Excellent hardness property of bulk MoN fabricated by a novel method

Abstract

Molybdenum nitrides (MoNs) are important materials for their excellent physical and chemical properties, but synthesizing stoichiometric and bulk materials is still a great challenge. In this paper, a new method to prepare bulk molybdenum nitrides was proposed. A novel method based on an untraditional in situ gaseous nitrides under high pressure is developed. In the synthesizing, the sandwiched structure with metal pellet core inside and two pellets of solid nitrogen source outside was used to synthesize bulk molybdenum nitrides. Cubic structured MoN (c-MoN) and hexagonal structured MoN (p-MoN) are synthesized at high pressure and high temperature (HPHT) using molybdenum and melamine as precursors. In both as-synthesized nitrides, p-MoN has an excellent Vickers hardness (Hv) of 29 GPa under a relative low load, which is much harder than that of TiN under the same applied load of 0.49 N. The asymptotic hardness of p-MoN approaches to that of WC (~22 GPa), which is widely used as a hard material. This method not only helps us to find new phase of transition metal nitrides but also provides an useful way for synthesizing high quality bulk transition metal nitrides.

Keywords

• Molybdenum nitrides
• Vickers hardness
• HPHT
• Bulk material