Search results

The microstructure of rheo-diecasting is mainly non-dendritic, be composed of globular primary grains (bright) and eutectic (dark).
It is seen that the microstructure of semi-solid magnesium alloy casting in as-cast state shows non-dendritic characteristic, being composed of globular primary grains (α-Mg) and eutectics (α-Mg + Mg17Al12).
The eutectic compounds (Mg17Al12) are dissolved quickly into the α-Mg matrix during solution treatment, at the same time, the size of grains increases significantly, and a few block compounds are appeared at the grain boundary.
The mechanical properties of semi-solid magnesium alloy casting can be improved significantly with an aging heat treatment, which should be attributed to brittle eutectic compounds dissolves gradually into α-Mg matrix on one hand, furthermore, the stress concentration at a grain boundary is lower and more twinning deformation occur in the inner of grain[19].
It is seen that big gas holes and large numbers of tiny porosities were observed in casting after heat treatment.

Results and discussion Parallel scratches and grain boundaries on the initial samples were clearly visible as a result of steel production process.
After the modification process scratches and grain boundaries almost disappeared (Fig. 2a).
Obtained results showed the bigger improvement of tribological properties for higher REE concentrations Authors suppose that improvement of tribological properties is connected with following reasons: (i) fine grains formation in the modified material as a result of very high cooling rate ii) enrichment of grain boundaries with REE (iii) nitrogen presence of modified layer [13, 14].
Even a REE concentration as small as 0.3 at.% remarkably reduced the number of surface failures while the concentration of 3.75 at.% and 6.2 at.% the surfaces are practically free of failures.
The scales are compact, adhere very well to the substrate and has smaller grains in contrast to untreated material (Fig.5).

The grain size and the amounts of pores were greatly affected by sintering temperature and composition.
In Fig.3 (b), the optimum sintering temperature of the Plan B ceramic was reduced from 1300 °C to 1250 °C, but the surface still has some pores and the grain shape was irregular.
The surface microstructure was to achieve densification, instead of the irregular grains, the average size of 2-6μm polygonal grains appeared.
The other is the external loss, which are mainly affected by the combined effects of the second phase, the oxygen vacancy, the grain size and the compactness [12,13].
Meanwhile, the number of grain boundaries also has an obvious effect on the Q × ƒ values.

Thermal wave propagation in solids is influenced by characteristics of microstructures, average grain size and grain boundaries, precipitations, impurities and imperfections, all of which contribute to the energy dispersion of the carriers like phonons and electrons inside the material.
For example, a decrease in the grain size in ferrous steel with a low carbon concentration gives an increase in the mechanical resistance of the material and thus provides better resistance to fracture [4, 5].
Palanichamy et al [15] have reported the use of longitudinal and shear wave velocity measurements for average grain size in austenitic stainless steel.
The average grain size after annealing is found to be in the range of 25-35mm from metallographic technique.
After particular duration, the defects will reach the grain boundary where they themselves will act as defect centers or scattering centers to contribute to the thermal conductivity in the opposite direction (Umklapp scattering).

As known from Magnesium and its alloys, the h.c.p. lattice structure of the α-phase in the Ti6Al4V only provides a limited number of active glide planes that makes forming of this material at room temperature only possible to a very limited extent [4].
The as-received microstructure is shown in Fig. 2 (left), consisting of equiaxed 10 µm grains of the h.c.p. α-phase with small amounts (~10 vol.%) of intergranular b.c.c. β-phase.
The samples deformed at 400°C without cooling showed a severely deformed microstructure with elongated grains parallel to the macroscopic forming force (Fig. 8 a).
While at the same temperature, with cooling behind the deformation tip, mostly equiaxed grains with partially elongated grains could be observed (Fig. 8 e).
It was found that without cooling deformation at 850°C leads to the highest deformation depths but pronounced hardening of the material due to grain refinement, together with a high local thickness reduction of the sheet material.

The hardness and elastic modulus of films were obtained using the nanoindenter Nano Hardness Tester-2 (NHT2) + Micro Scratch Tester (MST) supported by CSM Company, and the number of testing points were 8 at least.
The calculated grain sizes of the ZrN-Ag films were shown in Fig. 4.
For the ZrN film, the grain size is ~28.185 nm.
For the ZrN-Ag films, the grain size decreases rapidly with increasing Ag content.
When the Ag content was lower than 6.1 at.%, the hardness enhancement could be resulted from the fine grain strengthening [20,21].

As the B4C:Cu2+molar ratio declines, an increasing number of copper nano-particles deposit on the surface of B4C particles.
As is shown in Fig.6d-f, with the increase of pH value, the copper grain size declines.When pH value is 11, the regular copper grain can be obtained due to the time grain growth process needed is enough in pow pH condition, so that copper grain grows along with crystal plane <111>and<220>.When pH value is 12, the regularity of copper grain is not obvious.
When pH value is 13, copper nano-particles cluster formated due to copper grain size was so small that had a specific greater surface area caused particle aggregation. 4.

Thus, it is possible to fill the pores of fine-grained ceramic fuel with any nanopowder.
This leads to an increase in the fission cross section for fuel nuclides and to a slight increase in the reactor power (since the number of neutrons produced by all fissions).
Composite cermet tablet fuel based on fine-grained MOX and nanosized U.
The technology proposed by the authors of [12] can be easily generalized to the manufacture of pellet-metal-ceramic MOX-U fuel based on fine-grained MOX and nanopowder U for BN-type reactors [8, 13].
Composite cermet pellet fuel based on fine-grained MN and nanoscale U.

More examples include the measurements of recrystallization and phase transformation kinetics, during which dislocations in the specimen are swept away by newly formed grains leading to a stress valley on the stress-log(time) curve from which the recrystallization or phase-transformation start and finish times can be detected [23].
On the other hand, the precipitation progress between Ps and Pf cannot be quantitatively measured using the method because of the nonlinear correlation between the precipitated fraction and the number of dislocations pinned by the precipitates.
The material undergoing recrystallization can be considered as a mixed microstructure consisting of work-hardened and recrystallized grains.
(6) where sW is the strength of the work-hardened grains and can be calculated using Eq. 2 or 3, and sR is the strength of the recrystallized grains and can be calculated by a linear equation similar to Eq. 3.
The stress reduction was clearly due to the dislocation elimination by phase transformation during which the dislocation dense austenite was replaced by dislocation free a grains.

The electrical resistance of the BGA packages increased with the number of reflows.
The thickness of these IMCs increased with the number of reflows.
reported that the grain growth of Cu6Sn5 intermetallics caused the time exponent to be 1/3 in the interfacial reactions between the Sn-37Pb solder and Cu substrate [10].
The shear force increased up to 4 reflows, and then decreased with the number of reflows.
Fig. 7 shows the electrical resistance of the packages as a function of number of reflows.