Interplay between decarburization, oxide segregation, and densification during sintering of nanocrystalline TaC and NbC

•Nanocrystalline powders of TaC and NbC were sintered to high density at 1300-1400 °C.•Sintering process was studied in detail and the sequence of decarburization, oxide segregation, and densification phenomena was observed.•Sintered ceramics demonstrated hardness of 20-22 GPa due to submicron grain size and carbon deficiency.•The effects of experimental variables such as time of ball-milling, sintering temperature, and content of excess carbon were documented.