Interfacial reaction between ZrNbHfTa foil and graphite: Formation of high-entropy carbide and the effect of heating rate on its microstructure

The interfacial reaction between graphite and a ZrNbHfTa foil was investigated using a spark plasma sintering (SPS) machine. The interlayer was converted during the treatment into a high-entropy carbide by the reaction between the alloy and the graphite substrate. The degree of conversion depended on the processing time and temperature, but could be completed in only 16 s using the flash-spark plasma sintering process. The final microstructure was strongly influenced by the heating rate. Flash-SPS processing (heating rate about 120 °C/s) melted the alloy, which was then squeezed and deformed before its conversion to the high-entropy carbide (Zr,Nb,Hf,Ta)C. On the contrary, when conventional heating was used (i.e., 10 °C/min) the metal reacted with the graphite substrate before it melted. This concept appears to be generally applicable to different graphite/metal systems, with particular implications in the fields of graphite/metal joining.