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A number of voids are found in the tensile fracture surfaces when the welding temperature is below 1100oC.
The grains of 40Cr steel grow obviously when the welding temperature is higher than 1100oC.
The volume of the ferrite with coarse grains in the side of 40Cr increases significantly, and the depth is about 300 microns, indicating that the carbon diffusion from 40Cr to Cr12MoV occurs in welding.
A large number of hollows can be found in the fracture surface of samples in tensile test when the welding temperature is below 1100oC.
The grains of 40Cr steel grow conspicuously when the welding temperature is higher than 1100oC.

It reduced the residual glass phase, and increased the number and the length diameter ratio of β-Sialon grains [7].
When fine-grained material had the large proportion of grain boundaries and damaged along the grain boundary, crack propagation took a roundabout way.
Therefore, the z=1of β-Sialon grain was significantly more slender than the z=3 of β-Sialon grain.
The material appeared a large number of pores, and the relative density decreased.
The coordination number of B atoms, N atoms were 4, and the lattice constant was 3.615 Å.

A novel process of ultrasonic-assisted underwater wet arc welding was proposed to improve the joint properties, a number of ultrasonic-assisted underwater welding experiments were then carried out, and the effects of pulse frequency on weld formation, joint hardness and microstructure were investigated.
To demonstrate the effectiveness of the above system, a number of ultrasonic-assisted underwater wet arc welding experiments were carried out at different pulse frequencies.
The overheated zone of joint locates in the high temperature range of solid phase lines, in which austenite grain grows seriously and widmanstatten structure readily occurs subject to the rapid cooling of water, thus the joint toughness becomes poor.
As arc ultrasonic occurs in underwater welding, the forced vibration of test piece accelerates the rate of heat conduction, which restrains the growth of austenite grain while promoting the transformation from austenite grain to pro-eutectoid ferrite, finally obtaining the fine uniform HAZ microstructure.
At the same time, the arc ultrasonic vibration yields an effective mechanical stirring on molten pool, thus refines the grain, and increases the rate of crystallization and the acicular ferrite.

The initial coarse grains of Ti-50.9at%Ni were obviously refined after eight ECAE processes.
Effects of pressing number on the transformation behavior have been investigated in detail.
Good one way shape memory and superelasticity were obtained for the submicron-grained Ti-50.9at%Ni alloy.
After eight passes ECAE, the microstructure was further refined and it was difficult to recognize the ultimate grains or grain boundaries under optical microscope (Fig.1c).
Good one way shape memory and superelasticity were obtained for the submicron-grained Ti-50.9at%Ni alloy.

The SEM images indicated that in as-cast alloys, the Al2Ca intermetallic compound was located at grain boundaries with a lamellar structure, and the Al2Sm intermetallic compound was homogeneously distributed in the α-Mg matrix or near the grain boundaries with a polygonal structure, and the Al11La3 intermetallic compound was located at grain boundaries with a needlelike structure.
Moreover, the Sm addition also declined the number of the β-Mg17Al12 phase compared to that in AZ91 alloy in Fig. 3(a).
It could be found that there is the largest number of precipitated phases in AZ91-1.5Ca-0.5Sm-0.3La alloy , and all the above intermetallic compounds are generated (see Fig. 1), which precipitated in the α-Mg matrix or along the grain boundaries and will obviously restrict the movement of the adjacent grain boundaries.
However, the segregation phenomenon of Al2Sm appeared near the grain boundary.
Greer, Grain refinement of Al alloys: Mechanisms determining as-cast grain size in directional solidification, Acta.

These models are applied for optimization of the grain size and % volume of recrystallization.
The equations proposed for recrystallized grain size by Sellars are employed by the researchers at Kawasaki Steel for their model [3].
Grain size of the developed microstructure was determined using Clemex Vision Image Analyzer.
Table 1 GA Based FLC for Hot Deformation Process Process Parameters GA Parameters Process Ke Kce Ku Population Size 20 Crossover Probability 0.7 1.0267 0.9928 135.0964 Mutation Probability 0.005 10 1 18.20 Number of Generations 50 Fig.2 Closed Loop Response of Grain Size (SP=30µm) Fig.3 Closed Loop Response of Vol.
However there are number of parameters to be chosen in advance, to ensure the effectiveness of the controller.

Then, the twins originate in ERX grains.
The g¢ phases of the DD6 alloy have a solution temperature of approximately 1315°C [2], thus at 1100°C, a large number of g¢ phases still exist, as shown in Fig. 5.
Fully ERX grains nucleated after standard heat treatment.
And the twins occurred in fully ERX grains.
This effect prevents twins forming in cellular grains.

After deformation to a strain of 0.2, many grains can be seen to contain multiple twins and a small number of DRX grains can be observed to have formed at original grain boundaries.
In some regions, the "necklaces" of DRX grains decorating the pre-existing grains, and DRX grains associated with twins, have broadened considerably.
The SRX grains seemed to grow within the twinned region at a greater rate than in the original grain.
Larger original grains can be seen to be subdivided by twins that were previously filled with SRX grains but now contain DRX grains.
Instead, the colonies of DRX grains become stabilised and unrecrystallized grains remain.

The lamellar grains of Ti3SiC2 have the dimension of 16 µm in length and 4 µm in thickness for the fine-grain (FG) sample, and 50 µm in length and 15 µm in thickness for the coarse-grain (CG) sample.
SEM image and XRD pattern of fine-grain(FG) Ti3SiC2 (a and b), coarse-grain(CG) Ti3SiC2 (c and d), fine-grain(FG) Ti3AlC2 (e and f), and coarse-grain(FG) Ti3AlC2 (g and h).
Total number of cycles was 19 at 900 o C, 18 at 1050 o C, and 19 at 1200 o C during the period of 40 hr.
Barsoum et al. [2] previously explained that the effect of grain size was quite subtle, and the coarse-grain (CG) sample oxidized slightly slower than the fine-grain (FG) sample, owing to the anisotropy of oxidation.
It seems that, instead of the grain size, the anisotropy of matrix grains and the amount of retained TiCx affect the oxidation resistance much.

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.