This method first fuses the desired alloy by arc melting.Then, the alloy button is crushed into smaller pieces, which is followed by ball milling into powder. The need for alloying at an elemental level is achieved by processing in the liquid state, while the requirement for the appropriate particle cut is accomplished by pulverization. Complex non-equiatomic compositions can be created by arc melting without incurring significant contamination from ball mil-ling by this route.
Fig.4 Particle size ranges of high-entropy alloys obtained from various powder synthesis techniques
Out of the four reports that employ this method, three reported ball milling to less than 44 um particle size, while one is <34 um, as illustrated in Fig.1. Information regarding milling parameters adopted, such as rotation speed, duration, milling media, quantity of powder charged, and other essential experimental data, is notavailable. However, from the authors' experience, it is estimated that up to 90% of the powder weight charged would be recovered in this process, thereby making it a high yield process. The particle shape is irregular since the particles are fragmented pieces of the cast button. Hence, the powder flowability is likely to be influenced adversely; but the spray parameters can be adjusted to take this into account. The coating microstructure that evolves from these powders is relatively homogeneous in terms of the phases observed since alloy formation has already occurred during the casting procedure.
Huang et al. were the first to generate thermal sprayed HEA coatings, and AM-MM was their method of choice. These coatings, as well as those documented by Hsu et al, exhibited excellent oxidation resistance, which depends largely on both, the alloy com-position, and the microstructural homogeneity of the feedstock.
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