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The microstructure of high-entropy alloys with refractory elements and Al as constituents can be considered to be analogous to superalloys. These so-termed refractory high-entropy superalloys (RHSAs) can show remarkable compressive strength up to temperatures exceeding 1200 °C. Here, we examine the microstructure and properties - compressive, tensile, and fracture toughness - of a precipitation-hardened, body-centered cubic, RHSA, Al0.5Nb1.25Ta1.25TiZr, at ambient temperature (RT) to 1200 °C. Two dual-phase microstructures comprising ordered B2 (brittle) and disordered A2 (ductile) phases were produced in this alloy - one with B2 as the matrix, the other with A2 - for evaluation of the mechanical properties. Under compression, both microstructures display RT compressive strengths above 1.5 GPa and considerable ductility exceeding 40% at elevated temperatures; the alloy with the A2 matrix has ∼15% compressive ductility even at RT. However, properties are very different under tensile loading; at all temperatures, both microstructures fail predominately in an intergranular mode in the elastic regime at a fracture stress less than 200 MPa and ductility below 0.15%. The microstructure with the A2 matrix has a KIc fracture toughness of ∼15 MPa√m at RT, although at all temperatures above 800 °C, measured KIc values for both dual-phase microstructures are less than 5 MPa√m. In this study, we investigate the microstructural origin of these mechanical properties, and emphasize the importance of evaluating these alloys in tension.

Temperature is known to affect deformation mechanisms in metallic alloys. As temperature decreases, the stacking-fault energy in many face-centered cubic (fcc) alloys decreases, resulting in a change of deformation mode from dislocation slip to deformation twinning. Such an impact of temperature can be more complex in compositionally heterogeneous microstructures that exhibit, for example, local concentration fluctuation such as that in multi-principal element alloys. In this work, we compare the dislocation behavior and mechanical properties of a fcc Cr20Mn10Fe30Co30Ni10 high-entropy alloy at ambient and liquid-nitrogen temperatures. We find that a network of stacking faults is formed by uniformly extended dislocations at ambient temperatures with low stacking-fault energy, whereas at lower temperatures, uneven dissociation of dislocations becomes significant, which results in severe dislocation pile-ups together with their pronounced entanglement. Our findings indicate that as the stacking-fault energy decreases with decreasing temperature, the heterogeneity of the distribution of elements becomes more dominant in tuning the local variation of lattice resistance. As a result, the change in dislocation behavior at low temperatures strongly affects microstructural evolution and consequently leads to significantly more pronounced work hardening.

Strategies involving metastable phases have been the basis of the design of numerous alloys, yet research on metastable high-entropy alloys is still in its infancy. In dual-phase high-entropy alloys, the combination of local chemical environments and loading-induced crystal structure changes suggests a relationship between deformation mechanisms and chemical atomic distribution, which we examine in here in a Cantor-like Cr20Mn6Fe34Co34Ni6 alloy, comprising both face-centered cubic (fcc) and hexagonal closed packed (hcp) phases. We observe that partial dislocation activities result in stable three-dimensional stacking-fault networks. Additionally, the fraction of the stronger hcp phase progressively increases during plastic deformation by forming at the stacking-fault network boundaries in the fcc phase, serving as the major source of strain hardening. In this context, variations in local chemical composition promote a high density of Lomer-Cottrell locks, which facilitate the construction of the stacking-fault networks to provide nucleation sites for the hcp phase transformation.

We have successfully developed bulk-metallic glass (BMG) composites reinforced with intertwined dendritic alumina, inspired by the structure of nacre (Abalone shells). We harness the dendritic growth of ice crystals in a thermal gradient to assemble an alumina with dendritic pore architecture, which is then infiltrated with BMG-forming melt to make a bioinspired, micrometer-scale, intertwined BMG-alumina composite. The composite exhibits ultra-high strength with exceptional relative compressive strength, far better than ceramic particulate BMG composites. The method presented here can be further exploited to produce novel BMG composites with excellent mechanical properties.

Bioinspired ceramics with micron-scale ceramic "bricks" bonded by a metallic "mortar" are projected to result in higher strength and toughness ceramics, but their processing is challenging as metals do not typically wet ceramics. To resolve this issue, we made alumina structures using rapid pressureless infiltration of a zirconium-based bulk-metallic glass mortar that reactively wets the surface of freeze-cast alumina preforms. The mechanical properties of the resulting Al2O3 with a glass-forming compliant-phase change with infiltration temperature and ceramic content, leading to a trade-off between flexural strength (varying from 89 to 800 MPa) and fracture toughness (varying from 4 to more than 9 MPa·m½). The high toughness levels are attributed to brick pull-out and crack deflection along the ceramic/metal interfaces. Since these mechanisms are enabled by interfacial failure rather than failure within the metallic mortar, the potential for optimizing these bioinspired materials for damage tolerance has still not been fully realized.

Metals often lose their ductility at cryogenic temperatures owing to the decreased mobility of dislocations. TRansformation-induced plasticity (TRIP), a toughening mechanism at room temperature, can increase damage susceptibility at low temperatures, as the resultant martensite phases can become more brittle than the parent phases. Herein, we develop a high-entropy alloy (HEA) with an improved low-temperature impact-damage tolerance through a sequential plasticity mechanism. We design a trip-assisted dual-phase HEA (TADP HEA) and investigate the effects of Al addition on its mechanical properties upon deformation at different temperatures, depending on stacking fault energy (SFE). Our analysis shows that a senary (Cr20Mn6Fe34Co34Ni6)98Al2 HEA exhibits superior mechanical properties, including a 641 MPa yield strength (σy), 964 MPa ultimate tensile strength (σUTS), and 40% uniform elongation (ɛUTS) at ambient temperature (25 °C), and a 1 GPa σy, 1.5 GPa σUTS, and 36% ɛUTS at −100 °C. Notably, despite the presence of hexagonal-close packed martensite, the HEA exhibits a higher Charpy impact energy (406 J) than Cantor HEA (344 J) at −100 °C. We attribute this improvement to the sequential deformation mechanism of mechanical twinning and martensitic transformation in the HEA at −100 °C, which results in sustainable steady strain-hardening during deformation. We suggest that optimizing the sequential deformation mechanism by manipulating SFE in multi-component alloys can be an effective route for improving the damage tolerance of metals at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

Background: Botulinum toxin is a crucial therapeutic tool with broad indications in both cosmetic and medical fields. However, the expanding cosmetic use and increased dosages of botulinum toxin have raised concerns about resistance, making it essential to study the awareness and management practices among healthcare professionals. Methods: A survey was conducted among clinical physicians using botulinum toxin. The study investigated their experiences, awareness, and management practices related to toxin resistance. Real‐time mobile app‐based surveys were administered to clinicians attending the 45th International Academic Conference of the Korean Academy of Laser and Dermatology (KALDAT) on December 3, 2023. Results: Among 3140 participants, 673 clinical physicians completed the survey. Of these, 363 clinicians (53.9%) reported experiencing botulinum toxin resistance. Regarding the resistance rate, 59.4% indicated less than 1%, 36% reported approximately 1%–25%, and 95.4% reported less than 25%. Efforts to prevent resistance included maintaining intervals of over 3 months (54.8%), using products with lower resistance potential (47.0%), employing minimal effective doses (28.2%), and minimizing re‐administration (14.9%). Conclusion: In the South Korean aesthetic medicine community, a majority of clinical physician's report encountering botulinum toxin resistance. Given the potential loss of various benefits associated with resistance, there is a need to establish appropriate guidelines based on mechanistic studies and current status assessments. Educating clinicians on applicable guidelines is crucial. [ABSTRACT FROM AUTHOR]