Abstract
Microwaves at the ISM frequency of 2450 and 5800MHz have been exploited to prepare FeCoNiCrAl-family high entropy alloys by direct heating of pressed mixtures of metal powders. The aim of this work is to explore a new microwave assisted near-net-shape technology, using powder metallurgy approach for the preparation of high entropy alloys, able to overcome the limits of current melting technologies (defects formation) or solid state ones (time demanding). Results show that direct microwave heating of the powder precursors occurs, and further heating generation is favored by the ignition of exothermal reactions in the compound. Microwave processing, exploited both for the ignition and sustaining of such reactions, has been compared to reactive sintering in laboratory furnace and mechanical alloying in a planetary ball milling. Results demonstrate that microwave required the shortest time and lowest energy consumption, thus it is promising time- and cost-saving synthetic route.
Highlights
High-entropy alloys (HEA) are a class of multi-component alloys composed of 5 or more principal constituent elements and each with a concentration between 5 and 35 atomic% [1]
The aim of this work is to explore a new microwave assisted near-net-shape technology, using powder metallurgy approach for the preparation of high entropy alloys, able to overcome the limits of current melting technologies or solid state ones
Results show that direct microwave heating of the powder precursors occurs, and further heating generation is favored by the ignition of exothermal reactions in the compound
Summary
High-entropy alloys (HEA) are a class of multi-component alloys composed of 5 or more principal constituent elements and each with a concentration between 5 and 35 atomic% [1]. Regardless of the HEA composition, this family of alloys shows several interesting features; in particular they tend to form simple solid solution phases with the possible presence of nanostructures or even amorphous structures [3], presenting Vickers hardness ranging from 100 to 1100 HV30, accompanied by a good thermal stability and excellent resistance to anneal softening [4]. Due to this broad spectrum of properties, the HEA have many potential applications [5], including mechanical parts and furnace parts requiring high strength, thermal stability and wear and oxidation resistance. The advantage of applying microwaves to combustion synthesis reactions resulted in high purity of the products [10], rapid ignition of the reaction [11], possibility to control the products microstructure [12] and cooling rate after synthesis, especially in presence of ferromagnetic reactants [13]
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