Disclosed herein are embodiments of methods, devices, and assemblies for processing feedstock materials using microwave plasma processing. Specifically, the feedstock materials disclosed herein pertains to unique powder feedstocks such as Tantalum, Yttrium Stabilized Zirconia, Aluminum, water atomized alloys, Rhenium, Tungsten, and Molybdenum. Microwave plasma processing can be used to spheroidize and remove contaminants. Advantageously, microwave plasma processed feedstock can be used in various applications such as additive manufacturing or powdered metallurgy (PM) applications that require high powder flowability.