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Effect of Chemical Composition on Grain Refinement of AlxCoCrFeNi High Entropy Alloys with NiAl Grain Boundary Precipitates Hiroyuki Y.
In this way, grain boundary precipitation is effective in obtaining ultrafine-grained microstructure in HEA.
Thus, the grain refinement by the NiAl grain boundary precipitates is effective in the improvement of strength-ductility balance.
Summary The effect of x on grain refinement of AlxCoCrFeNi alloys was investigated focusing on the NiAl grain boundary precipitates.
Acknowledgement This work was supported by Grant-in-Aid for Challenging Exploratory Research (JSPS KAKENHI Grant Number 17H03415) in Japan.

For samples sintered at high temperatures, a significant change of grain morphology was observed and a large number of plate-like grains develop, see Figs. 1d, 1e and 1f.
However, in the present work, the plate-like grains are not the minority, and the grain sizes of these grains are not abnormally large.
Grain growth exponent.
Change in grain morphology may certainly result in a change in grain growth exponent.
Therefore, the grain size employed in the present study is underestimated for the plate-like grains and approximately true for the equiaxed grains.

The grain refinement mechanism of the Al-5Ti-1B grain refiner was studied.
The grain refinement mechanism of the Al-5Ti-1B grain refiner was studied.
Table 1 Experimental scheme of grain refinement Experimental number Addition amount (%, mass percentage) Al-5Ti-1B Al-10Ti Al-4B TiB2 powder 1 0.2 — — — 2 — 0.1 — — 3 — — 0.05 — 4 — — — 0.0064 5 — 0.1 0.05 — 6 — 0.056 — 0.0064 Results Fig. 1 Microstructures of Al-5Ti-1B (a), Al-10Ti (b), Al-4B (c) and TiB2 powder (d) Fig.1 shows the microstructure of the Al-5Ti-1B, Al-10Ti, Al-4B master alloy and TiB2 powder.
It is well known that the microstructure of as-cast pure Al without adding any grain refiner is composed of coarse columnar grains with the average grain size of 2800 μm.
Since there are a large number of TiB2 particles in Al-5Ti-1B master alloy and each TiB2 particle is a heterogeneous nucleus of an α-Al grain, hence the Al-5Ti-1B master alloy is an efficient grain refiner of pure aluminum and aluminum alloys.

The simulated results of the grain growth by the model are very close to the grain growth of Al2O3-based ceramic materials.
The initial size of grain is D0.
It is assumed that the requirement of heat for grain growth in the total heat is R1, heat causes the growth of grain, the conversion factor is r.
(12) The parameters r, R1, R2, R3 are positive number. α is the consumption rate of heat, β is the consumption rate of space.
This model is a new model of grain growth.

In case of the <100>-tilt grain boundaries two different configurations were examined: (1) grain boundaries with <100>-tilt axis and a grain boundary normal direction close to (010) and (2) grain boundaries with a <100>-tilt axis and a grain boundary normal direction close to (110).
The average grain size was determined for each sample by measuring the grain sizes of at least 300 grains (for large grain sizes) and 800 grains (for small grain sizes).
This system delivers information of the average grain size and grain size distribution
The number of measured orientations was in the range of 5 5 2 10 to 7 10⋅ ⋅ .
In contrast, if the grain boundary forms a continuous interfacial slab as in high angle grain boundaries, vacancies can reach the dislocations easily through the grain boundary plane by grain boundary diffusion.

Qualitatively, it could be stated that for 250°C, the number density of precipitates formed within the grain and at grain boundaries is higher with having finer distribution for the different aging times compared to 330°C.
Fig. 4 (a, b) compare the values of number density of precipitates developed both within the grains and at grain boundaries at varying aging times for 250°C and 330°C temperatures.
For instance, an increase of ~300 % and ~308 % in number density of precipitates formed inside the grain and grain boundary, respectively are obtained for over aging from 330°C to 250°C (Fig. 4).
Variation of the number density of precipitates for varying aging times at two different aging temperatures (250°C and 330°C) present (a) within the grain (continuous precipitates) and (b) at the grain boundary.
(The values of number density of continuous precipitates within the grain have been acquired from our previous work [7].

From these images above, it can be seen that in all simulation results, with the lapse of simulation time, the average grain size of the matrix gradually increases, the number of grain decrease, and the grain boundary moves to its curvature center.
Fig. 2 Change curves of average grain size with time Fig. 3 Logarithm analyses curves of grain growth The reason for this is that the number of the second phase particles in the matrix are different because of the different size distributions when the volume fraction and the average size of particles are same.
As shown in Fig. 4, when the size of the second phase particle fits lognormal distribution, the number of the big particle is abundant, the total number of the second phase particles decreases, and then the pinning effect on grain boundary is weakened at the same volume fraction.
Fig. 4 Distributions of second phase particles (a) Distributions of particles’ number; (b) Distributions of particles’ volume fraction Conclusions A modified grain growth CA model is set up, which investigates the pinning effects of the second phase particles with different size distributions on grain growth.
The exponent of grain growth is not a constant number and decreaces gradually with the increasing of pinning force.

This paper deals with the cavity formation and growth behavior of fine-grained 1420 Al-Li alloy during superplastic forming.
With the strain and temperature increasing, the total number and the average size of cavities increased.
The average grain size was about 10µ m.
Result Microstructure of fine-grained 1420 Al-Li alloy Fig.2 (a) showed the SEM micrograph of fine-grained 1420 Al-Li alloy.
Among them, the larger particles were crushed in the process of hot rolling and the broken particles randomly distributing both within the interior of grains and along the grain boundaries.

Introduction The importance of understanding three-dimensional (3D) grain growth for controlling materials properties is well-recognized, and a large number of experimental and theoretical studies have investigated fundamental microstructural mechanisms associated with thermal processing.
Since the incident beam irradiates a large number of grains with different orientations as it penetrates the sample, many Laue patterns are superimposed in a single raw image (e.g.
During the data analysis, distinctive reconstructed Laue images containing rows of a large number of sharp Bragg peaks were observed at a few isolated locations superimposed on the fcc Al patterns.
The initial hot-rolled microstructure consists of many grains ~5-10 µm in size, and a large number of low-angle boundaries are observed in this (001)-textured sample.
After annealing at 355ºC, many small grains have been consumed, and only a few of the original grains are unchanged.

This happens because the driving force for grain growth is the decrease in energy caused by the reduction of the number of grain boundaries per unit volume.
The total surface area of boundaries is decreased as grain size is increased, causing a reduction in the surface energy, i.e., when grains grow, the number of their boundaries is decreased and their total surface area energy decreases.
This is due to the number of grain boundaries.
It is clear then that the number of grain boundaries was probably the main cause for the difference found between the machining strengths in these two groups of specimens.
Coppini Index values are sensitive enough to characterize distinct values of machining strength in solid solutions with different number of grain boundaries; d. machining strength test may be performed preliminarily to discover the minimum number of steps in order to get more accurate results.