High entropy alloys are composed of more than 5 (usually no more than 13) major elements (metal or metal and non-metal), each with an atomic fraction greater than 5% and no more than 35%. The experiment used FeCoNiCrMn high entropy alloy, with a theoretical atomic ratio of 1:1:1:1:1 and a mass fraction range as shown in Table 1.

Table 1 Composition Table of FeCoNiCrMn

The particle size data is displayed as a percentage of volume accumulation, for example, the detection result is Dv (50)=100 μ m. It means that the particle size is less than or equal to 100 μ The powder of m accounts for 50% of the total sample amount. Due to the excellent sphericity of the atomized powder and the very small number of hollow spheres, the particle size value corresponding to sample Dv (50) can be considered as the median particle size of the sample.

Figure 1 Powder Accumulation Curve under Different Superheating Degrees

In order to study the effect of superheat on powder particle size, experiments were conducted at superheating temperatures of 100 ℃, 150 ℃, 200 ℃, and 250 ℃, with atomization pressure controlled at 5.0 MPa and insulation temperature controlled at 1100 ℃. The atomized powder is sieved through 50 mesh and mixed evenly, and its particle size is tested. The test results are shown in Figure 1.

According to experimental data, when the superheat is 100 ℃, Dv (50)=71.4 μ M; When the superheat is 150 ℃, Dv (50)=68.9 μ M; When the superheat is 200 ℃, Dv (50)=65.6 μ M; When the superheat is 250 ℃, Dv (50)=65.5 μ M. It can be seen that as the superheat of the alloy liquid increases, the median particle size Dv50 decreases accordingly; After the superheat reaches 200 ℃, the effect of the increase in superheat on the powder particle size decreases. The process of gas atomizing alloy liquid is usually divided into three stages: initial crushing, secondary crushing, and cooling solidification. After coming into contact with atomized gas, the alloy liquid is first pulled into a liquid film, which is then broken into small droplets by secondary crushing. Finally, the droplets cool down into solid powder, and the final particle size of the powder mainly depends on the state of secondary crushing.

If the superheat of the alloy liquid is low, it will solidify after its initial crushing, and will not be further broken into smaller particles by the gas in the secondary crushing stage, so the particle size of the powder is coarser. At the same time, when the superheat is below 100 ℃, due to the use of room temperature and high pressure gas for atomization, it enters the relatively open atomization barrel after being sprayed out through the narrow nozzle of the atomizer. The gas rapidly expands while participating in atomization, absorbing a large amount of heat, which will cause the nozzle that constrains the alloy liquid to quickly cool down. Due to the small inner diameter of the nozzle, the alloy liquid inside will solidify directly due to the slow flow rate, leading to the suspension of the atomization process. During the process of increasing the superheat from 100 ℃ to 200 ℃, the powder that solidified during the initial crushing will decrease, and the proportion of powder that can be crushed again will increase, resulting in a smaller powder particle size. When the superheat exceeds 200 ℃, the number of droplets that solidify after the initial crushing has dropped to a sufficiently low level, and the vast majority of droplets will participate in the secondary crushing process. Further increase in superheat can no longer significantly increase its proportion. Therefore, after the superheat exceeds 200 ℃, the particle size of the powder no longer changes significantly with the increase of temperature.

When using the atomization method to prepare FeCoNiCrMn high entropy alloy, changing the superheat can change the atomization state of the alloy liquid while keeping the atomization pressure and insulation temperature unchanged. The higher the superheat, the finer the particle size of the powder. When the superheat exceeds 200 ℃, the effect of superheat on powder particle size is significantly reduced.