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The values of KIC in AZ31 magnesium alloys were dependent on the grain size.
Introduction A number of magnesium alloys have been shown to exhibit excellent mechanical properties, such as high specific strength at room temperature and superplasticity at elevated temperatures [1-4].
From Fig. 1, the initial grain size was about 1.0 µm.
Effect of grain size refinement Many researchers have been pointed out that the values of fracture toughness are dependent on the grain size in a lot of kind of materials such as Ti-, Fe- and Al-alloys [23-25].
The values of KIC in AZ31 magnesium alloys were increased with grain refinement.

According to the mechanical and microstructure test results, increasing in welding pass number causes reduction in grain size and increasing in average hardness of HAZ.
Also inter-pass slag inclusion defect occurred in high number of passes.
For example increasing welding current intensity causes increasing in heat input which leads to grain growth in HAZ and then reduces mechanical properties of weldments.A105 and A106parts joined together with TIG method by changing current intensity and pass numbers, then macro and microscopic evaluations, hardness, tensile, impact and bending tests accomplished.
Due to the increase of heat input with increasing of current from 80 to100am, the grain size of the HAZ in the S3 increased then hardness decreased from 149 in S2 to 141HV in S3.
(b) is clear that the HAZ grain size in the S4(80amps-5pass) (S2) is smaller than in S2(80amps- 3 passes ).

We want now to adapt it to the grain boundary precipitation.
No deformation of lattice and no disorientation between the two grains are taken into account.
At long time (fig. 2a), one observes approximately the same number of NbC precipitates on the GB and in the bulk.
Figure 3 : Evolution of the size of the precipitate in number of atoms by precipitate during a thermal aging at T=900K and the concentration CC=CNB=0.5%at.
Figure 4 : Evolution of the size of the precipitate in number of atoms by precipitate during a thermal aging at T=900K and the concentration CC=CNB=0.5%at.

The number of cyclic treatment was varied from 0 to 20 cycles.
With increasing the number of heat treatment cycles, the W/W grain boundary area is changed to W/matrix boundaries by the penetration of matrix phase.
Variations of measured impact energy with number of heat treatment cycles.
This anisotropy of plastic deformation in the W grain may be increased with increasing the number of heat treatment cycles.
Residual stresses in W grains measured by XRD were also increased with increasing the number of heat treatment cycles.

Goss grains({011}<100>) are nucleated within shear bands in deformed {111}<112> and{111}<110> grains. {111}<112> grains nucleate in deformed {111}<110> grains and new{111}<110> grains nucleate in deformed {111}<112>grains. {111}<112> grains have an evident advantage both in number and growth rate over α grains, thus the controlling of annealing time can contribute to the increase of {011}<100> texture.
With the increasing of annealing time, as shown in Fig.1 (b), new Goss grains({011}<100>) are nucleated within shear bands in deformed {111}<112> and{111}<110> grains and the number of shear bands is the highest in deformed {111}<112>grains.
Since {111}<112> grains have an evident advantage both in number and growth rate over α grains, when the annealing time increasing to 180s, the area fraction of {011}<100> component drops down to 0, while {111}<112> component is the dominant component.
(2) {111}<112> grains nucleate in deformed {111}<110> grains and new {111}<110> grains nucleate in deformed {111}<112>grains.
Few Cube grains ({100}<001>) are nucleated within shear bands in deformed {111}<112> grains

A notable inference was that the variation in grain refinement was not significant with the increase in number of passes corresponding to effective strain values ranging from 1.16 to 4.64.
As the number of passes increase, there is some recovery of the deformed microstructure because of specimen heating before every pass.
A plot of ultimate tensile strength (UTS) and % elongation versus the number of passes is shown in Fig. 4.
This was possible as they were processes augmented by high compressive stresses which lead to higher number of passes (19 passes in case of HE).
The maximum number of passes and effective strain values of the GP and CGP processes were lower when compared to the other SPD processes and hence lower the grain refinement that was achieved.

Four evaluation indexes including the mean protrusion height of abrasive grains Hm, the standard deviation of grain protrusion height Hv, the standard deviation of the distance between two adjacent grains Dv and the number of micro cutting edges per square millimeter Nm were put forward to assess wheel topography and grinding performance.
According to the above three aspects, several statistically indexes of the wheel topography were calculated and a dominant evaluation index was grain number including static cutting edge number and dynamic cutting edge number[4].
Considering the randomness of grain shapes and their distribution, four evaluation indexes were proposed to estimate the grinding performance of the wheel based on correlative literature, which were mean protrusion height of the abrasive grains Hm, standard deviation of the grain protrusion height Hv, standard deviation of the distance between two adjacent grains Dv and the number of the micro cutting edges per square millimeter Nm.
The grit number and concentration of the grinding wheel were 80 and 100% respectively.
Furthermore, the number of micro cutting edges indicated that the dressing process could make the abrasive grain sharper.

It has been shown that doping enhances the formation of grain blocks with a radial gradient in the direction of grain growth.
Separation into fractions was performed by sieves with numbers: 0.020, 0.056, 0.100, 0.160, 0.400 and 0.630 mm.
This alloy is also characterized by the formation of grain blocks with a radial gradient in the direction of grain growth.
The shape of the grains varies in fractions.
Fig. 6 Size distribution of grains with corresponding grain anisotropy for a fraction of 0.160-0.400 mm of Fe82,0Nd12,0B6,0 alloy Table 1 Average values of the maximum grain length and anisotropy Fraction, mm Parameter №1 №2 №3 №4 0,0-0,020 The maximum grain length, microns 4,079 5,013 8,868 8,556 The average grain anisotropy, counts 1,989 2,243 1,626 2,236 0,020-0,056 The maximum grain length, microns 6,794 11,321 12,934 9,311 The average grain anisotropy, counts 2,021 2,334 2,032 2,113 0,056-0,100 The maximum grain length, microns 10,962 28,536 12,702 7,689 The average grain anisotropy, counts 2,063 2,775 1,519 1,958 0,100-0,160 The maximum grain length, microns 29,632 40,802 60,577 9,710 The average grain anisotropy, counts 2,263 2,354 2,142 2,104 0,160-0,400 The maximum grain length, microns 19,47 43,544 44,621 6,167 The average grain anisotropy, counts 2,034 2,130 2,002 1,758 0,400-0,630 The maximum grain length, microns 41,867 37,516 75,778 8,367 The average grain anisotropy,

We measured the grain sizes by counting the number of grains intercepting each line using the following equation.
(number of cycles to failure = 11,050,521).
We counted the number of grains within the ODA.
This number includes grains crossing the ODA boundary.
(number of cycles to failure = 21,345,292).

Microdiffraction patterns taken from the area about 2 µm2 demonstrated a number of grains separated by high-angle grain boundaries.
The resulting grain structure can be effective obstacle for the development of grain boundary sliding.
It is clear that the large grains forming during superplasticity result in more difficult accommodation of grain boundary sliding by nucleation, slip and annihilation of dislocation on grain boundaries.
The revealed changes in phase composition of the alloy can also lead to enhancement of grain boundary mobility and acceleration of grain growth process that increases the grain boundary sliding resistance.
The changes in phase composition can also results in increase of grain boundary mobility and acceleration of grain growth.