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A combination of welding stresses and reduced ductility of an alloy due to melting of the grain boundary material, i.e., grain boundary liquation, results in intergranular cracking in HAZ.
Grain Boundary Segregation Mechanism.
Absorption of vacancies at grain boundaries during cooling from the elevated temperature after thermal processing can produce a concentration gradient of complexes, which would drive the complexes to diffuse from within the grain to the grain boundary region.
This results in vacancies associated with complexes being absorbed at the grain boundaries and a build up of excessive concentration of solute atoms in the vicinity of grain boundaries.
The number and length of cracks were observed to increase with an increase in the concentration of S and B.

The grain morphologies reveal that irregular-type and cubic-type grains coexist, and pores are observable on the surface.
Because vaporization of Bi2O3 (or Bi+3) is unavoidable, the number of vacancies in the stoichiometric NBT-BT3 ceramic increases considerably, causing distortion of the unit cell.
The number of pores and the amount of excess Bi2O3 are believed to be the two most important factors.
From the morphology revealed by the SEM image in Fig. 1, a decrease in the number of pores appears to be the primary cause of this increase.
The excess Bi2O3 segregates at the grain boundary of NBT-BT3 and inhibits grain growth by filling the space between the grains.

Introduction During the fabrication processes of integrated circuits, the interconnect materials are subject to a number of thermal cycles.
To date, there have been many studies of the various factors affecting hillock formation, such as the grain size [1], grain orientation [2] and grain-boundary characteristics [2].
Thus, the most plausible site for hillock nucleation might be the grain-boundary triple points.
The number of these points is proportional to one over the square of the grain size (d -2) [1].
The hillock density decreases with increasing film thickness, because the number of plausible nucleation sites for hillock formation, such as grain-boundary triple points, decreases.

The better ferroelectric properties of Ca0.4Sr0.6Bi4Ti4O15 thin film originate from the relatively high concentration of a-axis oriented grains.
And the average grain size of the thin films increases in the rough as x varying from 0 to 0.6.
It has been reported that for bismuth-layered perovskite films the rod-like grains are presented in (119) preferentially oriented films, while the ball-like grains may corresponded to the a-axis preferred orientation and the plate-like grains are c-axis preferred orientation [9-11].
As shown in Fig. 2, the number of crystallites in ball-like shape approximately increases firstly (0≤x ≤ 0.6) then decreases (0.6As x sequentially increasing from 0.6 to 1.0, the number of rod-like and plate-like grains of films increases while the number of ball-like grains cuts down, this is corresponding to the XRD results of Fig. 1.

Introduction The electrical properties of grain boundaries (GBs) depend on their structure, thermal prehistory, interaction with impurities etc.
Influence of the dislocation number on the FET characteristics.
The analysis clearly proved that the number of dislocations in the GB decreases when W gets smaller.
In Fig. 8 the drain current ID is shown as a function of the dislocation number.
Fig. 8: The drain current ID measured at 300 K increases as the dislocation number decreases.

Prior austenite grain size.
It can be seen that the grain is anisometric and fine.
The results are shown in Table 3 and Fig. 2c.The grain size is mainly concentrated below 18μm.When the quenching temperature increases by 10℃,the number of grain with size between 6μm and 12μmdecreases from 3928 to 3325,and the number of grain with size between 12μm and 18μmincreases from 1277 to 1459, but the average grain size is almost unchanged.
Fig.1Mechanical properties after different heat treatment: (a) rockwell hardness; (b) tensile strength and yield strength; (c) impact toughness Table 3 Results for prior austenite grain size measurement Quenching temperature minimum grain diameter maximum grain diameter Average grain diameter 910 1.09 39.05 8.01 920 1.18 47.06 8.31 Fig.2(a) OM image of prior austenite grain size quenching at 910℃；(b) OM image of prior austenite grain size quenching at 920℃；(c)Statistical results for grain size quenching at 910℃ and 920℃;(d) OM image of microstructure for process2-3.
Fig.3(a) TEM image of martensite lath for process number 1;(b) TEM image of martensite lath for process number 2-1;(c) TEM image of martensite lath for process number 2-2;(c) TEM image of martensite lath for process number 2-3 Analysis of carbides.

There is evidence that grain boundary regions are sometimes distinct from grain interiors.
Let these be related thus wallcell cell fβ=ρ where f is a number less than unity.
In grains having only are set of microbands, sub-boundary sharpening is most probable, but in grains containing two sets, rapid formation of "blocky" sub-grains is most likely to occur.
It has been known for many years that there is an optimum cold rolling reduction for good drawability in ferrite, being of the order of70%75% for Al killed steels and ~80%-85% for IF steels, and the reason for this optimum reduction is that near ~{100} recrystallised grains are formed in increasing numbers as cold rolling increases.
Also a large grant from the Croucher Foundation, numbered 394/064/1115 was the seed money for the start of this work, and the foundation is heartily thanked for its support.

Solute dragging of the grain boundaries due to Nb or Ti is also considered to be the reason for the larger retardation in spite of the limited number of quantitative discussion.
In the secondary electron images, grain boundaries are usually recognised as a boundary of light and dark contrast, and not only large-angle grain boundaries but also small-angle grain boundaries with the misorientation of a few degrees could be clearly recognised in the image.
Therefore, if two FIM images before and after passing the grain boundary or one FIM image containing the information of two grains are taken, the misorientation can be calculated.
The measured width of 5 nm GB 5 nm 20 nm 0 10 20 30 40 50 0 10 20 30 40 Nb+Fe ( x10 3 ions) Number of Nb atoms Fig.2 A ladder diagram across cell boundary in Fe-0.09Nb alloy quenched just after hot-compression at 725°C.
where Nv is the number of atoms per unit volume, k is the Boltzmann constant, and T is temperature.

When cold deformation, using the control deformation degree and the annealing temperature to refine the grain, the grain is finer and the grain boundary is more, and the grain boundary has the effect of obstructing the slip deformation [4].
It could be agree with that the 4 kinds of new zirconium with the same of the original grain size .
Compared with process 1 and process 3, it can be seen that the heat treatment temperature is invariable, the larger the cold-rolled shape variable, the finer the grains, the greater the grain boundary area, the more winding grain boundary, the more unfavorable the crack expansion, the higher the yield strength of the material.
Which showed that the effect of increasing the deformation of cold rolling on the fine grain enhancement was more obvious when the original grain size of the material was the same.
The comparison process 3 and process 4 also found the same rule, the increase in annealing temperature resulted in grain coarsening, grain size increased, the less the grain boundary, the material yield strength decreased.

From the Vickers hardness test of base metal, weld metal and HAZ, the hardness numbers of each specimen were obtained.
This is indicated by the shape of the fracture surface of the sample which is not flat, which means that the fracture does not cut the grain but follows the grain boundary.
numbers 1, 2, 3 are the base metal area on the left, while numbers 4, 5, and 6 are in the HAZ area, then numbers 8, 9 and 10 are in the Weld area.
Meanwhile, numbers 11 and 12 are the the right HAZ area.
And finally numbers 13, 14, 15 are the right base metal area.