Prediction the structure, mechanical properties and melting point ofD8_m‐Mo₅SiB₂andCmcm‐Mo₅SiB₂

Abstract

Mo 5 SiB 2 is an ideal candidate for high temperature material. Although the D8 l -Mo 5 SiB 2 has been published, the other phases and the related properties of Mo 5 SiB 2 are still unclear. Here, two possible Mo 5 SiB 2 phases (D8 m -Mo 5 SiB 2 and Cmcm-Mo 5 SiB 2 ) are predicted by using the first principles method. The structural stability, mechanical properties, melting point and electronic structure of Mo 5 SiB 2 are studied. The results show that the D8 m -Mo 5 SiB 2 and Cmcm-Mo 5 SiB 2 are thermodynamically and dynamically stables. The calculated bulk elastic modulus, shear modulus and Young's modulus of the Cmcm-Mo 5 SiB 2 are close to D8 l -Mo 5 SiB 2 . In addition, the predicted Cmcm-Mo 5 SiB 2 has high melting point (2518.5 C) compared to the D8 l -Mo 5 SiB 2 and D8 m -Mo 5 SiB 2 . In particular, the predicted D8 m -Mo 5 SiB 2 exhibits better plasticity than the D8 l -Mo 5 SiB 2 . The calculated density of states and Mulliken overlap population shows that the D8 m -Mo 5 SiB 2 and Cmcm-Mo 5 SiB 2 all exhibit metallic behavior. The metallic behavior mainly depends on the electronic interaction between Mo atom and B atom near Fermi level. Furthermore, the bond length of Mo-B bond in the D8 m -Mo 5 SiB 2 is longer than the other two structures, which may be the reason why the ductility of the former is better than the latter. K E Y W O R D S first-principles method, mechanical properties, melting point, Mo 5 SiB 2 , structural prediction 1 | INTRODUCTION The search for excellent high-temperature materials is also a big challenge for the development of modern industrial [1-8]. Mo 5 SiB 2 ternary silicide is regarded as an ideal candidate material for aero-engine turbine blades and industrial gas turbine hot-end components because of its high melting point, good mechanical properties and good oxidation resistance [9-15]. In 1957, Nowotny et al. have been studied the phase diagram of Mo-Si-B ternary silicide by using the phase diagram method. The Mo-Si-B ternary phase is discovered for the first time [16]. In 1958, Aronsson discovered by powder photography that this Mo-Si-B ternary phase has a body-centered tetragonal structure (D8 l ) similar to Cr 5 B 3 , and gave its lattice parameters a = b = 6.02 Å, c = 11.07 Å [17]. As we all know, the good oxidation resistance, excellent mechanical properties and good ductility are necessary conditions for high temperature materials [18][19][20][21][22][23][24]. In terms of mechanical properties, Mo 5 SiB 2 ternary silicide has high single crystal elastic constants at room temperature (RT): C 11 = 480 GPa, C 33 = 415 GPa, C 12 = 166 GPa, C 13 = 197GPa, C 44 = 174GPa and C 66 = 143 GPa [25]. Furthermore, the bulk elastic modulus, shear modulus and Young's modulus of Mo 5 SiB 2 are 271GPa, 152GPa and 385GPa, which indicate that Mo 5 SiB 2 is an extremely high temperature material [26]. In addition, it is found that there are numerous dislocations in the Mo 5 SiB 2 crystal, which will benefit its ductility [27,28]. In terms of oxidation resistance, Akinc et al. have been ...

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