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After two-step aging, the grain of the aluminum bumper is small and evenly distributed, leading to good mechanical properties.
Lili Yang [9] who is the researcher of Shanghai University found that the Cu element accelerated the clusters formation during aging process, the number of the precipitates increased.
From the metallographic picture we can see that, after two-step aging, the grain boundary on the substrate is clearly visible, the grain is small and evenly distributed, the grain boundary has a dispersed distribution of the second phase particles, which are conducive to the improvement of alloy strength.
(3) After two-step aging, the grain of the aluminum bumper is small and evenly distributed, so it is good for the mechanical properties.

A lower heating rate (30°C /h) is a favorite to decrease the number and size of bubbles.
Under pressure, Bi-2223 grains more trend to grow up along the rolling plane and arrange more orderly.
In Fig. 3, the number and size of bubbles increases with the increase of heating rate.
Above all, a lower heating rate (30°C /h) is a favorite to decrease the number and size of bubbles.
A lower heating rate (30°C /h) is a favorite to decrease the number and size of bubbles.

Further investigation of the cells clarified that the boundary of cells is a low angle grain boundary with dislocation cell wall and segregation of certain elements such as Nb and Ti.
These results indicate that the boundaries of cells are low angle grain boundaries (LAGBs), which exhibit one or both of tilting and twisting misorientations between adjacent cells.
In fact, the value of k (92 MPa∙µm-1/2) is comparable to or higher than that reported for a high angle grain boundary (HAGB) in polycrystalline pure Ni (68 MPa∙µm-1/2) [15].
Acknowledgement This work was supported by CREST-Nanomechanics: Elucidation of macroscale mechanical properties based on understanding nanoscale dynamics of innovative mechanical materials (Grant Number: JPMJCR2194) from the Japan Science and Technology Agency (JST).
Hug, Hall-Petch behaviour of Ni polycrystals with a few grains per thickness, Mater.

Some of those characteristics are the high speed growth, the capability to stabilize soils likely to be eroded, the uptake of CO2 from the atmosphere [2], floor fixing, flow control, thermoregulation and providing of habitat for a large number of animals species.
In order to obtain the mechanical properties of the Guadua a., several tests were made: shear parallel to grain, compression parallel to grain and tensile parallel to the grain, based on the procedure of NTC 5525 standard [11].
Additionally, tensile perpendicular to the grain tests, using an adaptation of the proposed by Pacheco [12] and perpendicular compression or radial compression test [13] were made.
MOISTURE PROPERTIES [MPa] [MPa] % Compression parallel to grain strength Specimens with knot 46.70 2.88 13.03% Specimens without knot 48.27 4.43 11.30% Total 47.60 3.84 12.17% Perpendicular compression without mortar grouting strength 10.68 3.66 14.27% Perpendicular compression with mortar grouting strength Specimens without metallic band 13.55 4.77 Specimens with metallic band 15.24 6.04 Shear parallel to grain strength Specimens with knot 8.48 1.38 14.04% Specimens without knot 8.30 1.39 14.38% Total 8.39 1.36 14.21% Tensile parallel to the grain strength Specimens with knot 124.00 33.80 11.77% Specimens without knot 164.70 51.03 8.94% Total 144.30 28.79 10.36% Tensile perpendicular to the grain strength 1.08 0.50 11.67% Screwed rods of SAE 1020 steel with 1/2 inch were used for the transverse and longitudinal bolts, with a tensile strength of 300

(2) Work Hardening Mechanisms in Metal Cutting There are a large number of opinions about hardening mechanism, and most scholars suggest that the hardening is a high degree of fibrosis of the workpiece material grain, leading to lattice distortion, stretched and broken grain in the process of plastic deformation, so that the hardness of the machined surface is higher than the original surface.
Due to the compression and friction in the cutting process, surface lattice distortion is generated, with some grain crushed and elongated.
Since the uneven deformation between the grains produces residual stress between grain boundaries, the border area increased, thereby the metal deformation and slipping are prevented, and the metal plastic decreases.Precipitates of plastic deformation: In the plastic deformation process, some metal materials would have the precipitation of the ultrafine particles.
In addition, work hardening has a relationship with material grain size.
Work hardening of fine grain material is greater than that of the coarse grain material.

The yttria content in zirconia grains is 1.3 mol.%, which is lower than the content usually added to monolithic Y-TZP (3.0 mol. %), due to the stabilization effect of the alumina matrix.
A fraction 0.3 wt.%, of Cr2O3 is also added to the mixture of raw materials, Cr mainly solving into the alumina grain structure after sintering.
Note that, due to the high transparency of zirconia, CL bands from neighboring alumina grains were partly visible even when the electron beam was centered at zirconia grains.
The CL spectrum recorded in the Al2O3 and ZrO2 grains of the material studied in this paper are shown in Fig. 1 (a) and (b), respectively.
According to Zecchina et al. [23], oxygen chemisorbs dissociatively onto Cr3+ ions to form Cr=O surface groups; such a process involves the systematic presence of Cr3+ ions with two vacancies (coordination number 4) that chemisorbs only one oxygen atom.

Initial excited state (IES): oscillations Controlling wave process Dislocation Nucleation Center Dependence of Ms on D (size of austenite grain) Mechanism of wave generation (amplification) by non-equilibrium electron subsystem Fig. 1.
Estimations of the number of martensitic crystals generations, the martensite proportion under athermic macrokinetics, and the temperature Mf  (the temperature of the finish of MT for an alloy of given сomposition) were accomplished in [32] using the model of symmetrical orthogonal joints of martensitic crystals.
Chashchina, Grain Size Dependence of the γ→α Martensitic Transformation Starting Temperature, Physical Mesomechanics. 13 3-4 (2010) 195-202
Owen, Effects of austenitizing temperature and aaustenite grain size on the formation of athermal martensite in an iron-nickel and an iron-nickel-carbon alloy, Metall.
Solution of the Critical Grain Size Problem, Germany, Palmarium, 2012

Molybdenum enhances grain refinement and retards grain growth during high temperature exposure.
Data consisted of the maximum load applied to each specimen and the number of cycles completed prior to complete failure of the specimen.
Specimens that didn’t fail within the specified maximum number of cycles were designated as “run-out” specimens and noted with a right pointing arrow on each plot.
The α case in SP 700 is less well defined and no continuous layer of α grains is obvious in the 788°C (1450°F) and 845°C (1550°F) conditioned material (Fig. 3a).
After the 885°C (1625°F) exposure, however, a distinct layer of continuous α phase is present, along with a significant transition zone containing increased α grains.

Jining city is a typical coal grain complex area.
Jining city is a typical coal grain complex area.
Up to now, the city has about 300000 acres farmland has stopped producing grain,and it is in urgent need of loss reduction.
At the same time, every year the economic losses of the reduced grain and economic crop amounted to 600000000 yuan.
The five plates of the"Ji Yan Zou Qu jia" city group structure , formed a large number of coal mining subsided land.

While in traditional metal materials, the relationship between hardness and grain size can be described by Hall-Petch formula, therefore, the hardness will be decreased with decreasing the grain size[1-4].
Due to HCF test results was influenced by many factors, so the number of cycles were different when stress ratio, surface state and value of stress intensity were same.
It will make the surface grain refined.
The number of twins and the dislocation density will increase correspondingly, which significantly improves the strength and hardness of the surface material.
[4] Van Swygenhoven H, Grain boundaries and dislocations, Science. 296(2002)66-67