Development of novel metal-ceramic composites via arc plasma-induced accelerated reaction

Abstract

New design or optimization for conventional processing of metal-ceramic composites has been intensively investigated since mechanical and thermal properties of the composites depend on the materials' processing history. With an appropriate combination of matrix and reinforcements, the liquid-state processing has been considered relatively cheap and simple route for the synthesis of metal-ceramic composites. However, the chemical reaction between reinforcements and molten alloys results in the interfacial reaction that degrades the properties of the composites. This has stimulated an interest for the development of in-situ processing routes where reinforcements are spontaneously synthesized during the process. However, the in-situ routes commonly require high temperature and long processing time due to the thermodynamics and kinetics related to the reaction. Thus, it is necessary to optimize the condition of conventional process or develop novel processing routes for the metal-ceramic composites. Here, arc plasma processing is introduced to develop a novel fabrication route for the in-situ synthesis of metal-ceramic composites. The high temperature processing is advantageous for the in-situ formation of reinforcing materials, the acceleration of the in-situ reaction and the strong interfacial bonding between the matrix and reinforcements. The aim of this study is to investigate the feasibility of developing novel metal-ceramic composites, the forming mechanism of the fabricated composites and the applicability of the resulting composites synthesized by arc plasma-induced accelerated reaction. Arc plasma-induced volume nitridation of aluminum was observed during arc melting under argon and nitrogen mixed atmosphere. The nitridation process resulted from the instantaneous chemisorption of nitrogen, enhanced nitrogen diffusion and improved wetting of aluminum nitride (AlN) by arc plasma-induced reaction. The aluminum matrix was explosively nitrided, showing the in-situ formation of particulate composites with volume fraction of 40 vol.% which is the highest values among ever reported in-situ Al-AlN composites formed by using nitrogen gas as a reagent. Arc plasma-induced liquid phase displacement reaction was carried out by arc melting aluminum with the ceramic powders as sacrificial materials. The liquid aluminum simultaneously infiltrated and reacted with silicon nitride (Si3N4) powder preform, leaving in-situ formed AlN reinforced aluminum matrix composites. The displacement reaction between Al and Si3N4 led to the volumetric expansion of nitride phase, which enables us to fabricate aluminum matrix composites with high volume fraction of nitrides. The candidate alloy matrix using the arc plasma processing can be extended from pure metals to multi-component alloys like bulk metallic glasses (BMGs). Using Al-AlN particulate composites as a sacrificial reagent, the zirconium nitride (ZrN) reinforced BMG matrix composites were synthesized by arc melting. The in-situ formation of ZrN resulted in the improvement of mechanical properties, which is advantageous for the structural applications of BMGs. The newly developed metal-ceramic composites above showed attractive thermal or mechanical properties due to the in-situ formation, uniform dispersion of reinforcements and the strong interfacial bonding. This indicates that the arc plasma processing can be promising routes for the synthesis of novel metal-ceramic composites in various gas-liquid-solid systems.