Search results

The mold temperature reduction from 550 °C to 450 °C leads to the grain size decrease and the little yield strength increase.
A large number of gas pores, irregularities and metal penetration is observed without alloying additions.
The result of this treatment is globular grain clearly visible boundaries, inside of which is typical annealing twinning (2b).
It is condition of more intense nucleation during solidification and the formation of relatively fine-grained structure.
From the viewpoint of hardenability the best result was obtained for the alloy (test number 3, Table 2).

TEM observation revealed that point defect clusters were distributed densely inside grains after the impact compression, possibly due to the effect of high-speed deformation.
In recent years, a number of processes to modify the material performance have been also proposed by combining the strain hardening with the grain refinement by using severe plastic deformations (SPDs).
Kim et al. [8] have showed that the 6061 aluminum alloy processed by 1 pass or the number of passes in ECAP does not show the age-hardening at 175 ˚C.
A large number of precipitates (probably, β’’-Mg2Si phase) were homogeneously distributed through the Al grains in the peak aged conditions.
A large number of point defects were clearly observed.

The wire of 3mm in diameter exhibited an equiaxed microstructure consisting only β single phase and fine grain with less than 10mm size when the alloy is heat treated at 1003K for 1.8Ks.
At present, the microstructure is known that a large number of nanocrystal disturb and gradually develop a large number of discontinuous fault or free dislocation, that is a morphology with numerous stacking fault.
It shows fine equiaxed grains with the larger grain size of approximately 5~10µm, without lath-like features.
The microstructure would be prone to brittle fracture and does not have good elastic behavior, but the legs for spectacle frame must meet the needs of good mechanical properties and fine equiaxed grains in the following process or service conditions.
(2) Fine grains with less than 10mm size and single β structure gained by solution-treating at 1003 K for 1.8 ks contributes to a better balance of good shape memory effects and good mechanical properties, which is good for the production of the spectacle frame.

The average grain size increased as the concentration of excess PbO increased from 10 mol% to 20 mol%.
The grain size of PLMNT-10 ceramics was about 3-5μm, while the size of the maxium grain in the PLMNT-15 and PLMNT-20 ceramics was larger than 7μm, and the number of the large grains in the PLMNT-20 ceramics is obviously much more than that in the PLMNT-15 ceramics.
The more liguid forms, the faster the grains grow.
So the average grain size of PLMNT-20 ceramics is larger than those of PLMNT-15 and PLMNT-10 ceramics.
It maybe resulted from the difference of grain size of PLMNT ceramics with different excess PbO.

On the basis of microstructure observations, the first exhibits adiabatic shear bands, which called instability domain, the second represents fine recrystallized grain structures, which called stability domain.
Although a number of studies have focused on the hot deformation behavior of as-cast GH4169 alloy[3,4], it often cracks in forging.
These exhibits fine recrystallized grain structures with serrated grain boundaries.
At temperatures of 1100˚C，grain growth occurs as shown in Fig. 3(d), which may be caused by δ phase precipitates and carbides dissolution.
Fine recrystallized grain structures produced at 0.01s-1, 950˚Cowing to the δ phase precipitates and grain growth occurred above 1050˚C owing to phase precipitates and carbides dissolution. 3.

It can be observed that the microstructure becomes finer with the addition of CeO2 and the number of cell grains increased, in contrast the FeNi alloy coatings appears lenticular with high aspect ratio needle-like grains that are typical of a thermal sprayed coating.
During the course of crystallization, CeO2 can act as heterogeneous nucleation site for crystal nucleation during solidification because of the high melting point of CeO2(2500°C), which will improve the tendency towards forming more grains, therefore the number of crystal nuclei will increase and the grains will be refined[8].
In addition, during the growth of the nucleated grains, CeO2 particles will be pushed by the solid/liquid interface to the grain boundaries as observed in metal matrix composites [9].
Then the grain is further refined, as a result, the smaller grains will account for the improvement in wear resistance and hardness.

Fig.3.a showed morphology of fracture surfaces at 600℃, the fracture mode was intercrystalline brittle fracture, fracture surface was uneven and liked stone, there were a small amount of cracks and voids between grains.
Fig.3.c showed morphology of fracture surfaces at 750℃, the fracture mode was typical intercrystalline brittle fracture, fracture surface was uneven and liked crystal sugar, its ductility was poor mainly because large number of ferrite precipitated along austenite grain boundaries.
Fig.3.e showed morphology of fracture surfaces at 1000℃, fracture surface was relatively flat and had a large number of coarse grains and a small amount of fine grains.
Fig.3.f showed morphology of fracture surfaces at 1100℃, fracture surface was more flat and only had fine grains.
Its ductility was very good mainly because dynamic recrystallization occurred at this temperature and the grain boundary easy moved when deformation occurred [7 - 8].

It shows that the grain can not be refined obviously before Er reach a certain amount.
This may be associated with the nuclear of Al3Er and segregation of Er in grain boundary.
We can see that the refinement of grain depend on increasing rate of nucleation and decreasing growing velocity of grain.
It was also confirmed that there are some sphere or like-sphere second phase particles in grain and grain boundary by SEM observation in as-cast Al-4.5Mg-0.7Mn-0.4Er alloys.
The solution of Mn in the lattice gap of Al will decrease the number of gap.

The choice of electrode for SMAW lies on a number of factors, like weld material, welding directions and the preferred weld properties.
The analysis of weld metal shows the presence of self cooled pearlite grain structure and ferrite at grain boundaries with formation of some patches of ferrite.
The observation of heat affected zone reveals the formation of coarse parlite grains with patchy free ferrite.
The experimental analysis of base metal microstructure reveals that the base metal having pearlite ferrite grain structure with an hardness value of 134.6.
[12] L. leinonen, Superior properties of ultra-fine-grained steels, Acta polytechical, 44 (2004)

Table 1. 5 groups’ basic formula of Mn-Zn ferrite mol% Elements Sample number 1 2 3 4 5 Fe2O3 52.5 52 52 51 51.5 MnO 26.5 26 25 25 23.5 ZnO 21 22 23 24 25 Sample preparation.
The grain characteristic of high permeability Mn-Zn ferrite is big, grain boundary tidiness and obvious with high density and low porosity.
Grain scale will influence the coercively that bigger grain will has smaller coercivity.
This is big ones in the ferrite grain.
In ordinary, initial permeability is in direct proportional to grain size, and grain thickness is in inverse with porosity.