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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.

As seen in Fig. 1 (a), the hot-forged Ti-1023 consists of large β grains with an average grain size of 500 μm.
The β grains contain a high volume fraction of α plates with a low aspect ratio, and nearly continuous distribution of α along the grain boundaries is also observed.
It is clearly seen that stress induced martensites (SIMs) are formed within some β grains in Ti-1023 heat-treated at 760℃ and a large number of SIMs are observed in the sample in heat-treated condition of 820℃.
The number of martensites in the large β grains of the sample heat-treated at 820℃ is much larger than that of the sample at 760℃.
In general, higher temperatures or longer time resulted in larger β grain sizes with a lower volume fraction of stress induced martensite and their presence was restricted to the neighbourhood of grain boundaries.

A large number of voids are observed close to internal and external surface, Fig. 1 b.
Grain I is characterized by high density of microtwins with the average distance between them of ~ 0.8 μm and a vast number of related large voids.
In grain II without profound mesostructural elements the number of voids is close to the value fixed in grain I, but their average size was significantly smaller, Table 1.
In grain III high density of low-angle grains (misorientations) is observed, thus leading to the absence of a single grain orientation, i.e. to grain fragmentation.
Quantitative characteristics of radiation porosity in three adjacent grains in the region close to the internal cladding surface Region Grain I Grain II Grain III Number of voids, pcs 1247 1022 218 Maximum void size, nm 340 100 116 Average void size, nm 55 44 46 Calculated swelling value, % 2.9 1.0 0.3 Thus the connection between radiation porosity and local material structure was revealed.

At a low value of Z abnormally large grains formed during annealing.
Although a number of studies have been undertaken on the static recrystallization of cold rolled interstitial free steel [e.g. 2-5], there is only minor reference in the literature to the recrystallization behaviour following warm working.
The average linear intercept ferrite grain size thus achieved was 25µm [10].
After 30 s a few new strain free grains can be observed.
In Figure 4c a number of the large apparently recrystallized grains contain, in their interior, a few low angle boundaries.

The effect of current density on the preferred orientation of grains Some literatures proposed that there may be correlation between whisker formation and grain orientations, while some people argued about that [7].
Figure 3.5 shows the results of the measured grain orientations of the as-plated samples.
Also, it can be seen that current density (in the range 1.5-3.0 A/dm2) has an effect on the preferred grain orientation of coatings.
However, the formation of dislocations can end this phenomenon, and a new preferred orientation of grains may form [6].
However, there is no obvious evidence that can explain the relationship between whisker formation and grain orientations.

The number of biomedical applications of hydroxyapatite (HA) ceramics can be increased if the bioactivity is improved.
The number density of dislocations was observed to be low (0-8 per grain) in both materials.
d(31-4-1)=2.147 Å Continuous grain boundary 2 nm d(30-30) = 2.147 Å Fig. 5: HRTEM image showing a continuous grain boundary in 0.4wt%Si-HA.
This study was founded on the assumption that the incorporation of silicon into phase pure HA would increase the number of dislocations in this material.
In particular there appeared to be a higher number of triple-junctions in the Si-HA samples.

The gas and smoke absorbed during solidification of short circuited melted mark occurred in such environment will certainly have an effect on grain shape, grain size, holes distribution and impurity element distribution of organization of melted mark.
Introduction With the social development, home appliances are becoming electrified gradually, so the fire caused by electrical equipment is also increasing year by year, the number of which has been on the top of all kinds of fire.
During the 15 years from 1993 to 2007, there were 1,527,600 fire accidents totally in China, wherein, electrical fire accidents were 373,700, accounting for 24.5% of the total number of fire accidents [1,3].
The smoke particle on the surface of the wire during the process of short circuit melt and solidification influenced the nucleation, crystallization, holes formation, grain growth and so on of melting part.
Fig. 4 5g Fig.5 Conclusions The amount of smoke content and the viscosity of smoke in fire environment play a decisive role in the size and distribution of holes, grain shape, melt transition area and etc. of the internal organization of short circuited melted mark.

In addition, that the nano-particles adsorbed on the surface of grains will hinder the growth of grains and lead to refine grains and increase the grain boundaries, thus melting caused by slight changes in the temperature.
The microstructure of Sn-30Bi-0.5Cu after adding nano-Ag was shown in Figure 2, indicating a large number of Ag3Sn micro-nano particles were adsorbed on grain boundaries [22].
(2)The Grain boundary strengthening.
Due to the high melting point of these particles and no reaction with the matrix, the added inert nano-particles such as TiO2, Al2O3, ZrO2, and so on, may become the core of heterogeneous nucleation, to increase grain numbers, and particles adsorbed on grain boundaries will impede the migration of grain boundaries, refining grains.
The generated IMC adsorbed at grain boundaries and dispersed in the matrix, will hinder the migration of grain boundaries, refining grains.

Fig. 4 (c) shows that, in the central undeformed area (3#), the reversed austenite grains mainly locate in the original austenite grain boundaries, while some of them distribute within grains.
The reason is as follows: (1) Tensile deformation is good for reversed austenite transforming into martensite, because martensite transformation is a process with volume expansion [10, 11], the interface between the new generation of martensite and austenite is large angle boundaries which reduce the proportion of the small angle grain boundaries; compression deformation promotes martensitic transformation to a lesser extent relative to the tensile deformation, thus large angle grain boundaries are improved to a lesser extent; (2) When grain was stretched, the density of the dislocation in matrix will be decreased for that some of the dislocation in matrix disappeared by tangling and rearranging , which will reduce the number of small angle grain boundaries and improve the proportion of large angle grain boundaries; when grain was squeezed, the dislocation density of per unit area decreased and the number of small angle grain boundaries increased, so as to reduce the proportion of large
angle grain boundaries.
This is because of that the concentration of stress in the original austenitic grain boundary is larger, which will make it easier for reverse austenite to transform into martensite; and the stress concentration will be reduced for large size grains will coordinate mutually in the process of deformation, and at the same time the stability of reversed austenite in grains will become higher for boundary protection.
Besides, the retained austenite mainly locates within grains.

The grains and grain boundaries were not attacked at the beginning of the first peak -168 mVSCE and started to be revealed at 18 and 216 mVSCE in the potentiodynamic polarization test.
Stefec et al. [34] have conducted a systematic study of the pitting resistance of cold rolled specimens and reported a direct correlation between the level of deformation and the number of pits formed.
The signatures of grain fragmentation are noted from c) to f).
Randle, Sigma-Boundary Statistics by Length and Number, Interface Science, 10 (2002) 271-277
Randle, Twinning-related grain boundary engineering, Acta Materialia, 52 (2004) 4067-4081