Fracture mode transition from intergranular to transgranular in (TiZrNbTaCr)C: The grain boundary purification effect of Cr carbide

(TiZrNbTaCr)C high-entropy carbide ceramics with different Cr content are fabricated by hot-pressing and the mechanical properties are tested. With increasing Cr content, the fracture mode changed from intergranular to transgranular. Nanoindentation tests indicated that this transition is ascribed to the enhancement of grain boundary strength and atom probe tomography (APT) analysis confirmed indeed different grain boundary impurity concentration ascribed to a purification effect of Cr carbide. Besides, the mismatch degree between the atoms at and in the vicinity of grain boundaries as well as the grain size may also impact grain boundary strength. The fracture toughness presents a decline tendency with increasing Cr content, and its relationship with fracture mode transition is discussed.