Abstract
For the purpose of exploring new hard materials and doping methods, the structural, mechanical and electronic properties of WCoB and W2CoB2 ternary boride were investigated with 0, 8.33, 16.67, 25 and 33.33 at.% V doping content and W2CoB2 with 0, 5, 10, 15 and 20 at.% V doping content by first-principle calculations. The cohesive energy, impurity formation energy and formation energy indicate the structural stability of V doped WCoB and W2CoB2. The elastic constants and mechanical properties imply that V doping leads to the decrement of shear modulus and the increment of ductility. Two different kinds of hardness models verify that V doping contributes to the decrement of hardness, which is closely related to shear modulus. The electronic structure is analyzed by DOS (density of states), PDOS (partial density of states) and charge density difference, which indicate the formation of weaker B–V covalent bonds, W–V and W–W metallic bonds lead to the decrement of mechanical properties. Compared with previous studies of Cr, Mn doped WCoB and W2CoB2, V doping leads to worse mechanical properties and hardness, indicating V may not be a suitable choice of doping transition elements.
Highlights
Ternary borides, including Mo2 FeB2, Mo2 NiB2, WCoB, were fabricated by reaction bronizing sintering, which solved the poor sintering property of binary borides [1]
In order to explore the effects of V doping on the mechanical properties and electronic structure of WCoB and W2 CoB2, we first examine the stability of a lattice with different V doping contents
The cohesive energy (Ecoh ) has been calculated, which is defined as follows: Ecoh = (Etotal − aEw − bECo − cEB − dEV )/(a + b + c + d) where Ecoh is the cohesive energy of V doped WCoB and W2 CoB2 ; Etotal is the total energy of V doped
Summary
Ternary borides, including Mo2 FeB2 , Mo2 NiB2 , WCoB, were fabricated by reaction bronizing sintering, which solved the poor sintering property of binary borides [1]. Yang [29] and Sun [30] used first-principle calculation to find Mn doping improves the mechanical properties of Mo2 FeB2 ternary boride and verified the results by experiment with the highest hardness and TRS up to 89.4 HRA and 1290 MPa, respectively. Wang [31] and Lin [32] studied the effects of different contents of Cr, Ni, Mn doped Mo2 FeB2 ternary boride. It is worth pointing out that the effects of different contents of Cr, Mn doped WCoB on mechanical properties and electronic structure have been studied by first-principle calculation in our previous work [35,36]. The previous studies of Cr, Mn doping WCoB is calculated by unit cell, which cannot provide sufficient details on the variation of W2 CoB2 in different doping contents. The mechanical properties and hardness of Cr, Mn, V doped WCoB and W2 CoB2 are discussed
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