Search results

a horita@zaiko.kyushu-u.ac.jp, blangdon@usc.edu Keywords: Aluminum alloy, Grain refinement, High-pressure torsion, Severe plastic deformation, Ultrafine grains.
It is convenient in practice to express the total strain in terms of the total number of rotations applied.
Figure 4 shows a montage of the internal microstructure on the longer plane of this specimen after N = 1, where N is the number of turns: the plane of sectioning is illustrated at the upper right in Fig. 4.
To evaluate the significance of continuing processing to a larger number of turns, Fig. 7 shows a montage of the microstructures on a longitudinal section after a total of 2 turns.
(3) After two turns, the microstructure at the edge in the mid-section was uniform with equiaxed grains, high angle boundaries and an average grain size of ~130 nm.

Austenite final grain size was measured .
grain size.
The experiment also shows that steel with higher Nb content has lower grain growth kinetics and has the finer austenite grain size.
Higher cooling rate after hot rolling and recrystallization will produce finer autenite grain size, and steel with higher Nb content has lower grain growth kinetics and has the finer austenite grain size. 2.
Tech, vol 24, Number 2, (2008.)

During annealing process, the twin grains disappeared and the original bulky organization was replaced by recrystallization grain, while the grain refinement was obvious with the grain reduction to 20-60μm.
Some initial grain steered to favor orientation by grain rotating, initiated new twin, secondary twin and crossed twin[7].
It shows that grain refinement is obvious, twins disappeared during annealing, crystal grain siae changed from 200~300μm to 20~30μm.
Put number in table 1 and R2/R1 into (1), and table 2 show the calculation results.
At the same time the size of grain decreeased to 20-60μm which indicated that the grain refinement was obvious.

The domain size is 3mm wide by 4mm high, giving a total number of 600×800 cells.
A thin layer of fine grains grew from prefixed seeds and only a few long columnar grains succeed in growing due to the competitive nature of the growth.
Equiaxed grains are formed immediately from a thin layer of fine columnar grains near the surface.
Density of nuclei in bulk liquid changes from 6.5×1010 (number of nuclei/m3) (Fig. 3 (a)) to 6.5×1014(number of nuclei/m3) (Fig. 3 (e)).
-4 -3.5 -3 -2.5 -2 2 2.5 3 3.5 4 4.5 -4 -3.5 -3 -2.5 -2 2 2.5 3 3.5 4 4.5 -4 -3.5 -3 -2.5 -2 2 2.5 3 3.5 4 4.5 -4 -3.5 -3 -2.5 -2 2 2.5 3 3.5 4 4.5 Log (G) [K/m] Log (V) [m/s] Log (V) [m/s] Log (V) [m/s] Log (V) [m/s] Log (G) [K/m] Log (G) [K/m] Log (G) [K/m] 1wt%Cu1wt%Cu 3wt%Cu 7wt%Cu 5wt%Cu 1wt%Cu Equiaxed Grains Equiaxed Grains Equiaxed Grains Equiaxed Grains Columnar Grains Columnar Grains Columnar Grains Columnar Grains Figure 4 Progress maps showing the effect of alloy solidification range on the CET: (a) open and filled diamonds indicate equiaxed and columnar grains for Al-1wt%Cu; (b)open and filled circles indicate equiaxed and columnar grains for Al-3wt%Cu; (c) open and filled triangles indicate equiaxed and columnar grains for Al-5wt%Cu; (d) open and filled squares indicate equiaxed and columnar grains for Al-7wt%Cu.

Then the alloys were subjected to ECAP in a tool with a channel intersection angle of 45° at a temperature of 450 °C along the BC route [20], the number of cycles was 6.
ECAP provides the formation of a homogeneous sub-fine-grained structure in the alloys, while the average grain size, decreasing 100-200 times, is 0.3-0.5 microns.
According to TEM data, grain boundaries free of dislocations are observed in the coarse-grained state.
After ECAP, a complex diffraction contrast is observed at the grain boundaries, which indirectly indicates an increase in the density of dislocations at the grain boundaries.
During mechanical tests, it was found that in the coarse-grained state, the tensile strength of the Ti49.5Ni50.5 alloy is 720 MPa, and after the ECAP increases with the number of passes and reaches a maximum (1350 MPa) for 6 passes, which is almost 90% higher than in the coarse-grained quenched state (Fig. 2).

Measured structural characteristics were the profile intensities NA (the mean number of grain profiles per unit area of the section plane) and the chord intensities NL (the mean number of profile chords per unit length of the test line).
The estimate of the grain intensity NV (the mean number of grains per unit volume) was obtained following the recommendation of the ASTM E-112 Standard [11] as [NV] = 0.8Π(NA) 3/2, where Π denotes the geometric mean of NA(•), (for a discussion of this relation see [12, 13]).
The surface intensity SV (the mean grain boundary area per unit volume) was estimated as [SV] = 2ENL and the length intensity of grain boundary junctions LV (the mean length of triple grain junction per unit volume) as [LV] = 4ENA, where E denotes the arithmetic mean with respect to all examined planes or directions (the relation [SV] = 2ENL is the standard stereological relation, the relation [LV] = 4ENA follows from the fact that the mean number of profile vertices is 6, hence 2ENA estimates the mean number PA of triple points per unit section area and [LV] = 2PA is again the standard stereological relation).
The estimated mean grain volumes are of the same order - 4 and 12 µm3, but a grain of the volume exceeding 10 4 µm3 (see [10]).
Lowe (editors): Ultrafine Grained Materials III.

When a large number of high-power electrical appliances work together in the same system, the current of the electrical system will exceed its rated current.
White color represents the air poles in the melted marks and other colors represent different grain orientations relevantly; black color represents grain boundary. 3.2 Grain misorientation in melted marks of copper wire The grain misorientation (grain boundary angle) of the PMMs and OMMs are obtained (Fig. 2).
The horizontal ordinate delegates those grain boundary angles >15° and the vertical ordinate is on behalf of the relative frequency of each grain boundary angle correspondingly.
The ratios of high-angle grain boundaries to total grain boundaries in melted marks are calculated.
PMMs of copper wires were filled with columnar crystals in which there was a large number of air pores scattered, whereas the OMMs of copper wires were occupied by numerous dendrite crystals in which air pores were hardly detected.

The austenite grain in the HAZ is considerably coarser when compared to the grain size of the parent metal.
Since grain coarsening in the HAZ is accompanied by some loss in toughness, limits have been placed on the recommended weld heat input to constrain grain growth in the HAZ region.
In the case of prior-austenite grain boundaries, the number and size of the M/A particles have the most important influence on the Charpy impact results.
Increasing the number and size of M/A particles at the grain boundaries leads to the increase of the statistical probability of cracking and the crack propagation.
Under dynamic fracture, the failure takes place in a very short time, and thus there is no sufficient time for a crack to find a weak plane and eventually the crack propagates from one grain to the near neighboring grain and extends to the prior-austenite grain boundaries.

Small new grains formed at triple points and more rarely within grains.
This was particularly important as etched NaCl creates unwanted topography that reduces the number of successfully indexed pixels.
Orientation filtering to remove "noise" in maps proved very useful and reduced the number of artefact subgrains, which were often single or double pixels along boundaries.
At this very low misorientation the EBSD maps showed the subgrain boundaries and the correlation with LM was good but the number of artefact boundaries also increased.
Some long subgrain boundaries cut completely across a grain, dissecting it into two smaller grains.

Since superplasticity requires a very small grain size, typically <10 µm, it is feasible to process HEAs using severe plastic deformation in order to introduce significant grain refinement.
Furthermore, when the number of alloying elements increases beyond five, the contribution of the configurational entropy to the total free energy becomes sufficiently significant that it can overcome the enthalpies of compound formation and phase separation and thereby stabilize the solid solution state relative to any multi-phase microstructure [1-3].
It is reasonable to anticipate that there may be an opportunity to achieve a combination of high solid solution strengthening and good ductility if the solid solution phase possesses a simple crystal structure, such as a face-centred cubic (fcc) lattice, where there will be a large number of active slip systems [1-4].
Thermo-mechanical processing is generally employed in industry to achieve the requisite small grain sizes but this processing is capable only of producing grain sizes of the order of a few micrometers and it is not possible to achieve exceptional grain refinement into the submicrometer and nanometer range.
Experiments show that HPT has an advantage over ECAP because it produces both smaller grain sizes [12] and a higher fraction of grain boundaries having high angles of misorientation [13].