Degree Of Amorphization Research Articles

Performance and characterization of bamboo-based activated carbon prepared by boric acid activation

Exposure to formaldehyde (HCHO) may have serious harm to human health because of its existence in indoor air. It is a simple and effective solution to remove formaldehyde from the environment by adsorption. Activated carbon is the primary adsorbent for the formaldehyde pollution control strategy. In this study, bamboo-based activated carbon (BAC) was prepared from bamboo charcoal (BC) by boric acid activation method and applied to remove formaldehyde in the air at room temperature. The structure and physicochemical properties of BAC were investigated by N2 adsorption-desorption, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscope, thermogravimetric and X-ray photoelectron spectroscopy. The results showed that the oxygen-containing functional group, amorphous degree and specific surface area of BAC were improved compared with BC, which improved its formaldehyde removal performance. The specific surface area and formaldehyde removal rate of BAC were 289.21 m2/g and 93.25% respectively, which were 288.37 m2/g and 49.95% higher than those of BC. This study provides a new idea for a better understanding of BC adsorbent that controls HCHO pollutant.

Mechanical Amorphization of Chitosan with Different Molecular Weights.

Mechanical amorphization of three chitosan samples with high, medium, and low molecular weight was studied. It is shown that there are no significant differences between the course of amorphization process in a planetary ball mill of chitosan with different molecular weights, and the maximum degree of amorphization was achieved in 600 s of high intensity mechanical action. Specific energy consumption was 28 kJ/g, being comparable to power consumption for amorphization of cellulose determined previously (29 kJ/g) and 5–7-fold higher than that for amorphization of starch (4–6 kJ/g). Different techniques for determining the crystallinity index (CrI) of chitosan (analysis of the X-ray diffraction (XRD) data, the peak height method, the amorphous standard method, peak deconvolution, and full-profile Rietveld analysis) were compared. The peak height method is characterized by a broader working range but provides deviated CrI values. The peak deconvolution method (with the amorphous Voigt function) makes it possible to calculate the crystallinity index of chitosan with greater accuracy, but the analysis becomes more difficult with samples subjected to mechanical processing. In order to refine the structure and calculation of CrI by the Rietveld method, an attempt to optimize the structure file by the density functional theory (DFT) method was performed. The averaged profile of amorphous chitosan approximated by an eighth-order Fourier model improved the correctness of the description of the amorphous contribution for XRD data processing. The proposed equation may be used as a universal standard model of amorphous chitosan to determine the crystallinity index both for the amorphous standard method and for peak deconvolution of XRD patterns for arbitrary chitosan samples.

Characterization of sulfonated raw coal products as enhanced adsorbents for toxic methyl parathion pesticide: Advanced equilibrium investigation and effect of acid concentration

Raw coal (R.C) was treated with different H2SO4 concentrations (75, 85, and 95 %) via sulfonation modification, and the sulfonated products (SC-75, SC-85, and SC-95, respectively) were used as adsorbents for the toxic methyl parathion (MPn) pesticide. The XRD investigation reflected increase in the amorphization degree with increasing the acid concentrations as well as the surface area (2.8 mmol/g (SC-75) and 8.4 mmol/g (SC-95)) and acid density value (6.4 m2/g (SC-75) and 26.4 m2/g (SC-95)). With increasing acid concentration, sulfonation increasingly functionalised coal with active oxygenated chemical groups (–COOH and –S3OH); this was reflected by MPn adsorption capacities at R.C, SC-75, SC-85, and SC-95 saturation states of 210.2, 321.4, 392.5, and 560 mg/g, respectively. The sulfonation and acid concentration effects were assessed considering steric and energetic mathematical parameters of the monolayer model with one energy site as an advanced isotherm model. The adsorption site densities of R.C, SC-75, SC-85, and SC-95 at 83.45, 120.4, 136.77, and 165.4 mg/g, respectively, demonstrated that sulfonation and high acid concentration provide additional active functional groups in the coal structure. Considering the steric n parameter, each active site on the SC-95 surface adsorbs approximately four MPn molecules, in contrast to three and two molecules on SC-85 and SC-75, respectively. Energetic assessment [Gaussian (˂8 kJ/mol) and adsorption (˂40 kJ/mol) energies] demonstrated MPn uptake of MPn by sulfonated coal samples via different processes such as electrostatic attractive forces, van der Waals forces, dipole bonding, π–π interactions, and hydrogen bonding. Thermodynamic functions demonstrated MPn uptake via endothermic and spontaneous reactions.

Synthesis of Oil Palm Fronds Charcoal as Adsorbent to Reduce Levels of Fe (III) in Peat Water

The high content of carbon compounds in palm fronds (OPF) makes them potentially useful as an adsorbent. The carbonization method was used for the adsorbent synthesis process. This process began with collecting palm frond waste and then drying and sifting the adsorbent particle. This process resulted in the escape particles with a size of 80 mesh and suspended particles with 120 mesh. Then this process continued by carbonizing the palm fronds with temperature variations starting from (400, 500, and 600°C) for 60 minutes to obtain Charcoal Oil Palm Fronts (COPF). The obtained COPF was determined for moisture and ash content and characterized using FTIR, XRD, and SEM to determine the surface, functional groups, degree of amorphism, crystallinity, and surface morphology. The adsorption efficiency of COPF was applied to the adsorption of Fe (III) in peat water under varying contact time, adsorbent mass, and peat water volume conditions. The water and ash content of COPF qualify the technical quality requirements for activated charcoal according to SNI 06-3730-1995. FTIR analysis detected the presence of vibrations of the C-O, O-H, C=O, C-C, and C-H functional groups on the COPF surface. The XRD pattern showed the existence of a semi-crystalline (002) and (100) plane structure, which is shown at scattering angles of 2θ = 22o and 42o. The surface morphology of COPF showed that as the carbonization temperature increased, the number of pores formed increased, and the pore size decreased. The best adsorption test results were obtained with a contact time of 30 minutes, an adsorbent mass of 1.00 g, and a peat water volume of 100 mL. The highest Fe adsorption efficiency was achieved by COPF 500, where the adsorbed mass was 0.054 mg. Increasing the carbonization temperature causes the water content to decrease and the ash content to increase. High water content and ash content cause a decrease in adsorption efficiency because they can cover the pores of the adsorbent.

Effect of melt thermal history on magnetic properties and thermal stability in Fe–Si–B–C amorphous alloy

Melt thermal history is highly heritable to the structure of metallic glass frozen by rapid quenching liquid. In this paper, the influences of melt thermal history above liquidus temperature on magnetic properties and thermal stability have been systematically investigated in Fe75Si9B12C4 amorphous alloy. The results show that both magnetic properties and thermal stability of the alloy show a non-overlapping feature for the alloys undergone melt heat preservation during heating and cooling process, respectively. It was found that melt thermal history can significantly affect the structural change of the alloy, and thus results in hysteresis behaviors of magnetic properties and thermal stability through changing degree of amorphization. These findings could help understand the melt thermal history and design preparation technology of soft magnetic amorphous alloys.

Utilizing the cross-linked effect and reconstruction strategy of phytic acid to build Fe-Co-Ni trimetallic amorphous carbon-matrix compounds as efficient oxygen evolution catalyst

Developing low-cost electrocatalysts with excellent activity is significant for accelerating the slow oxygen evolution reaction (OER). In this work, an effective electrocatalyst is prepared via the cross-linked effect and reconstruction strategy based on inexpensive transition metals (Fe, Co, and Ni) and phytic acid (PA). The feasibility of utilizing the cross-linked effect and reconstruction strategy is due to that PA molecules with strongly electronegative phosphoric acid groups possess a great deal of complexing sites, which can facilitate the formation of large cross-linked network by randomly complexing Fe, Co and Ni ions. And the carboatomic rings in PA molecules will reconstructed as carbon-matrix when PA molecules decompose. The above structural evolution of large cross-linked network and reconstructing process is rigorously analyzed through the characterization methods such as XPS. These analysis results indicate that FeCoNi-PA-300 possesses a high degree of amorphization, an abundant nanoporous structure, and a small nanoparticle size, resulting in a large electrochemically active area. Consequently, FeCoNi-PA-300 just needs low overpotentials of about 271 mV and 286 mV to obtain the current densities of 50 and 100 mA cm−2, respectively. Meaningfully, this synthetic method is a general strategy to meliorate the OER activity and electrical conductivity of other catalysts.

STUDY OF ISOTHERMS OF WATER VAPOR SORPTION FOR HYDROPHILIC POLYMERS

Various models and equations of water vapor (WV) sorption for hydrophilic polymers were considered. However, these models often do not correspond to the sorption mechanism. This study is based on the thermodynamics in binary systems and the Van Krevelen method of polar group contributions in the sorption of WV. Moreover, it was shown that the mechanism of WV sorption by various hydrophilic polymers is the absorption of water molecules in the volume of amorphous domains of these polymers. As a result, a universal physicochemical equation was proposed allowing adequately to describe the sorption isotherms of WV by amorphous hydrophilic polymers knowing only the chemical formulas of repeating units of these polymers. To calcu-late the sorption isotherms for semicrystalline polymer samples, it is necessary to use an additional parameter, namely the degree of amorphicity (Y). The adequacy of the derived equation was verified for samples of cellulose and other natural polysaccharides, as well as for samples of synthetic hydrophilic polymers such as polyvinyl alcohol, polyamide-6, and polycaprolactone having various Y-values. The verification showed that the experimental isotherms are almost identical to the isotherms calculated by the universal equation.

Novel Novolac Phenolic Polymeric Network of Chalcones: Synthesis, Characterization, and Thermal-Electrical Conductivity Investigation.

A series of novolac phenolic polymeric networks (NPPN) were prepared via an acid-catalyzed polycondensation reaction of formaldehyde with chalcones possessing a p-phenolic OH group. When p-hydroxybenzaldehyde was treated with formaldehyde under the same conditions, a phenolic polymer (PP) was obtained. The resulting polymers were isolated in excellent yields (83–98%). Isolated polymers (NPPN, PP) were characterized using FTIR, TGA, and XRD. The results obtained from the TGA revealed that all prepared phenolic polymers have high thermal stability at high temperatures and can act as thermosetting materials. XRD data analysis showed a high degree of amorphousness for all polymers (78.8–89.2%). The electrical conductivities and resistivities of all chalcone-based phenolic networks (NPPN) and p-hydroxybenzaldehyde polymer (PP) were also determined. The physical characteristics obtained from the I-V curve showed that the conductivity of phenolic polymers has a wide range from ultimately negligible values of 0.09 µS/cm up to 2.97 μS/cm. The degree of polarization of the conjugated system’s carbonyl group was attributed to high, low, or even no conductivity for all phenolic polymers since the electronic effects (inductive and mesomeric) could impact the polarization of the carbonyl group and, consequently, change the degree of the charge separation to show varied conductivity values.

Effect of Amorphousness Degrees and Intermolecular Interactions between Lithium Perchlorate (LiClO4) and Polylactic Acid (PLA) on the Conductivity PLA-Based Polymer Electrolyte Performance

Background: The polymer electrolyte membrane serves as a separator and electrolyte in an energy storage device. The structural properties of the host polymer electrolyte have a significant impact on the conductivity value. Objective: The purpose of this study is to investigate the effect of amorphousness and intermolecular interaction degrees between LiClO4 and PLA on the conductivity performance of prepared PLA- based polymer electrolyte film. Methods: The polymer electrolyte film of LiClO4-complexed PLA was prepared with various weight percentages of LiClO4 salt (10%, 20%, 30%, 40%, 50%, and 60%) in PLA by using a solution casting technique. Results: PLA with 50% LiClO4 had the highest degree of amorphousness and the highest percentage of interacting carbonyl groups, which resulted in the highest conductivity of 2.56 x 10-5 S cm-1. Conclusion: Finally, the optimum composition of LiClO4 for the amorphousness, interaction of carbonyl group and conductivity are obtained, which can be used for further research to improve the conductivity value to apply it into energy storage devices’ development.

Alkali-hydrothermal activation of mine tailings to prepare one-part geopolymer: Activation mechanism, workability, strength, and hydration reaction

Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing CO2 emissions. Mine tailings (MTs) rich in Si and Al can be served as a promising precursor for geompolymer preparation only when the severe defect in the low reactivity is overcame. Alkali-hydrothermal activation technology was used to enhance the reactivity of MTs, and then activated tailings (ATs) and slag served as the precursors for the one-part geopolymer (OPG) preparation. Activation mechanism of MTs, workability, compressive strength, and hydration reactions of OPG samples were studied. The crystalline mineral phases in the MTs reacted with NaOH to form the amorphous sodium aluminosilicate, thus increasing the amorphization degree. High NaOH content favored the MTs activation, and the ATs with high NaOH content tended to create a higher initial pH and release more active species (Si and Al) for the slag hydration. The increase of NaOH content shortened the setting time, decreased the fluidity, and increased the strength of OPG samples. This was because the duration of the induction period was shortened and the hydration rate in the acceleration period of OPG samples was improved with increasing NaOH content, which generated large amounts of calcium–sodium aluminosilicate hydrate (C(N)-A-S-H) gel and yield the compact microstructure. However, excessive NaOH content resulted in a poor microstructure, and it is likely responsible for the reduction in strength.

Impact of Thermally Reducing Temperature on Graphene Oxide Thin Films and Microsupercapacitor Performance.

In this work, a thermally reduced graphene oxide (TRGO) thin film on microscopic glass was prepared using spray coating and atmospheric pressure chemical vapour deposition. The structure of TRGO was analysed using X-ray diffraction (XRD) spectroscopy, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet–visible spectroscopy (UV-Vis) suggesting a decrease in oxygen functional groups (OFGs), leading to the restacking, change in colour, and transparency of the graphene sheets. Raman spectrum deconvolution detailed the film’s parameters, such as the crystallite size, degree of defect, degree of amorphousness, and type of defect. The electrochemical performance of the microsupercapacitor (µ-SC) showed a rectangular cyclic voltammetry shape, which was maintained at a high scan rate, revealing phenomenal electric double-layer capacitor (EDLC) behaviour. The power law and Trasatti’s analysis indicated that low-temperature TRGO µ-SC is dominated by diffusion-controlled behaviour, while higher temperature TRGO µ-SC is dominated by surface-controlled behaviour.

Atomic-level diffusion at the amorphous Zr50Cu50/crystalline Cu interface: A molecular dynamics study

The interdiffusion and atomic structure of the interface between metallic glass Cu50Zr50 and crystalline Cu were investigated using molecular dynamics simulations. We show that the interdiffusion of atoms at the amorphous/crystalline interface is mainly manifested as the diffusion of crystalline Cu atoms into amorphous atoms, and only a very small amount of amorphous atoms diffuse into crystalline Cu. And the temperature and diffusion time are proportional to the thickness of the diffusion layer. The H-A bond index and Voronoi polyhedron distribution method were used to analyze the structure type and cluster distribution of the interface atoms. the results show that the diffusion will cause the amorphization of the atoms on the crystal side of the interface, and the higher the temperature and the longer the diffusion time, the higher the degree of amorphization of the interface atoms. And the size of the amorphized region is related to the temperature, and the dividing plane between the amorphized atoms and the crystal atoms gradually moves to the crystal side with the increase of temperature. In addition, the diffusion behavior of atoms at the amorphous/crystal interface with different crystal orientations exhibits anisotropy, and some atoms at the interface between the 〈110〉 oriented crystal and amorphous are transformed from FCC structure to HCP structure during the diffusion process.

In-situ observation of magnetic vortices and their manipulation by external fields in Tb(Co1−xFex)5 ribbons

Nontrivial spin textures including magnetic vortices, skyrmions, and merons possess intriguing properties that are suitable for the application in further spintronics devices. The stability of topological spin textures in a broad temperature span is imperative for their potential applications as information carriers. In this study, we show the in-situ observation of the magnetic domain configuration and their manipulation under temperature and in-plane magnetic field in amorphous or nanocrystalline Tb(Co1−xFex)5 (x = 0.5, 0.8, 1.0) ribbons using Lorentz transmission electron microscopy. The results demonstrate that the formation of magnetic vortices is highly dependent on the degree of amorphization of Tb(Co1−xFex)5 ribbons and intrinsic magnetic parameters, which can be controlled by the composition. The higher the Fe content, the stronger the degree of amorphous in Tb(Co1−xFex)5 ribbons. Whereby, high-density magnetic vortices develop inside domain walls in the TbFe5 ribbon. Moreover, no matter how the degree of amorphization changes, magnetic domain structures including vortices in these ribbons have good thermal stability in the temperature range of 120–300 K, while the evolution of magnetic domains under the application of magnetic field is greatly affected by the degree of amorphization. The cross-tie domain walls consisted of magnetic vortices and antivortices form as applying a proper magnetic field in TbFe5, in contrast with the unchanged magnetic domains in Tb(Co0.5Fe0.5)5. This study provides a guideline for the design of magnetic vortex materials and soft magnetic materials.

Comminution and amorphisation of Diaqua-bis(Omeprazolate)-Magnesium Dihydrate: An analysis of the energies involved

Size reduction of Diaqua-bis(Omeprazolate)-Magnesium Dihydrate (DABOMD) crystals, an active pharmaceutical ingredient (API) which inhibits gastric acid secretion and its related disorder in mammals, has been investigated using a planetary ball mill and a single ball mill. The outcome of milling shows that DABOMD undergoes prominent comminution and amorphisation processes that occur parallel to each other, with planetary ball mill causing higher amorphisation rate compared to the single ball mill. To establish a relationship between the degree of comminution and amorphisation, the energies of the planetary ball mill and the single ball mill were quantified using a collision model derived from the literature, and through tracking the milling jar with high speed-camera, respectively. In addition, energies were calculated using the Discrete Element Method (DEM) simulations of both mills. The energy obtained from the DEM simulation of the planetary ball mill is lower than the calculated energies from the literature collision model. This could be due to the fact that the collision model does not consider additional factors affecting the motion of balls, such as friction between the balls and balls and the wall. However, the energy calculated from the DEM simulation is higher than that generated from high speed video tracking of the milling jar for the single ball, since as shown by the DEM the movement pattern and the velocity magnitude of the ball is different to those of the jar, resulting in higher relative collision velocities than the jar velocity itself. Nevertheless, it was found that the planetary ball mill produces higher energy than the single ball mill which explains the difference in the amorphisation obtained in the two mills. This methodology enables quantification of the changes that arise with the milling of a solid (i.e. comminution and amorphisation) with respect to the energy level involved.

Hyperthermia-Induced In Situ Drug Amorphization by Superparamagnetic Nanoparticles in Oral Dosage Forms.

Superparamagnetic iron oxide nanoparticles (SPIONs) generate heat upon exposure to an alternating magnetic field (AMF), which has been studied for hyperthermia treatment and triggered drug release. This study introduces a novel application of magnetic hyperthermia to induce amorphization of a poorly aqueous soluble drug, celecoxib, in situ in tablets for oral administration. Poor aqueous solubility of many drug candidates is a major hurdle in oral drug development. A novel approach to overcome this challenge is in situ amorphization of crystalline drugs. This method facilitates amorphization by molecular dispersion of the drug in a polymeric network inside a tablet, circumventing the physical instability encountered during the manufacturing and storage of conventional amorphous solid dispersions. However, the current shortcomings of this approach include low drug loading, toxicity of excipients, and drug degradation. Here, doped SPIONs produced by flame spray pyrolysis are compacted with polyvinylpyrrolidone and celecoxib and exposed to an AMF in solid state. A design of experiments approach was used to investigate the effects of SPION composition (Zn0.5Fe2.5O4 and Mn0.5Fe2.5O4), doped SPION content (10–20 wt %), drug load (30–50 wt %), and duration of AMF (3–15 min) on the degree of drug amorphization. The degree of amorphization is strongly linked to the maximum tablet temperature achieved during the AMF exposure (r = 0.96), which depends on the SPION composition and content in the tablets. Complete amorphization is achieved with 20 wt % Mn0.5Fe2.5O4 and 30 wt % celecoxib in the tablets that reached the maximum temperature of 165.2 °C after 15 min of AMF exposure. Furthermore, manganese ferrite exhibits no toxicity in human intestinal Caco-2 cell lines. The resulting maximum solubility of in situ amorphized celecoxib is 5 times higher than that of crystalline celecoxib in biorelevant intestinal fluid. This demonstrates the promising capability of SPIONs as enabling excipients to magnetically induce amorphization in situ in oral dosage forms.

Deformation and film formation mechanisms during high velocity impact of silicon carbide nanoparticles

Molecular dynamics simulations were conducted to study the factors that affect deformation behavior that occurs during high-speed impact of SiC nanoparticles onto flat substrates. For these simulations, a 6 nm particle was impacted onto a (110)-oriented SiC substrate and the particle impact velocity (3000–4000 m/s), particle orientation, and impact angle (0°–75°) were systematically varied. A broad range of impact behaviors were observed and categorized from elastic with no particle sticking to plastic with significant particle deformation and sticking. High impact velocities and near normal impact angles were found to enhance particle sticking. Particle orientation also had an effect. For some impact conditions, disordering of the lattice within the particle was observed and quantified. Particle impacts that resulted in the greatest degree of amorphization also exhibited significant deformation. This suggests that amorphization followed by viscous flow in the disordered region of the particle is the primary deformation mechanism responsible for particle sticking.

The effect of B and Ti–Al intermetallics additions on the microstructure and mechanical properties of hot-pressed B4C

In this work, we studied the microstructure and mechanical properties of hot-pressed B4C, B4C + 5 wt% TiAl, and B4C + B + 5 wt% TiAl. The X-ray diffraction and Raman spectroscopy results showed that the addition of Ti–Al alone did not led to Al doping in B4C, and it did not reduce the degree of amorphization of B4C generated under high shear stresses. In contrast, the co-addition of Ti–Al and B resulted in both B and Al solid solutions in the B4C and effectively mitigated the amorphization of B4C. Electron probe microanalysis (EPMA) and energy dispersive X-ray spectroscopy (EDS) analyses suggested that the co-addition of Ti–Al and B promoted the interdiffusion of lightweight elements such as B, C, Al, Mg, and Si at high temperatures, resulting in a dense body with uniformly distributed second phase. The transmission electron microscopy (TEM) observations of the B4C + B + 5 wt% TiAl sample showed that a nano–core–shell structure with aggregated dislocations in the shells which was generated at TiB2 grains due to the segregation and dissolution-precipitation between TiB2 and B-rich boron carbide. The short-range ordered substitution of B and the disordered doping of Al in B4C led to lattice distortion and expansion, resulting in the formation of high-density defects, including stacking faults and nano-twins, improving the mechanical properties for B4C. The B4C + B + 5 wt% TiAl sample exhibits a combination of fascinating properties, including low density (2.52 g/cm3), high Vickers hardness (35.53 ± 0.83 GPa) and moderate fracture toughness (4.37 ± 0.35 MPa m1/2).

A molecular dynamics survey study of impact-induced amorphization in yttria nanoparticles

The impact of a single yttria (Y2O3) nanoparticle onto a yttria substrate was studied as a function of particle velocity (300–1200 m/s) and diameter (5–12 nm) for three particle orientations and two substrate orientations using molecular dynamics simulations. Impacts resulted in minimal dislocation motion but extensive disordering of the crystal lattice without approaching the melting temperature. The resulting amorphous microstructure was both precisely coincident with plastic strain and retained until the end of the simulation, suggesting a deformation mechanism of amorphization-facilitated viscous flow. Further analysis revealed that the degree of amorphization depended primarily on the impact velocity and secondarily on the orientations of the particle and substrate, with significant second-order effects from variable interactions.

Models of Water Vapor Sorption by Hydrophilic Polymers

Various models and equations of water vapor sorption by hydrophilic polymers were considered. It was shown that these models often do not correspond to the sorption mechanism. These models can be mathematically adapted to the experimental isotherm regardless of the real sorption mechanism. Even when sorption occurs according to the same mechanism, various authors use different models and equations. This study is based on the volume absorption mechanism and the Van Krevelen method of group contributions. As a result, a universal physicochemical equation was proposed, which makes it possible to adequately describe the sorption isotherms of amorphous hydrophilic polymers knowing only the chemical formulas of repeating units of these polymers. To calculate the sorption isotherms for semicrystalline samples, it is necessary to use an additional parameter, namely the degree of amorphicity (Y). The adequacy of the derived equation was verified for samples of cellulose and other natural polysaccharides, as well as for samples of synthetic hydrophilic polymers such as polyvinyl alcohol, polyamide-6, and polycaprolactone having various Y-values. The verification showed that the experimental isotherms are almost identical to the isotherms calculated by the universal equation.

Nanoscale origin of the crystalline-to-amorphous phase transformation and damage tolerance of Cantor alloys at cryogenic temperatures

Based on recent experimental studies, crystalline-to-amorphous phase transformation has been proposed as a mechanism to enhance the damage tolerance of Cantor alloys at cryogenic temperatures. In this study, we provide atomistic insights, via molecular dynamics simulations, into the origin of the solid-state amorphization ahead of a crack tip, and report the deformation mechanisms contributing to cryogenic damage-tolerance. We show that the amorphization stems from the formation of multi-dislocation junctions due to the low stacking fault energy. This leads to high lattice resistance to dislocation glide and facilitates nucleation of amorphous nuclei. The deformation mechanisms in the amorphous/crystalline dual phase regions include high-density Shockley partial dislocations and multi-dislocation junctions in the crystalline region, as well as radiation-shaped shear bands and amorphous bridges in the amorphous region, which are rarely found in conventional alloys at low temperature. The amorphous bridges lead to crack shielding. Furthermore, altering the chemical composition changes the work-of-fracture and hence the damage tolerance. The Rice-criterion ductility (ratio between surface energy and unstable stacking fault energy) is an important factor affecting the degree of amorphization, which is useful for the mechanics-based design of Cantor alloys.