The phase decomposition in non-equimolar (ZrHfVNbMoW)Cx complex concentrated carbides via carbon content regulation

(Zr0.196Hf0.02V0.196Nb0.196Mo0.196W0.196)Cx complex concentrated ceramics (CCC) with variable carbon nonstoichiometry are fabricated by hot-pressing sintering at 2100 degrees C for 1 h. The influence of carbon content on phase decomposition behavior and microstructural evolution is investigated. With the decreasing carbon content, the phase transformation of single-phase solid solution -> discontinuous precipitation -> spinodal decomposition -> single-phase occurs, consistent to the binary phase diagram with miscibility gap. The single-phase solid solution decomposes into (ZrHfNb)C-rich and (VMoW)C-rich phases during the phase separation. For spinodal decomposition, the nodular microstructure is formed with coherent crystal orientation relationship of (ZrHfNb) C-rich phase {011} // (VMoW)C-rich phase {011}. The spinodal decomposition leads to in-situ hardening and toughening effects due to the interface hardening and fine microstructure. The spinodal decomposition into two high entropy phases could potentially be beneficial to tailor properties and demonstrated in a future work.