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These forces make zirconia grains aggregate together and coalesce to form bigger grains.
Because of the larger pinning effect of the dispersed grains, the grain Fig. 3.
Thus, large zirconia grains mainly remain at the grain boundaries without being captured into the matrix grains.
With the grain boundaries diffusion and grains combining, few single zirconia grains or small aggregate of zirconia grains are embedded in alumina matrix grains before they can coalesce with others.
Acknowledgement This research is financially supported by the Promotional Foundation for the Excellent Middle-aged or Young Scientists of Shandong Province under grant number 02BS049.

Further, grain structure and grain boundary character are analyzed in detail to discuss the deformation mechanism.
Grain Structure.
They are distinguished by number of high KAM points.
Grain Boundary Character.
The fine grains remained during the deformation through grain boundary sliding or dynamic recrystallization.

Equation (7) and Fig. 4 also show that, for a given annular flaw size, a solid containing large a number of small pores will have the Young's modulus less affected by the presence of pores than a solid containing a small number of large pores.
Clearly, in this range of grain sizes, the strength of the polycrystalline alumina is controlled entirely by the flaw size rather than the grain size.
In fact in small grain size ceramics, where the flaw size is much larger than the grain size, the inherent flaw size may control the strength rather than the grain size.
It is shown that a solid containing larger number of small pores will have higher strength than a solid containing smaller number of larger pores.
At sufficiently small grain sizes, the strength becomes independent on grain size and the major factor that controls the strength is the flaw size which for nanocrystalline ceramics such as alumina (Fig. 5) can be much bigger than the grain size.

The M23C6 carbides precipitate preferentially at grain boundaries, and then coarsening remarkably with increasing aging time.
After aging, the number of twins structure is decreased even to be disappeared gradually with the aging time increase, it can be observed more precipitated phase which distributed in the interior of grain and grain boundary. as shown in Fig.2 (b).
There are also a small number of particles larger than 300nm inside the grains and at the grain boundaries.
After aged for 94 h, some newly formed M23C6 carbides are found to precipitate along the grain boundaries and in the interior of grains (Fig. 3(a)).
Besides the Cu-rich phase, also there are some precipitates of M23C6 carbides at the grain boundary during aging at 750℃ in 300h, the M23C6 carbides with small size can pin dislocation at grain boundary which can act strengthening function.

The mean grain size and grain distribution and surface roughness were determined by using the Nova NT-MDT Image Analysis Software.
The surface reveals well defined grain boundaries with an average grain size of 15 nm (Fig. 4a).
A mean grain size of the order of 5-10 nm is observed.
Annealing at 400ºC for 2 hours significantly improved the crystalline properties and altered the stoichiometry in the WO3 and Fe-doped WO3 films, which increased the number of oxygen vacancies in the films.
An increase in number of oxygen vacancies is considered to be highly beneficial for gas sensing.

It conclude that some spherical shape phases of Ca2Mg6Zn3 distribute in the grain interior, and the other compounds continous precipitate at grain boundaries.
A fine-grained material is harder and stronger than the coarse one.
It is because that the fine-grained materials have the greater total grain boundary area which impedes dislocation motion.
The d is the average grain diameter, and are constants for a particular material.
Actually, the improvement of the yield strength is 10MPa, the numbers demonstrate that strengthening by grain size reduction is more, the strengthening mechanisms of the MZCxZr alloys is mainly the grain size reduction strengthening effect.

However, at 200 �exposure, a great number of θ' precipitates at the expense of T1 may be responsible for higher tensile strength in the Ag-free alloy than that of the independent addition of Ag and combined additions of Ag and Ce alloys. 1.
It can be clearly seen from Fig.1(d) and Fig.3(c) that there are similar features in grain boundaries between unexposed and exposure alloys.
Grain boundary after exposures 1000h at 107 is� still clear and there is no extensive development of PFZ near grain boundaries and no presence of equilibrium phases at grain boundaries.
Therefore, the main reason that tensile strength of the Ag-free alloy 1 at 200 exposure is greater than � that of the other two Ag-containing alloys results from presence of a great number of ��� phases in the Ag-free alloy 1.
When thermal exposure at 200� ,a number of θ' precipitates at the expense of T1 phases in Ag-free alloy make the tensile strength higher than that of the independent additions Ag and combined additions of Ag and Ce alloys .

At lower deformation, these bands are parallel and start and terminate at the grain boundaries.
As the strain level increases, the number of the twins band increases and they intersect each other.
This figure shows also the presence of annealing twins in some grains, specially in larger grains, which give evidence of a low value of the SFE in the alloy.
At lower deformation (Fig. 3a), it is observed a microstructures of nearly equiaxed grains with straight deformation twins present only in a few grains.
The major gliding activity is located in the not twinned austenite grains.

To determine the maximum number of cycles N max (critical true strain) the cycles were repeated until the sample was broken.
The number of measurement points (in the range of 30149-54335) of EBSD analysis was adequate for the applied magnification and resolution of the microscope.
They are limited to the area of grain interior and only occasionally show tendency for getting beyond grain boundaries.
Yield strength and tensile strength of the copper strip after the number of passages equal to the one third of the maximum value is 350 and 360 MPa, respectively.
In the samples subjected to RCS process increase of hardness with increase of number of cycles is registered, however after maximum number of cycles slight decrease of hardness in the samples was observed in comparison to the samples subjected to 2/3 of the critical number of cycles, which can show presence of some critical value of deformation above which hardness increase is not observed, probably due to processes of dynamic recovery which decreases density of dislocations in the material.

Deformation at all test conditions leads to modification of the coarse-grained lamellar microstructure to fine-grained one.
The recrystallized grain size is less than the thickness of the initial α-plates.
Firstly, the rise of hydrogen concentration in the alloy can lead to an increase of the number of recrystallization nucleating centers.
Secondly, the hydrogen addition reduces α-grain growth as confirmed by measurements of grain size after annealing at 650°C in air (Fig.6).
Hydrogen influence on α-grain growth in CP titanium during annealing.