Influence of Local Lattice Distortion on Elastic Properties of Hexagonal Close‐Packed TiZrHf and TiZrHfSc Refractory Alloys

Abstract

The unique mechanical properties and local lattice distortion (LLD) for hexagonal close‐packed (HCP) multiple principal element alloys (MPEAs) are very rarely studied so far. Employing density functional theory calculation based on special quasirandom structure, this work studies the influences of LLD on elastic properties for both novel hexagonal TiZrHf(Sc) MPEAs. Compared to the pristine structures, the lattice stability of distorted random structures is improved evidently. Moreover, LLD obviously lessens the shear elastic properties, which may be an ubiquitous phenomenon irrespective of the lattice types of MPEAs. These results also uncover the apparent improvement in malleable behavior and shear anisotropy for HCP MPEAs. So, the influence of LLD on elastic properties for HCP MPEAs is profound. The degree of LLD is further studied via the standard deviation of near‐neighbor (NN) and next NN bond length distributions as an effective indicator of LLD. More significant distortion uncovered in TiZrHf alloy corresponds consistently to the stronger effects of LLD in TiZrHf alloy. Bader's charge and charge density distribution also demonstrate the underlying impact on LLD for both HCP MPEAs, so electronic nature is a significant factor for LLD. The present study provides guideline for designing mechanical properties of TiZrHf‐based HCP MPEAs engineering materials.

Additive manufacturing of defect-free TiZrNbTa refractory high-entropy alloy with enhanced elastic isotropy via in-situ alloying of elemental powders

“…Previous studies have suggested that the local lattice distortions in a material can also affect the elastic isotropy/anisotropy. In particular, higher local lattice distortions have been shown to correlate with increased elastic isotropy 72 , large microscale residual stresses can also influence lattice distortions 73 . As previously mentioned, laser-based AM techniques result in extremely high cooling rates which can induce significant thermal residual stresses.…”

Modeling and Analysis of Yielding and Strain Hardening in Metastable High‐Entropy Alloys

“…The equivalent plastic strain rate can be expressed as [37] ε p equ 0 ¼ ε 0 σ e σ flow m 0 (24) where σ flow is the flow stress and m ij ¼ 20 is the rate-sensitivity exponent.…”

“…However, the quantitative prediction of mechanical properties in the dual-phase metastable HEAs has not yet been established due to the lack of the strengthening model. [22][23][24][25][26][27][28][29][30] To solve this critical issue, we develop a physically based constitutive model to quantitatively evaluate the contribution of various strengthening mechanisms to strength during deformation, considering the effect of lattice distortion, dislocation, grain boundary, and phase interface. The current model can capture accurately the flow stress, which can be used as a helpful tool to predict the mechanical properties of the metastable HEAs.…”