Search results

The billets were obtained from commercially available coarse-grained, hot-extruded rod and fine-grained, hot-rolled plate.
Fine-grained samples were successfully processed at 200 °C, while coarse-grained ones must have been heated up to 250 °C to avoid fracture.
The initial microstructure of the rod was heterogeneous with coarse grains (~80 µm) surrounded by colonies of small grains (~10 µm), as shown in Fig. 1a.
However, in some cases, fracture occurred before reaching the intended number of passes.
Part of this research was supported by the Engineering and Physical Sciences Research Council [grant number EP/G03477X/1].

Effects to grinding wheel physiognomy by grain size and organization number were analyzed and grain distribution was visually represented.
A grinding wheel was supposed to be composed by massive, random distributive abrasive grains, and mathematical modeling started from abrasive grain modeling [2-4].
For one abrasive grain: ( )idd i fkdd += 10 (1) id is diameter of abrasive grain i (mm); 0d is average diameter of certain abrasive grains (mm); dk is grain diameter variation factor; dif is random uniform number generated by the computer.
Abrasive grains were supposed to be distributed equably in the volume of zyx lll ×× , so the number of abrasive grains contained in is N and N equals to: 3 0/6 dlllVN zyxg π = (3) gV is abrasive grain proportion of the grinding wheel (volume ratio between abrasive grain and grinding wheel).
The roughness of grinding surface related to the wheel-per-area-grain-number, grains distribution and tooth marks.

In addition, the number of austenite grains per unit area was evaluated.
In addition, the numbers of austenite grains per unit area under different strain were evaluated, and the results are shown in Fig. 3.
Fig. 3 Effect of strain on the number of austenite grains per unit area The schematic representation of dynamic strain – induced boundary migration is shown in Figure 4 (black lines: prior austenite grain boundary; red lines: dislocations).
The dislocation density within Grain A is relatively lower than that within Grains B, C, D or E, so the Grain A has a high growth driving force [20].
Grain E Grain A Grain D Grain C (c) (b) (a) Dislocations-free regions Grain B Fig. 4 Schematic representation of dynamic strain – induced boundary migration: (a) the initial austenite grain structures, (b) the distribution of dislocations after deformation, (c) the dislocations density driving austenite grain boundaries migration Conclusions 1.

The control of grain boundaries (GBs) is the key to improve the efficiency and production yield.
The atomic number of Fe (26) is nearly two times larger than that of Si (14), which would give rise to higher brightness in ADF images.
Large residual strain inside grains acts as the driving force for the formation of SA-GBs.
In most commercial mc-Si wafers, the grains are not grown in large size due to non-optimized growth condition.
Thus, sub-grains and SA-GBs possess both strong electrical activity and large strain.

In this paper, Nc is defined as the number of cycles when a crack or a slip greater than the grain size is observed using a microscope for the first time on the polished surface.
Solid plots show the number of cycles to fracture (Nf), while the open plots show the number of cycles to crack initiation (Nc).
Fig. 4 Relationship between stress amplitude and number of cycles to fracture or crack initiation.
The horizontal axis in these graphs denotes the number of cycles standardized by Nc (N/Nc).
When the horizontal value increases, the number of cycles increases.

Based on the protrusion depth, this study found that only small number of grains can be considered as active grains.
The ground surface profile from the UVAG with DET was analyzed [2] and the possibility that only a small number of grains, probably one, are active during the grinding process was highlighted, but it has not yet been known how the 3D grain protrusion parameters were related to the ground surface.
Fig. 4 shows typical successful samples for the possible active grains identification where the number bullet shows the highest grains in sequence for the top 5 µm.
All successful samples only have a small number of possible active grains while some only have one possible active grain.
All successful samples have some of their possible active grains located within the estimated active grain locus.

The number of triple junctions in polycrystals is comparable in the order of magnitude with the number of boundaries.
Scheme of the grain boundary system with a triple junction, a - width of the middle grain; 2θ - value of the vertex.
GB I GB III Grain 3 Grain 2 Grain 1 GB II 2θ θ a/2 a/2 θ y x ϕ v V GB III GB II GB I Experimental The experiments were carried out on tricrystals of high purity (99,999%) aluminium with a grain boundary geometry as shown in Fig. 1.
The position of the grain boundary system and the angle θ were recorded from the grain boundary grooves.
The value of compensation temperature for the grain boundary with triple junction systems and individual tilt grain boundaries in Al are given in the Table 2.

An intensive GBS, migration of grain boundaries, a considerable growth of grains, absence of dislocations in grain boundaries, dislocation substructure and gliding lines in grains were typical for their creep.
It stopped when a growth of grains stopped.
As can be seen, fine grain is not enough for SP.
Due to the above said, in grains there occurs dislocation structure, intensive gliding of dislocations, lines and bands of gliding are formed, a number of lattice dislocations in grain boundaries grows.
Then there grows a number of dislocations, approaching the boundaries.

Relatively higher grain refinement rates are observed during initial passes.
Linear intercept method was employed to estimate the average grain sizes and the ambiguity in grain size measurement arising from deformed microstructure is minimized by measuring the number of intercepted grains from superimposition of grids on the image in different orientations (00,450,900).
The photograph of constrained groove pressed OFE copper sheet after different number of passes shown in Fig.1 clearly reveals rough surface finish marked with waviness caused by the sharp corners present in the grooved die profile during repetitive pressing of sheets.
The average grain sizes obtained in CGP processed OFE copper sheets as a function of accumulated plastic strain shown in Fig. 3a clearly indicates the reduction in grain sizes with increasing number of CGP process.
As the accumulated strain increases, the grain refinement reduces significantly (Fig.3a) and the average grain sizes obtained at the end of third pass is 39mm (Fig. 2b) which are comparable to grain sizes reported earlier in CGP processed commercial purity copper [7].

It was found through experiment that, the grain was very coarse in the cast ingot of 5N5 high purity aluminum, and the average grain size is about 60mm.
The grains are very coarse, and the average grain size is about 60 mm.
After eight ECAP passes of Route BC (Fig. 4(b)), the grain was refined furtherly, and the average grain size is less than 50μm.
We can see the presence of a large number of dislocations and the dislocation has occurred tangles, and has formed cellular sub-structures.
A large number of dislocations appear again in the sample after eight passes, maybe because that the dislocation was restarted under the shear deformation.