SEM and AFM images of the samples, the film which is the roughest and most compact contains the most MgB2 grains while the film which is the smoothest and loosest contains the least MgB2 grains.
The main reason of this difference is the connection among grains in the film.
Since the connection is not enough tight, the grains may not form a perfect circuit.

However, locally porous structures were formed when overmuch glass was added because of enwrapped air bubbles and rapid grain growth.
The grain morphology was observed by a scanning electron microscope (SEM, Field-emission Sirion200, FEI, Netherlands).
In addition, the fast grain growth was induced at the place rich in CBS glass, meaning that CBS glass probably reacted with BNT ceramics.
The fast grain growth occurred in the sample with high glass content may indicate that chemical reactions happened between CBS glass and BNT matrix.
This is because the grain growth at higher sintering temperature tends to decrease the intrinsic dielectric loss.

For the TMT processed 6156 alloy, though no obvious precipitates can be observed in the matrix, tangled dislocations around primary phase in the matrix, as well as a high density of dislocations piled up at the grain boundary were observed.
The grain boundary of the T4 sample is relatively clean.
No obvious grain boundary precipitates (GBP) or precipitation free zone (PFZ) can be observed, and no dislocation pile-up exhibits at the grain boundary.
Continuous GBP as well as PFZ can be observed at the grain boundary of T6 alloy.
A large number of dislocation pile-ups at the grain boundary, and no GBP or PFZ can be observed.

Prior austenite grain sizes of the CGHAZ in Steel A are given in Table 9.
Coarse grained HAZ prior austenite grain sizes in Steel A.
Coarse grained HAZ prior austenite grain sizes in Steel B.
The primary austenite grain size is larger than the parent plate. 5.
A number of parameters were tested and evaluated by transvers etched samples.

The average α(Al) grain size, Al13(Cr,Fe)2 spheroid diameter and interparticle spacing are 0.6 µm, 0.12 µm and 0.3 µm, respectively.
The recrystallized grains form upon the hot extrusion of the rapidly solidified powder.
Due to the plastic deformation at a relatively high temperature, new recrystallized grains with low concentration of lattice defects nucleate at a number of sites in the structure, e.g. at boundaries of original deformed grains.
New grains tend to grow, but migration of grain boundaries is strongly suppressed by Al13(Cr,Fe)2 particles.
If the k value is equal to 171 MPa µm1/2 [9], and the average grain size of 0.6 µm is used, then Eq. 2 gives the value of ∆σHP = 221 MPa.

The formation of a fine-grained ferrite-pearlite microstructure, of grain size 7-9 µm, reflected these changes of properties.
This was the result of an increase in the number of fine precipitates (~10 nm), with resulting decrease in the inter-particle spacing, giving more effective precipitation strengthening.
The average ferrite grain size was determined to be 15.7µm.
The proeutectoid ferrite had a sub-grain structure.
Sub-grain boundaries represent ordered dislocation agglomerates.

The crystal structure of faujasite, where Si or Al are at the corner of framework and these are linked by oxygen bridges represented by the lines (after [1]) Zeolite synthesis depends on the use of highly reactive starting materials, a relatively high pH, a high degree of saturation resulting in large numbers of nuclei, and a relatively low temperature.
The image shows the presence of grains of various sizes and pores as well as cracks around the central grain.
Akolekar et al. [17] observed similar grains in the well-developed crystalline zeolite-A made from metakaolinite and referred to them as zeolitic grains.
Figure 7 revealed that the average size of zeolite grains in this sample is 7.5 mm.
The presence of substantial cavities on its surface were originated from the loss of grains during polishing.

In this way the steel producers reduced the risk of precipitation of carbides, mainly on the grain borders.
Carbides precipitation, determined by the diffusion of chromium from the grains to the grain’s borders, leaves the adjacent zones deprived by chromium, with an insufficient concentration of this alloying element (<10,5%Cr), and in this way, incapable to form chromium oxide (Cr2O3) and to passivate the component.
As a result, the corrosion process starts on the grain borders and advances on these limits in the depth of the material.
Analyzing the base material, using an optical microscope, we observed an austenitic structure formed by polygonal grains.
As we got closer to the brazed zone, the base materials grains became larger and the grain limits became more evident (thickened), as ca be observed in figure 5.

Furthermore, it then causes recrystallization of defect microstructure during the dehydrogenation stage to grain refinement.
Research on the effects of hydrogen on the microstructure of the titanium alloy Ti-6Al-4V showed that the processes causing the high-temperature hydrogen treatment of grain refinement and alloy plate structure occur in a 50 -100 μm surface layer.
The thickness of the layer in which the fragmentation of platelets was observed increased with the number of hydrogen-treatment cycles.
The process steps and parameters were: · Step 1: hydrogenation - soaking for 30 min. at 600 °C, · Step 2: cyclic heat treatment - number of cycles 10, temperature: 250 to 25°C, 100% H2, · Step 3: dehydrogenation - anneal 30 min. at 550 °C in a vacuum.
A number of delaminations oriented parallel to the sample surface were observed (Fig.1b, c and Fig, 4.5).