Search results

The Effect of High Temperature Grain Refinement on the Isothermal Ferrite Grain Growth Kinetics in Steel S460 J.S.
Ferrite initially forms on grain boundaries before growing in to the austenite grains.
Similarly to the undeformed specimens (Fig. 2), the primary ferrite nucleates at the austenite grain boundaries and grows into the austenite grain
This homogeneous microstructure increased the grain boundary area and therefore the number of potential nucleation sites for the ferrite grains.
· The deformation step refined the prior austenite grain size, which in turn increased the ferrite grain growth kinetics due to an increase in the grain boundary area when compared to undeformed specimen

The as-received hot-rolled U720Li alloy bar had been subjected to a large number of prior processing steps, so fully homogenous microstructures were got as shown in Fig. 1.
We can see that the alloy consists primarily of a fine mean grain size (20μm) gamma(γ) grains and primary gamma prime(γ’) with a size of 0.5-2.5μm between the γ grains or in the interior of grains.
The grain sizes were measured via two methods, linear intercept and determination of grain area, each of which gave similar results.
So grain growth rate increases when heating temperatures are higher than 1130°C, as well as the grain growth time exponent.
The primary γ’ phase pinned the grain boundary and hindered the γ grain growth.

By now there exist a number of models describing the non-equilibrium grain boundaries.
The goal of the present study is to incorporate the spatially dependent diffusivity in individual grains into Fisher model of grain boundary diffusion.
The estimations of ΔS and Δd at T = 500 K for a number of FCC metals are given in Table 1 for T = 500 K; the linear dislocation density for non-equilibrium boundaries was supposed to be r = 108 m-1 which is typical for the SPD-processed materials [2, 4].
The numbers at the curves correspond to the distance from the source in units.
Finally, it should be noted that expressions – for layer activity (which represents an average concentration of tracer atoms in the selected layer) include three parameters: grain boundary width d, grain boundary diffusivity Dgb and bulk diffusivity value at the grain boundary-grain interior interface D1.

In the last decades a lot of research focused on ultrafine grain microstructures (grain size lower than 5 µm).
With increasing the accumulated strain, pancaking of deformed grains increase and so the number of nucleation sites for ferrite increases.
Heavy Austenite Deformation The mechanism of Heavy Austenite Deformation has been investigated by means of a number of tests on samples of steels 30MnB4 and 18MnB2, deformed of 50 % at temperature Ar3+70°C at two different strain rates (1 s1 and 30 s1) and two different prior austenite grain size (10 µm and 50 µm).
Increasing strain rate is not effective on grain size refining: on the contrary, ferrite grain size tends to increase when strain rate rises.
Microstructure of steel 30MnB4 with UF ferrite grain size 3.3 µm.

The results showed that number of grains and seed-setting percentage of two L. chinensis ecotypes fluctuated within a certain range.
Variation coefficients of single spike grain number and seed-setting percentage were 79.37% and 87.2% higher.
The number of grains and seed-setting percentage of two L. chinensis ecotypes under saline-alkali soil habitat were lower than those under sandy soil habitat.
Results The number of grains and percentage of seed-setting.
From the average number of metrics (Table 1), the number of grains and seed setting percentage yellow- green ecotypes of L. chinensis were 1.124 to 1.302 times higher than grey-green ecotypes’ under the saline-alkali soil habitat, but number of grains is slightly lower than the gray-green L. chinensis ecotypes under the forest edge sandy soil habitat.

Once equiaxed grains formed, further reduction in the grain size was not observed with the further cycles.
It is noticeable to find that there is abnormal large grain after five cycles in Fig. 3(b).
Recovery is supported by the fact that the number of dislocations inside grains seemed rather small after five cycles in Fig. 3 (b).
Conclusions Ultrafine grained pure Al sheets with average grain size ~0.5 μm were successfully fabricated by ARB at room temperature.
Tensile strength increases largely with the number of the ARB cycles, reaches a maximum of 228 MPa after the first cycle, and then it decreases to ~210 MPa, beyond that showing a gradually decline with the further cycles.

Since the adoption of the ISO metric sieves thus the old AFS grain fineness number can no longer be calculated and the average grain size, expresses as micrometers (µm) is now used.
The permeability number for moulding sand from Mansfield Sand Company mixed with 6% water is 21 [13].
Effects of Water and Clay on the Permeability Number Fig. 5.
The effect of moisture and clay on the permeability number.
Fig. 5 displays the effect of clay on permeability number of sample.

It was revealed that UFG aluminum and magnesium alloys with a bimodal grain size distribution exhibit a number of anomalies in mechanical behavior.
Grain size distributions of aluminum and magnesium alloys after various numbers of passes of equal channel angular pressing (ECAP) is reported in [1-12, 15-17].
Grain size was 300 nm.
Mesocracks arise in the volume filled by fine grains and can intersect coarse grains.
UFG Al-Mg alloys have fine grain size of 1 μm and coarse grain size of 20 μm.

A great number of investigations were carried on for ultrafine-grained titanium alloys produced by different methods; however, these mostly deal with the structure and mechanical properties of studied materials, while the physical properties of materials are studied insufficiently.
An area of ~1.8 μm2 cut from the pattern with a selector diaphragm shows a great number of micro-diffraction rings (Fig. 1), which is suggestive of the formation of grain-subgrain structure with grain sizes of less than a micron.
The strength properties of alloys having ultrafine-grained structure are enhanced by 1.5-2 times relative to the respective coarse grain counterparts (Table).
The effect of hydrogen concentration on the construction strength of the Ti-6Al-4V alloy: 1 – coarse grained state, 2 – ultrafine-grained state.
Hence the increase in the ultrasound rate might be attributed to the ultrafine-grained structure having lower density relative to the coarse grained structure.

The severe plastic deformation results in creation of high number of lattice defects.
We have found that microstructure of HPT-deformed Mg contains two kinds of regions: (a) "deformed" regions with UFG structure (grain size 100-200 nm) and high number of randomly distributed dislocations, and (b) "recrystallized" regions with low dislocation density and grain size of few microns.
It has been demonstrated that ultra fine grained (UFG) metals with grain size around 100 nm can be produced by high pressure torsion (HPT) [3].
A number of UFG metals exhibit favorable mechanical properties consisting in a combination of very high strength and a significant ductility.
Typical feature of UFG structure is a high number of defects introduced by severe plastic deformation.