High-entropy alloys are composed of more than 5 (generally no more than 13) major elements (metals or metals and non-metals), and the atomic fraction of each major element must be greater than 5% and not more than 35%. The experiment uses FeCoNiCrMn high-entropy alloy, the theoretical atomic ratio is 1:1:1:1:1, and the mass fraction range is shown in Table 1.
The particle size data is displayed as a percentage of volume accumulation. For example, the test result is Dv(50)=100μm, which means that the powder with a particle size less than or equal to 100μm accounts for 50% of the total sample. Since the sphericity of the aerosolized powder is very good and the number of hollow spheres is very small, the particle size value corresponding to the sample Dv(50) can be regarded as the median particle size of the sample.
In order to study the effect of the temperature of the tundish on the particle size of the powder, under the conditions of a superheat of 200°C and an atomization pressure of 4.0 MPa, the effects of different tundish temperatures on the particle size of the powder were observed. The test result is shown in Figure 1.
According to the experimental results, when the holding temperature is 1100℃, Dv(50)=56.2μm; when the holding temperature is 1150℃, Dv(50)=56.9μm; when the holding temperature is 1200℃, Dv(50)=57.3μm. Since the detection error of the Malvern 3000 laser particle sizer at 50~80μm is ±1μm, it can be considered that the holding temperature has almost no effect on the particle size of the powder. Insulation is one of the most important links in the process of gas atomization powder making. It means to pour the alloy liquid into a funnel-shaped tundish, enter the atomizer through a special guide tube at the bottom of the tundish, and then be atomized into powder. . During the heat preservation process, the alloy liquid passes through the buffer of the tundish and becomes a stable and continuous low-speed liquid flow into the atomizer, which provides a prerequisite for the stable atomization of the powder.
Under normal circumstances, the alloy liquid will form a very thin solidified layer on its inner surface after passing through the draft tube. With the continuous flow of the alloy liquid, the solidified layer will be continuously heated by the alloy liquid with higher superheat until it melts again. When the atomization is finally completed, the inner surface of the draft tube will not adhere to the solidified layer. Since the inner diameter of the draft tube is only a few millimeters, before the alloy liquid is poured into the holding crucible, the holding crucible needs to be preheated to a certain temperature, which can control the thickness of the initial solidified layer. If the holding temperature is not enough, the initial solidified layer will become thicker, resulting in that the actual diameter of the draft tube is much smaller than its designed diameter, the flow rate of the alloy liquid is greatly reduced, and the heat it brings is not enough to melt the solidified layer that has formed. It will continue to thicken until the draft tube is completely blocked.
The heat preservation temperature range of 1100℃~1200℃ designed in this experiment is based on the long-term production experience data of Jiangsu Willary New Material Technology Co., Ltd. When the temperature is below 1100℃, the probability of furnace blockage is greatly increased, and when it is above 1100℃ , Almost no furnace blockage. Since the holding temperature is above 1100℃, the solidified layer no longer affects the actual diameter of the draft tube, and the flow rate of the alloy liquid is only affected by its superheat and atomization pressure. When these two parameters are not changed, the alloy liquid is broken for the first time And the secondary crushing state will not change, and the final particle size will not change greatly.
In the case of constant superheat and atomization pressure, the influence of the holding temperature on the particle size of the powder can be ignored.
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