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In addition, the re-welding process can increase the HAZ dimensions and its coarse-grain region (CGHAZ), which is located exactly at the weld-toe and by considerable hardness and low fracture toughness.
It is well-known that the lower the grain size, the higher the material toughness.
In the same way, the higher the grain size, the lower the hardness/mechanical strength.
Consequently, the austenitic grain size of the second weld repair is higher than that of original weld bead, as mentioned previously.
Acknowledgement: The authors are grateful to FAPESP/process number 99/11948-6, CNPq and FUNDUNESP.

On the other hand, a fine-grained microstructure without cavies or pores that induced by various types of deformation treatments is an alternative [3, 9, 10].
According to the model of Estrin [19] that the spacing between impenetrable obstacles or grain boundaries decides the mean free path of dislocations, in which the mean free path is determined by both dislocation-dislocation interaction and barriers in grain or twin boundaries (TBs).
Since the formation of twins subdivide grain to more twin boundaries, which offers additional barriers to dislocation movement.
As seen in Fig.3a, a large number of deformed area are observed in grain/TBs, the tangled dislocations are observed in both TBs and interior of twin(IT),which demonstrates that the presence of twinning provides an effective role in prohibiting dislocation movement during the deformation.

Zhou, Grain refinement in solidification of highly undercooled eutectic Ni-Si alloy, Mater.
They also observed a significant refinement of the grain structure with increased undercooling, an observation common to many other deeply undercooled systems [[] S.
Herlach, Physical-mechanism of grain-refinement in solidification of undercooled melts, Phys.
Cochrane, Grain refinement and the stability of dendrites growing into undercooled pure metals and alloys, J.
Melt encasement, within a high purity flux, was employed to reduce the number of potential heterogeneous nucleation sites allowing the attainment of high undercoolings.

This means that the adjacent field of this given point will be ground by the grains which are only located at the curve (Γ1).
And a curve of a set of curves {Γ2} is the cutting trace of the grain at a point of the path curve (Γ1) in relation to the workpiece.
As shown in Fig.3, the curve (Γ2) is the cutting trace on the workpiece made by the grain at the point Q*.
It can be imagined that a cutting grinder can be generated by arraying the grains evenly on the path curve (Γ1).
When the angle β is changing with the time, the grains that are arrayed on the curve (Γ1) will sweep the adjacent field of the given point of the workpiece.

The average grain size of Si particles decreased from 3.56μm to 2.41μm and the aspect ratio decreased from 5.11 to 3.17 (Fig. 2a and Fig. 2b).
In the fusion zone, both columnar dendrites and columnar grains grew from the fusion line to the weld center (Fig. 4a).
As can be seen, the eutectic silicon phase transformed from a coral-like structure to a fine granular morphology and the matrix phase transformed from columnar dendrites to fine equiaxed grains in the weld zone (Fig. 4a and Fig. 5a) [10].
Columnar grains perpendicular to the fusion line disappeared after the treatment in the fusion zone (Fig. 4a and Fig. 5a).
It was also noticed that some small grey particles of Fe-containing phase and fragmented silicon particles spheroidized and the averaged silicon particle size and α-Al grain size increased through the treatment [5,10,11].

.%) to Al-based alloys is realized to refine the cast grain structure, to increase recrystallization temperature and to improve mechanical properties [1–2].
Despite a number of investigations of the Al–Mg as well as Al–Sc–Zr-based alloys there are considerably less systematized data about the Al–Mg–Sc–Zr-based alloys in the literature.
Results and Discussion Fine (sub)grain structure in the range from 0.5 µm to 1.5 µm was observed in the as-extruded alloy in the cross section of the extrusion direction.
The fibre-like fine grained structure of the alloy persists the annealing.
The EBSD analysis of the alloy at 550 °C for 4 h and 32 h revealed recrystallized grains of the size ~ 15 – 30 µm (see Fig. 7).

FESEM images and EDS analyses showed that TiC spherical grains constituted the matrix of the TiC-TiB2, and a number of TiB2 platelets were embedded in the TiC matrix, whereas a few of Cr metallic binder phases were distributed in between TiC spherical grains and TiB2 platelets.
It is considered high hardness of TiC-TiB2 benefited from the achievement of fine-grained microstructure and near full density, as shown in Fig. 4, while high fracture toughness of ceramics is attributed to crack deflection, crack-bridging and pull-up of small-size hard TiB2 platelets, as shown in Fig. 5 and Fig. 6.
Meanwhile, the high bending strength of TiC-TiB2 composite benefited from the fined-grained microstructure, high fracture toughness and small-size defect of the ceramics.
XRD, FESEM and EDS analyses showed that TiC spherical grains and TiB2 platelets constituted the matrix of the ceramics.

Recently, a number of methods such as organic foam impregnation, gel casting, and protein foaming have been used for the preparation of porous ceramics [3-8].
As shown in Fig.2, Ti/1.1Al/TiN =1.0:1.1:1.0 at 1300°C holding for 2 h specimens, powder sintering synthesis under the scanning electron microscope to observe the surface morphology and the crystal grain growth.
Figure (a) shows that the sample is a typical lamellar grain.
From the graph (b), the internal structure of synthetic samples were found closely, because the Al powder evaporation caused by empty, while the outer surface of a small amount of very fine crystal grain, but the Ti2AlN grain growth has been quite perfect, homogeneous surface structure, crystal size and average thickness can be visual width were 2~3 μm and 4~6 μm.
Ti2AlN grain edge in the sample showed passivation or circular, indicating that Ti2AlN may be generated by a dissolution precipitation mechanism.

Grain size and morphology of the particles were observed using a field emission scanning electron microscopy (FE-SEM, Hitachi S4800).
The more carbon and smaller grain size of Sample 2 is believed to benefit the electrochemical properties due to the enhancement of electronic conductivity and the shortening of diffusion length of lithium ions in Li4Ti5O12 particles.
It can be seen that Sample 1 with the absence of sucrose shows a large dense spherical aggregate structure with smooth surface morphology and each of the spherical grains is made up of a large number of fine cubic crystalline grains, as shown in Fig. 3(b).
The homogeneous particle size distribution and smaller particle size of the sample with sucrose as an additional carbon source (Sample 2) could be also attributed to the presence of much more carbon generated from sucrose, which could effectively inhibit the grain growth of the material.

Materials and Methods The selected starting materials were Grade 1 titanium powder supplied by AP&C (grain size in the range of 75-180 µm), used by the authors in prior research, and B4C ceramic particles provided by ABCR GmbH & Co KG (grain size in the range of 45-75 µm) [15].
Therefore, with increasing travel speed, a greater number of unreacted boron carbide particles are observed (Figure 5-A.1 vs B.1, or D.1 vs E.1).
Concentrated heat resulting from lower travel speeds and higher current intensities could induce a reduction in grain size, thereby elevating hardness.
Conclusions As conclusions of the conducted research, the following points can be drawn: · Higher feed rates contribute to reduced heat exposure, leading to enlarged grain size and consequent hardness reduction.
Grain size augmentation may occur due to increased heat input, resulting in reduced hardness.