First-principles quantum molecular calculations of structural and mechanical properties of TiN/SiNx heterostructures, and the achievable hardness of the nc-TiN/SiNx nanocomposites

TiN/SiNx heterostructures with one monolayer of the interfacial SiNx have been investigated in the framework of first-principles molecular dynamics calculations in the temperature range of 0 to 1400 K with subsequent static relaxation. The atomic configurations, thermal stability and stress-strain relations have been calculated. Among the heterostructures studied, only the TiN(111)/SiN/TiN(111) and TiN(111)/Si2N3/TiN(111) ones are thermally stable. Upon tensile load, decohesion occurs between the TiN bonds adjacent to the SiNx interfacial layer for TiN(001)/SiN/TiN(001) and TiN(111)/Si2N3/TiN(111) heterostructures, and inside the TiN slab for TiN(001)/Si3N4/TiN(001) and TiN(110)/SiN/TiN(110) ones. Upon shear, failure occurs in TiN near the interfaces in all the heterostructures, except for the TiN(001)/Si3N4/TiN(001) one, for which the plastic flow occurs inside the TiN slab. Based on these results we estimate the maximum achievable hardness of nc-TiN/Si3N4 nanocomposites free of impurities to be about 170 GPa.