Low temperature heat capacity of severely deformed metallic glass

The low temperature heat capacity of amorphous materials reveals a low-frequency enhancement (boson peak) of the vibrational density of states, as compared with the Debye law. By measuring the low-temperature heat capacity of a Zr-based bulk metallic glass relative to a crystalline reference state, we show that the heat capacity of the glass is strongly enhanced after severe plastic deformation by high-pressure torsion, while subsequent thermal annealing at elevated temperatures leads to a significant reduction. The detailed analysis of corresponding molecular dynamics simulations of an amorphous Zr-Cu glass shows that the change in heat capacity is primarily due to enhanced low-frequency modes within the shear band region.Comment: 5 pages, 2 figure

Investigation of relaxation behavior in highly rejuvenated bulk metallic glasses by in-situ synchrotron X-ray scattering

Relaxation behaviors of highly rejuvenated Zr50Cu40Al10 bulk metallic glass was investigated using synchrotron X-ray scattering coupled with differential scanning calorimetry. The relaxation of rejuvenated volume is found to correspond to a marked exothermic event prior to the glass transition. High-energy synchrotron X-ray measurements of the structure factor show that annihilation of rejuvenated volume correspond to a sharpening of the scattering peaks. The calculated reduced pair distribution function suggests that the atomic re-arrangement in the second shell are largely responsible for the reduction in the free volume and decrease in full-width at half-maximum of the Total Structure Factor observed during structural relaxation. Mechanical properties in the highly rejuvenated metallic glass were evaluated as a function of annealing temperature

Characterization of ordering in Fe-6.5%Si alloy using X-ray, TEM, and magnetic TGA methods

Fe-6.5wt%Si steel surpasses the current extensively used Fe-3.2wt%Si steel in lower iron loss, higher permeability, and near zero magnetostriction. As a cost effective soft magnetic material, Fe-6.5wt%Si may find applications in motors, transformers, and electronic components. However, the brittleness of the alloy poses processing challenges. The brittleness in Fe-6.5wt%Si is attributed to the formation of ordered phases. Evaluation of the amount of ordered phases is important for the research and development of Fe-6.5wt%Si. This paper aims to find effective ways to evaluate the ordering degree through a comparison of various characterization techniques. In order to tune the ordering degree, various speeds were used to prepare Fe-6.5wt%Si samples via melt spinning. The varying wheel speed changes the cooling rate, which was confirmed by thermal imaging. In addition to the widely used TEM and normal theta-2theta X-ray diffraction methods, two quantitative methods were adopted for this Fe-6.5wt%Si system to study the ordering degree. One method is based on rotating crystal XRD technique, and the other is magnetic thermal analysis technique. These two methods effectively quantified the varying degree of ordering presented in the samples and were deemed more suitable than the TEM, normal theta-2theta XRD methods for Fe-Si due to their ease of sample preparation and short turn-around time

Rapid Assessment of the Ce-Co-Fe-Cu System for Permanent Magnetic Applications

This work focuses on the rapid synthesis and characterization of quaternary Ce(CoFeCu)5 alloy libraries to assess their potential viability as permanent magnets. Arrays of bulk specimens with controlled compositions were synthesized via laser engineered net shaping (LENS) by feeding different ratios of alloy powders into a melt pool created by a laser. Based on the assessment of the magnetic properties of the LENS printed samples, arc-melted and cast ingots were prepared with varying Fe (5–20 at.%) and Co (60–45 at.%) compositions while maintaining constant Ce (16 at.%) and Cu (19 at.%) content. The evolution of the microstructure and phases with varying chemical compositions and their dependence on magnetic properties are analyzed in as-cast and heat-treated samples. In both the LENS printed and cast samples, we find the best magnetic properties correspond to a predominantly single-phase Ce(CoFeCu)5 microstructure in which high coercivity (Hc \u3e 10 kOe) can be achieved without any microstructural refinement

Enhanced Expression of Deoxynivalenol-Degrading Enzyme DepB in Bacillus subtilis by Optimizing Expression Elements

A deoxynivalenol-degrading enzyme DepB was successfully expressed in Bacillus subtilis RIK 1285 in this study, but the fermentation level of DepB was low, which hinders its application in food and feed processing. Thus, an integrative strategy of transcriptional and translational regulation was explored to enhance the expression level of DepB. First, nine single strong promoters were selected to replace the original promoter P43, among which the recombinant bacteria mediated by the promoter PspoVG gave the highest enzyme activity of 29.59 U/mL after fermentation. Second, four promoters (P43, PsacB, PspoVG, and PaprE) with relatively high DepB expression levels were chosen to construct a dual-promoter system. DepB mediated by the dual promoter PaprE-PspoVG reached the highest activity of 48.87 U/mL. Moreover, the DepB activity of Mutant-5 with optimized core region (-35 and -10 boxes) of PaprE-PspoVG reached 69.17 U/mL, which was 4.79 times higher than that of the original strain (14.45 U/mL). Finally, DepB expression level was further improved by optimizing the ribosome binding site (RBS) sequence of the promoter PspoVG, and the enzyme activity of RBS15 reached 115.15 U/mL, which was 7.97-fold higher than that of the original strain. The results suggest that combined transcriptional and translational regulation is an effective strategy to improve the fermentation level of recombinant proteins

Enhanced Expression of Pullulanase in Bacillus subtilis by New Strong Promoters Mined From Transcriptome Data, Both Alone and in Combination

Pullulanase plays an important role as a starch hydrolysis enzyme in the production of bio-fuels and animal feed, and in the food industry. Compared to the methods currently used for pullulanase production, synthesis by Bacillus subtilis would be safer and easier. However, the current yield of pullulanase from B. subtilis is low to meet industrial requirements. Therefore, it is necessary to improve the yield of pullulanase by B. subtilis. In this study, we mined 10 highly active promoters from B. subtilis based on transcriptome and bioinformatic data. Individual promoters and combinations of promoters were used to improve the yield of pullulanase in B. subtilis BS001. Four recombinant strains with new promoters (Phag, PtufA, PsodA, and PfusA) had higher enzyme activity than the control (PamyE). The strain containing PsodA+fusA (163 U/mL) and the strain containing PsodA+fusA+amyE (336 U/mL) had the highest activity among the analyzed dual- and triple-promoter construct stains in shake flask, which were 2.29 and 4.73 times higher than that of the strain with PamyE, respectively. Moreover, the activity of the strain containing PsodA+fusA+amyE showed a maximum activity of 1,555 U/mL, which was 21.9 times higher than that of the flask-grown PamyE strain in a 50-liter fermenter. Our work showed that these four strong promoters mined from transcriptome data and their combinations could reliably increase the yield of pullulanase in quantities suitable for industrial applications

Ageless Aluminum-Cerium-Based Alloys in High-Volume Die Casting for Improved Energy Efficiency

Strong chemical reactions between Al and Ce lead to the formation of intermetallics with exceptional thermal stability. The rapid formation of intermetallics directly from the liquid phase during solidification of Al-Ce alloys leads to an ultrafine microconstituent structure that effectively strengthens as-cast alloys without further microstructural optimization via thermal processing. Die casting is a high-volume manufacturing technology that accounts for greater than 40% of all cast Al products, whereas Ce is highly overproduced as a waste product of other rare earth element (REE) mining. Reducing heat treatments would stimulate significant improvements in manufacturing energy efficiency, exceeding (megatonnes/year) per large-scale heat-treatment line. In this study, multiple compositions were evaluated with wedge mold castings to test the sensitivity of alloys to the variable solidification rate inherent in high-pressure die casting. Once a suitable composition was determined, it was successfully demonstrated at 800 lbs/h in a 600-ton die caster, after which the as-die cast parts performed similarly to ubiquitous A380 in the same geometry without requiring heat treatment. This work demonstrates the compatibility of Al REE alloys with high-volume die-casting applications with minimal heat treatments

Unveiling the mechanism of phase and morphology selections during the devitrification of Al-Sm amorphous ribbon

The complex interplay between energetic and kinetic factors that governs the phase and morphology selections can originate at the earliest stage of crystallization in the amorphous parent phases. Because of the extreme difficulties in capturing the microscopic nucleation process, a detailed picture of how initial disordered structures affect the transformation pathway remains unclear. Here, we report the experimental observation of widely varying phase selection and grain size evolution during the devitrification of a homogeneous melt-spun glassy ribbon. Two different crystalline phases θ−Al5Sm and ɛ−Al60Sm11 are found to form in the different regions of the same metallic glass (MG) ribbon during the devitrification. The grain size of the ɛ−Al60Sm11 phase shows a strong spatial heterogeneity. The coarse-grained ɛ−Al60Sm11 phase coupled with the small volume fraction of the θ−Al5Sm phase is preferably formed close to the wheel side of the melt-spun ribbon. Combining experimental characterization and computational simulations, we show that phase selection and microstructure evolution can be traced back to different types and populations of atomic clusters that serve as precursors for the nucleation of different crystalline phases. Inhomogeneous cooling rates cause different structure orders across the glass sample during the quenching process. Our findings provide direct insight into the effect of structural order on the crystallization pathways during the devitrification of MG. It also opens an avenue to study the detailed nucleation process at the atomic level using the MG as a platform and suggests the opportunity of microstructure and property design via controlling the cooling process