Precipitation of (Ti, Zr, Nb, Ta, Hf)C high entropy carbides in a steel matrix

In this study, arc melting was used to precipitate (Ti, Zr, Nb, Ta)C and (Ti, Zr, Nb, Ta, Hf)C particles in-situ within a steel matrix. Energy dispersive X-ray spectroscopy revealed that these particles are solid-solutions of their constituents (TiC, ZrC, NbC, TaC and HfC) while crystal orientation data from electron backscatter diffraction showed that the particles are either single crystals or an agglomerate of a few crystals. X-ray diffraction revealed that their lattice constants can be approximated using the rule of mixtures. The hardness of (Ti, Zr, Nb, Ta, Hf)C measured using nano-indentation was found to closely match that of TiC (the hardest and stiffest of the monocarbide constituents), indicating that the hardness is higher than what the rule of mixtures suggests. Nonetheless, better homogenization of the high entropy carbide should lead to significantly better properties. Additionally, considering the high melting points of TaC and HfC, (Ti, Zr, Nb, Ta, Hf)C may have interesting high temperature applications. Furthermore, using this approach, it should be possible to design new (Ti, Zr, Nb, Ta, Hf)C-reinforced steel matrix composites for a variety of engineering applications.