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In this study, 3D interconnected nanoporous (3DNP) TiVNbMoTa HEAs were synthesized from the (TiVNbMoTa)25Ni75 as-cast precursor alloy using the liquid metal dealloying (LMD). The as-cast precursor demonstrated the initial dendritic microstructure consisting of fcc and hcp phases. At 600 °C after 1 h, tiny ligaments about 10 nm thickness were homogeneously synthesized. At 900 °C, the bulk transformation intensively took place at the original precursor alloy. Specifically, the dendritic morphology of the original phases disappeared, and the fraction of fcc phase decreased from 63% to 20%. This pre-transformation behavior significantly influences the dealloying mechanism. Kurdjumov–Sachs orientation relationship (OR) governed the ligament formation at the prior fcc phase while Pitsch-Schrader (P–S) OR controlled the ligament evolution at the prior hcp phase. An unusual mechanism of two-step dealloying was observed at the fcc phase region when the dealloying rate was decreased at the reaction front. The dissolution of Ni occurs by stepwise transformations of fcc=>hcp=>bcc. The prior fcc grain was transformed to the abnormally large hcp ligaments and tiny bcc ligaments. Then, the abnormal hcp ligaments were further dealloyed to smaller bcc ligaments following the P–S OR. This study pave the way for the design of compositionally complex porous materials with a customized morphology and advanced physical properties by dealloying. © 2021 The Authors.

Low modulus biomaterials are in focus as potential candidates for biomedical implants ensuring a fast healing of hard tissues. The close match between elastic properties of an implant material and bone are critical to eliminate stress-shielding effect. In this study, we synthesized a low modulus interpenetrating-phase composite of Ti and Mg by liquid metal dealloying. Its Young's modulus value is in the range of that found for human bone which allows for biomedical applications of this material. Unexpectedly, the Young's modulus value of the composite (17.6 GPa) is several times lower than that of each individual constituent phases, namely, Mg (45 GPa) and Ti (110 GPa). Using micromechanical modelling, it is demonstrated that the origin of the anomalously low modulus can be related to a weakened interface between the constituents. © 2020

Laser based powder bed fusion is a promising manufacturing method that can be used for the fabrication of hard magnets such as NdFeB with nearly any given geometrical shape. However, the weak performance, e.g., low coercivity, of the 3D-printed magnets currently hinder their application. In this work, we demonstrated a proof-of-concept of powder bed additive manufacturing of heavy rare earth free NdFeB magnets with technologically attractive coercivity values. The 3D-printed NdFeB magnets exhibit the highest (up-to-date for the additively manufactured magnets without heavy rare earth metals) coercivity values reaching μ0Hc = 1.6 T. The magnets were synthesized using a mixture of the NdFeB-based and the low-melting eutectic alloy powders. The essential function of the eutectic alloy, along with binding of the NdFeB-based magnetic particles, is the significant improvement of their coercivity by the in-situ grain boundary (GB) infiltration. The fundamental understanding of the magnetization reversal processes in these 3D-printed magnets leads to the conclusion that the excellent performance of the additively manufactured hard magnets can be achieved through the delicate control of the intergrain exchange interaction between the grains of the Nd2Fe14B phase. © 2020 Acta Materialia Inc.

High-entropy nanomaterials possessing high accessible surface areas have demonstrated outstanding catalytic performance, beating that found for noble metals. In this communication, wereport about the synthesis of a new, nanoporous, high-entropy alloy (HEA) possessing open porosity. The nanoporous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%) was fabricated from a precursor (TaMoNbV)25Ni75 alloy (at%) by liquid metal dealloying using liquid magnesium (Mg). Directly after dealloying, the bicontinuous nanocomposite consisting of a Mg-rich phase and a phase with a bulk-centered cubic (bcc) structure was formed. The Mg-rich phase was removed with a 3M aqueous solution of nitric acid to obtain the open, porous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%). The ligament size of this nanoporous HEA is about 69 ± 9 nm, indicating the high surface area in this material. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Surface functionalization is an effective approach to change the surface properties of a material to achieve a specific goal such as improving the biocompatibility of the material. Here, the surface of the commercial biomedical Ti-6Al-7Nb alloy was functionalized through synthesizing of a porous surface layer by liquid metal dealloying (LMD). During LMD, the Ti-6Al-7Nb alloy is immersed in liquid magnesium (Mg) and both materials react with each other. Particularly, aluminum (Al) is selectively dissolved from the Ti-6Al-7Nb alloy into liquid Mg while titanium (Ti) and niobium (Nb) diffuse along the metal/liquid interface to form a porous structure. We demonstrate that the porous surface layer in the Ti-6Al-7Nb alloy can be successfully tailored by LMD. Furthermore, the concentration of harmful Al in this porous layer is reduced by about 48% (from 5.62 ± 0.11 wt.% to 2.95 ± 0.05 wt.%) after 30 min of dealloying at 1150 K. The properties of the porous layer (e.g., layer thickness) can be tuned by varying the dealloying conditions. In-vitro tests suggest improved bone formation on the functionalized porous surface of the Ti-6Al-7Nb alloy. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

A bulk interpenetrating-phase composite consisting of immiscible Fe and Mg metals is fabricated by liquid metal dealloying. The composite exhibits an anomalously low value of the Young's modulus of 20 ± 3 GPa, when probed in compression. The Young's modulus values obtained from nanoindentation and ultrasonic measurements are, however, significantly higher than that in compression, but still remain lower than theoretical values obtained from the Hashin-Shtrikman bounds and a micromechanics model. Such a deviation is explained by the weak interfaces between Fe and Mg phases that promote phase boundary sliding upon mechanical loading, leading to a low effective modulus. © 2019

Here, we developed open porous TiHf alloys by liquid metal dealloing. To form metalpolymer composites, these scaffolds were impregnated by polymer. The composites mimic mechanical behavior of cortical bone and occupy previously unclaimed region at the Ashby diagram in the area of intermediate strength and lowstiffness. The scaffolds significantly contribute to strength (215–266MPa) and stiffness (15,6–20,8 GPa) of the composites while the polymer phase provides their high strain rate sensitivity (0,037–0,044)., В настоящей работе были разработаны пористые TiHf сплавы методом деаллоинга в жидком металле. Для получения металл-полимерных композитов разработанные пористые сплавы были пропитаны полимером. Настоящие композиты имитируют механическое поведение кортикальной кости и занимают ранее незанятую область на диаграмме Эшби (средние значения прочности и низкие значения жесткости). Металлическая фаза существенно влияет на прочность (215–266 МПа) и жесткость (15,6–20,8 ГПа) настоящих композитов, в то время как полимерная фаза обеспечивает высокую чувствительность к скорости деформации (0,037–0,044).

Ti and Ti-TiB composite materials were produced by selective laser melting (SLM). Ti showed an α΄ microstructure, whereas the Ti-TiB composite revealed a distribution of needle-like TiB particles across an α-Ti matrix. Hardness (H) and reduced elastic modulus (Er) were investigated by nanoindentation using loads of 2, 5 and 10 mN. The results showed higher H and Er values for the Ti-TiB than Ti due to the hardening and stiffening effects of the TiB reinforcements. On increasing the nanoindentation load, H and Er were decreased. Comparison of the nanoindentation results with those derived from conventional hardness and compression tests indicated that 5 mN is the most suitable nanoindentation load to assess the elastic modulus and hardness properties. The wear resistance of the samples was related to their corresponding H/Er and H3/Er2 ratios obtained by nanoindentation. These investigations showed that there is a high degree of consistency between the characterization using nanoindentation and the wear evaluation from conventional wear tests.

Metallic glasses (MGs) inherit their amorphous structure from the liquid state, which predetermines their ability to withstand high loads approaching the theoretical limit. However, the absence of slip systems makes them very sensitive to the type of loading and extremely brittle in tension. The latter can be improved by precipitation of ductile crystals, which suppress a catastrophic propagation of shear bands in a glassy matrix. Here we report a novel approach to obtain MG-matrix composites with tensile ductility by flash Joule heating applied to Cu(47.5)Zr(47.)5Al(5) (at.%) metallic glass. This homogeneous, volumetric and controllable rapid heat treatment allows achieving uniformly distributed metastable B2 CuZr crystals in the glassy matrix. It results in a significant tensile strain of 6.8 +/- 0.5%. Moreover, optimized adjustment of the heat-treatment conditions enables tuning of microstructure to achieve desired mechanical properties.

Okulov, I. V., Volegov, A. S., Attar, H., Bönisch, M., Ehtemam-Haghighi, S., Calin, M., & Eckert, J. (2017). Composition optimization of low modulus and high-strength TiNb-based alloys for biomedical applications. Journal of the Mechanical Behavior of Biomedical Materials, 65, 866-871. Available here

Okulov, I. V., Bönisch, M., Okulov, A. V., Volegov, A. S., Attar, H., Ehtemam-Haghighi, S., ... & Prashanth, K. G. (2018). Phase formation, microstructure and deformation behavior of heavily alloyed TiNb-and TiV-based titanium alloys. Materials Science and Engineering: A, 733, 80-86. Available here