Search results

To refine the microstructure, alloys are subjected to a modification by introducing grain refiners into the casting mold before pouring.
For providing uniform distribution of grain refiners over alloy, one uses special mixing devices that create turbulent flow field inside the molten metal and thereby intensify the diffusion processes promoting the uniform distribution of grain refiners.
The Power number is a function of the Reynolds number, , the Froude number, and the ratio of the diameter of the agitator to that of the crucible, .
Euler number vs Reynolds number.
The Euler number decreases exponentially with respect to the Reynolds number.

The grain size increases from 67 nm (S600) up to 284 nm (S1000) due to the grain growth during heat treatment.
The resistivity decreased with the increased of grain size and crystallite size due to the reduction of grain boundary effect which might improved their grain connectivity.
Therefore, in order to assess the clear picture of the effect of grain boundaries and grain structure network as a function of sintering temperature, Pr0.85Na0.15MnO3 system have been synthesized via wet chemical methods to investigate their structural and transport properties.
However, a rapidly grain growth were observed at 1000 ºC.
Sintering temperature leading to the grain growth, hence provide better intergrain connection.

AA2024-T3 had a fine, equiaxed grain structure, whereas AA2099-T8E77 had a substantial amount of recrystallized grains.
This has been achieved by effectively managing a number of factors, including the control of impurity elements, such as H, Na, K and P that are present during the preparation of Li-containing alloys, as well as using grain refining elements such as Mn and Zr.
EBSD analysis showed a relatively homogenous grain size for alloy 1.
Compared to alloy 2, some regions of smaller grains were observed, however, the vast majority of the microstructure was comprised of extremely large recrystallised grains.
The number of corrosion sites noted on both alloys was similar; however, the depth and types of corrosion observed were different.

In UAG, the cutting trace of the abrasive grain in terms of its oxy coordinate can be obtained by Eq.(1): (3) According to Eq.(2) and Eq.(3), the length of the cutting trace of an abrasive grain within the contact arc in UAG can be expressed [9]: (4) The number of the acting abrasive grain per unit time N would be N=Cbvs, where C is the distribution density of the abrasive grain on the grinding wheel periphery and b is the grinding wheel width.
The average undeformed chip thickness ha is set as the single grain cutting depth.
The velocity of the abrasive grain is 1m/s.
Under the absence of UV, the single grain cut of depth is 1.5μm.
The contact type between the grain and the SPH workpiece isCONTACT_NODES_TO_SURFACE.

It is attributed to the hexagonal closed-packed (hcp) structure of magnesium, which is characterised by a low number of operating slip systems to enable plastic deformation.
The load decrease is attributed to grain refinement since smaller grains facilitate grain boundary diffusion [21].
The microstructure of as supplied material was characterised as heterogeneous with the mean grain size equal to 48 µm for coarse grain regions and 5 µm for fine grained regions.
It is concluded that temperature controls the grain refinement process while processing route has no significant effect on grain size.
Langdon, Using grain boundary engineering to evaluate the diffusion characteristics in ultrafine-grained Al–Mg and Al–Zn alloys, Materials Science and Engineering A 371 (2004) 241–250

Introduction Polycrystalline materials are composed of a large number of micro-grains with different orientations, shapes and sizes.
Because of the periodic arrangement of atoms in a grain, the mechanical properties of the grain are not isotropic.
The elastic mechanical properties of any grain in a polycrystalline depend on the spatial orientation of the grain.
Symmetry of Cubic Grain and Constitutive Relation of Cubic Grain For a given Cartesian reference coordinate system in space, the reference grain I is chosen as the one with three edges of the cell of a cubic grain consistent with the three axes of the given coordinate system.
The orientation of any grain in a polycrystalline can be obtained by the action of the rotation tensor R on the reference grain I.

Large elongated areas are the recrystallized regions and the small grains are subgrains.
After heated at 152℃ for 8h，the grain interior precipitates coarsened with an average radius of about 2~10nm and grain boundary precipitates coarsened.
Prolonging the second aging time to 16h, the grain interior precipitates coarsened continuously and the grain boundary precipitates distributed discontinuously gradually.
After the under aged treatment, the main precipitates in the alloy were GP zones and η' phases in the grains and the grain boundaries were distributed continuously.
It could be explained by the discontinuous grain boundary precipitates which provided blocks for crack propagation along the grain boundary.

Another defining characteristic of nanopowders is the large number of interfaces.
The simulated crystallite is composed of three grains.
It is assumed that the intergranular regions are heated to higher temperatures relative to the regions within the grains, since the crystallite melting would first occur along the grain boundaries; then the grains would start melting.
A group of atoms is assumed to form a cluster, provided the number of these atoms is no less than the number of atoms on the first coordination sphere in the close-packed lattice.
It can be seen that the curve representing the number of clusters formed flattens out with time.

The grain size studied is 25/50 mm as for any material studied for use as railway ballast.
Proctor test experiments make it possible to study the behaviour of these local materials with a particular grain size (25/50) under the effect of compaction.
The principle of the test is to apply the same compaction energy by finding by an appropriate calculation, the number of strokes per layer.
What makes Diack special is that there are three types of facies that are not found anywhere else: a fine-grained facies, mainly represented by basanites, a medium-grained facies, less abundant than the previous facies and a coarse-grained facies, represented by a fully crystallised sandstone rock.
These different types of facies have geometric characteristics related to the overall grain geometry: granularity, grain size and shape, angularity and roughness, and mechanical characteristics evaluated according to grain hardness and strength.

The other cylinder surfaces are strong obstacles to dislocation motion (grain boundary).
The dislocation microstructure fills the whole grain, localized in a set of intense slip bands.
First, cross-slip spreads the dislocation microstructure inside the grain.
(c) Plastic strain of the surface versus number of cycle.
A quantitative prediction of the irreversible slip in the grain surface is plotted in the Fig. 2c, as a function of the number N of cycles.