Search results

Microstructure examination on hardened layer revealed that the increase of hardness is due to formation of fine grain martensitie structure.
Cross section of non-melted treated surface (50 X); (a) 0.35 m/s, (b) 0.30 m/s & (c) 0.25 m/s Further examination using SEM (Fig.8) reveals that the brighter region (point (a)) of hardened layer consists of fine grain hard martensitic structure.
However, the darker region (point (c)) consists of larger grain tempered martensite microstructure.
The transition zone (point (c)) is about 20 µm, and consist of larger grain size compared to HAZ and unaffected base material.
The hardness number increased as the operating current increased.

The statistical analysis of the compression strength resulted significant deviations the presence of which may be based on grains, poor stirring the mixture during placing, predisposed surfaces or micro cracks created during sampling in the railway track bed.
To avoid the releasing grains during cutting and polishing they required to be strengthen by the vacuum impregnation method.
Furthermore, it was calculated, the gravel fragments (grains of railway ballast or crushed stone mixture) occupy 0.88% of the entire volume.
The extent of poorly mixed components, quantity, size of contaminating grains, the disproof of horizontal or vertical micro cracks are shown in Figures 6, 8, 9.
Acknowledgement The paper was prepared with the support of the program Competence Centers of Technology Agency of the Czech Republic (TAČR) within the Centre for Effective and Sustainable Transport Infrastructure (CESTI), project number TE01020168.This research was carried out under the project CEITEC 2020 (LQ1601) with financial support from the Ministry of Education, Youth and Sports of the Czech Republic under the National Sustainability Programme II.

The grain size measurement, x-ray diffraction (XRD) phase analysis, radiography test is carried out after FWTPET process.
Input and Output of in absence-hole on the tube in-absence of supporting the specimen Experiment number IP OP TRS (rpm) TP (mm) DOC (mm) TS (MPa) 1 700 0 0.5 582.5 2 700 1 1 525.7 3 700 2 1.5 578.9 4 1000 0 1 610.7 5 1000 1 1.5 661.1 6 1000 2 0.5 624.3 7 1300 0 1.5 651.8 8 1300 1 0.5 762.2 9 1300 2 1 668.6 The impact of each input values identified by Analysis of Variance (ANOVA) for the welding process which is not having a hole on the circumference the tube in the non-existence of backing plate.
The base metal and its grain size were restrained as 36.9 µm and 52.3 µm in diameters.
The size of the grain at the region of the interface was 19.919 µm.
Hence, amplified hardness about the region of the welded interface is due to the combined consequence as a refinement of the grain and severe deformation as plastic region among (TTP) during FWTPET process as displayed in Fig.3.

Table 1 is the grain size of copper foils at different current densities obtained by EBSD statistical analysis.
According to the theory of fine grain strengthening, the finer the crystal grains, the more the number of grain boundaries, and the greater the hindrance to dislocations, resulting in an increase in the tensile strength of the copper foil.
Table 1 The grain size of copper foils at different current densities Current density [A/dm2] 8 12 14 20 26 Grain size [μm] 0.69 0.78 0.91 0.84 0.68 Fig. 7 is the SEM image of a tensile pattern of a copper foil at a current density of 8 A/dm2, 14 A/dm2 and 26 A/dm2.
The relationship between the grain size and elongation of copper foil at different current densities shows a negative correlation.
According to the theory of fine grain strengthening, the fine grain also increases the shape of the copper foil.

The oxide scale formed on the uncoated substrate contains Cr-rich equiaxed grains (Fig. 7b) around 2 µm in size.
In the case of coated samples, a continuous Y-rich scale, formed of finer grains of about 0.3 µm, is surmounted by larger grains rich in Cr and O.
However, an increase of the size of external Cr-rich oxide grains (Fig. 8b) was observed, compared to that oxidised at 850°C.
After oxidation at 950°C, the morphology of coated and uncoated samples look similar, except that the oxide grain size is still finer when Y2O3 coating had been applied, even if some coarse grains are still present.
A number of studies [21-25] investigated the favourable effects of the reactive element on the oxidation rate, diffusion mechanism and scale adherence of chromia forming alloys.

Materials and experimental setup The specimens used in the experiment are commercial polycrystalline NiTi tubes with grain sizes of around 80nm (NDC company, USA).
They were all mechanically polished by fine grained sand papers to reach a final surface roughness of about 0.15μm.
As shown in Fig. 1, the axial length of the helical domain LM is related to the number of the helical coils N by: N=LM/lp
We can apply the energy minimization principle to determine the coil number N of the self-organized helical domain.
The measured coil number N of the helical domain in 7 different NiTi tube geometries used and the theoretical prediction by Eq. 7.

A number of approaches developed by S.
Results and Discussion One of the most well-known steel hardening mechanisms, in which resistance to brittle failure is not decreased, is grain-boundary and sub-structural hardening observed in this work.
An additional factor is an increased disorientation of the boundaries of substructure elements, in particular, grain conglomerates (meso-level).
Moreover, a number of splittings are found, which testify to the formation of a large number of secondary micro-cracks, the coalescence of which forms the front of a macro-defect.
Since micro-cracks are localised both within the grain and on its boundaries, the mixed brittle-plastic failure was observed in hydrogenated steel [11].

Zr, Sc are able to refine the grain size in material preparation and to reduce grain growth during forming) or by innovative preparation procedures (e.g. severe plastic deformation and friction stir processes are able to induce high strain rate superplasticity).
Material behaviour study and optimization Recently, some authors have reported a SP behaviour in some "coarse-grained" commercial alloys, denoting that one of the most important requirements, i.e. a fine and equiaxed grain microstructure, is not essential for achieving SP deformation [8].
In spite of this, the majority of SP metallurgists continue to work on new strategies for preparing new micro- and sub-micro-grained SP alloys and for preventing grain coarsening during forming.
Reducing the initial mean grain size and its growing during the forming process can decrease the forming time giving new chances for SPF applications.
Surely, a great number of works have been missed in this paper, but the new trend of SPF simulation is clear and defined.

In this paper texture formation in a number of nickel-based alloys was studied in order to determine which deformation texture characteristics are responsible for the sharp texture formation under primary recrystallization.
The average grain size before rolling is given in Table 1.
Note that the critical concentration of the alloying element that changes the type of texture also affects the grain-growth kinetics upon recrystallization [3].
In low alloys, somewhat coarser grains appear upon primary recrystallization, but they grow slowly as the annealing temperature 121 increases up to some certain value at which secondary-recrystallization grains appear.
In high alloys, the primary recrystallized grains monotonically increase, and secondary recrystallization does not occur.

The FTIR absorbance spectra were performed in the wave number range 400-4000cm-1.
The result indicated that the grains of the film were regular in size and shape.
Those grains also uniformly distributed on the SiO2/Si substrate.
The AFM results also confirmed that the grains of the film were uniformly distributed on the substrate.
The average grains size and surface roughness of the films was calculated and measured with AFM.