Search results

With the increase of the cold deformation degree of the alloy, a large amount of slip band and twin band appear in the crystalline grain, shape of crystalline grain change too, the main deformation between crystalline grains are movement and rotation (as shown in Fig.3b ~ e).
With the increase of deformation degree, the crystalline grain is elongated in the drawing direction, the more deformation is, the more remarkable the crystalline grain extends is, every crystalline grain can not almost be distinguished from each other clearly.
Because of the crystalline grain distortion during the deformation, elongation and refinement of the grains, ultra structure and asymmetric deformation, deformation resistance characters, such as strength limit, yield strength and hardness, increase with the augment of deformation.
Dimples are nucleated at grain boundary and twin boundary.
We found that when cold deformation degree is small, there is a large number of stacking faults in the alloy (as shown in Fig. 7c), this prove that the stacking fault energy of the alloy is low.

Fig.1(a)-(b) and (c)-(d) show that the increase of the enhanced solid solution temperature lead to the decrease of grain size.
Table 1 Microhardness test results Number Microhardness (HV0.2) 1 240.1 2 252.8 3 205.3 4 270.9 parent material 246.4 Tab.1 shows that the hardness of the sample 4 is the highest, sample 2 is the second, and sample 3 is the worst.
Fig.1 (b), (d) and (e) show that the grains in Fig.1 (b) and (d) are smaller than the grains in Fig.1 (e),but the grains in Fig.1 (a) and (c) are smaller than the grains in Fig.1 (b) and (d).
Sample 3 was worn by the groove and a large number of flanges appeared, indicating that the surface of sample 3 was soft.
(1) After solid solution treatment, the grain size of 1-4 of the sample is smaller and longer than that of the parent material; Segmental strengthening solid solution can refine grain more than one-time strengthening solution

Grain size in Fig. 1(a) and particle size in Fig. 2 confirm the growth of AlN grains during sintering even without sintering additives like C3A.
Fig. 5 Grain growth of AlN particles A and B at around 1900 K.
Fig. 7(a) shows the formation of four edge dislocations at around 1900 K during sintering and grain growth of AlN particles.
The result suggests the possibility that longer heat treatment during sintering may decrease the number density of edge dislocation in the AlN ceramics.
(4) Prolonged heat treatment at the sintering temperature may decrease the number density of edge dislocations in the grains of AlN ceramics

With increasing Y fraction, the granular precipitates in the grain interior become larger, and those at the grain boundaries partially connect to each other, forming curving precipitates larger (Fig.1c).
The addition of the rare earth element Y can result in the formation of a large number of alloy nucleus.
Therefore, the degree of incomplete cooling of the composition increases and the number of structures increases.
The results shows that Y addition in grain size to improve and microstructure change.
The microstructure of the Ti-Nb-Y alloys consists of matrix and Y rich precipitates, which are dispersed both in the grain size and at the grain boundaries.

In the present study, the bulk nanocomposites samples by spark plasma sintering were named as "NX", where "X"is a number denoting the weight percent of nanopowders in the sample.
It is clear observed that the grains of N0 and N100 samples have a homogeneous distribution.
The increasing grain boundary densities according to the higher contents of nanosized particles might result in the increase of Seebeck coefficient by potential barrier scattering at grain boundaries [6].
One may anticipate that κ could be further decreased if even smaller grain sizes could be achieved.
The electronic contribution can be calculated by employing the Wiedemann-Franz law, TLcσκ 0= , where L0 is Lorenz number.

Total crack length, number of cracks and maximum crack length were recorded.
Three outcomes were measured in the Varestraint samples, number of cracks, total crack length and maximum crack length.
The number of cracks in the alloys tested correlated to little but grain size.
For example alloys 2195 I and II could not be differentiated on the basis of number of cracks found.
Cracks were more abundant in finer grain materials, primarily because more grain boundaries were available to crack.

A newly developed alloy contains a number of complex widely scattered intermetallics with much finer and fewer Sn and Si particles.
As expected, the AS20S lining showed fewer Sn and Si particles and a larger number of intermetallics present than found in the AS16 and AS1241 linings respectively.
The Al grain size of the AS20S system was found to be somewhat finer than that of the AS1241 but coarser than that of the AS16 lining.
For the AS20S system, the misorientation angle seems to be closer to the ideal random distribution with peak value at 45 o whereas for the AS16 lining, the distribution of grain orientations appeared to be deviating significantly from the random distribution giving a lower average value of 32 o indicating a preferred alignment of the matrix grains.
Table 2: Nanohardness numbers and elastic modulus values measured via nanohardness test for different phases in the lining surface of finished bearings.

Among the different characterization methods commonly used electron backscatter diffraction (EBSD) appears to be the unique technique able to observe retained austenite grains often no larger than 1 µm.
It allows to measure orientation gradients within individual grains of each different phase.
During the γ → ά transformation, the martensite appears and grows inside the austenite grains.
The intensity of the ODF´s is generally high due to the low number of measured grains, see Fig. 3.
- A color etching procedure adapted from LePera method ensures the distinction of ferrite, bainite and austenite/martensite grains by optical microscopy (OM).

As the problem is typically more pronounced in fine-grained materials, the main body of existing literature is devoted to the characterization of sheets or forgings of Alloy 718.
The influence of grain size on dwell-fatigue crack growth was studied by Pédron et al. [1] on wrought material which showed that coarse grained material performed better than fine grained material.
The crack interaction with the secondary phases also plays an important role, where e.g. studies by Viskari et al. [8] and Ponnelle et al. [9] highlight the role of grain boundary precipitates in fracture resistance.
Thus, in dendritic microstructures both grain boundaries and interdendritic regions can act as preferential paths for dwell-fatigue crack propagation.
Acknowledgements The work was funded by Clean Sky JTI CfP project number 323478.

Introduction The effect of grain refinement on the mechanical properties of the metallic materials has been an area of significant interest over the last decade.
Independent investigations carried by Hall [1] and Petch [2] formed the basis (σ α d-1/2) for further studies on reducing the grain size of a polycrystalline materials.
Since then, several investigations [3-6] were performed on polycrystalline materials wherein a significant increase in strength with grain refinement was observed.
Acknowledgement This project was supported by the NSTIP Strategic Technologies Program, grant number (12-NAN2635-02), Kingdom of Saudi Arabia.
Effect of grain refinement on mechanical properties of ball-milled bulk aluminum.