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The relationship between grain growth and sintering aids is very complicated.
Normal grain growth is beneficial.
What needs to be suppressed is the growth of abnormal grains caused by secondary recrystallization.
Not all sintering aids that inhibit the growth of crystal grains are helpful forsintering.
Tab. 2 The influence of the types of sintering aids on the performance of permeable bricks sintering aids type Porosity (%) Compressive strength (MPa) Permeability coefficient (cm/m) CaCO3 51.7 1.9 1.7×10-2 CaO 38.8 2.9 0.9×10-2 MgO 82.3 0.2 3.5×10-2 Fig. 2 Scanning electron micrograph of different sintering aids Fig. 3 SEM images of different content of CaCO3 When different CaCO3 content is used as sintering aid, it can be seen from Fig.3 that as the content of CaCO3 gradually increases, the number of pores increases.

Due to the high number of parameters, which influence the scanning strategy and therefore thermal gradients and solidification velocities, the attainable properties of these materials are not fully evaluated.
Due to the very fine as built microstructure, where the γ grains have the size of a few µm, also creep via grain boundary sliding is more likely than in the coarse grained heat treated microstructure.
Fujitsuna, Effects of lamellar spacing, volume fraction and grain size on creep strength of fully lamellar TiAl alloys, Materials Science and Engineering.

The soil in the area consists of up to 50% fine-grained material, followed by sand and gravel.
Figure 2a shows the soil grain characteristics and Figure 2b shows the grain size distribution graph.
Fig. 2. a) soil characteristic, b) grain size distribution and c) the Flume test setup Experiment process and measurements.
Acknowledgments The author would like to thank the research grant from the Electricity Generating Authority of Thailand, contract number 64-N203000-11-IO.SS03N3008593 for the research grant.

An increasing diffusion coefficient with increasing interstitial content was reported in Pd alloys, in which interstitial solute atoms fill trapping sites, which are a consequence of the high density of grain boundaries or dislocations [11].
Table 3 - Diffusion prefactors and activation energy for different nitrogen content in TVCA alloys Nitrogen content (wt%) Prefactor Do (10 -10 cm2/s) Activation energy (eV) (0.023±0.003) 8.08 ± 0.02 1.64 ± 0.02 (0.016±0.006) 7.63 ± 0.01 1.66 ± 0.01 (0.030±0.002) 10.18 ± 0.01 1.66 ± 0.01 (0.040±0.002) 17.06 ± 0.01 1.64 ± 0.01 (0.042±0.005) 18.76 ± 0.01 1.63 ± 0.03 The TVCA alloys studied here are polycrystalline with small grains (see Fig. 2) and contain a large number of grain boundaries, which can form trapping sites for nitrogen atoms and in consequence, increase the nitrogen diffusion coefficient.
This increasing in the diffusion coefficient was attributed to the fact that nitrogen atoms fill trapping sites, which are a consequence of the high density in grain boundaries present in the sample.

The Nb(C, N) precipitates that form within the austenite matrix act to pin the grain boundaries and prevent recrystallization and excessive grain growth, thereby reducing the overall size of the ferrite grain [1, 2].
Nb precipitation kinetics in ferrite has been studied to a limited extent [3], compared to the number of investigations lavished on precipitation in austenite.
FE-SEM is being used because of the easier specimen preparation and larger and continuous areas of inspection possible (e.g. many grain boundaries can be inspected for precipitate activity).

The ferrite grain size is 100µm in the commercial pure iron sheet, 20µm in the IF ferrite sheet and 300µm in the low alloy sheet.
Although the number of plots is not enough, it is found that 0.2% proof stress follows the Bailey-Hirsch relationship given by the Eq. 5.
Dislocation density, ρ/m-2 IF ferrite Pure iron 1 10 14x 1 10 15x 1 10 16x 5 10 15x Limit of dislocation density Bailey-Hirsch relationship 1.2 1.0 0.8 0.6 0 0.4 0.2 σσσσ0.2 [GPa] = 0.1 + 1 X 10 -8ρρρρ1/21/21/21/2 1.1GPa (Dislocation density; ρ)1/2 /108m-1 0 0.2 0.4 0.6 0.8 1.0 1.2 0 0.2 0.4 0.6 0.8 1.0 1.2 0.2% proof stress, σ0.2 / GPa Dislocation density, ρ/m-2 IF ferrite Pure iron IF ferrite Pure iron IF ferriteIF ferrite Pure ironPure iron 1 10 14x1 10 14x 1 10 15x1 10 15x 1 10 16x1 10 16x 5 10 15x5 10 15x Limit of dislocation density Bailey-Hirsch relationship 1.2 1.0 0.8 0.6 0 0.4 0.2 1.2 1.0 0.8 0.6 0 0.4 0.2 σσσσ0.2 [GPa] = 0.1 + 1 X 10 -8ρρρρ1/21/21/21/2 1.1GPa Fig. 6 Relation between 0.2% proof stress and dislocation density in cold-rolled ferrite. 0 1.0 2.0 3.0 4.0 5.0 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.2% proof stress, σ0.2 /GPa Vickers hardness, HV /GPa Cold-rolled iron Annealed iron Ultrafine grained
iron [6] σσσσB ≒≒≒≒ HV / 3 (Tensile strength) (0.2% proof stress) σσσσ0.2 ≒≒≒≒ σσσσB -0.1 0 1.0 2.0 3.0 4.0 5.0 0 1.0 2.0 3.0 4.0 5.0 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0.2% proof stress, σ0.2 /GPa Vickers hardness, HV /GPa Cold-rolled iron Annealed iron Ultrafine grained iron [6] σσσσB ≒≒≒≒ HV / 3 (Tensile strength) (0.2% proof stress) σσσσ0.2 ≒≒≒≒ σσσσB -0.1 Fig. 5 Relation between 0.2% proof stress and Vickers hardness in cold-rolled iron and ultrafine grained iron [6]. such a large strain region [9].

.), which is compared to a threshold quantity, for a given number of cycles.
This choice then makes it possible to define the probability of crack initiation within a grain.
The probability of microcrack initiation in a grain corresponds to the probability of finding a grain with a threshold stress σth that is less than the applied equivalent stress σeq.
In this work it will be assumed that crack initiation is essentially a surface phenomenon, where the quantity S01 corresponds to the surface area of an individual surface grain and SΩ1 is the total surface area of a specimen.

It is observed that as the SHT temperature increases, grain growth take place along with some dissolution and coarsening of Mg2Si and β-Al5FeSi intermetallic phases.
The average grain size was measured as 164 µm in as-cast, 209 µm in SHT-530 ℃, 243 µm in SHT-560 ℃.
Decrease in hardness with increase in temperature and time is due to grain growth and dissolution and coarsening of hard Mg2Si and β-Al5FeSi intermetallic phases [3, 21].
Over ageing, results to transformation of β˝ that mostly contribute to the hardnness of the alloy, to a number of other coarser metastable phases like β´, B´, U1, U2.
The significant results and conclusions of the present work are as follows: · SHT temperature and time beyond 530 ℃ and 1 hours results in grain growth and coarsening of the Mg2Si and β-Al5FeSi intermetallic phases and thus, hardness of the alloy decreased

Numerous studies have been conducted on the thermal performance of magnesium alloys, and a number of magnesium alloys possessing high TC, including Mg-Zn-Zr and Mg-Zn-Mn, have been developed [5,6].
From Fig.2(a), it is seen that AlN particles are distributed inside the grains and at the grain boundaries, surrounded by the white eutectic structures.
Previous studies revealed that AlN might serve as a nucleation core for α-Mg in Mg-Al alloys [13], but in the current study, the wettability between AlN and Mg was poor, and the grain size of the composites almost does not change with the content of AlN.
Taylor, Grain refinement by AlN particles in Mg–Al based alloys, J.

The inset shows a magnified image of a single PPy grain.
A careful observation of the grains, as seen from the magnified SEM image (inset of Fig. 1(b)) reveals ‘cauliflower’ like morphology.
The surface ‘roughness’ offered by the cauliflower grains is beneficial in FE behavior, as it assist in enhancing the local electric field.
The bright field emission images comprised of large number of tiny spots suggests that the emission is from the PPy grains.