Search results

This can be taken from fig.2 for a number of ELC and CMn steels.
Ferrite grain sizes are estimated an ASTM number well above the scale of 10.
As demonstrated in fig.3, these ferrite grains connect with a layer of ultra fine ferrite grains.
The abnormal grain growth seems to initiate at the interface between larger ferrite grains below the strip surface and the ultra fine-grained ferrite layer developed at some distance below the strip surface.
Second, the presence of deformed or even static recrystallised ferrite grains at the interface with the fine-grained ferrite layer.

AlTiC grain refiners form a relatively new alternative to the existing class of AlTiB grain refiners for achieving fine equiaxed grain structure in aluminum alloys during casting and solidification.
Furthermore, commercial Al-5Ti-B grain refiner was also added to A3003 alloy to compare grain refinement ability with Al-Ti-C grain refiner fabricated in the present study.
The Al-Ti-B grain refiner produced some grain refinement too, but the refinement started at relative longer holding time than that from the Al-Ti-C grain refiner.
Fig. 3 Grain size measurement result of A3003 alloy unrefined, refined through the addition of Al-Ti-B refiner and Al-Ti-C refiner Two conditions need to be fulfilled to obtain efficient grain refinement: (i) a sufficient number of potential nuclei must be present in the melt and (ii) a large fraction of potential nuclei must be activated.
TiAl3 is known to have more number of planes that have good orientation relationship with aluminium in comparison to TiC or TiB2.

Table 1: Table shows the duration and number of thermal cycles time.
The cyclic thermal process also demonstrated a decrease in the volume fraction of DIM with increasing temperature and number of cycles.
Therefore, the nuclei inherit the orientation of the parent subgrains and change in austenite grain orientation occurs only after a reasonable grain growth [14].
(c) increase recrystallised fraction can be noted with increasing number of thermal cycles.
Therefore, an increase in the strain heterogeneity due to the thermal cycle could be responsible for the grain refinement of the cold deformed austenite grains.

This research aimed to investigate, with the aid of the analysis of variance (ANOVA), the influence of the use of three load cycles to obtain the modulus of elasticity in compression parallel to grain (Ec0), in tensile parallel to the grain (Et0), in bending (Em) and in compression perpendicular to the grain (Ec90) of Angico Preto (Anadenanthera macrocarpa) wood specie.
For the number of cycles and stiffness were manufactured 12 samples, totaling 144 specimens.
Material and Methods The properties of Angico Preto wood specie used in evaluating the influence of the number of load cycles (1, 2, 3) were the modulus of elasticity in compression (Ec0) and in tensile (Et0) parallel direction to the grain, in bending (Em) and in the normal compression to the grain (EC90), obtained according to the assumptions and methods of calculation of the Brazilian standard ABNT NBR 7190 [7].
By number of load cycles and property of stiffness investigated were fabricated 12 samples, totaling 144 specimens.
ANOVA results for the factor number of load cycles.

While majority of the fragmented grains are ≤ 30 nm in size, almost equal number of grains measure ~ 20, 50 and 60 nm.
Contrast in high resolution images arises out of a complex interference of the direct beam and a number of the diffracted beams, the phase part of which is lost in the image.
The other term is sensitive to the projected potential of the atoms present in the material and number of atoms in each column under consideration.
As Ti is alloyed with Ta and Nb, their presence in the column and/or local change in thickness which will in turn change the number of atoms in each column may lead to such kind of variation in the contrast in the image.
Although extensive grain refinement takes place, all the grains do not fragment equally due to the variation in orientation of the grains.

Introduction In a number of recent publications (see, for example, [1-3]), it is shown that grain boundaries in metallic micro- and nanocrystalline materials obtained by severe plastic deformation substantially differ from that in ordinary polycrystals of recrystallized origin.
In [5-7 et al.] this method was successfully applied to study grain boundaries in a number of polycrystalline transition and noble metals.
The same is demonstrated by electron diffraction patterns (Fig. 1b) in which a great number of point reflections are located on the Debye rings, which means that the grains are high-angle.
Grain boundaries are still strongly curved, and dislocation density in the grains is high.
Figures 1 and 2 denote the spectrum component numbers.

The recombination activity of grain boundaries has been shown to depend on their impurity gettering ability, the property which depends on the grain boundary structure [2].
Small Angle (SA) grain boundaries, also called Sub-Grain Boundaries (sub-GBs) adjoin grains with small crystallographic misorientation, typically less than [7].
Results and Discussion Figure 1 show the microstructure of near sub-GB dislocations, in two ingot positions namely wafer number 551 and 559, approximately 2.5 mm apart.
(a) is from wafer number 551, 8 wafers below (b) .
The dislocations are localized near the sub-GB and the density of dislocations has increased from wafer number 551 to 559.

Although certain limitations exist, the LUMet technique offers a very reliable characterization platform with a number of potential applications in metallurgical process engineering.
Grain size measurements.
Results and Discussion Austenite Grain Growth.
This temperature region is often associated to the occurrence of abnormal grain growth with a wide grain size distribution leading to a strong contribution to attenuation coming from a small number of large grains.
At the grain coarsening temperature, the laser ultrasonic grain size was overestimating the average size of the structure.

Consider two grains joined at a grain boundary.
When deformation is carried out at temperature sufficient for grain boundary dislocation spreading, the number of dislocations dissociated at grain boundaries is very high (a planar density of dislocation 108m-1 corresponds to the volume density of dislocations 2*1017 m-2).
He supposes there are "active grain boundaries" and "passive grain boundaries".
"Active grain boundaries" are able to absorb a higher density of grain boundary dislocations than "passive grain boundaries".
Fig.5 and Fig.6 demonstrate the temperature of the drastic grain growth increases with the strip thickness because the number of grain neighbors and possible directions of stress relaxation are increased with the strip thickness too and consequently the driving force and grain boundary mobility are decreased. 1mm -20 0 20 40 60 80 100 120 140 160 180 0,0 0,2 0,4 0,6 0,8 1,0 Mean grain size, mm Time, sec Fig. 3.

Generally with the rise of temperature, stacking fault energy of ferrites increases and, dislocation climb and cross-slip occurs more easily, which produces a large number of sub-structures to increase the critical value Zc.
And the emergence of a large number of dislocations makes grains divide into more and tinier sub-grains and the strain-induced fine carbide particles precipitate inside grains and in grain boundaries.
Meanwhile, the carbide precipitation hinders the dislocation motion which makes a large number of dislocations accumulate here or in grain boundaries, and finally dynamic recrystallization occurs, obtaining uniform and tiny microstructures of which average size is less than 0.5μm.
Therefore, on this condition, recrystallization nucleation occurs rarely, the grain size that is about 1.5～2 μm is much larger than that of the above two conditions and there are a large number of dislocations in grain boundaries, as shown in Fig. 9.
As shown in Fig. 7, dynamic recrystallization occurs when the Z value is relatively high and it is a discontinuous process.9 After deformation, there are still considerable dense dislocations and a large number of fine carbides distributing inside grains and grain boundaries.