Disclosed herein are embodiments of systems and method for processing feedstock materials using microwave plasma processing. Specifically, the feedstock materials disclosed herein pertain to metal powders. Microwave plasma processing can be used to spheroidize the metal powders and form metal nitride or metal carbide powders. The stoichiometry of the metal nitride or metal carbide powders can be controlled by changing the composition of the plasma gas and the residence time of the feedstock materials during plasma processing.