First-Principles Calculation Of Mo₂FeB₂ And Ti(C,N) Cermets With Element Doping

Mo₂FeB₂ and Ti(C,N)based cermets have high melting point,high hardness and relatively good wear resistance.Hence,they have broad application prospects as a kind of die and mould materials.In this dissertation,Mo₂FeB₂ and Ti(C,N)based cermet were prepared by vacuum sintering,and the effects of alloy doping and chemical composition on the microstructure and mechanical properties were studied.Based on the first principle calculation,the effect of addition on the electrical properties,elastic properties and theoretical hardness of the hard phase were studied by the Material Studio software.The electrical and elastic properties of Mo₂FeB₂ and Ti(C,N)phase are calculated.The results show that both Mo₂FeB₂ and Ti(C,N)are brittle materials and satisfy the structural stability analysis.The hardness of Mo₂FeB₂ and Ti(C,N)phase is mainly derived from B-B,B-Mo bonding and Ti-C,Ti-N bonding,respectively.The effects of Mn and Ni additives on the microstructure and mechanical properties of Mo₂FeB₂ based cermet were studied.The experimental results showed that Mn additive reduced the particle size of the hard phase,but the Ni additive had no obvious effect on the microstructure.Both Mn and Ni additives increase the transverse rupture strength(TRS),but reduce their hardness.The results of the first principle show that the Mo₂(Fe,Mn)B₂and Mo₂(Fe,Ni)B₂ phase formed by the addition of Mn and Ni have good stability.Compared that of Mo₂FeB₂ phase,Mo₂(Fe,Mn)B₂ and Mo₂(Fe,Ni)B₂ phase have a relatively high plasticity and low hardness.Ti(C_1-x,N_x)(x=0.3?0.5 and 0.7)based cermet were prepared by vacuum sintering.The effect of C/N on the microstructure and mechanical properties was studied.The results showed that the particle size of Ti(C,N)cermet was gradually refined with the increase of N content.When the C/N was 3/7,the pores of cermet increased obviously.The content of N has no obvious effect on the TRS,but the hardness decreases with the increase of N content.The first principle calculation results show that with the increase of N content,the young's modulus E and the theoretical hardness H_v of Ti(C,N)decrease,but the plasticity increases.Based on the first principle calculation,the effects of Mo additive on the electrical properties,elastic properties and theoretical hardness of Ti(C,N)phase are studied.The results show that the hardness of(Ti,Mo)(C,N)phase is reduced and the plasticity is increased compared to Ti(C,N)phase.Besides that the addition of Mo enhances the wettability between hard phase and bonding phase and improve the TRS,the Mo addition improves the toughness of hard phase,which turns to be another reason to explain an increased TRS.