Cr-assisted low-temperature densification of(Ti,Zr,Nb,Ta,Mo)C high-entropy carbides with ultrafine grain and enhanced hardness

While the use of low-melting-point metals as sintering aids for high-entropy carbide(HEC)ceramics has been well established,their existence can compromise hardness due to residual metallic inclusions.This study demonstrates an innovative strategy to meet this challenge,where(Ti,Zr,Nb,Ta,Mo)C high-entropy carbide ceramics with ultrafine grains and enhanced hardness are obtained through chromium(Cr)-metal-assisted spark plasma sintering(SPS)at a temperature as low as 1600℃.The results show that the addition of 5 vol%Cr promotes the formation of highly densified single HEC phase ceramics with a high relative density(98.4%)and an ultrafine-grained microstructure(0.17μm).This low-temperature densification mechanism can be attributed to Cr’s solid-solution effect within the matrix and the increased carbon vacancies generated during sintering.The grain size of the(Ti,Zr,Nb,Ta,Mo)C ceramics with 5 vol%Cr metal addition is significantly smaller than that of Cr-free(Ti,Zr,Nb,Ta,Mo)C ceramics sintered at 2000℃(3.03μm)or via traditional low-temperature liquid-phase sintering(1.3–1.5μm).Importantly,the addition of 5 vol%Cr substantially increased the hardness of the ceramics,with a remarkable increase from 23.57 to 28.16 GPa compared to that of the pure(Ti,Zr,Nb,Ta,Mo)C ceramics,owing to the fine-grain strengthening and solid-solution strengthening mechanisms.This work highlights the uniqueness of Cr metal as a sintering aid in achieving densification and hardness improvements in(Ti,Zr,Nb,Ta,Mo)C ceramics,offering a promising strategy for improving the properties of HEC materials for further development in the near future.