Phase-transition assisted mechanical behavior of TiZrHfTax high-entropy alloys

Abstract

Recent developments of high-entropy alloys with high strength and high ductility draw attention to the metastability-engineering strategy. Using first-principle theory, here we demonstrate that reducing the Ta level in the refractory TiZrHfTax system destabilizes the body-centered cubic (bcc) phase and leads to the appearance of the hexagonal close-packed (hcp) phase embedded in the bcc matrix. The alloying-induced features of the elastic parameters for the cubic and hexagonal structures are mapped out in details, and strong sensitivity to the crystal lattice and chemistry is revealed. Results show softening of the bcc matrix with decreasing Ta concentration which ensures ductile behavior. However, the elastically nearly isotropic hcp precipitates possess enhanced resistance against shear which promotes strengthening of the TiZrHfTax dual-phase system. The present atomic-level insight provides strong evidence to the experimental observation, and emphasizes the significance of quantum-design for advanced multi-phase high-entropy alloys with excellent strength-ductility combinations.

An Ultra‐Low Modulus of Ductile TiZrHfTa Biomedical High‐Entropy Alloys through Deformation Induced Martensitic Transformation/Twinning/Amorphization

“…[ 28 ] Additionally, the SIM α′ exhibits a notable strain‐hardening (Figure 3a), which is mainly attributed to: i) microstructural refinement due to the dynamic Hall‐Petch law; [ 20,29 ] ii) the mechanical discrepancy between the SIM α′ and BCC matrix, stemming from noticeable elastic anisotropy. [ 42 ] Upon further straining (≈5–20%), nearly all of the BCC phase is transformed into the SIM α′ phase and SIM α′ twins, resulting in a significant decrease in the strain‐hardening rate (Figures 3a, 6, and 9).…”

“…[38][39][40] The EMTO method has been successfully applied to various alloy systems to predict the phase stability. [41][42][43] In this study, we focused on TiZrHfTa Bio-HEAs with a low bonding force, and Ti 25 -Zr 25 -Hf 25 -Ta 25 (at%) alloy (called Ta 25 alloy) was selected as our prototype alloy. By altering the Ta, Hf, and Zr contents, the BCC phase stability was delicately balanced to simultaneously achieve a single metastable BCC phase with the TRIP effect, ultimately resulting in an ultra-low modulus and noteworthy ductility.…”

“…[ 38–40 ] The EMTO method has been successfully applied to various alloy systems to predict the phase stability. [ 41–43 ]…”