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Mechanical metamaterials are architectured cellular materials with unusual properties. Herein we report another type of metal mechanical metamaterials—their elastic admissible strain (EAS) is on the order of 0.1, compared to about 0.01 for common metallic materials. Four conditions are required for a metal mechanical metamaterial to achieve this super EAS: (i) bending-dominated deformation; (ii) low density; (iii) an appropriate lattice topology, and (iv) an intrinsically high EAS for the lattice strut constituent material. The findings of this work extend perspectives on metal mechanical metamaterials. [ABSTRACT FROM AUTHOR]

• The Gong-Chen model requires no experimental parameters and is easy to apply. • It can be used as a generic solidification model up to the solid fraction (fs) of 0.9. • When fs > 0.9, its applicability depends on both solute diffusion and partition coefficient. • The Gong-Chen model requires f s Lever > 1, which has been examined and justified. • The Won-Thomas model provides the most practical predictions but requires experimental input. It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation models has been proposed. However, the use of these models often requires essential experimental input information, e.g. , the secondary dendrite arm spacing (λ), cooling rate (T ˙) or actual solidification range (Δ T). This requirement disables these models for alloy solidification with no measured values for λ, T ˙ and Δ T. Furthermore, not all of these required experimental data are easily obtainable. It is therefore highly desirable to have an easy-to-apply predictive model that is independent of experimental input, akin to the Lever rule or Scheil-Gulliver model. Gong, Chen, and co-workers have recently proposed such a model, referred to as the Gong-Chen model, by averaging the solid fractions (f s) of the Lever rule and Scheil-Gulliver model as the actual solid fraction. We provide a systematic assessment of this model versus established solidification microsegregation models and address a latent deficiency of the model, i.e., it allows the Lever rule solid fraction f s to be greater than one (f s > 1). It is shown that the Gong-Chen model can serve as a generic model for alloy solidification until f s reaches about 0.9, beyond which (f s > 0.9) its applicability is dictated by both the equilibrium solute partition coefficient (k) and the solute diffusion coefficient in the solid (D s), which has been tabulated in detail. [ABSTRACT FROM AUTHOR]

• Type 2 α/α variant boundary ([ 11 2 ¯ 0 ] / 60 ∘) prevails in AM Ti-6Al-4V and Ti-4Al-2V alloys with equiaxed prior-β grains, while Type 4 α/α variant boundary ([ 10 ¯ 55 3 ¯ ] / 63. 26 ∘) in AM Ti-6Al-4V and Ti-6Al-2Sn-4Z-2Mo alloys with columnar prior-β grains. • Alpha-variants tend to exist as Category I triple-α clusters in equiaxed prior-β grains while as Category II clusters in columnar prior-β grains. • Less significant variant selection in columnar prior-β grains leads to more uniform distribution of the 12 α phase variants than in equiaxed prior- β grains. • The α/α variant boundary energy and distribution of α-variant Schimid factor can be noticeably different in AM α-β Ti alloys with columnar or equiaxed prior-β grains. The crystallographic arrangements of the α-phase variants in α-β titanium alloys remains less identified due to the crystallographic complexity involved while being essential to understand the α-β microstructural intricacy. To improve the current understanding, specimens of two columnar-grained α-β Ti alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo) and two equiaxed-grained α-β Ti alloys (Ti-6Al-4V and Ti-4Al-2V) were fabricated by laser metal powder deposition (LMD). Electron backscatter diffraction (EBSD) analyses were applied to more than 105 α-phase variants in each alloy. The results revealed that the Type 4 α/α variant boundary ([ 10 ¯ 55 3 ¯ ] / 63. 26 ∘) is prevalent in the two columnar-grained α-β alloys while the Type 2 α/α variant boundary ([ 11 2 ¯ 0 ] / 60 ∘) is common in the two equiaxed-grained α-β alloys. Further EBSD characterisation indicates that α-variant selection tends to be more prevalent in equiaxed prior-β grains, featured by the Category I triple-α-variant clusters, which mostly terminate on dense { 10 1 ¯ 1 } planes with lower boundary energy. Conversely, columnar prior-β grains show significant Category II triple-α-variant clusters, which mostly terminate on less dense { 4 1 ¯ 3 ¯ 0 } planes with higher boundary energy. Self-accommodation to compensate for the β→α transformation strain is assumed to be the major underlying mechanism. The implications of these findings for understanding the tensile strengths are discussed in conjunction with the Schmid factor of α-variants calculated in columnar- and equiaxed-grained Ti-6Al-4V. [Display omitted] [ABSTRACT FROM AUTHOR]