Search results

There are a number of observations [1-8] demonstrating that β-phase contributes to the SCC of AlMg alloys.
Samples were solution heat-treated (SHT) at 450°C for 30 minutes, followed by air-cooling, and then given one of a number of sensitisation heat treatments (see Table 1).
Grain boundary attack was found to vary greatly among individual grain boundaries.
The boundary between grains 1 and 2 shows continuous attack, the boundary between grains 1 and 3 as well as the boundary between grains 2 and 4 show discontinuous attack, whereas the boundary between grains 2 and 3 shows no attack.
This different susceptibility to corrosion attack for each boundary can be related to the grain boundary crystallographic misorientation using EBSD. 0 10203040506070 Attacked mode Misorientation angle, degree continuous discontinous unattacked Assessment of a large number of boundaries has shown that there is a threshold in the vicinity of 20°, below which there is negligible attack (Fig. 3).

This paper presents a fractal analysis of the self-sharpening phenomenon of the grain cutting edges in cBN grinding.
Representative single crystal cBN grain was used for cBN wheel.
And then, the number of cubes intersected with 3D-profile N(r) is counted.
If there is a fractal nature in this 3D-profile, the relationship between N(r), r and fractal dimension DS is given by () SD rrN − ⋅=α (1) where α is constant number.
As shown in Fig. 2 (a), square grid with mesh size r1 is set on a 3D-profile of the top surface of grain cutting edge.

The value of Si is from 1 to Q and Q is the maximum value of the grain orientation.
Grain boundary is formed among the adjacent sites with different orientation.
If the new orientation is accepted, the site may belong to other grain, otherwise the site belongs to the old grain.
One MCS is equal to the attempt step times N which is actually the total number of crystal lattice sites in the simulation domain.
Gao et al.[9] related the Monte Carlo simulation time (tMCS) to real time by two different models, which are a grain boundary migration model and an experimental data based model, and the two models is given by Eq. (1) and Eq. (2), respectively. 1 2 2 2 0 2 2 2 1 1 4 ( ) exp exp n m a a MCS a L AZV S Q t t K � hK R RT γ λ λ     ∆  = + −             (1) 1 0 1 1 ( ) exp ( ) n n n a MCS n L Q K t t K K RT λ λ ⋅     = + −         (2) where tMCS is Monte Carlo simulation time, t is real time, L0 is the initial grain size at t=0, K1, n and n1 are model constants, λ is the lattice point spacing, γ is grain boundary energy, A is the accommodation probability, Z is the average number of atoms per unit area at the grain boundary, Vm is volume of specific mol, Na is Avogadro's number, h is Planck's constant, K is Boltzmann's constant, R is the gas

Fracture adjacent structure of fracture Middle structure of no fracture specimen specimen 100× 100× Stretch structure of fracture specimen 500× Stretch structure of no fracture specimen 500× Thread head structure of fracture specimen 100× Thread head structure of no fracture specimen 100× Fig. 3 Comparison of microstructures between fracture specimens and no fracture specimens According to Fig. 3, no significant grain coarsening or abnormal structure area was observed in both fracture and no fracture specimens (100×) with grain fineness number being normal.
Besides, the screw thread heads were also uniform tempered sorbite with same grain fineness number [5].
But the holes formed were quite special: some holes distributed along the grain boundary, some presented in the second phase particles position of the grain.
B element usually distributed at the grain boundaries and it is very important for grain boundary strengthening.
Therefore, B was extremely rare since it showed such high content in grain from the analysis experiment, which indicated that B element at the grain boundary would migrate into the grain and formed the second phase particles, resulting in weakening of boundary strengthening.

The grain boundary activation energy of the samples decreases with increase in sintering temperature due to enhancement in grain contacts.
Most studies on LSP reported on their phase transition phenomenon while limited numbers reported on their conductivity behaviour.
The total conductivity of samples (not shown) is similar to the grain boundary conductivity due to the domination of grain boundary effects.
The grain boundary resistance decreases with increase in conductivity.
The sample sintered at 700 °C exhibits grains of different sizes which may be due to creation of larger number of nucleation centres.

The hardness test curve showed that the hardness increased gradually with an increasing number of deformation passes.
These phases are collinear within the same grain, but have different orientations between different grains.
The grain is dividing into smaller grains along the kink band, and the grain size decreases and distributes more uniformly with deformation passes increasing.
Some kink grain boundaries gradually evolved into large angle grain boundaries, which effectively divide the original grain and the refined grains.
(4) With an increasing number of deformation passes, the volume of cuboidal particles gradually decreases and they become more uniformly distributed within the matrix.

Also the number of ferrite grains which direction 〈101〉 are parallel with transversal direction of rolling (notification 〈101〉 ║ TD) showed a well observable increment.
A strong correlation between the hydrogen permeability and number of ferrite grains in which normal direction of rolling is the normal of {111} plane is observed at the beginning of cold rolling.
As the fragmentation of the carbides increased, the number of randomly oriented ferrite grains Fig. 6.
When each coarse carbide were fragmented, increasing deformation level again increased the number of ferrite grains in which normal direction of rolling is the normal of {111} plane, as well as the hydrogen permeation time.
Conclusion In cases when no other significant changing in the microstructure can be observed, which can act as major trapping site for the hydrogen, increasing number of ferrite grains in which normal direction of rolling is the normal of {111} plane increases the hydrogen permeation time.

From the average grain size, the grain number per unit volume (N) can be estimated.
It is reported that the mechanism of grain refinement has three types: a large number of nucleation before solidification; recrystallization mechanism and dendrites fusing during recalescence.
When V=25 m/s, the columnar grains disappear, and Fe7Co3 intermetallic compound forms fine equiaxed grains, as presented as Fig. 3(c).
With the increase of nuclei number of metastable dendrite, under high undercooling, grain coarsening emerged.
According to the experimental results, the grain number per unit volume (N) of Fe7Co3 intermetallic compound in ribbons was estimated by the average grain size.

The grain size is refined from the initial ~75 µm grain size down to ~1.5 µm.
The initial grain size is ~75 µm.
Though the extrusion ratio was only 15.4, the resulting grain structures are mostly recrystallized and equiaxed fine grains.
The finest grain size achieved is 0.7 µm.
Acknowledgement The authors gratefully acknowledge the sponsorship from National Science Council of Taiwan, ROC, under the project number NSC 91-2216-E-110-006.

Ultrafine-grained (UFG) structure with grain size 1-2 μm and coarse grain (CG) 20-30 μm were obtained by thermal annealing at a temperature below the recrystallization temperature [12].
Microcracks propagate mainly along grain boundaries and have uneven branching.
The numbering of stages is retained by the previously introduced Ivanova V.S. and Terentyev V.F. classification [4, 5] regardless of their availability.
Their number is not significant, and the dimensions do not exceed 3 μm.
a) b) Figure 5 – Microstructure of the submicro-crystalline sample They are poorly noticeable with an increase in x 1000, obtained with the help of an optical microscope, but their number is much larger than the number of twins detected for the UFG structure.