Search results

Globular carbides provide a much lower number of defect initiation sides than lamellar carbides.
However, most of the carbides are distributed evenly within the ferrite grains.
The carbides were formed not only at grain boundaries, but also inside of ferrite grains.
The typical ferrite grain size was in the range of micrometers.
Kučerová, Rapid Spheroidization and Grain Refinement Caused by Thermomechanical Treatment for Plain Structural Steel.

All billets were annealed at 773 K for one hour to give a homogeneous microstructure with an initial grain size of ~1 mm.
This is consistent with the well-established reduction of grain size that occurs in pure aluminum when processing by ECAP [4].
These weaker regions shrink with increasing numbers of passes and are essentially absent after 3 passes.
By plotting histograms of the numbers of fractions of the individual microhardness values within increments of 5 on the scale of Hv, as shown in Fig. 3, it is readily apparent that the hardness and the degree of homogeneity both increase with increasing numbers of passes.
Figure 4 clearly reveals the decrease in the weaker region of lower hardness with increasing numbers of passess.

It is obvious that a large number of reinforcement particles agglomerate in the matrix, indicating that the higher content of reinforcement are added, the more regions of agglomeration occurs.
The only distinct difference in the composites is the number of damping peak, as shown in Figs.9 (b), (c) and (d).
Grain refining technology of magnesium alloys [J].
Grain refinement of AlNp/AZ91D magnesium metal-matrix composites[J].
Fu.Grain refinement by AlN particles in Mg–Al based alloys[J].J.

The purpose of the aging treatment is to precipitate the second phases from supersaturated solution to strengthen the matrix of the alloy.The size, number and distribution of the precipitated phase decide the strength, toughness and stress corrosion resistance of the alloy.The typical aging treatments include: peak (T6), duplex , retrogression and re-aging (RRA) and bimodal aging.
After peak aging, the intracrystalline coherency GP zones and small half coherent fine dispersion η' phase precipitates and the coarsing continuous chain η phase distributes on the grain boundaries, this kind of grain boundary microstructure is very sensitive to stress corrosion cracking and spalling corrosion[10].
The uniform disk phases are mainly formed in the alloy intracrystalline, larger size η' phases are precipitated on the grain boundary and the rough and steady η phases is formed on the large angle grain boundaries.
Along with the time prolonged, intracrystalline η' phase coarsened and stable η phase on grain boundary grew up, and the precipitate free zone on the grain boundary is obvious.
RRA includes three stages: ① T6 temper pre-aging, after aging, partially coherent η′ dispersion phase precipitates in the intracrystalline and grain boundary forms chain incoherent η phase; ② Retrogression treatment at high temperature for short time, after retrogression treatment, intragranular η′ phase dissolved back, continuous chain precipitated phase on grain boundary begins to merge together and distributes no longer continuously, this grain boundary microstructure improves the properties of stress corrosion resistance and spalling corrosion, but the intracrystalline dissolved η′ phase makes the strength of the alloy reduce greatly; ③ T6 temper re-aging, the strength reaches the peak value and intracrystalline precipitates partially coherent dispersive η′ phase again, there are still discontinuous incoherent η phase particls on grain boundaries.

Figure 2(b) shows the micro-topography of back surface of ceramics applied laser power of 25J, and through analysis we can find that ceramical grain size is very tiny which even reaches less than 1µm, ensuring the formation of TZP.
Fracture majored in intergranular crack, lying with dimples formed by certain quantity of grain being pulled off.
This is because when transformed t-ZrO2 was held at room temperature, phase transformation flexible compress strain energy was stored in ceramics base, therefore, ZrO2 grain is of high strength and little transgranular fracture occurs while intergranular crack dominates the fracture; in the other hand, as the bonding force among grains is weaker compared with grain itself, when it comes into contact with the crack expansion, once the shearing stress induced exceeds bonding force, grain will be pulled off and dimple structure is formed although the stress delivered to the grain is less than its fracture strength[6,7].
(1) Fig.3 Phase transformation in back surface of ZrO2 ceramics by laser shock processing Where is the Volume fraction of j-phase, is i-section diffracted ray, of which i=1, and is an intensity factor, from expression (2): (2) Where N is the number of phases, is a structure factor, is an angle factor, is Debye • Wawro temperature factor.
TZP can be obtained at room temperature mainly because zirconia grain was under the constriction from surrounding material.

.%, Al-Mg alloys are susceptible to stress corrosion cracking (SCC) and point corrosion after annealed above 100℃ due to the precipitation of highly anodic β phase(Mg5Al8) at grain boundaries[1].
After annealed at 100,150℃, alloy is only prefer to precipitate β phase at localized region(such as grain boundary) to form continuous distribution（Fig. 6a）,this will increase the SCC susceptibility of alloy.
When annealed at 200,250℃, alloy start recrystallization, β phase can nuclei and grow evenly both in matrix(there are many dislocations, shown in Fig.6b) and at grain boundary, β-phase uniformly distribute throughout the matrix and grain boundary in a globular form（shown in Fig.6c）to bring with high SCC resistance.
After annealed at 300, 350℃, alloy is composed of recrystallized coarse grain, the number of grain boundary and dislocations decreases, some β-phase dissolve and re-precipitated with other β-phase to form larger rod shapeβ phase at grain boundaries（Fig. 6d）.
Once those continuous network distribution of coarsen β-phase are eroded, large fraction of grain will be exfoliated from Al matrix, which leads to high SCC susceptibility of alloy at high annealed temperature. 4.

However, during the austenite-ferrite transformation, the ferrite grains prefer to nucleate at the boundaries of prior austenite grains rather than the interiors of prior austenite grains.
On the one hand, these fine oxide inclusions inhibit austenitic grain growth through the pinning effect [3].
Recently, the magnesium was added into the molten Ti-deoxidized steel as the trace element, which refines the grains [8-10].
According to the results of EDX, it is known that in 611 inclusions, the number of Mg-contained inclusions is 22, and most of them (19) coexist with Ti.
Fig.2 SEM micrographs and EDX spectra of typical inclusions Fig.3 shows the intragranular ferrite grains emanating from inclusions.

The annular section at a distance about 2 millimeters to the hole edge has big grains.
The crystal grains at hole edge are made of a big number of ferrite and a little of pearlite shown as Fig. 7 (A).
Soon after the grains become small gradually, and the grains are smallest at a distance of 4mm shown as Fig. 7 (C), the microstructure is same as normalizing microstructure.
The refined grain zone is useful to improve performance of the workpiece.
Instead the hardness at refined grain zone is higher than the hardness of part material.

Table1 Chemical composition of samples tested (wt%) number C1 C2 C3 C4 C5 C6 C7 C8 Carbide 2 2 2 2 2 2 2 2 Low-melting components 2 2 2 2 2 2 2 2 Mischmetal 0 0.01 0.015 0.05 0.1 0.15 0.2 0.25 Cu margin margin margin margin margin margin margin margin Results and discussion Effect of mischmetal on inoxidizability.
This means mischmetal elements can indeed refine the crystal grains of copper, and the effects have been impressive.
There is only 0.2% more of the mischmetal in the 0.6 mischmetal-copper compound, but this reduced the size of crystal grains by 1/2 to 1/4.
Fig.5 shows that the copper-based grain surface takes a layered form.
It suggests that there is a great amount of mischmetal element on the external layer of the grain, but none is found inside it, i.e. the copper grains are wrapped up in the mischmetal elements.

In the reinforced concrete elements of such buildings the number of constructions with broken continuity is even greater.
Obviously, under the action of the pulse pressure, the directional arrangement of the grains of the aggregates occurs in a direction parallel to the tube generator.
Unlike ordinary concrete, the number of pores in concrete of vibro-shock-impulse pressing is extremely small.
At figure 3, the formation of reactionary rims around the grains of the aggregate as a result of modification of the cement stone is seen well.
Layering of packages, randomness of interlacing of threadlike crystals and a very small number of residual relics are obvious.