Enhancement of hardness in niobium carbide composites

Traditional cemented carbides are based on tungsten carbide (WC). Among alternative hard phases niobium carbide (NbC) shows high potential. Mechanical properties and microstructures of binderless NbC composites with different amounts of secondary carbides and different sized starting powders were investigated. Different sintering techniques such as FAST/SPS and the conventional SinterHIP technique were used to produce completely dense samples at different temperatures. Especially with the addition of secondary carbides a hardness increase from 1600 HV10 to above 1800 HV10 was measured. This closes the hardness gap of binderless NbC to binderless WC composites with similar grain size. Furthermore, NbC composites with secondary carbides showed an increase of fracture toughness to values of 4.5 MPa*m1/2, which could lead to their use as cutting tools. Results also include a comparison of hot hardness and other functional properties of binderless NbC and binderless WC composites as a function of grain size.