Search results

As shown in the SEM images, the grain size become smaller and the number of the pores increases with the increasing Na0.52K0.48 contents x.
For the simples with x=0.005-0.01, the average grain sizes are about 5-7 μm, as shown in Fig.1 (a)-(b).
However, the average grain sizes become 1-2 μm when x increases to 0.020-0.025, as shown in Figs. 1(c)-(d).
It can be seen from Fig. 5(a)-(c) that the structure becomes denser and grains size become bigger with increasing sintering temperature.
But for the sample sintered at 1080 ◦C, the microstructure becomes inhomogeneous and the grains size become small again, as seen in Fig. 5(d).

The indicated method allows to reduce the average grain size of the sintered ceramics by increasing the proportion of sub-micron grains, on the boundaries of which there is an effective inhibition of cracks at failure.
The median and lateral cracks are observed in the samples (Fig. 3), the front and the directions of propagation of which are broadly coincide with the model concepts and results of investigations of destruction of single crystal material, and some differences in scale, the number and depth can be attributed to their inhibition in the grain boundaries and residual pores.
Measurements and calculations of the maximum size of areas of spall fracture b, made for boron carbide samples with different content of nanopowder can give clear view about the degree of influence of the grain boundaries and residual pores on the process of crack propagation.
Obviously the grain boundary structure has a greater impact on the scale of the crack propagation in the studied polycrystalline material than its porous structure.
In this case, the scale of the cracks is affected by grain structure of ceramics and the residual porosity in the investigated range of its values does not have such effect.

This was due to the reduction in grain boundary area and carrier transport in the deposited films that contribute to the enhancement in carrier mobility [13].
Increased in the leakage current density with annealing temperature was due to large grain, small grain boundary area and compact film produced [16].
As stated by Sengupta et. al [11], the increased in annealing temperature will lead to the formation of compact, large grain size and reduction of grain boundary area and this resulted in increment in the ɛr value.
It can also be observed that, the increased in annealing temperature resulted in less presence of porosity and large grain size film.
Film with nanometer dimension particle was believed to increase the dipole moment per unit volume of the film due to the large number of particle per unit volume [19, 20].

Table1 Formula of specimens (wt%) Specimen code number Premixed powder α-Si3N4(%) 1 95 5 2 90 10 3 85 15 4 80 20 5 75 25 Results and discussions Effects of addition amount of Si3N4.
This is because the rise in firing temperature improves the densification behavior of the materials, closer binding between the crystalline grains.
The grains are more evenly and bind more tightly.
As the α-Si3N4 content is > 10%, the porosity of the specimens obviously gradually increases, the structure of the material becomes looser, the grain size are unevenly and the contacts between grains reduce.

The grain size of nanocrystalline powders is about 20-50 nm.
A large number of well-defined hexagonal-shaped AlN platelets are observed in the sample.
In a word, carbon powders act as diluents and grain-growth inhibitor here.
The grain size of AlN nanocrystalline powders is about 20-50 nm.
The presence of carbon in the mixture acts as diluents and grain-growth inhibitor.

This hypothesis was confirmed by a number of scientific researches [8] and has been practically implemented in technical solutions proposed thereon to relieve the 2nd kind micro-stresses by pre-heating the tools to a temperature close to the temperature of maximum operating capacity of the cutting inserts.
This model examines and solves the issue of determining the internal stresses of the 2nd kind, where spherical inclusions, i.e. grains of (Ti,W)C with a radius of r0 are surrounded by an infinite medium, i.e. bound by Co, as shown in Figure 4.
Subsequently, when the temperature decreases by the value of ΔТ, internal stresses begin to arise due to the difference in linear expansion coefficients of the cobalt link and grains (Ti, W)C.
At this temperature the hard tool alloy field is conventionally assumed as homogeneous, and the cobalt binder and grain materials (Ti, W) C are considered as elastic elements.
The carbide grain core is the beginning of a spherical coordinate system with r, φ, θ parameters as shown in Figure 5.

The Co-Cr powders can be used for DMLS process because presents good sintering properties and the size and the spherical form of grain permit to obtain sintering probes.[1,2] Microstructures and properties of Co-Cr alloy powders used for DMLS process The powders of Co-Cr alloy presents good mechanical strength, good resistance to corrosion and a degree of cleaning identical to that of the glass.
The powders Co-Cr alloy shows spherical grain size like in figure 1 and figure 2, the grain ranging around 20 microns size.
SEM of Co-Cr sintered probes (x10 000) When realize a microscopy to a great scale like in figure 7 the porosity is more evident and can remark some spherical grains that are not sintered.
Acknowledgment This work is supported by the Sectorial Operational Programme Human Resources Development (SOP HRD), financed from the European Social Fund and the Romanian Government, under the contract number POSDRU/159/1.5/S/138963 – PERFORM.

The Mg-added Al-Si alloys, AC4CH alloys, exhibit high strength, toughness and corrosion resistance and are extensively applied to a number of automotive components, while the Cu-added Al-Si alloys, AC4B alloys, have high strength even at elevated temperatures and are used for various engine components.
In Fig.4, several microstructure parameters, the grain size of the α-Al phase (D), the shape factor of the α-Al phase (F), the length of the β phase, are represented.
The grain size and shape factor of the α-Al phase are defined as D = (4A/π)1/2 , F = P 2/4πA, where A and P are the cross section and periphery length of the α-Al phase.
It is found that the recrystallized microstructure is first formed and then the preferential dissolution of the eutectic phase and recrystallized grain boundaries of the α-Al phase proceed with increasing temperature.
After preferential dissolution of the grain boundaries, the simultaneous separation and spheroidization of the α-Al phase occur, and then characteristic semi-solid microstructures are formed.

Using a combination of Nb (1 0 0) and peaks, as well as for Cr, the grain size was calculated according to the XRD pattern and the following equation: B cosθ = 0.94/d+ 4εsinθ （1） where B is peak integral width, θ Bragg angle, d the grain size (nm), ε the lattice distortion and λ is the X-ray wave length.
The broadening of X-ray diffraction peaks is associated with the refinement of grain size.
At the very beginning, MA leads to a fast decrease of the grain size to less than 90 nm.
Acknowledgement This work was supported by the national natural science foundation of China, under contract number 50474009.

The microstructure and the grain size distribution were determined by scanning electron microscopy.
Manganites are a very interesting object of investigation in view of a number of interesting properties as charge and orbital ordering, Jahn Teller effect, spontaneous and induced phase transitions.
The micrograph shows the uniform grain size and homogeneity of the material obtained by the solution method; the mean particle size is in nanoscale range (~80 nm) and also sinterization has occurred.
The micrographs of the ceramic route obtained powders revealed a grain size in the range of 2-7 µm.
The structure and the ferromagnetic behavior of the PC obtained nanopowders are related to the effect of preparation on structure, grain sizes etc.