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Highlights • Coordination number and strain state affect the vacancy formation in twin boundary. • The vacancy diffusion in 10 1 ¯ 2 , 10 1 ¯ 1 and 11 2 ¯ 2 TBs planes is unidirectional. • The vacancy diffusion in (11 2 ¯ 1) TB plane is isotropic. • Low formation energy and migration barrier of vacancy enhance atom transport in TBs. Abstract The distinct atomic structure of twin boundary (TB) significantly affects the physical and mechanical behaviors of materials. In this work, the local atomic structure, the formation and diffusion of vacancy in (10 1 ¯ 2), (11 2 ¯ 1), (11 2 ¯ 2) and (10 1 ¯ 1) TBs of α-Ti were investigated in details using ab initio calculations. Our calculations illustrated that most atoms at or close to the TBs have lower atom coordination number (CN), thereby experiencing the positive changes of local volume and tension strain. The CN and strain state significantly affect the vacancy formation. It's shown that vacancy can easily form in these TBs, with the lower formation energy in the range of 1.26–1.59 eV. Our calculations further shown vacancy diffusion are somewhat anisotropic in 10 1 ¯ 2 , 10 1 ¯ 1 and 11 2 ¯ 2 TBs planes. Vacancy prefers to diffuse along the direction of 1 ¯ 2 1 ¯ 0 in (10 1 ¯ 2) and (10 1 ¯ 1) TBs, and along the twinning direction of 11 2 ¯ 3 ¯ in 11 2 ¯ 2 TB, with the migration barriers of ∼0.43, ∼0.27, and ∼0.31 eV, respectively. Vacancy diffusion in (11 2 ¯ 1) TB plane is isotropic, with the migration barrier of ∼0.25 eV. Our calculations demonstrated that the fast diffusion channel mediated by vacancy for metallic atoms transport in these TBs can be mainly ascribed to the lower migration barrier and formation energy of vacancy in TBs. [ABSTRACT FROM AUTHOR]

By first-principles calculation, elastic properties of seven single phase high-entropy alloys (HEAs) with excellent properties are presented in our work. A new method Maximum Entropy (MaxEnt) was adopted. The method is an algorithm that can be used to study the lattice distortion effect of HEAs. CP2K first-principles simulation package was employed for calculation. The comparison of calculated elastic properties of TaNbHfZrTi with experimental data is made and the agreement is found to be quite good. Elastic properties of AlMoNbTiV are close to the calculated data from Coherent Potential Approximation (CPA), and the reasons were discussed. The influence of lattice distortions on elastic properties were also studied. Furthermore, elastic properties of a series of refractory HEAs were predicted. These results demonstrate that MaxEnt model can properly describe HEAs. [ABSTRACT FROM AUTHOR]

The solid solution alloys containing short-range order (SRO) structure, such as CuNi alloys, are not well structurally described using conventional quasi-disordered models. Based on the first-principles calculations, the optimal cluster-plus-glue-atom (CPGA) models of six typical solid solution CuNi alloys were demonstrated. These CPGA models are better to be used to describe the microstructure of the six CuNi alloys at the atomic scale from the viewpoint of energy. Our further study shown that the stabilities of CPGA models are highly related to the symmetry of initial CPGA models and the aggregation degree of solute atoms in CPGA models. In the condition of low solute Ni concentration, the stability of CPGA model is mostly determined by the symmetry of initial CPGA model, the CPGA model with high symmetry is more stable. As the concentration of solute Ni increasing, the aggregation degree of solute Ni atoms in CPGA models plays more and more important role. The CPGA model with higher aggregation degree of solute Ni is more stable. The simple selection method of optimal CPGA models, therefore is proposed, and which can be extended to other bielement solid solution AB alloys with positive mixing enthalpy of A-B. Using the selected CPGA models, we found the third additive atoms having negative mixing enthalpy with solvent and solute atoms prefer to reside the central site of characteristic principal cluster (CPC) of CPGA, and thereby enhancing the stability of alloys. Our studies provide a distinctive perspective to select the optimal CPGA models of solid solution alloys containing SRO structure and design alloy using the optimal CPGA model. [ABSTRACT FROM AUTHOR]

The grain boundary (GB) is critical to the mechanical properties of NiAl. The addition of B in NiAl can lead to the increase of yield strength due to its segregation in GB. To elucidate the B-induced enhancement of GB, we investigate the segregation state and its strengthening mechanism of the additive B in the typical ∑5(3 1 0)[0 0 1] GB of NiAl at atomic scale using the first-principles method. Our calculations shown that the additive B atom prefers to segregate at the interstitial I 1 site of GB, in which case it is surrounded by four first-nearest-neighboring (1NN) and two second-nearest-neighboring (2NN) Ni atoms. It is found the segregated B prefers to bond with its neighboring Ni instead of Al atoms. Our calculations further shown not only the intergranular cohesion is improved by the covalent bonding between the segregated B and its four 1NN Ni atoms, but also the intra-planar cohesion of GB is enhanced by the covalent bonding between the segregated B and its two 2NN Ni atoms. The covalent bonding between B and Ni atoms mainly stem from the contribution of B- p and Ni- d states, partly from the weak interactions of B- s and Ni- s states. Our first-principles tensile test shown that the yield stress and ductility of NiAl are indeed improved due to the segregation of B in GB. [ABSTRACT FROM AUTHOR]