Influence of the Mo10Ni3C3B phase on the hardness and fracture toughness of Mo-Ni-C-B cermet: experimental and theoretical study

Abstract

The high productivity of the cutting material is fully determined by its properties, especially the structure and phase composition. A whole range of materials with different physical and mechanical properties can be obtained by controlling these parameters for alloys of the same system. Cermets are materials that combine the high temperature resistance and hardness of ceramics and ductility of metals. Cermets based on the Mo-NiB system are promising materials in applications to cutting processing. Earlier, in this system doped with carbon, a new κ-phase Mo 10 Ni 3 C 3 B with hexagonal P63 / mmc crystal structure was detected. We obtained the decreasing of hardness and comparable values of the fracture toughness of Mo 2 NiB 2-Ni cermets due to the formation of Mo 10 Ni 3 C 3 B phase. To understand the effect of the Mo 10 Ni 3 C 3 B phase on the mechanical properties of the cermet, first-principles calculations were applied to investigate the elastic, electronic, and thermodynamic properties of this phase. Its mechanical and anisotropic properties were calculated based on the obtained elastic constants. Additionally, for a better understanding of the nature of interatomic bonding, an analysis of the electron localization function (ELF), calculated from first principles, was performed. We found that the Mo 10 Ni 3 C 3 B phase had a 42 % lower hardness and increased ductility compared to the Mo 2 NiB 2 boride, which is expressed in the value of the bulk modulus-shear modulus ratio above the brittleviscous transition. As follows from the results of the ELF analysis, a possible reason for this is the more isotropic nature of interatomic bonds, which indicates their higher degree of metallicity.