Study On Mechanical Properties And Electronic Structure Of Nitride Hard Phase In High Speed ​​Steel

High speed steel with high hardness, super wear resistance, high heat resistance and good toughness, mainly used in the manufacture of complicated thin blade, metal cutting tools with impact resistance, high tenperature and cold extrusion mould, etc. The main hard phases are transition metal carbides, nitrides and borides in high speed steel. Due to the content of hard phases is less in the high speed steel, it is hard to experimental preparate, and researches of nitrides are fewer, so that this paper mainly focuses on the calculations and rearseaches about Binary-system MN, M2N, Mn-N system and Ternary-system M2CN nitrides hard phases in high speed steel by methods of first-principles calculations combination with semi-experiential theory. The ground state properties of these compounds are obtained and offer reliable theoertical guidance. The main research contents and results in this paper as follow:The cohesive energy and formation enthalpy of nitrides are negative and they indicate that nitrides hard phases in high speed steel are thermodynamic stability;The elastic constants of nitrides are obtained by stress-strain and satisfy the mechanical stability conditions to determine the structural stability. The results indicate all nitrides have structural stability except Mn3N2.The mechanical moduli of other metal nitrides can be calculated from the known elastic constants, which include bulk modulus (B), shear modulus (G), Young’s modulus (E) and Poisson’s ratio (v). The B/G or Poisson’s ratio illustrate the material is brittle or toughness. The Poisson’s ratio of MN (M=Ti, V, Zr, Nb and Ta) is range from 0.13 to 0.17, which show these nitrides are brittle; The Poisson’s ratio of M2N (M=Cr, V, Nb and Ta) nitrides is range from 0.26 to 0.31, it uncover these M2N nitrides are ductile and reflect the metallic character of them; The Poisson’s ratio of Mn4N nitrides is 0.16 and show the nitride is brittle, the Poisson’s ratios of Mn2N0.86 and MnN are 0.36 and 0.27 and indicate they are ductile. The shear modulus and hardness of ternary compound M2CN(M=Ti, V, Zr, Nb, Hf 和 Ta) with the same main group elements are the same oder as Ti2CN> Zr2CN> Hf2CN and V2CN> Nb2CN> Ta2CN. The other ternary compound are brittle expect Ta2CN. The mechanical anisotropy character of these nitrides indicates that the anisotropic in Young’s modulus is stronger than its of the bulk modulus. Moreover, the anisotropy in young’s modulus of ternary compound with first V B group metal elements is stronger than its of the first IV B the metal elements.We analyze electronic density of ststes of M2N, Mn-N systems and M2CN, the results show that these nitrides are chemically bonding behavior of metal and covalent bonds, and the pd hybridization occurs when close to the Fermi level. Analysis of overlap populations in Mulliken method indicate bonding behaviors of nitrides are the combinations of covalent and metallic bonds.