A process for heating a powder material by microwave radiation so that heating of the powder material is selective and sufficient to cause complete melting of the particles. The process entails providing a mass of powder comprising a quantity of filler particles of a metallic composition, and subjecting the mass to microwave radiation so that the filler particles within the mass couple with the microwave radiation and are completely melted. According to one aspect, the mass further contains at least one constituent that is more highly susceptible to microwave radiation than the filler particles, and the filler particles are melted as a result of heating by microwave radiation and thermal contact with the at least one constituent. According to another aspect, the powder mass is thermally pretreated to induce an irreversible increase in its dielectric loss factor prior to melting by microwave irradiation.