Search results

Introduction The sequential or simultaneous action of plastic deformation and electric current in different alloys, including shape memory TiNi alloys, leads to a number of interesting phenomena.
In the austenitic alloy after EPR (е=1.2) annealing at 500°С forms the nanograined structure with a mean grain size of 80 nm (Fig. 2a).
In the martensitic alloy the same annealing leads to a grain size of 100 nm (Fig. 2b).
However, a smaller grain size of 60 nm can begin to form at 450 °С (Fig. 2c).
The average grain size in the Ti50.0 Ni50.0 alloy is lower that that in the Ti49.2Ni50.8 alloy. 4.

Fig. 2(b) shows the spinel grains doesn’t bond tightly and only part direct binding exist between grains showing the sintering was incomplete.
From the Fig. 3(a) it could be observed that the specimen T4 has denser structure, less porosity and high direct bonding between the grains.
It can also be seen from Fig. 3(b) that the spinel grains bond tightly and had high direct bonding showing the sintering was well.
More cracks exist especially between the large grains.
That small spinel grains have high direct bonding showing well sintering, but large grains did not bind well.

The same is true of press and sinter powder Injection molding processes because of the shape complexity and dimensional tolerances which cannot be achieved without extensive machining operations Powder injection molding (PIM) is an emerging technology for the cost-effective production of large numbers of small metals parts.
It is thought that the porosity is reduced when the sintering temperature increased and this lead to the formation of grain.
The grain boundary formation is a result of the grain coalescence process and though the orientation of the microstructure is slightly different, they essentially have a similar grain shape.
Microstructure of sintered Inconel 718; Sample A (a) and Sample B (b) Observations over a range of magnifications reveals that increasing temperature has significantly improved the homogeneity of the microstructure, specifically the pore size is reduced and the grain are more evenly distributed.
The high densification of sample B was achieved due to the particles which became interconnected signifying that under the condition of high temperature, grain displacement and plastic deformation occur which eliminating the pores, and therefore grain growth takes place along with the densification during the sintering process[5].

Scandium is an effective grain refiner and increases the recrystallization temperature in aluminium alloys.
The addition of scandium has changed grain structure of Al-Si-Mg alloy from columnar to fine equiaxed.
First, grain refinement during casting or welding, second precipitation hardening from Al3Sc particles and lastly, grain structure control from Al3Sc dispersoids [4].
Scandium when added in small concentrations is known to refine the grain structure of cast metal and to form a supersaturated solid solution upon solidification.
Limmaneevichitr , Grain refinement mechanism in Al-Si-Mg alloy with Scandium, Journal of alloy and Compounds, 542 (2012) 177-186

MgO is a traditional additive for Al2O3 because it can reduce the sintering temperature and decrease grain size.
The amount of MgO was varying from 0 to 5vol%, with the material numbers changing from AC2NM0 to AC2NM5, as shown in Table 1.
The drastic decrease of fracture toughness is basically related to the small grain size of the grain boundary.
Chantikul et al.[11], the intrinsic toughness diminishes as the grain size decreases due to the reduced load bridging capability of the smaller grain bridges.
That is to say, MgO could inhibit grain growth of Al2O3-TiN-TiC ceramic composite, eventually form homogeneous and dense ceramics.

Films prepared at PO2=10 Pa had a high degree of (111) orientation and densely packed grains.
I(hkl) is the intensity of the (hkl) plane, I0(hkl) is the corresponding intensity in the Joint Committee on Powder Diffraction Standards data file, and N is the number of preferential growth orientations.
The film deposited at 5 Pa exhibits a uniform surface morphology with a low density of small grains.
For PO2=7.5 Pa, the grain size increases and the grains become more dense.
At 10 Pa and 12.5 Pa, the films have a high density of grains with irregular shapes and variable sizes that may result from the second phase observed in the XRD patterns [16, 17].

The grain refinement effect increases and then decreases with increasing pressure.
And these defects can provide a number of new nucleation sites, resulting in increasing neucleation efficiency[9].
The reason for this is that the atoms on the grain boundaries are disordered and many vacancies exist, resulting in the lower density and the higher energy than that in the grain.
And the grain with a higher potential would be protected as a cathode.
It is well known that the finer the grain of the alloy is, the larger the proportion of grain boundary area is.

The LSMO properties are modified by sintering temperature, which ruled the grain size and grain boundary properties [3, 4].
The SEM images showed LSMO samples have different grain size where the grain size increases with increasing sintering temperature.
This implies a decreasing number of grain boundaries by increasing sintering temperature, in agreement with Ref. [3].
Table 1 summarized the properties of grain size, µHC and MSP of LSMO samples.
We remark that MR values are not ruled by the physical properties i.e. grain size as reported in Refs. [3].

After 30mins, there were large number of slip bands of plastic deformation in a-phase.
From a, we can see that there were a large number of narrow strips of twins on surface of simple after cavitation erosion for 3h.
And these twins cut the a matrix grain into small pieces.
While around kI phase, there appeared a large number of dislocation bands with different slip direction inside of the a matrix.
For more crystal defects exist in the grain boundaries, they were often first to be destroyed.

Fig. 2(b) clearly demonstrates that there are a large number of dislocations and twins in Cu matrix.
Finally, a large number of crystal defects such as dislocations and twins are formed [9].
At the same time, the addition of Gr is beneficial to grain refinement and achieve "fine grain strengthening" [10].
Conclusions (1) There are a certain number of pores in the Gr/Cu composites prepared by powder metallurgy, and the number of pores increases with the increase of Gr content
There are a large number of dislocations and twins in Cu matrix