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Mean grain diameter in processed zone of alloy in multi-pass FSP increased with increase in number of processing passes [8].
AZ31 alloy under FSP has defects-free, fine grains at rotational speed of 1000 rpm while producing relatively coarse grains at higher rotational speed [12].
Average grain diameter is one of the vital microstructural features.
Average grain diameter of unprocessed & FSP-processed AZ91 Mg alloy.
Microstructural evaluation revealed that, optimal grain refinement with average grain diameter of 39 μm, was attained at higher tool rotational speed of 1000 rpm.

However, the deformation between grains of domestic wirebar is slightly uneven and coordinated, some grains are seriously broken, and some grains are only slightly deformed, and resulting in uneven grain size.
Segregation of Ag atoms at grain boundaries in domestic Cu-2Ag wirebar Table 4.
It can be seen that there are a few large and deep dimples on the tensile fracture of domestic Cu-2Ag wirebar, while there are a large number of uniform and fine dimples on the tensile fracture of imported Cu-2Ag wirebar, which further indicates that the microstructure and properties of imported wirebar are more uniform.
The mechanism of grain refinement improving the plasticity of materials is that the deformation can be dispersed in more grains, so each grain can bear smaller and more uniform deformation, and there are fewer dislocations in each grain.
The grain size of domestic Cu-2Ag alloy wirebar is obviously too large and uneven.

Samples denoted with second level number "0" (f.ex., 14-0) have not been exposed to any oxidation. 2.
Samples denoted with second level number "1" (f.ex., 14-1) have been exposed to isothermal exposure at 1173 K in static air for 120 hours. 3.
The best fit was attained for the TiO2 phase from the card number 77-0441 of the ICDD data base.
The next one to this outer sublayer ('2' in Fig. 1a) was composed of grains of α-Al2O3 phase corresponding to that from the card number 46-12-12 of the ICDD data base.
The best fit was attained for the γ-TiAl phase from the card number 05-0678 of the ICDD data base.

The grain size of primary Sn decreased observably with the micro addition of B and a large number of fine reinforcement particles were found in the solder.
Theoretical analyses have shown that boron benefits precipitation strengthening, solution strengthening and grain boundary strengthening[6].
Table 1 Solder alloys and their composition Sn(%) Ag(%) Cu(%) Ni(%) B(%) Sn-1.0Ag-0.5Cu Bal. 1.0 0.5 0 0 Sn-1.0Ag-0.5Cu-0.05Ni Bal. 1.0 0.5 0.05 0 Sn-1.0Ag-0.5Cu-0.05N-0.02B Bal. 1.0 0.5 0.05 0.02 Results and Discussion Microstructure and intermetallic morphology As illustrated in Fig. 1(a)-(c), the microstructural observation shows that the grain size of primary Sn decreased with Ni, Ni-B addition and the grain size of Sn-1.0Ag-0.5Cu- 0.05Ni-0.02B alloy was the finest of the three solder alloy systems.
As shown in Fig. 2(b), with Ni-B addition, a mass of tiny precipitates are distributed both at the grain boundaries and within the grains, but the most of the precipitates gathered in grain boundaries and shaped network-like.
Conclusions (1) The fine reinforcement particles that enriched at the grain boundaries restrained the growth of primary Sn and the grain size of Sn-1.0Ag-0.5Cu- 0.05Ni-0.02B alloy was the finest of the three solder alloy systems

The measured microstructure parameters, i.e. volume fractions of the two phases, grain size ratio, and grain boundary areas are calculated for each structure.
From the SEM images the interfaces between the Al2O3 grains and between Al2O3 grains and pores were also determined from the number of intersections of random lines with the respective type of interfaces.
The experimental grain boundary areas between grains of different phases correspond well to the areas obtained for the model structures (Fig. 7a).
The ratios of average chord length of alumina grains to that of zirconia grains are in good agreement (Fig. 7b).
Tensile stresses of more than 0.89 GPa are obtained for 10% of the grain boundary area between the alumina grains.

Small spherical grains(200nm) composed of Ti and N were confirmed by a TEM with an EDS, These were identified to be TiN by XRD profiles.
Using a high-resolution micrograph(Fig. 4-b), many edge dislocations were observed, suggesting that the grain had been subjected to high stress during firing.
Furthermore, the fact that Ti does not exist in the grains or the grain boundary phases seems to suggest that all of the TiO2 was changed into TiN.
From the relationship between the number of loading cycles and the bending strength of the specimen after cyclic indentation under conditions of P=2500N and f (frequency)=10Hz, we determined that the bending strength of the specimens without TiN particles declined as the number of cycles was increased, while that of TiN particle-dispersed Si3N4 specimens held the same value as before indentation.
The limiting of crack propagation probably results from compressive residual stress at the grain boundary.

Microstructurs of plats in the L direction in Fig. 2a shows that the average grains size is about 2μm.
There are a little second phase particles on the grain boundary.
The matrix average grains is about 3μm and some second phases distributing on the grain boundary are also can be seen in Fig. 2b.
The second phase particles on the grain boundary which can be seen in Fig.2a were elongated and broken to be new grains during hot extrusion.
A large number of precipitated second phase particles are produced during two-stage aging treatment.

The site selection, between grain boundary of austenite and intragranular inclusion, has been widely discussed in conjunction with austenite grain size and the grain boundary suppression by allotriomorphic ferrite [11-12] or boron segregation [12- 14].
Then, there is a possibility that the number of nucleation site is overestimated when post-weld characterization was applied.
A one-to-one correspondence between the number of active inclusions and the number of acicular-ferrite plates is not expected.
Figure 5 shows that new ferrite plate precipitates from the grain boundary between austenite and precipitated ferrite.
The number of effective inclusion for heterogeneous nucleation and the aspect ratio of ferrite plate, depending on phase transformation temperature, were directly estimated.

With the increase of aging time, the high melting point intermetallic compounds Al2Ca and Al4Ca are increased obviously in number and the phase of Mg17Al12 has a dramatic decrease in number.
As is shown in fig. 1, with the increase of aging time, the dimension and the number of black block eutectic structure decreases, but transgranular granular phases increases.
The main reason of AZ magnesium alloys poor temperature resistance is the poor thermal stability of β-phase, α supersaturated solid solution near grain boundary separate out non-continuously easily.
Ca improves the melting point of β-phases and not only improve the thermal stability, but also make most of β-phase distribute along grain boundary.
At the same time, hinder the grain boundary sliding effectively at high temperature.

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Aluminosilicate grain