Microstructure Design of Steel‐Spinel Composites via Spark Plasma Sintering Process

Compact steel‐spinel composites with a specific microstructure were produced by spark plasma sintering, using powder mixtures of high‐alloy steel AISI 316L, MgO, and Cr 2 O 3 or Fe 2 O 3 as starting materials. The reaction diffusion between MgO and Cr 2 O 3 or Fe 2 O 3 always led to the formation of an Mg‐based spinel. The thermodynamic phase stability of the respective corundum‐like oxide with respect to the oxygen partial pressure decided about the presence or absence of side reactions, which were utilized as an efficient tool for microstructure design of the steel‐spinel composites.The use of Fe 2 O 3 as one of the starting compounds initiated various redox reactions that promoted the formation of mixed spinel phases at the steel/ceramic interface and the transformation of MgO to (Mg, Fe)O, which accommodates, in addition to iron, also other divalent alloying elements from the steel. The phase composition of the composites and the spatial distributions of individual phases and their chemical compositions were investigated using X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, electron backscatter diffraction, and electron probe microanalysis. The microstructure formation was substantiated by thermodynamic calculations. The role of oxidizing and reducing agents that are involved in the microstructure design is discussed.