A first-principles study on the potential of MAB2 (M=Nb, ta; A=Co, Ni) ternary borides as friction-resistance cermet.

A first-principles study was performed to assess the potential of MAB 2 (M = Nb, Ta; A = Co, Ni) ternary borides as friction-resistance cermet. The formation energy, decomposition energy, phonon dispersion curves and elastic constants were calculated to evaluate stabilities. The bulk modulus, shear modulus, Pugh's ratio, Poisson's ratio and elastic anisotropy were adopted to analyze elastic properties. The Debye temperature was used to reflect thermal conductivity. The density of states, charge density and Mulliken population were performed to reveal physical mechanisms. Through calculational results, MAB 2 possesses structure and mechanical stabilities, and then MAB 2 has excellent elastic properties. Both NbNiB 2 and TaCoB 2 are ductile materials; in addition, the thermal conductivity of NbNiB 2 and NbCoB 2 are satisfying. The calculations imply MAB 2 is a mixture of covalent, ionic and metallic bonds, indicating covalent bonds are vital. Especially, the theory hardness of NbCoB 2 , NbNiB 2 , TaCoB 2 and TaNiB 2 are 25.30, 27.71, 30.78 and 31.91 respectively, indicating MAB 2 has high-hardness potential. The comprehensive properties are more outstanding in MAB 2 than in MAB. The method from atomic scale to macroscale can accelerate optimization of novel friction-resistance cermet. • Studying the potential of MAB 2 -type borides as friction-resistance cermet. • Ratio of B in MAB 2 borides playing a vital role. • MAB 2 borides belonging to a mixture of covalent, ionic and metallic bonds. • Covalency mainly affecting properties of MAB 2 Borides. • Optimization way from atomic scale to macroscale. [ABSTRACT FROM AUTHOR]