First-principles Study On The Effect Of Atomic Structure Ordering On Mechanical Properties Of Tungsten-based Solid Solutions

Due to its high density,high melting point,high hardness,good corrosion resistance,and radiation resistance,pure tungsten is widely used in nuclear fusion,armor-piercing bombs,high-temperature structural materials and other fields.Pure tungsten is an intrinsically brittle metal with a high ductile-brittle transition temperature and almost no ductility at room temperature,which greatly limits the application of tungsten and its alloys.Tungsten alloys are usually composed of two phases:a matrix phase and a binder phase,and the matrix phase is generally a tungsten-based solid solution,so its toughness and brittleness are the key to the application of tungsten alloys.Short-range order is one of the strengthening mechanisms of solid solutions,which can alter the brittleness/ductility of solid solution phases by modulating the solute-solvent electron interactions.Thus,the phase stability,mechanical properties and thermodynamic properties of W-V,W-Nb and W-Ta solid solutions were systematically studied.On this basis,the effect of atomic structural ordering on the ductility and brittleness of W-V,W-Nb and W-Ta solid solutions is analyzed,and the interaction mechanism between short-range ordering and solid solution softening and hardening is emphatically discussed.The main conclusions are as follows:（1）Stable ordered phases exist in W-X（X=V,Nb and Ta）solid solutions,and the most stable phase structures are C11_b W₂V,D0₃ W₃Nb and C11_b W₂Ta,respectively.At the same time,it is found that with the decrease of temperature,the W-X solid solution will undergo disordered and orderly transformation at some composition points,and the transformation temperature point is much lower than the melting point of the W-X solid solution.（2）The elastic properties（bulk modulus,shear modulus,Young’s modulus and hardness）of W-X solid solution all decrease with the addition of X.The values of short-range ordered structure and disordered structure of bulk modulus are not very different under the same composition,while for shear modulus,Young’s modulus and hardness,the short-range ordered structure has a great influence:under the composition point of W₆₇X₃₃,the G,E and Hv values of the ordered structure are higher than those of the disordered structure;while under the composition points of W₅₀X₅₀,W₇₅X₂₅ and W₂₅X₇₅,the G,E and Hv values of the ordered structure are lower than those of the disordered structure.At the same time,the disorder-to-order transition will have softening and hardening effects on the elastic properties with the change of temperature.（3）The short-range order will have a great influence on the ductility and brittleness（G/B value）of the W-X solid solution:the softening of the W-Ta solid solution is analyzed,and it is found that the less the number of strongly covalent W-W bonds,the better the center symmetry.The short-range ordered structure exhibits toughness,while the short-range ordered structure with more W-W bonds and broken centrosymmetry exhibits brittleness.For the W-V solid solution,the order softening phenomenon is consistent with that of the W-Ta solid solution,that is,the more ordered the short-range ordered structure,the smaller the G/B value,and the better the toughness;The effect of ductility and brittleness of solid solution is not very obvious.The hardening of the C11_b structure is mainly due to the abnormal lattice distortion and poor centrosymmetry.