A new multi principal element alloy synthesized by microwave powder metallurgy technique

Multi principal element alloys (MPEAs), consisting of five or more alloying elements at near equiatomic concentrations and forming bcc and/or fcc solid solution phase, were recently developed. According to the literature research, the synthetic route to produce MPEAs should guarantee short alloying time, efficient cooling and capability to operate in controlled atmosphere. Such conditions can be achieved using high frequency electromagnetic fields, like in microwave heating. Microwave assisted combustion synthesis of pure metal powders mixtures as reactants has already been used during the last decade by the authors to prepare intermetallics, functionally-graded materials, and recently to produce multi-principle alloys. Moreover the addition of SiC in these alloys increases the mechanical properties and oxidation resistance at high temperature, as demonstrated in a recent paper by the authors. In this work a new MPEA (Al15Mn20Fe25Co15Ni25) was prepared with and without the addition of SiC, using powder metallurgy route and exploiting microwave as way of generating heat inside the precursors and hence to start the reactive sintering. Results show that direct microwave heating at 2450 MHz of the powder precursors leads to the ignition conditions, with an evident exothermal event ascribable to the mixing enthalpy, and then self-sustaining of the synthesis occurs. The temperature and duration of the microwave-assisted process resulted much lower than other conventional powder metallurgy routes, but at the cost of a higher residual porosity. Sample characterization confirmed that the powder metallurgy approach is suitable to retain the shape of the load imparted during forming by uniaxial pressing.