Microwave plasma as an efficient energy source for metal powder melting in additive manufacturing and powder metallurgy

Achieving rapid and energy efficient melting of metal powders remains a significant challenge in powder metallurgy and advanced manufacturing processes such as metal-based material jetting, where conventional thermal systems are slow, power intensive, and unsuitable for high liquidus temperature alloys. This study investigates a microwave plasma assisted melting approach using a custom-designed single mode cavity capable of sustaining stable metal-microwave discharge at low incident power. Electromagnetic simulations were performed using COMSOL Multiphysics® to analyse mode structure, field localisation, and current density concentration at particle contacts, while controlled experiments examined discharge evolution, thermal response, and melting behaviour of aluminium, bronze, AISI 316 L, and AISI 410 L powders. Heating rates exceeding 600 °C/min were achieved at 300 W, enabling complete melting of AISI 410 L (liquidus ≈ 1550 °C) within 150 s. All alloys produced dense ingots with relative densities above 97%, and microhardness values significantly higher than their cast counterparts. XRD and microscopy revealed refined microstructures and phase evolution associated with rapid plasma assisted solidification. A threefold increase in powder mass required only a 1.37× increase in melting time, demonstrating favourable energy coupling and scalability. This work demonstrates a fully controlled microwave plasma approach for direct melting of metal powders inside a single mode cavity without the use of susceptors, addressing long standing limitations of multimode systems and conventional heating methods. The results establish a fast, low power, and material flexible melting route with strong potential for metal additive manufacturing, particularly for thin powder bed and droplet-based material jetting applications.