Reaction spark plasma sintering of niobium diboride

• High dense niobium diboride (NbB2) is obtained by in situ processing of niobium and boron by SPS in a single step process.
• Application of load at low temperature region was found to favor the sinterability of the compacts.
• Hardness of NbB2 is found to decrease with increase in indentation load due to indentation size effect (ISE).

Niobium diboride (NbB2) is synthesized and consolidated by the spark plasma sintering technique. Elemental reactants such as niobium (Nb) and boron (B) were subjected to two stage heat treatment, initially at 1200 °C for synthesis and followed by densification at the temperatures in the range of 1700 °C to 1900 °C. High dense NbB2 (~ 97.7%ρth) is obtained at 1900 °C after 15 min holding period. Load application during heat treatment stage is found to improve the sinterability of the niobium diboride compacts. Hardness, elastic modulus and indentation fracture toughness of the high dense NbB2 are measured as 20.25 GPa, 539 GPa and 4 MPa m1/2 respectively.