As high-entropy alloys (HEAs) are being actively explored for next-generation structural materials, gaining a comprehensive understanding of their creep, fatigue, and fracture behaviors is indispensable. These three aspects of mechanical properties are particularly important because (i) creep resistance dictates an alloy’s high-temperature applications; (ii) fatigue failure is the most frequently encountered failure mode in the service life of a material; (iii) fracture is the very last step that a material loses its load-carrying capability. In consideration of their importance in designing HEAs toward applicable structural materials, this article offers a comprehensive review on what has been accomplished so far in these three topics. The sub-topics covered include a comparison of different creep testing methods, creep-parameter extraction, creep mechanism, high-cycle fatigue S–N relation, fatigue-crack-growth behavior, fracture toughness, fracture under different loading conditions, and fractography. Directions for future efforts are suggested in the end.

In this study, we have successfully grown hBN/graphene heterostructures on copper thin films using chemical vapor deposition in a single process. The first and most surprising result is that graphene grows underneath hBN and adjacent to the Cu film even though it is deposited second. This was determined from cross-sectional TEM analysis and XPS depth profiling, which chemically identified the relative positions of hBN and graphene. The effect of various growth conditions on graphene/hBN heterostructures was also studied. It was found that a pressure of 200 torr and a hydrogen flow rate of 200 sccm (∼1 H2/N2) yielded the highest quality of graphene, with full surface coverage occurring after a growth time of 120 min. The resulting graphene films were found to be approximately 6–8 layers thick. The grain size of the nanocrystalline graphene was found to be 15–50 nm varying based on growth conditions.

Two series of binuclear metal phthalocyanine complexes M2(PcTN)2Nap and M2(PcTA)2Nap (M = Mn2+, Fe2+, Co2+, Cu2+) were designed and synthesized through the liquid solvent method and amination reaction. Elemental analysis, IR, and UV-vis spectroscopy were applied to characterize the compounds. To evaluate their catalytic performance, all the compounds were respectively added into the electrolyte of Li/SOCl2 battery systems as well as three-electrode systems for cyclic voltammetry (CV) measurements. The research studies indicate that the average discharge voltage and discharge time of the battery could be effectively enhanced by 0.2440 V and 810.7 s when compared with the battery in the absence of the compounds. As for capacities of the batteries containing catalysts, they were also found to have an improvement of 51.78–91.62%. Among the effects of diverse metal ions on the catalytic performance of phthalocyanines, the complexes whose center metal ions were Mn2+ or Co2+ exhibited relatively high catalytic performance. Meanwhile, combined with experimental results of CV analyses, the suggested catalytic mechanism of binuclear phthalocyanines for catalyzing Li/SOCl2 batteries had been proposed.

The microstructure and tensile property of extruded Mg–6Zn–1.5Ca (wt%) alloy were examined by means of electron backscattered diffraction, scanning and transmission electron microscopy. A bimodal microstructure featuring fine dynamically recrystallized (DRXed) grains with weaker texture and coarse-deformed region with strong basal texture and fine precipitates was achieved in the as-extruded Mg–Zn–Ca alloy, which resulted in a yield strength as high as 305 MPa and a moderate elongation to fracture of 8.6%. Dynamic precipitation was detected in the deformed region, which inhibited the dynamic recrystallization process. The texture intensity in the DRXed region was weakened compared with that in the deformed region, which was associated with the preferred nucleation during dynamic recrystallization. Such texture weakening effects gave rise to an obvious ductility improvement for the as-annealed alloy.

A hierarchical porous carbon with bimodal pore size distribution was synthesized using pyrolysis and controlled activation of polymer gel derived from furfuryl alcohol and phloroglucinol using a soft templating approach. Symmetric capacitors made using the synthesized carbon electrodes in neat 1-butyl 3-methylimidazolium tetrafluoroborate showed a specific capacitance of 141 F/g at 1 A/g when cycled between 0 and 3.8 V at room temperature. The capacitor also showed 90% capacitance retention over 5000 cycles. Equivalent circuit modeling of impedance spectra was done to monitor changes and provide microstructural details during cycling and temperature studies. Cyclic voltammetry showed the presence of specific adsorption of the electrolyte ions on the carbon electrode and this was in good agreement with strong dependence of specific capacitance on temperature. Such strong interaction along with the nature of electrical double layer formed in the hierarchical porous carbon results in widening the voltage stability window of the capacitor.

Valvular heart diseases lead to over 300,000 heart valve replacements worldwide each year. Bioprosthetic heart valves (BHVs), derived from glutaraldehyde (GLUT) crosslinked porcine or bovine pericardium, are often used. However, valve failure can occur within 12–15 years due to progressive degradation and/or calcification. Being innovated by previous amino reagent studies used for GLUT detoxification and carbodiimide [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, EDC] chemistry, in this study, we developed a new fabrication method that utilizes exogenous amino donor arginine or lysine carbodiimide combined treatments to better stabilize the extracellular matrix of porcine pericardium. The carboxyl group density, amine content, differential scanning calorimetry, collagenase and elastase degradation, calcification by rat subdermal implantation, cytotoxicity, and platelet adhesion were characterized. We demonstrated that exogenous amino donor carbodiimide combined treatment for pericardiums had better resistance to elastase degradation (1.63 ± 0.11% and 1.44 ± 0.24% in arginine or lysine versus 3.68 ± 0.16% and 3.04 ± 0.11% in GLUT and GLUT/EDC control) and calcification (0.624 ± 0.193 and 0.637 ± 0.213 Ca µg/mg tissue in arginine or lysine versus 1.610 ± 0.124 and 1.512 ± 0.075 Ca µg/mg tissue in GLUT and GLUT/EDC control). This new strategy combined arginine or lysine and carbodiimide crosslinking would be a promising method to produce more robust BHVs with better structural stability and anticalcification property.

The post-processing treatment plays an important role in tailoring the mechanical and biological properties of the three-dimensional powder-printed porous scaffolds. Depending on scaffold material composition, a combination of post-processing treatments can be used to tailor these properties. This work probes into the impact of post-processing on the microstructure and deformation behavior of 3D-printed scaffolds. In this study, we have chosen CaSO4·xH2O (POP), a system for 3D powder printing and two different post-processing methodologies, namely chemical conversion and polymer infiltration. POP-based scaffolds were fabricated using water-based binder with up to 55% interconnected microporosity and moderate compressive strength of 1.5 MPa. Microcomputed tomography (µCT) is extensively utilized to determine the accuracy and efficacy of the adopted printing and post-processing approach. It was shown that the reproducibility of the fine features depends not only on the size but also on the presence of neighboring features. Crucially, µCT-based microstructure modeling and finite elemental simulation were attempted to computationally capture the compression behavior, in silico. Finally, in situ compression coupled with µCT imaging provided us an insight into fracture behavior of 3D powder-printed scaffolds.

We develop an asymmetric aqueous supercapacitor using iron oxide anode and cobalt oxide cathode. The anode was fabricated using electrospinning of carbon precursor/iron oxide precursor blend followed by pyrolysis and in situ electrochemical conversion (to oxide) to form the binder-free and freestanding composite anode which delivered a capacitance of 460 F/g at 1 A/g and retained 82% capacitance after 5000 cycles. The superior performance is attributed to easy electrolyte accessibility as well as the porous fibrous carbon morphology, facilitating volume expansion of iron oxide. The cobalt oxide cathode was prepared using a simple chemical synthesis technique. The electrodes were chosen based on high over potential to water splitting reactions in 6 M KOH electrolyte resulting in a potential window of 1.6 V. The asymmetric device operated in 1.6 V achieved a capacitance of 94.5 F/g at 0.5 A/g while retaining 75% of its capacitance after 12,000 cycles, delivering energy and power densities of 40.53 W h/kg and 2432 W/kg, respectively.

Flower-like AgI/Bi5O7I hybrid photocatalysts were fabricated via a hydrothermal method and the subsequent heating process with AgI/Bi4O5I2 as the intermediate. X-ray powder diffraction, Raman, X-ray photoelectron spectroscopy, diffuse reflectance spectra, scanning electron microscopy, transmission electron microscopy, photoluminescence, and electrochemical methods were used to reveal the structure, elemental content, morphology, and charge separation capabilities of the as-prepared samples. The photocatalytic test showed that the AgI/Bi5O7I composites own much higher photoactivity than pure AgI and Bi5O7I. Based on the result of XPS analysis, the composite is believed to be the Ag/AgI/Bi5O7I system. Due to the suitable band potentials of AgI and Bi5O7I, the ternary system can form a heterojunction structure which works in a Z-scheme mechanism with Ag nanoparticles as the transfer media. The guided charge transfer in the composite prolongs the life time of charge carriers and eventually leads to the high photocatalytic activity of AgI/Bi5O7I. Additionally, the flower-like structure of the composite also contributes to the photocatalytic reaction.

In this work, a high-temperature low-cycle fatigue (LCF) behavior of a newly developed austenitic oxide dispersion strengthened (ODS) steel is investigated. The LCF tests were performed in air at 650 °C under three different strain amplitudes (±0.4, ±0.5, and ±0.7%) with a nominal strain rate of 10−3 s−1. The measured cyclic stress response showed four distinct stages which include short initial stable cyclic response followed by a prolonged hardening with subsequent short saturation and finally crack initiation and growth stage. The rate of hardening and the duration of stages are a function of applied strain amplitude. Microstructural investigations were carried out to shed light on the deformation mechanisms. After cycling, the overall microstructure appears stable without any modifications in grain shape and size. In addition, twinning and stacking fault fractions remain unchanged. However, cyclic hardening is an aftermath of dislocation multiplication whose rate is also a function of applied strain amplitude. Furthermore, oxide particles, as well as fine grains, inhibit strain localization by restricting three-dimensional dislocation structure formation that are associated with the development of extrusions and intrusions and are readily observed in conventional austenitic non-ODS steels.

The evolution of carbides and the coarsening behavior of L12 ordered γ′ phase in Ni–25Cr–20Co alloys aged for varying time from 1000 to 5000 h at 700 and 750 °C were discussed in this paper. The mechanical properties of the alloys after aging were also discussed. Due to the changing of predominated resistance factor, a few of the γ′ precipitates’ shape changed from spherical to cuboidal after aging at 750 °C for 3000 h. The sizes and volume fraction of the γ′ precipitates were measured after aging at both temperatures. The experimentally determined temporal exponent of the γ′ coarsening indicated that the coarsening kinetics is in accordance with both models: the classical matrix diffusion LSW model and the trans-interface diffusion-controlled model. Additionally, the coarsening rate of the γ′ precipitates is dominated by the diffusion coefficients of Nb based on the classical LSW model. Furthermore, the yield strength curves of the alloys aged at 700 °C showed different trends at both test temperatures which is related to the influence of γ′ coarsening on the critical resolved shear stress.

In this paper, corrosion behavior of 2198 Al–Cu–Li alloy in different aging stages is investigated using immersion and electrochemical measurements in 3.5 wt% NaCl aqueous solution. The corrosion resistance is found to decrease from the solution-anneal to the peak-aged condition but increase after the peak-aged, which is due to microstructure evolution of three main kinds of precipitating phases with the aging process: T1 (Al2CuLi), θ′ (Al2Cu), and a few δ′ (Al3Li) phases. The anode T1 phase grows and increases with the aging treatment and becomes nearly unchanged after the peak-aged. Moreover, the cathode θ′ phase slightly decreases in the over-aged. The potentiodynamic polarization curves also indicate the most positive corrosion potential and the lowest corrosion current density in the peak-aged. The results of electrochemical impedance spectroscopy are in agreement with the corrosion morphologies. Furthermore, the related equivalent circuit is established to investigate the corrosion mechanism of this alloy.

Atomic layer deposition (ALD) of air stable cobalt and nickel complexes based on tridentate enaminones N,N-(4,4,4-trifluorobut-1-en-3-on)-dimethylethyldiamine (Htfb-dmeda) and N,N-(4,4,4-trifluorobut-1-en-3-on)-dimethylpropyldiamine (Htfb-dmpda) successfully produced metallic cobalt and nickel thin films. Detailed X-ray photoelectron spectroscopy (XPS) studies on the binding interaction of the first precursor monolayer with the surface functional groups elucidated the chemisorption behavior of the new precursor systems. A reactive remote hydrogen plasma was used as the co-reactant to activate the precursor decomposition yielding metal hydroxide intermediates. Subsequent hydrogen plasma etching of as-deposited films resulted in phase-pure metallic films through a recrystallization process, verified by surface and sub-surface XPS. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed pinhole-free films, with low surface roughness (0.2 ± 0.06 nm root mean square, RMS) for both, cobalt and nickel thin films. Herein, the competitive role of hydrogen as etchant and reactant was demonstrated as prolonged plasma exposure time periods resulted in the formation of metal hydrides. This is mostly due to the catalytic dissociation of molecular hydrogen on transition metal surfaces, which already occurs upon low energy input.

Positron annihilation spectroscopy and differential scanning calorimetry were used to evaluate the changes of the atomic configurations in Zr-based metallic glasses (MGs) due to alloying and plastic deformation. The correlation between the atomic configurations of MGs and the amorphous-to-icosahedral phase transition due to heating was investigated. The results indicate that the free volume frozen in the as-cast Zr60Al15Ni25, Zr65Al7.5Ni10Cu17.5, and Zr65Al7.5Ni10Cu17.5Ag5 MGs substantially decreases in sequence. More excess free volume is introduced in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling. The annihilation of free volume due to alloying considerably stabilizes the icosahedral structure of MGs, which enhances the nucleation and growth of quasicrystals upon heating. However, the nucleation and growth of quasicrystals are considerably suppressed in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling, during which the more introduced excess free volume results in substantial destruction of short-range order with 5-fold symmetry. The present work further provides direct evidence for the prevalence of icosahedral short-range order in MGs.

Functionally graded materials (FGMs) in which the elemental composition intentionally varies with position can be fabricated using directed energy deposition additive manufacturing (AM). This work examines an FGM that is linearly graded from V to Invar 36 (64 wt% Fe, 36 wt% Ni). This FGM cracked during fabrication, indicating the formation of detrimental phases. The microstructure, composition, phases, and microhardness of the gradient zone were analyzed experimentally. The phase composition as a function of chemistry was predicted through thermodynamic calculations. It was determined that a significant amount of the intermetallic σ-FeV phase formed within the gradient zone. When the σ phase constituted the majority phase, catastrophic cracking occurred. The approach presented illustrates the suitability of using equilibrium thermodynamic calculations for the prediction of phase formation in FGMs made by AM despite the nonequilibrium conditions in AM, providing a route for the computationally informed design of FGMs.