Search

This study aimed to explore the effect and mechanism of chondrocyte apoptosis on the chemotaxis of osteoclast precursors (OCPs) during bone destruction.The relationship between cartilage and bone destruction was verified with a rat temporomandibular joint osteoarthritis (TMJOA) model. The pan-caspase inhibitor Z-VAD-FMK (ZVAD) was applied to confirm the chemotactic effect of chondrocyte apoptosis on OCPs. Synthesis and release of the key chemokine CX3CL1 in apoptotic and non-apoptotic chondrocytes was assessed with IHC, IF, WB, and ELISA. The function of CX3CL1-CX3CR1 axis in the chemotaxis of OCPs was examined by CX3XR1 inhibitor AZD8797 (AZD) and si-CX3CL1. The regulatory effect of p38 MAPK on CX3CL1 release was verified by p38 inhibitor PH-797804.A temporal and spatial association between cartilage degradation and bone resorption was found in the TMJOA model. The caspase-dependent chondrocyte apoptosis promoted chemotaxis of OCPs, which can be restrained by ZVAD. CX3CL1 was significantly upregulated when chondrocytes underwent apoptosis, and it played a critical role in the recruitment of OCPs, blockage of CX3CL1-CX3CR1 axis resulted in less bone resorption in TMJOA. P38 MAPK was activated in apoptotic chondrocytes, and had a regulatory effect on the synthesis and release of CX3CL1. After inhibition of p38 by PH-797804, the chemotactic effect of apoptotic chondrocytes on OCPs was limited.This study indicates that apoptosis of chondrocytes in TMJOA enhances chemotaxis of OCPs toward osteoclast precursors through upregulation of the p38-CX3CL1 axis, thereby promoting the activation of local osteoclasts.

Nondestructive cryogenically thermal cycling has been a simple but effective treatment to enhance mechanical properties of glassy materials. However, how the structural heterogeneities on nanometer scales are affected by thermal cycling is still an issue. Here, we report the response of spatial heterogeneities in three selected Ti41Zr25Be28Fe6, Zr56Co14Cu14Al16 and Zr42Y14Co22Al22 (at.%) metallic glasses (MGs) with different compositions to the thermal cycling, which show significantly different structure and properties after the same treatments and could be ascribed to the joint contribution of relaxation and rejuvenation induced by thermal cycling. The rejuvenation is initially prevailed in a Zr-Y-containing MG, whereas the relaxation is dominant in a Cu-Co-containing MG, both eventually entering into a dynamic equilibrium state. By employing nanometer-scale structural models, the intrinsic correlation between the spatial heterogeneity and thermal cycling is proposed. The discovery could provide the fundamental understanding of the role of spatial heterogeneity in influencing the macroscopic properties of MGs via thermal cycling and help design high-performance glassy materials by tailoring their atomic structures with suitable thermal treatments.

The single-phase face-centered cubic (fcc)-structured Fe50Mn27Ni10Cr13 high entropy alloy (HEA) exhibits good ductility but low strength, which presents a challenge. By Mo-alloying and thermomechanical treatments, we have designed the (Fe50Mn27Ni10Cr13)100-xMox (x = 0–6 at.%) alloy series with a wide range of mechanical properties. The careful control of secondary phases introduced in the cold-rolled and annealed (Fe50Mn27Ni10Cr13)Mo2 sample resulted in an enhanced tensile strength from 250 MPa to 665 MPa, still having ∼25 % ductility. TEM investigations of this alloy revealed the presence of deformation twins, dislocation cells, and ordered bcc nano-particles embedded in the ductile fcc matrix post-deformation. The observed deformation structures are an indication of successful cooperation between deformation twinning and precipitation strengthening in enhancing the tensile strength at maintained ductility compared to its cast counterpart. This work provides insight into the tunability of the mechanical properties of non-equiatomic HEAs via alloying and thermomechanical processing.

Scripta materialia 186, 268 - 271 (2020). doi:10.1016/j.scriptamat.2020.05.002, We reveal a slow-to-fast dynamics transition in the as-cast Cu$_{46}$Zr$_{46}$Al$_8$ (at.%) metallic glass (MG) at a temperature below the glass transition upon heating, which depends on the competition between free volume annihilation and thermally-activated atomic mobility, well consistent with the bond-length change of Cu-Cu pairs. The activation of $��$-relaxation at high temperatures could be related to the bond-length extension of Cu-Cu and Zr-Zr like-atom pairs together with the shortening of Cu-Zr unlike-atom pairs. Our results provide new insights into the correlation of dynamics with atomic structure in MGs and will be helpful to the understanding of ageing behaviors in MGs., Published by Elsevier Science, Amsterdam [u.a.]

Improving the thermostability and mechanical properties of metastable amorphous materials are critical for their potential applications. Here we report the achievement of a wide variety of nanostructures and properties in Ni-Nb metallic glass thin films (MGTFs) by tuning the substrate temperature (Tsub) during magnetron sputtering. By gradually increasing Tsub close to glass transition temperature (Tg) from room temperature, we evidence the transition from the hierarchical nanostructure with microcracks to the denser nanostructure with a smoother surface and smaller column/particle size. This transition contributes to the enhanced plastic deformation stability and nanomechanical properties, thermal stability, and optical reflectivity in the visible light wavelength. We explain the nanostructure evolution with Tsub based on the competition between the shadowing effect and surface diffusion. The shadowing effect is dominant in low-Tsub films and promotes the voided boundaries, while surface diffusion is remarkably enhanced at high Tsub (0.76–0.87 Tg) to form dense intergrain boundaries. This finding provides a promising avenue towards producing novel functional MGTFs with controllable nanostructures and properties without any post-treatment.

Osmanthus fragrans Lour., one of the top 10 most popular flowers in China, is known for both its beauty and fragrance. It is rich in flavonoids, a class of secondary metabolites with significant neuroprotective, free-radical scavenging, and anti-oxidant activity. To understand the mechanisms regulating flavonoid biosynthesis, we conducted transcriptome sequencing O. fragrans flowers to analyze gene expressions during the full flowering stage. The RNA was isolated separately from petals of cvs. Yingui and Dangui, which were treated or not with jasmonic acid, salicylic acid, or abscisic acid. A total of 142 029 unigenes were denovo assembled, and 50 918 unigenes were annotated. The differentially expressed genes were identified, annotated, and classified. The results of transcriptome sequencing and real-time PCR revealed higher expressions of phenylalanine ammonia-lyase (PAL), PAL1, chalcone synthase (CHS), flavanone-3-hydroxylase (F3H), flavonol synthase (FLS), and lower expressions of dihydroflavonol-4-reductase (DFR), anthocyanidin synthase (ANS) in 'Yingui' than in 'Dangui'. Such an expression pattern facilitated the higher accumulation of flavonoids in 'Yingui'. Several genes of the flavonoid biosynthesis pathway were upregulated by jasmonic acid and salicylic acid in both the cultivars leading to flavonoid accumulation in their petals. In the v-myb avian myeloblastosis viral oncogene homolog 1(MYB1)-overexpressing petals, the expressions of PAL, PAL1, CHI, and FLS increased. The results suggest that MYB1 may participate in the flavonoid biosynthesis pathway and regulate the expression of some upstream genes in O. fragrans.

In this paper, the OpenACC heterogeneous parallel programming model is successfully applied to modification and acceleration of the three-dimensional Tokamak magnetohydrodynamical code (CLTx). Through combination of OpenACC and MPI technologies, CLTx is further parallelized by using multiple-GPUs. Significant speedup ratios are achieved on NVIDIA TITAN Xp and TITAN V GPUs, respectively, with very few modifications of CLTx. Furthermore, the validity of the double precision calculations on the above-mentioned two graphics cards has also been strictly verified with m/n=2/1 resistive tearing mode instability in Tokamak., 31 pages, 13 figures

The simple skill measure known as Percent Correct (PC) has been widely used in Australian climate services to measure the accuracy of public forecasts of the probability of above or below median conditions. Since it is simple and intuitive, it has been well accepted by users who are not familiar with the complexities of forecast verification. However, a major disadvantage of PC is that it only measures the categorical outcome of events and ignores the magnitude of anomalies in both the forecast distributions and observed outcomes. In this paper, we introduce the Weighted Percent Correct (WPC) verification metric. Instead of just focusing on the categorical outcome, WPC includes the magnitude of the observed anomaly (departure from the median for above/below median forecasts), which is then applied as a weighting to the PC score. The WPC has many similarities to the PC, with a score of 100 % indicating a perfect forecast, and a score of 50 % or below indicating an unskilled forecast (as applied to above/below median). The advantage of the WPC for users is that it downplays very small anomalies in the observations, but highlights areas with significant anomalies that were correctly forecast. This is a particular advantage for places like Australia, where large areas are seasonally dry, and most anomalies during those dry seasons are so small that they are of little relevance to users and their applications. Some examples are given that show the advantages of WPC over PC, and to highlight how it is also intuitive, easy to use and simple to communicate – aspects that stakeholders need to make decisions.

Radon is the main background source of dark matter and neutrino experiments. Radon concentration (mBq/m3) measurement by liquid scintillation detector is a highly sensitive method at low temperatures using silicon photomultipliers (SiPMs) arrays. The SiPM performance characteristics are closely related to the lower detection limit of the detector. In this study, we built an automatic and accurate low-temperature measurement system to study the single photoelectron (SPE) spectrum, SPE resolution, optical crosstalk, and after-pulse of the SiPM at different temperatures. As a result, we obtained the variation trend of the SiPM parameters at different temperatures, and the SiPM optimal working conditions were obtained, which can improve the detector's sensitivity.

AIM To objectively examine the agreement and correlation between four-dimensional (4D) flow magnetic resonance imaging (MRI) and traditional two-dimensional (2D) phase-contrast (PC) MRI with the reference standard of Doppler echocardiography for measuring peak blood velocity at the cardiac valve and great arteries, and to assess if 4D flow MRI offers an advantage over the traditional 2D method. MATERIALS AND METHODS The literature was searched systematically for studies that evaluate the degree of correlation and agreement between 4D flow MRI or 2D PC MRI and Doppler retrieved from PubMed, EMBASE, and the Cochrane Library. A meta-analysis was conducted to determine the peak velocity pooled bias with 95% limits of agreement (LoA) and correlation coefficient (r) for 4D flow MRI and 2D PC MRI compared with Doppler. RESULTS Ten studies that compared 4D flow MRI with Doppler and 12 studies that compared 2D PC MRI with Doppler were included. 4D flow MRI showed an underestimation with bias and 95% LoA of -0.09 (-0.41, 0.24) m/s (p=0.079) while 2D PC MRI showed a poorer agreement with a bias and 95% LoA of -0.25 (-0.53, 0.03), p=0.596. 4D flow MRI and 2D PC MRI showed a strong correlation with R=0.80 (95% CI 0.75, 0.84; p

Clarifying the crystallization path, from the thermodynamic point of view, is of importance for the structure and properties of metallic glasses (MGs). The influence of oxygen on the crystallization pathway of Ni65Zr35 MG was investigated by in-situ heating transmission electron microscopy (TEM). As temperature increases, crystalline Ni7Zr2 and t-ZrO2 phases are formed first rather than the Ni10Zr7 and Ni21Zr8 phases, which are the main crystallization products following the phase diagram. Oxygen changes the crystallization pathway by varying the Ni/Zr ratio, indicating that the effects of oxygen on the crystallization in nanometer-sized MG cannot be neglected even in high vacuum TEMs.

Nanometer-scale phase separation has been explored in an Al60Ge30Mn10 amorphous alloy, where all atomic pairs have negative heats of mixing. Here we use a combination of experimental (X-ray diffraction, X-ray absorption fine structure, small angle X-ray scattering and transmission electron microscopy) and simulation (Ab initio molecular dynamics and reverse Monte Carlo) techniques to resolve the atomic- and micrometer-level structures in the phase-separated Al60Ge30Mn10 amorphous alloy. Three characteristic peaks appear in the structure factor, linking with three kinds of composition fluctuation regions with different heterogeneous structures. The origin of three characteristic peaks is investigated in details and attributed to different atomic pairs. By analyzing the local chemical ordering between main polyhedra, we find that various phases exhibit differences in atomic structure, composition and bond-orientational order. The results obtained here provide atomic-scale understanding of the nanometer-scale phase separation phenomenon in Al60Ge30Mn10 amorphous alloy.

The effects of loading rate on creep behavior and shear transformation zone (STZ) in magnetron sputtered La-Co-Al and Zr-Cu-Ni-Al amorphous alloy thin films were characterized through instrumented nanoindentation with a spherical indenter. It was revealed that with an increase in loading rate, both thin films became harder with a narrower distribution of mechanical response, and exhibited more pronounced creep displacement with higher creep strain rate. Based on cooperative shear model, both STZ volume and activation energy were calculated by measuring the strain rate sensitivity during creep, showing an increasing tendency with loading rate. However, the strain rate sensitivity was found to decrease with loading rate. Furthermore, structural heterogeneity density, estimated by analyzing the stressed volume at yielding, decreased with loading rate. Therefore, with increasing loading rate, the STZ event can only be activated at detectable structural heterogeneities with relatively larger volume, and the number of available fertile sites was decreased, resulting in postponed shear band formation and suppressed deformation mode transition.

Annealing of metallic glasses (MGs) at temperature near glass transition temperature (Tg) triggers relaxation and often hampers their performances in service. Rejuvenation treatment of MGs by thermal cycling is recently intensively investigated. However, the mechanism responsible for the structural rejuvenation still remains elusive. In this work, we present a systematic study on the rejuvenation effect of a Zr46Cu38Al8Ag8 MG annealed at 0.9Tg for various durations, subjected to thermo-cycling treatment. It is found that well relaxed samples after long-term annealing are almost unaffected, while short-term annealed samples exhibit large rejuvenation effect by thermo-cycling treatment. Using synchrotron X-ray diffraction, we find that thermal cycling results in a disordering at the short-range scale, where the rejuvenation effect is large in a heterogeneous sample. More interestingly, the thermo-cycling treatment on intermediate structure with 20 h-annealed sample relatively exhibits a high degree rejuvenation effect, as compared to shorter- and longer-term annealed samples. This finding indicates that the activation barrier for rejuvenation strongly depends on the original structural states, e.g., free volume, inherent stress and structural heterogeneity.

Cu(OH)2 nanowire arrays supported on nanoporous copper were synthesized via anodic oxidation at different voltages. Nanoporous copper was prepared through dealloying Zr50Cu50 amorphous ribbon to obtain a uniform aperture. This unique composite structure combines the excellent conductivity of nanoporous copper with the high catalytic activity of Cu(OH)2 nanowires and can be directly used as a support electrode to explore the electrocatalytic oxidation of glucose. The sensor showed a wide linear response range from 10.0 μM to 10.0 mM and high sensitivity of 1.866 mA cm−2 M−1. As such, it provides a basis for the future production of enzyme-free glucose sensors.

The effect of substrate temperature on growth behavior and microstructure-properties correlation of magnetron sputtered Ni60Nb40 films were systematically investigated. With substrate temperature increasing from 293 K to 493 K, and thickness changing from 50 nm to 1 μm, all films kept in amorphous state. The characteristic of columnar growth was clearly seen, with reduced interfacial fraction between adjacent columns and increased granule size at high substrate temperature. Through scaling analysis, films deposited at all temperatures grow in an anomalous roughening mode, and at 293 K for films thicker than 200 nm, a difficult roughening phenomenon was revealed. High substrate temperature can facilitate the surface kinetic roughening. Both decreased interface fraction-to-volume ratio by particle coarsening and reduced free volume by structure relaxation caused the dense atomic atomic packing and increased density, which may be the crucial reason for enhanced mechanical properties and thermal stability against crystallization.

Usually, the fracture of metallic glass accompanies with huge heat release, resulting in the well-known localized melting and formation of vein patterns. In this work, using X-ray tomography and tin-coating methods, we found that the shear fracture of metallic glass under compression can be also “cold” if slowing down the fracture process. The results clarify that the melting phenomenon is not a necessary outcome of shear-band fracture, while the temperature-rise relies strongly on the energy release per unit shearing time, even in the fracture process.

The influences of rare earth element yttrium (Y) on microstructure, mechanical properties and fracture characteristics of Ti-25Zr-xY (x = 0, 0.5, 1, 2, 3, 4, 5, at%) alloy were investigated. Compositional and microstructural characterization of the as-cast material was conducted by XRD, SEM and TEM. XRD analysis showed that no other phase was found in the specimens, which completely consisted of α and α-Y phases. Addition of trace amounts of Y to the Ti-25Zr alloys induced significant changes in the microstructure, including the decrease in sizes of prior β grain boundaries and α platelets size. The constitutional supercooling were responsible for the grain refinement. Owing to the low solubility and segregation of Y element in the Ti-Zr alloy, when the Y content was less than 1 (at%), the fine and uniformly distributed α-Y phases were dispersed within the grains. The refinement of grains and α-lath and dispersion of α-Y within the grains contributed to the desirable compression performance. By contrast, when the content of Y exceeded 1 at%, the grain boundary segregation of Y was more distinct. Consequently, the mechanical properties deteriorated remarkably because of the serious segregation of the brittle α-Y phase at grain boundaries.

Nano CuS/MoS2 composite catalysts were fabricated by chemically dealloying amorphous Ti30Cu70−xMox (x = 1, 2, 3 at.%) ribbons in acid solution. The composite catalysts presented as globular clusters composed of a large number of intersecting 20–40 nm-thick nanosheets, which was attributed to laminated materials aggregating on the surface of the product during dealloying. Compared with other alloy compositions, when x = 3, the dealloying product exhibited excellent photocatalytic activity and cycling stability for the degradation of methylene blue. These characteristics are mainly due to the large specific surface (∼31.12 m2 g−1) of the product and low recombination of photogenerated electrons and holes on its surface.

To develop an excellent low-dimensional magnetic material, the evolution of microstructure and soft magnetic properties in thin films with thickness as well as annealing treatment has been systematically investigated. Fe-Si-B-P-C thin films were fabricated using radio frequency magnetron sputtering. Microstructure of as-deposited and as-annealed thin films with various thicknesses have been characterized, and corresponding soft magnetic properties have been studied. The magnetic domain structure in thin films was further characterized via the magneto-optical Kerr microscope. It is revealed that all these as-deposited thin films exhibit a columnar structure, and the surface roughening is in accordance with the anomalous scaling. The coercivity gradually decreases from 4.8 Oe for 61 nm-thick film to 0.6 Oe for 608 nm-thick film, and almost remains constant with further increasing thickness, while the magnetic impedance ratio rises with thickness. After 473 K-annealing treatment coercivity decreases and magnetic impedance ratio increases, which can be attributed to the release of residual stress and the enhanced exchange coupling. After annealing at 573 K, although no obvious improvement in coercivity occurs, magnetic impedance ratio further rises due to the enhanced electrical conductivity and the reduced magnetic anisotropy. Severe crystallization takes place after annealed at 673 K, deteriorating soft magnetic properties of thin films. Therefore, the 573 K-annealed Fe-Si-B-P-C thin film with 1210 nm in thickness exhibits the best soft magnetic properties, having coercivity of 0.3 Oe, magnetic impedance ratio of 66.2% and relatively low magnetic anisotropy, which is a very promising soft magnetic material for sensor application.

Electrical resistivity in amorphous Mg65Zn30Ca5 thin films with thicknesses ranging from 49 nm to 1786 nm is investigated by four-probe method at 4–300 K. It is revealed that for thickness from 94 nm to 1786 nm the Ziman-Faber diffraction model can describe temperature-dependent electrical resistivity, while for 49 nm-thick film the two-level system scattering mechanism is validated below 40 K and Ziman-Faber diffraction model above 40 K. More interface fraction between the columnar structures with enhanced heterogeneity could be the possible origin of two-level system scattering in thinnest film, instead of denser atomic packing.

Previous studies have revealed that the shear band propagation of metallic glasses can be strongly influenced by decreasing the sample size, leading to the dramatically enhanced plasticity. Here we show that the sample size also affects the shear band fracture behavior. When reducing the sample size, the compressive shear band fracture mode is changed from the typical instant fracture with vein patterns into a gradual fracture mode without the formation of vein pattern. This can be explained by the marked reduction of energy dissipation density during shear band sliding in small samples and thus the enhanced shear band stability against the instable fracture.

To investigate the intrinsic effect of the pre-stress (σpre) on the onset of yielding, nanoindentation experiments are performed on two metallic glasses (MGs) which are elastically-bent and constrained within a home-made apparatus. Statistical calculations for the first pop-ins are made and noticeable decrease in maximum shear stress (τmax) is observed under tensile pre-stress, but only slight increase under compressive one, without considering the pre-stress effect on the ratio (0.29) of τmax to the maximum contact pressure (p0). This asymmetry phenomenon is related to the anharmonic and asymmetric nature of the interatomic interaction potential caused by the applied pre-stress. Moreover, finite-element analysis is conducted to obtain the elastic stress field of the pre-stressed region upon indentation, which becomes anisotropy and quarter-symmetric. τmax for the specimen is defined as 0.29p0 + 0.50σpre for the tensile-stressed region and 0.29p0 for the compressive-stressed region within elastic strain limit of MGs, which requires the correction for the intrinsic τmax with tensile σpre, but not for compressive σpre. The corrected τmax and activation energy barrier of shear transformation zone are found to be independent on σpre, suggesting that the intrinsic shear stress is a constant and the yielding of MGs obeys the maximum shear stress criterion.

Micro-nano structure of Cu2O/CuO composite array and CuO nanowire array on nanoporous Cu are successfully synthesized via anodic oxidation method. Nanoporous Cu with bicontinuous network was fabricated by chemical dealloying. The CuxO/NP-Cu (x = 1 and 2) composites can be used as supported electrode for supercapacitor. The specific capacitance of nanowires CuO/NP-Cu electrode is 143.63 F g−1 at a current density of 0.5 mA cm−2, which is better than CuO/Cu2O/NP-Cu and NP-Cu electrodes. This can be attributed to the synergistic effect of NP-Cu structure with large internal surface and the morphology of CuO nanowire, which are favorable for electron transfer and enhancement of charge-discharge rate.

With technological progress, the request for high power LEDs (HP-LEDs) as a replacement candidate for common lamp is increased. Due to dissipation of 70–85% of LED input power in form of heat, thermal management of LED packaging is unavoidable. A review of the literature related to thermal management of HP-LED based on the different materials and fabrication methods are used in LED packaging structure to provide a concise overview of the recent advances in this field of study. In this paper, different materials of LED packaging through the heat dissipation path, from LED chip until heat sink are evaluated by details. The state-of-the-art of micro/nano technology-based thermal solutions for three levels of (a) LED chip, (b) submount, and (c) carrier substrate are addressed. The fundamental of introduced thermal management solutions are material-based and fabrication-based solutions.

The proteasome inhibitor bortezomib is the most successfully applied chemotherapeutic drug for treating multiple myeloma. However, its clinical efficacy reduced due to resistance development. The underlying molecular mechanisms of bortezomib resistance are poorly understood. In this study, by combining in silico analysis and sgRNA library based drug resistance screening assay, we identified SENP2 (Sentrin/SUMO-specific proteases-2) as a bortezomib sensitive gene and found its expression highly downregulated in bortezomib resistant multiple myeloma patient’s samples. Furthermore, down regulation of SENP2 in multiple myeloma cell line RPMI8226 alleviated bortezomib induced cell proliferation inhibition and apoptosis, whereas, overexpression of SENP2 sensitized these cells to bortezomib treatment. We further demonstrate that knockdown of SENP2 in RPMI8226 cells increased SUMO2 conjugated IκBα that resulted in the activation of NF-κB. Taken together, we report that silencing of SENP2 and consequent activation of NF-κB through the modulation of IκBα sumoylation as a novel mechanism inducing bortezomib resistance in multiple myeloma.

Crystallization of metallic glasses (MGs) is a complex dynamic process, driven by thermodynamics and limited by kinetics, which often involves phase transformation from the metastable amorphous state, via intermediates, to the final stable crystalline states. The intermediate structural state remains mysterious at present but crucial for a deeper understanding of the physics and mechanisms of the crystallization process. Detailed structural characterization of the complex intermediate crystalline phases using transmission electron microscopy (TEM) provides a unique platform to study such issues. Here, we monitor the evolution of the crystallization process for Ni65Zr35 (at%) MG ribbon with structural heterogeneities. Direct visualization combined with compositional analysis reveal that the intermediate phase with Zr concentration higher than that of the MG consists of stacked nanometer-sized layers of Ni-rich units (Ni at% > 67%) and Ni10Zr7-like units, where the thin Ni-rich single layer gradually disappears with increasing annealing temperature. Our findings provide insight into the key role of Ni in the structural transition process, improving the understanding of the atomic diffusion-dominated crystallization in MGs.

Supplemental material, DS_10.1177_0022034520901710 for DPSCs Attenuate Experimental Progressive TMJ Arthritis by Inhibiting the STAT1 Pathway by S.J. Cui, T. Zhang, Y. Fu, Y. Liu, Y.H. Gan, Y.H. Zhou, R.L. Yang and X.D. Wang in Journal of Dental Research

The atomic dynamics in metallic glasses (MGs) are closely related to their stability. Due to weak resistance to nanocrystallization at high temperatures, we interestingly observe the slow atomic dynamics happening in an as-quenched La-Al-Ni MG sample compared with a sub-Tg pre-annealed one when cooling from about 0.99Tg (Tg the glass transition temperature). An intermittent aging behavior also appears in the as-quenched MG sample only on cooling but not on heating, nor does it appear in the pre-annealed sample on both cooling and heating, indicating that it could be thermal history dependent and related to the existence of nanocrystals. Differently, a sudden atomic dynamics transition from fast to slow is observed in the pre-annealed MG sample when the pre-annealing temperature is approached upon cooling, resulting from the configuration recovery to a low energy state created by pre-annealing. Our findings demonstrate that the thermal history can give rise to significantly different aging dynamics of MGs , providing an in-depth understanding of structural relaxation in disordered materials on the atomic level.

The secondary β-relaxation is an intrinsic feature in glassy materials. However, its structural origin is still not well understood. Here we report that the β-relaxations in La50Al15Ni35 and La50Al15Cu35 metallic glasses (MGs) mainly depend on the vibration of small Ni and Cu atoms in local cages. By using advanced synchrotron X-ray techniques and theoretical calculations, we elucidate that the tricapped-trigonal-prism-like polyhedra with more large La atoms in shells favor the local vibration of center Ni atoms, leading to the pronounced β-relaxation event. In contrast, the in-cage vibration of Cu atoms is somehow suppressed by the appearance of more shell Cu atoms. Nevertheless, they could easily diffuse out of the cages compared with Ni, thus triggering the onset of α-relaxation. This work provides a pathway to understand the different structural relaxation behaviors in MGs and other disordered materials from their local atomic packing and dynamics points of view.

The effect of composition tuning on glass forming ability (GFA), mechanical properties and atomic structure in ZrxCo84−xAl16 bulk metallic glasses (BMGs) with x = 51–58 has been investigated by using copper-mold suction casting, nanoindentation, high-energy X-ray diffraction, extended X-ray absorption fine structure experiments and ab initio molecular dynamics simulations, respectively. It is found that GFA firstly increases then decreases with increasing Zr content, exhibiting a maximum diameter of 7 mm with the Zr content of 55 and 56, while an abrupt reduction of bending plasticity occurs as the Zr content drops below 55. Both experimental and theoretical results find that GFA is remarkably enhanced, due to the abnormal reduction in the fractions of the Co-centered ⟨0, 2, 8, 1⟩, ⟨0, 3, 6, 2⟩ and ⟨0, 3, 6, 3⟩ polyhedra, and the denser atomic packing of Zr atoms around center Co atom, as the Zr content increases from 51 to 56. Meanwhile, the simultaneously improved plasticity is associated with the increased Co-centered ⟨0, 3, 6, 0⟩, and Al-centered ⟨0, 2, 8, 1⟩ and ⟨0, 3, 6, 2⟩ polyhedra, which provide more fertile sites for the nucleation of shear transformations. Further Zr addition to 58 increases remarkably the fractions of Zr- and Al-centered ⟨0, 1, 10, 2⟩ and ⟨0, 3, 6, 4⟩ polyhedra, and causes looser atomic packing of Co atoms around center Zr atom, leading to the reduction in GFA. However, the plasticity is not enhanced further but remains nearly constant, which may be related to the deteriorated effect on plasticity of the decreased fractions of Zr-centered ⟨0, 1, 10, 5⟩ and Co-centered ⟨0, 3, 6, 0⟩ polyhedra, and the increased fractions of Zr-centered ⟨0, 1, 10, 3⟩ and ⟨0, 2, 8, 4⟩ and Co-centered ⟨0, 2, 8, 0⟩ polyhedra. Compositional tuning, with internal structure tuned to favor both GFA and plastic flow, offers new possibilities in developing ductile BMG materials.