Search results

Previous work reported that Mg24Y5 phases can precipitate along the grain boundary and in the grain interior after heat treatment [12-14].
After extrusion, the tiny Mg24Y5 phases distribute on a-Mg matrix due to the occurrence of dynamic recrystallization, as shown in Fig. 2 (a) and (b), the shearing stripes and parallel streamlines which distribute along the extrusion direction are especially obvious and a large number of fine equiaxial grains distribute in the parallel streamlines.
It is known from the recrystallization nucleation mechanism, dislocation density of the adjacent grains is different due to the inhomogeneity of the extrusion deformation, one side grains with small deformation energy at grain boundary will bulge into the other side which have fine grain and high dislocation density by way the nucleation of grain boundary remotion and subgrain swallowing, distortionless recrystallized nucleus successively form, leading to a decrease in grain size.
As shown in Fig. 3, the secondary occupies a large grain boundary and shear band and this is considered to be an effective obstacle to grain boundary sliding and dislocation motion in the vicinity of the grain boundaries.
Pan, Effect of Ca addition on grain refinement of Mg–9Li–1Al alloy, J.

The average number of flat grains on the surface (NA), the average surface of the grain cross-section (aav) and the average diameter of the flat grain (dav) were determined.
The β phase separated by grain boundaries occurs in the microstructure.
Zones in which the β phase occurs as thicker irregular grains, are seen.
Tin deposits uniformly within grains and preferably on grain boundaries and precipitates and non-metallic inclusions.
The grain growth is caused by the β phase tendency to decrease the surface energy of grain boundaries, which is the lower the larger are grains, since surfaces of their boundaries are then smaller.

Change in BPR affects the total number of collisions, the motion pattern and the types of collision.
The number of collision per unit time could increase and produce more energy transferred to the powder particles and results in faster MA [3].
All of these changes were caused by the size of grain [4].
The powder mixture then became more refine and as a result, the grain size became smaller.
The increase of BPR from 5:1 to 10:1 resulted in an increase of number of hit between powder-ball-wall.

The elastic modulus is dependent on the fatigue load condition and the accumulated number of the load cycles.
The fitting constants are obtained, and the fitted equation is used to describe the degradation of Young’s modulus at N number of cycles.
However, the drawing process of the wires to 55% reduction of the area has resulted in finer grains in the cross-sectional area, while the longitudinal section displays elongated grains along the drawing direction with reduced pearlite interlamellar spacing (see Fig. 2 (c) and (d)).
Such grain refinement is due to the increased number of dislocations in the wire material during the drawing process.
The drawing process to 55% reduction resulted in finer grains in the cross-sectional area and elongated grains along the drawing direction in longitudinal section, which increased the strength of the wires.

Introduction Following the demonstration of superplasticity in a 3 mol% yttria stabilized tetragonal zirconia (3YTZ) by Wakai [1], there have been large number of studies on that material [2,3].
In fine grained ceramics, diffusion creep is likely to occur by matter transport along grain boundaries, as proposed by Coble [5], and this process involves n=1, p=3 and Q=Qgb, where Qgb is the activation energy for grain boundary diffusion.
A value of n~2 was attributed to grain boundary sliding, and higher values of n were related to a grain size and temperature dependent threshold stress.
Measurements after creep testing indicated that there was no significant change in either the grain size or the aspect ratio of the grains.
A very limited number of dislocations could be identified and they are shown by arrow marks.

Compared with common SIMA methods, the new SIMA methods could generate more spherical and finer grains.
The mean grain size(diameter d=1.74L) is 45µm.
Liquid, indicated by the presence of Mg17Al12 particles after quenching, has appeared not only along grain boundaries but also as tiny liquid pockets within the grains(Figure 3(b)).
It should be mentioned that quantitative metallography revealed that the total liquid fraction at 570ºC was about 42%, and 75% of the formerly liquid phase was concentrated around the solid grains and 25% occurs as entrapped liquid within the grains.
When the temperature reached the solidus temperature, remelting started at grain boundaries.

The machined area has a close relationship with both the density and grain size of abrasive.
Results and Discussion Effect of the grain size of abrasive.
Thus, the grain size of the abrasives directly influences the removal efficiency of the tiny-grinding wheel, and the grain size should be selected based on the field strength and the size of the EMR particles.
When the abrasive concentration reaches a certain level (6% or above), the number of the diamond abrasives constrained by the chains of the EMR particles tends to saturate, then redundant diamond abrasives can easy escape from the tiny-grinding wheel, leading to a stable size of the tiny-grinding wheel.
However, the machined diameters of diamond and SiC abrasives with the same grain size are similar and that with different grain sizes are quite different.

The sample number and heat treatment process seen Table 1. 2.
A large number of ferrite existed in the sample quenched at lower temperature, and part of them was independent existence as block shaped (Fig. 1(a)).
The austenite growth is mainly through the grain boundary migration, but the austenite has been split by ferrite which existed in the sub-temperature quenched microstructure, and impeded inhibiting austenite grain boundary migration.
At the same time, the lower quenching temperature was not benefit to atomic diffusion, so grain boundary migration was slow, the austenite grain growth was hindered [7].
(2) The austenite grain size of 35CrMo steel can be refined by sub-temperature quenching

It can be observed that the addition of CNT significantly increased the overall number of load cycles to failure.
Fatigue cycles are normalized by dividing the current cycle number (N) by the number of cycles to failure (Nf).
As strain advanced, dislocation tangles moved gradually towards the grain boundaries.
(a&b) TEM images of dislocation activity near grain boundaries in the Al-0.5CNT composites.
Dislocations arranged themselves into neat arrays near the grain boundary (arrows).

During this process, strip temperature is of great importance for controlling metallurgical transformation and grain size.
Introduction In cold-rolling process, the grains of steel are flatten, internally distorted and hardened by strain.
As the heating temperature rises, the microstructure and mechanical properties of steel go through three stages of transformation, recovery, recrystallization and grain growth.
Numerical results In this paper, the grid number in width direction is set to 20.
The number of tracer point along the length direction of strip is set to 300, so the grid Fourier number is about 10-3~10-4, depending on strip speed.