Search results

Decreasing grain size usually results in the mechanical properties improvement.
Final product properties are strongly dependent on the ECAP process parameters, such a temperature, type and number of passes and pressing rate, and also on the structure of the initial material.
In the case of AZ91 magnesium alloy the ultra-fine grained microstructure remains stable bellow 300 °C while increased temperatures (350 °C and 400 °C) leads to gradual grain coarsening [8,9].
Enhanced corrosion resistance of ultra-fine grained magnesium alloys prepared by SPD techniques was studied, however still only limited number of works describing the corrosion mechanism is available [4, 11, 12, 14, 15].
There are areas with small grains with the average grain size of 3.3 ± 0.5 µm with large amount of small Mg17Al12 particles, and areas with larger grains, with the average grain size of 9.9 ± 4.5 µm where the density of small Mg17Al12 particles is low.

In the machining process, as the silicon grains in the alloy affect tool wear greatly, the tool materials should have high performance.
Then, the silicon grain contacted with the tool tip.
Additionally, the rigid silicon grains in hardened layer can also induce micro breakage on the cutting edge.
Contrasted with cutting common metals, the hard silicon grains in the Si-Al alloys make the friction between the workpiece and the clearance face worse.
The micro pectinate grooves on the clearance face were mechanical wear produced by silicon grains and other hard grains in Si-Al alloy.

Among the methods capable of producing such structures a certain number (e.g. inert gas condensation, ball milling, rapid solidification techniques) result in production of powders and thin ribbons which must be subsequently consolidated.
Some of these samples were subjected to severe plastic deformation (SPD) by high pressure torsion described in [4] under pressure 6GPa and number of rotations N=5 for additional structure refinement.
Average grain size in these samples varies from 0.5 to 0.7 μm.
Domain walls do not limit separate grains, but encircle a lot of disoriented grains and form “exchange” domains.
Superposition of DS with image mode shows that in smaller grains domain walls are pinned at grain boundaries.

The minimum ferrite grain size obtained by the new TMCP is less than 1µm.
Vickers hardness and tensile strength increased with increasing number of process.
Fig.5 shows the relationship between Vickers hardness and number of passes of side extrusion.
Hardness increases with increasing number of passes of shear deformation.
Tensile strength increases with increasing number of passes of side extrusion.

Along with the remelting process, the columnar grain begins to grow to certain angle with axles, the shape of the metal pool gets closer to paraboloid shape.
(1) As the model is axle symmetric, in order to reduce the number of grid and save the computing time, half of the model was taken to calculate
The grain growth begins to be affected by the cooling of the side with the casting going.
The heat transfer at the bottom is more and more difficult, so the grain near the side begins to grow to the center along the opposite direction of the heat flow and the grain growth rate is also quick.
Reducing the coefficient of heat transfer at the side, the heat which distributes through the side decreases, so that the rate of heat transfer slows down and the grain mainly grows along axis thus the rate of grain growth slows down and the depth of the metal pool becomes shallower.

The S-Parameter reflects the number of photons with a low momentum shift (<3 x 10-3moc) [9] and is defined as the ratio of the counts in the central region of the peak to the total counts in the peak.
The number of different vacancy-type positron traps in the material can be studied by investigating the linearity between the annihilation S- and W-Parameters.
The grain size as a function of irradiation doses is depicted in figure (7).
Grain size of about 180 nm is obtained at 10 kGy of irradiation doses.
The measured S-parameter values can be used to determine the grain size of the alloy under investigation Grain size of about 90 nm is obtained at 70 kGy of irradiation doses.

The ultrafine grained (UFG) pure Cu thermal stability temperature decrease to 165-170 °C [3].
Such process take place by grain size (GS) decrease as well as dislocation density increase by passes number increase at equal-channel angular pressing (ECAP).
The heat treated samples number for all testing’s was at least three. 2.2.
The challenge of the science of tribology is materials with nano-columns inside the ultrafine grains as a result of extreme grain refinement by severe plastic deformation methods.
Ultrafine Grained Materials III.

The existence of Ba-b-Al2O3 phase as well as low sintering temperature and short holding time during reactive sintering inhibit grain growth and thus result in small grain sizes of the Al2O3 matrix.
Bright regions correspond to high atomic numbers (Ba), whereas dark regions correspond to lower atomic number (Al).
At 1400oC, the Al2O3 matrix exhibited fine grains and their average size was 0.78 mm.
With the increase in sintering temperature, grain growth occurs.
As shown in Fig. 6(b), the average grain size of the Al2O3 matrix attained 1.49 mm at 1500°C.

For the last decade, there have been a number of studies aimed at understanding the kinetics of IGC [3] and exfoliation corrosion [4].
Increasing the 'strength' of a texture means there is a high tendency for grains to orientate themselves with a similar crystallographic orientation as other grains, as opposed to 'weak' texture where the grains orientate themselves more randomly.
A strong texture results in low misorientation angles between adjacent grains.
Therefore, the tendency for the corrosion path to branch off a susceptible high-angle boundary will be reduced if the number of low-angle boundaries is increased, making IGC more directional.
As mentioned above grains will develop a preferred distribution of orientations.

To describe the corrosion morphology, two parameters were statistically determined: the number of corrosion defects propagating in the L direction and observed for a given distance in the ST direction (density of corrosion defects) and the average depth of corrosion defects in the L direction.
Taking into account the cumulated length of corroded surface observed in the ST direction, i.e. 80 mm, and the grain size in this direction (about 60 μm), almost 1000 grain boundaries and grains were observed for each test.
When the NHT samples were aged, the density and size of T1 precipitates in the grain boundaries increased but numerous T1 precipitates also formed inside the grains.
The galvanic coupling effect between the grains and the grain boundaries was reduced so that intergranular corrosion did not occur.
Fig. 3c suggested that the branching could be attributed to both an extent of the corrosion to a larger number of grain boundaries but also to the dissolution of subgrain boundaries.