Revealing the Effect of Phase Composition and Transformation on the Mechanical Properties of a Cu–6Ni–6Sn–0.6Si Alloy

In the present study, a Cu–6Ni–6Sn–0.6Si alloy is fabricated through frequency induction melting, then subjected to solution treatment, rolling, and annealing. The phase composition, microstructure evolution, and transition mechanism of the Cu–6Ni–6Sn–0.6Si alloy are researched systematically through simulation calculation and experimental characterization. The ultimate as-annealed sample simultaneously performs with high strength and good ductility according to the uniaxial tensile test results at room temperature. There are amounts of precipitates generated, which are identified as belonging to the DO22 and L12 phases through the transmission electron microscope (TEM) analysis. The DO22 and L12 phase precipitates have a significant strengthening effect. Meanwhile, the generation of the common discontinuous precipitation of the γ phase, which is harmful to the mechanical properties of the copper–nickel–tin alloy, is inhibited mightily during the annealing process, possibly due to the existence of the Ni5Si2 primary phase. Therefore, the as-annealed sample of the Cu–6Ni–6Sn–0.6Si alloy possesses high tensile strength and elongation, which are 967 MPa and 12%, respectively.     

Deformation and Phase Transformation of Disordered α Phase in the (α + γ) Two-Phase Region of a High-Nb TiAl Alloy

In this paper, the deformation and phase transformation of disordered α phase in the (α + γ) two-phase region in as-forged Ti-44Al-8Nb-(W, B, Y) alloy were investigated by hot-compression and hot-packed rolling. The detailed microstructural evolution demonstrated that the deformed microstructure was significantly affected by the deformation conditions, and the microstructure differences were mainly due to the use of a lower temperature and strain rate. Finer α grains were formed by the continuous dynamic recrystallization of α lamellae and α grains distributed around lamellar colonies. Moreover, the grooved γ grains formed by the phase transformation from α lamellae during hot rolling cooperated with and decomposed α lamellae. A microstructure evolution model was built for the TiAl alloy at 1250 °C during hot rolling.     

The Characteristic of Fe as a β-Ti Stabilizer in Ti Alloys

It is well known that adding elements, especially β-Ti stabilizers, are holding a significant effect on titanium alloy strength due to the solution and precipitate strengthening mechanisms. In order to reveal the Fe strengthening mechanism in titanium, this study investigate the effect of Fe on the stability of β-Ti and the phase transition between α, β and ω phase with first-principle calculations. According to our study, Fe is a strong β-Ti phase stabilizer could owe to the 3d orbital into e_g and t_2g states which results in strong hybridization between Fe-d orbital and Ti-d orbital. The phase transition from ω to β or from α to β becomes easier for Fe-doped Ti compared to pure titanium. Based on our results, it is found that one added Fe atom can lead the phase transition (ω → β) of at least nine titanium atoms, which further proves that Fe has a strong stabilizing effect on β-Ti phase. This result provides a solid guide for the future design of high-strength titanium with the addition of Fe.     

Phase Composition Effects on Dynamic Behavior and Strain Rate Sensitivity in Metastable β-Ti Alloys

In this study, high strain rate tension tests are conducted to determine and compare the dynamic mechanical behaviors and deformation mechanisms of different phase composition α-β metastable β-Ti alloys using a split Hopkinson tension bar. Two typical bimodal equiaxed α_p + β and lamellar α_s + β Ti-45551 alloy microstructures are formed through different hot working and thermal processing for investigating the effect of phase composition or microstructure on mechanical properties and strain rate sensitivity. It is demonstrated that dislocation nucleation and motion in the α/β phase and dislocation tangle or pile up at the α/β interface are typical deformation modes in both of the typical dual-phase Ti alloys at quasi-static loading conditions. Under dynamic loading, both the strength and ductility show a clearly positive strain rate dependence, which is directly related to dislocation activation in the α + β Ti-45551 alloy. Based on microstructure characterizations, it is shown that deformation twinning starts to become a major deformation mechanism in equiaxed α_p + β microstructures under dynamic loading conditions. However, deformation twins are not favored in the lamellar α_s + β Ti-45551 alloy due to its nano phase size. Finally, the mechanical behaviors and strain rate sensitivity are strongly dependent on the phase composition of metastable β-Ti alloys.     

Microstructure and Mechanical Properties of β-Titanium Ti-15Mo Alloy Produced by Combined Processing including ECAP-Conform and Drawing

At present, researchers pay great attention to the development of metastable β-titanium alloys. A task of current importance is the enhancement of their strength and fatigue properties. An efficient method for increasing the strength of such alloys could be severe plastic deformation. The object of this study was a medical metastable β-titanium alloy Ti-15Mo (ASTM F2066). The alloy in the (α + β) state was for the first time deformed by combined processing, including equal channel angular pressing-conform and drawing. Such processing enabled the production of long-length rods with a length of 1500 mm. The aim of the work was to study the effect of the combined processing on the alloy’s microstructure and mechanical properties. An ultrafine-grained structure with an average size of structural elements less than 100 nm was obtained. At the same time, high strength and ductility (σ_uts = 1590 MPa, δ = 10%) were achieved, which led to a record increase in the endurance limit (σ₋₁ = 710 MPa) under tension-compression terms.     

Mechanical Properties Enhancement of the Au-Cu-Al Alloys via Phase Constitution Manipulation

To enhance the mechanical properties (e.g., strength and elongation) of the face-centered cubic (fcc) α-phase in the Au-Cu-Al system, this study focused on the introduction of the martensite phase (doubled B19 (DB19) crystal structure of Au₂CuAl) via the manipulation of alloy compositions. Fundamental evaluations, such as microstructure observations, phase identifications, thermal analysis, tensile behavior examinations, and reflectance analysis, have been conducted. The presence of fcc annealing twins was observed in both the optical microscope (OM) and the scanning electron microscope (SEM) images. Both strength and elongation of the alloys were greatly promoted while the DB19 martensite phase was introduced into the alloys. Amongst all the prepared specimens, the 47Au41Cu12Al and the 44Au44Cu12Al alloys performed the optimized mechanical properties. The enhancement of strength and ductility in these two alloys was achieved while the stress plateau was observed during the tensile deformation. A plot of the ultimate tensile strength (UTS) against fracture strain was constructed to illustrate the effects of the introduction of the DB19 martensite phase on the mechanical properties of the alloys. Regardless of the manipulation of the alloy compositions and the introduction of the DB19 martensite phase, the reflectance stayed almost identical to pure Au.     

Recognition of the antigen-presenting molecule MR1 by a Vδ3+ γδ T cell receptor

Unlike conventional αβ T cells, γδ T cells typically recognize nonpeptide ligands independently of major histocompatibility complex (MHC) restriction. Accordingly, the γδ T cell receptor (TCR) can potentially recognize a wide array of ligands; however, few ligands have been described to date. While there is a growing appreciation of the molecular bases underpinning variable (V)δ1⁺ and Vδ2⁺ γδ TCR-mediated ligand recognition, the mode of Vδ3⁺ TCR ligand engagement is unknown. MHC class I–related protein, MR1, presents vitamin B metabolites to αβ T cells known as mucosal-associated invariant T cells, diverse MR1-restricted T cells, and a subset of human γδ T cells. Here, we identify Vδ1/2⁻ γδ T cells in the blood and duodenal biopsy specimens of children that showed metabolite-independent binding of MR1 tetramers. Characterization of one Vδ3Vγ8 TCR clone showed MR1 reactivity was independent of the presented antigen. Determination of two Vδ3Vγ8 TCR-MR1-antigen complex structures revealed a recognition mechanism by the Vδ3 TCR chain that mediated specific contacts to the side of the MR1 antigen-binding groove, representing a previously uncharacterized MR1 docking topology. The binding of the Vδ3⁺ TCR to MR1 did not involve contacts with the presented antigen, providing a basis for understanding its inherent MR1 autoreactivity. We provide molecular insight into antigen-independent recognition of MR1 by a Vδ3⁺ γδ TCR that strengthens an emerging paradigm of antibody-like ligand engagement by γδ TCRs.

Characterized by both innate and adaptive immune cell functions, γδ T cells are an unconventional T cell subset. While the functional role of γδ T cells is yet to be fully established, they can play a central role in antimicrobial immunity (1), antitumor immunity (2), tissue homeostasis, and mucosal immunity (3). Owing to a lack of clarity on activating ligands and phenotypic markers, γδ T cells are often delineated into subsets based on the expression of T cell receptor (TCR) variable (V) δ gene usage, grouped as Vδ2⁺ or Vδ2⁻.The most abundant peripheral blood γδ T cell subset is an innate-like Vδ2⁺subset that comprises ∼1 to 10% of circulating T cells (4). These cells generally express a Vγ9 chain with a focused repertoire in fetal peripheral blood (5) that diversifies through neonatal and adult life following microbial challenge (6, 7). Indeed, these Vγ9/Vδ2⁺ T cells play a central role in antimicrobial immune response to Mycobacterium tuberculosis (8) and Plasmodium falciparum (9). Vγ9/Vδ2⁺ T cells are reactive to prenyl pyrophosphates that include isopentenyl pyrophosphate and (E)-4-Hydroxy-3-methyl-but-2-enyl pyrophosphate (8) in a butyrophilin 3A1- and BTN2A1-dependent manner (10–13). Alongside the innate-like protection of Vγ9/Vδ2⁺ cells, a Vγ9⁻ population provides adaptive-like immunobiology with clonal expansions that exhibit effector function (14).The Vδ2⁻ population encompasses the remaining γδ T cells but most notably the Vδ1⁺ and Vδ3⁺ populations. Vδ1⁺ γδ T cells are an abundant neonatal lineage that persists as the predominating subset in adult peripheral tissue including the gut and skin (15–18). Vδ1⁺ γδ T cells display potent cytokine production and respond to virally infected and cancerous cells (19). Vδ1⁺ T cells were recently shown to compose a private repertoire that diversifies, from being unfocused to a selected clonal TCR pool upon antigen exposure (20–23). Here, the identification of both Vδ1⁺ T_naive and Vδ1⁺ T_effector subsets and the Vδ1⁺ T_naive to T_effector differentiation following in vivo infection point toward an adaptive phenotype (22).The role of Vδ3⁺ γδ T cells has remained unclear, with a poor understanding of their lineage and functional role. Early insights into Vδ3⁺ γδ T cell immunobiology found infiltration of Vδ3⁺ intraepithelial lymphocytes (IEL) within the gut mucosa of celiac patients (24). More recently it was shown that although Vδ3⁺ γδ T cells represent a prominent γδ T cell component of the gut epithelia and lamina propria in control donors, notwithstanding pediatric epithelium, the expanding population of T cells in celiac disease were Vδ1⁺ (25). Although Vδ3⁺ IELs compose a notable population of gut epithelia and lamina propria T cells (∼3 to 7%), they also formed a discrete population (∼0.2%) of CD4⁻CD8⁻ T cells in peripheral blood (26). These Vδ3⁺ DN γδ T cells are postulated to be innate-like due to the expression of NKG2D, CD56, and CD161 (26). When expanded in vitro, these cells degranulated and killed cells expressing CD1d and displayed a T helper (Th) 1, Th2, and Th17 response in addition to promoting dendritic cell maturation (26). Peripheral Vδ3⁺ γδ T cells frequencies are known to increase in systemic lupus erythematosus patients (27, 28), and upon cytomegalovirus (29) and HIV infection (30), although, our knowledge of their exact role and ligands they recognize remains incomplete.The governing paradigms of antigen reactivity, activation principles, and functional roles of γδ T cells remain unresolved. This is owing partly due to a lack of knowledge of bona fide γδ T cell ligands. Presently, Vδ1⁺ γδ T cells remain the best characterized subset with antigens including Major Histocompatibility Complex (MHC)-I (31), monomorphic MHC-I–like molecules such as CD1b (32), CD1c (33), CD1d (34), and MR1 (35), as well as more diverse antigens such as endothelial protein coupled receptor (EPCR) and phycoerythrin (PE) (36, 37). The molecular determinants of this reactivity were first established for Vδ1⁺ TCRs in complex with CD1d presenting sulfatide (38) and α-galactosylceramide (α-GalCer) (34), which showed an antigen-dependent central focus on the presented lipids and docked over the antigen-binding cleft.In humans, mucosal-associated invariant T (MAIT) cells are an abundant innate-like αβ T cell subset typically characterized by a restricted TCR repertoire (39–43) and reactivity to the monomorphic molecule MR1 presenting vitamin B precursors and drug-like molecules of bacterial origin (41, 44–46). Recently, populations of atypical MR1-restricted T cells have been identified in mice and humans that utilize a more diverse TCR repertoire for MR1-recognition (42, 47, 48). Furthermore, MR1-restricted γδ T cells were identified in blood and tissues including Vδ1⁺, Vδ3⁺, and Vδ5⁺ clones (35). As seen with TRAV 1-2⁻, unconventional MAITs cells the isolated γδ T cells exhibited MR1-autoreactivity with some capacity for antigen discrimination within the responding compartment (35, 48). Structural insight into one such MR1-reactive Vδ1⁺ γδ TCR showed a down-under TCR engagement of MR1 in a manner that is thought to represent a subpopulation of MR1-reactive Vδ1⁺ T cells (35). However, biochemical evidence suggested other MR1-reactive γδ T cell clones would likely employ further unusual docking topologies for MR1 recognition (35).Here, we expanded our understanding of a discrete population of human Vδ3⁺ γδ T cells that display reactivity to MR1. We provide a molecular basis for this Vδ3⁺ γδ T cell reactivity and reveal a side-on docking for MR1 that is distinct from the previously determined Vδ1⁺ γδ TCR-MR1-Ag complex. A Vδ3⁺ γδ TCR does not form contacts with the bound MR1 antigen, and we highlight the importance of non–germ-line Vδ3 residues in driving this MR1 restriction. Accordingly, we have provided key insights into the ability of human γδ TCRs to recognize MR1 in an antigen-independent manner by contrasting mechanisms.     

Reducing the γ′-Particle Size in CMSX-4 for Membrane Development

Colloidal emulsions for lipophilic drugs can be fabricated using premix membrane emulsification. The state of the art is the application of membranes made from, for example, polycarbonate or polyester, which, however, are prone to fouling and cause waste, due to the low number of cycles. With the use of metallic membranes made from the nickel based single crystalline superalloy CMSX-4, these key disadvantages are eliminated. However, instead, the pore size and the resulting droplet size distribution need to be adjusted and improved. This can be realized by tailoring the size of the γ′-particles, which is controllable by the time and temperature used during precipitation heat treatment and the quenching method after homogenization heat treatment. Therefore, we utilized different heat treatment protocols, varying the cooling rate (water quenching and air cooling) after homogenization heat treatment and the holding time and temperature during precipitation heat treatment. Then, we investigated the γ/γ′-microstructure, including the γ′-morphology and γ′-particle size. We show that water quenching has a significant impact on the γ/γ′-microstructure and often leads to irregular-shaped and poorly aligned γ′-particles after precipitation heat treatment. In comparison, air cooling, followed by a subsequent precipitation heat treatment, results in well-aligned and cubic shaped γ′-particles and is, therefore, favorable for membrane fabrication. A reduction in precipitation temperature leads to morphology changes to the γ′-particles. A reduction of the holding time during precipitation heat treatment diminishes the γ′-particle growth, resulting in smaller γ′-particles. Additionally, a suitable heat treatment protocol for membrane fabrication was identified with a γ′-edge length of 224 ± 52 nm and well-aligned, cubic shaped γ′-particles.     

In Situ Tensile Deformation and Mechanical Properties of α Platelets TC21 Alloy

The present study was focused on the relationship between an α platelet microstructure and the properties of TC21 alloy, and the tensile deformation process was revealed by in situ observation. To obtain the α platelet microstructures, the samples were administered a solution treatment (1000 °C for 15 min) and then cooled to room temperature by different cooling methods (furnace cooling (FC), open-door furnace cooling (OFC), air cooling (AC), and water quench (WQ), corresponding to an increased cooling rate). It is found that α platelets become thinner and colonies become narrower with the increase in cooling rate. The formation of the platelet microstructure is based on the preferred Burgers orientation relationship of {110}_β//{0001}_α and <111>_β//<112¯0>_α. The α platelets orientation changes with the cooling rate. These differences in α platelets thickness and orientation result in the excellent ductility of the sample with thick platelets and the high strength of the samples with thin platelets. During the in situ tensile deformation process, the crack propagation path is deflected in the presence of grain boundaries, α platelets, and α colonies with different orientations. The fracture of the sample with thick α platelets shows better ductility compared to those with thin α platelets.     

Mechanical Properties of the Composite Material consisting of β-TCP and Alginate-Di-Aldehyde-Gelatin Hydrogel and Its Degradation Behavior

This work aimed to determine the influence of two hydrogels (alginate, alginate-di-aldehyde (ADA)/gelatin) on the mechanical strength of microporous ceramics, which have been loaded with these hydrogels. For this purpose, the compressive strength was determined using a Zwick Z005 universal testing machine. In addition, the degradation behavior according to ISO EN 10993-14 in TRIS buffer pH 5.0 and pH 7.4 over 60 days was determined, and its effects on the compressive strength were investigated. The loading was carried out by means of a flow-chamber. The weight of the samples (manufacturer: Robert Mathys Foundation (RMS) and Curasan) in TRIS solutions pH 5 and pH 7 increased within 4 h (mean 48 ± 32 mg) and then remained constant over the experimental period of 60 days. The determination surface roughness showed a decrease in the value for the ceramics incubated in TRIS compared to the untreated ceramics. In addition, an increase in protein concentration in solution was determined for ADA gelatin-loaded ceramics. The macroporous Curasan ceramic exhibited a maximum failure load of 29 ± 9.0 N, whereas the value for the microporous RMS ceramic was 931 ± 223 N. Filling the RMS ceramic with ADA gelatin increased the maximum failure load to 1114 ± 300 N. The Curasan ceramics were too fragile for loading. The maximum failure load decreased for the RMS ceramics to 686.55 ± 170 N by incubation in TRIS pH 7.4 and 651 ± 287 N at pH 5.0.     

A First-Principles Study of the Cu-Containing β″ Precipitates in Al-Mg-Si-Cu Alloy

The nanostructured β″ precipitates are critical for the strength of Al-Mg-Si-(Cu) aluminum alloys. However, there are still controversial reports about the composition of Cu-containing β″ phases. In this work, first-principles calculations based on density functional theory were used to investigate the composition, mechanical properties, and electronic structure of Cu-containing β″ phases. The results predict that the Cu-containing β″ precipitates with a stoichiometry of Mg_4+xAl_2−xCuSi₄ (x = 0, 1) are energetically favorable. As the concentration of Cu atoms increases, Cu-containing β″ phases with different compositions will appear, such as Mg₄AlCu₂Si₄ and Mg₄Cu₃Si₄. The replacement order of Cu atoms in β″ phases can be summarized as one Si3/Al site → two Si3/Al sites → two Si3/Al sites and one Mg1 site. The calculated elastic constants of the considered β″ phases suggest that they are all mechanically stable, and all β″ phases are ductile. When Cu atoms replace Al atoms at Si3/Al sites in β″ phases, the values of bulk modulus (B), shear modulus (G), and Young’s modulus (E) all increase. The calculation of the phonon spectrum shows that Mg_4+xAl_2−xCuSi₄ (x = 0, 1) are also dynamically stable. The electronic structure analysis shows that the bond between the Si atom and the Cu atom has a covalent like property. The incorporation of the Cu atom enhances the electron interaction between the Mg2 and the Si3 atom so that the Mg2 atom also joins the Si network, which may be one of the reasons why Cu atoms increase the structure stability of the β″ phases.     

Improving the Mechanical Response of Al–Mg–Si 6082 Structural Alloys during High-Temperature Exposure through Dispersoid Strengthening

The feasibility and efficacy of improving the mechanical response of Al–Mg–Si 6082 structural alloys during high temperature exposure through the incorporation of a high number of α-dispersoids in the aluminum matrix were investigated. The mechanical response of the alloys was characterized based on the instantaneous high-temperature and residual room-temperature strengths during and after isothermal exposure at various temperatures and durations. When exposed to 200 °C, the yield strength (YS) of the alloys was largely governed by β” precipitates. At 300 °C, β” transformed into coarse β’, thereby leading to the degradation of the instantaneous and residual YSs of the alloys. The strength improvement by the fine and dense dispersoids became evident owing to their complementary strengthening effect. At higher exposure temperatures (350–450 °C), the further improvement of the mechanical response became much more pronounced for the alloy containing fine and dense dispersoids. Its instantaneous YS was improved by 150–180% relative to the base alloy free of dispersoids, and the residual YS was raised by 140% after being exposed to 400–450 °C for 2 h. The results demonstrate that introducing thermally stable dispersoids is a cost-effective and promising approach for improving the mechanical response of aluminum structures during high temperature exposure.     

Massive Transformation in Titanium-Silver Alloys and Its Effect on Their Mechanical Properties and Corrosion Behavior

In order to investigate the relationship between phase/microstructure and various properties of Ti–xAg alloys, a series of Ti–xAg alloys with Ag contents ranging from 5 to 20 wt% were prepared. The microstructures were characterized using X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All of the Ti–xAg alloys showed a massive transformation from the β-Ti to α_m phase, which has a different crystal structure from that of the matrix phase, but it has the same composition as the matrix α-Ti phase. As a result of solid-solution strengthening of α-Ti and massive transformation phase, the Ti–xAg showed better mechanical properties than the commercially pure titanium (cp-Ti). Electrochemical results showed that the Ti–xAg alloys exhibited improved corrosion resistance and oxidation resistance than cp-Ti.     

Effect of Nanoparticle Size on the Mechanical Strength of Ni–Graphene Composites

The effect of the size of nickel nanoparticles on the fabrication of a Ni–graphene composite by hydrostatic pressure at 0 K followed by annealing at 1000 and 2000 K is studied by molecular dynamics simulation. Crumpled graphene, consisting of crumpled graphene flakes interconnected by van der Waals forces is chosen as the matrix for the composite and filled with nickel nanoparticles composed of 21 and 47 atoms. It is found that the main factors that affect composite fabrication are nanoparticle size, the orientation of the structural units, and temperature of the fabrication process. The best stress–strain behavior is achieved for the Ni/graphene composite with Ni47 nanoparticle after annealing at 2000 K. However, all of the composites obtained had strength property anisotropy due to the inhomogeneous distribution of pores in the material volume.     

Cross-α/β polymorphism of PSMα3 fibrils

The formation of ordered cross-β amyloid protein aggregates is associated with a variety of human disorders. While conventional infrared methods serve as sensitive reporters of the presence of these amyloids, the recently discovered amyloid secondary structure of cross-α fibrils presents new questions and challenges. Herein, we report results using Fourier transform infrared spectroscopy and two-dimensional infrared spectroscopy to monitor the aggregation of one such cross-α–forming peptide, phenol soluble modulin alpha 3 (PSMα3). Phenol soluble modulins (PSMs) are involved in the formation and stabilization of Staphylococcus aureus biofilms, making sensitive methods of detecting and characterizing these fibrils a pressing need. Our experimental data coupled with spectroscopic simulations reveals the simultaneous presence of cross-α and cross-β polymorphs within samples of PSMα3 fibrils. We also report a new spectroscopic feature indicative of cross-α fibrils.

Amyloids are elongated fibers of proteins or peptides typically composed of stacked cross β-sheets (1, 2). Self-assembling amyloids are notorious for their involvement in human neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases (1, 2). Phenol soluble modulins (PSMs) are amyloid peptides secreted by the bacteria Staphylococcus aureus (S. aureus) (3–5). Of the PSM family, PSMα3 is of recent interest due to its unique secondary structure upon fibrillation. Whereas other PSM variants undergo conformational changes with aggregation, the α-helical PSMα3 peptide retains its secondary structure while stacking in a manner reminiscent of β-sheets, forming what has been termed cross-α fibrils (3, 4, 6). Although “α-sheet” amyloid fibrils have been previously observed in two-dimensional infrared (2DIR) (7) and associated with PSMs (8), the novel cross-α fibril is distinct from that class of structures. To avoid confusion between these two similarly named but distinct secondary structures, a comparison between the α-sheet domain in cytosolic phosphatase A2 (9) (Protein Data Bank [PDB] identification:1rlw) (10) and cross-α fibrils adopted by PSMα3 (PDB ID:5i55) (3) has been highlighted in SI Appendix, Fig. S1. Interestingly, shorter terminations of PSMα3 have been shown to exhibit β-sheet polymorphs (11). The proposed cross-α fibril structure of the full-length PSMα3 peptide has been confirmed with X-ray diffraction and circular dichroism (4). The present study aims to further characterize these fibrils with linear and nonlinear infrared spectroscopies.S. aureus is an infectious human pathogen with the ability to form communities of microorganisms called biofilms that hinder traditional treatment methods (12–14). PSMs contribute to inflammatory response and play a crucial role in structuring and detaching biofilms (11, 12, 14). While biofilm growth requires the presence of multiple PSMs (14, 15), Andreasen and Zaman have demonstrated that PSMα3 acts as a scaffold, seeding the amyloid formation of other PSMs (5). To effectively inhibit S. aureus biofilm growth, a better understanding of PSMα3 aggregation is needed.The α-helical structure of PSMα3 (12) presents a challenge for probing the vibrational modes and secondary structure of both the monomer and the fibrils. While IR spectroscopy has been used extensively to characterize β-sheets (16–19), the spectral features associated with α-helices are difficult to distinguish from those of the random coil secondary structure (20, 21). This limitation has left researchers to date with an incomplete picture of the spectroscopic features unique to cross-α fibers. The present work combines a variety of 2DIR methods to remove these barriers and probe the active infrared vibrational modes of cross-α fibers.The full-length, 22-residue PSMα3 peptide was synthesized and prepared for aggregation studies following reported methods (3, 4, 11). A total of 10 mM PSMα3 was incubated in D₂O at room temperature over 7 d. These data were compared to the monomer treated under similar conditions. Monomeric samples were prepared at a significantly lower concentration of 0.5 mM to prevent aggregation. Fiber formation was confirmed by transmission electron microscopy (see SI Appendix, Fig. S2 for details). Fourier transform infrared (FTIR) spectra were taken for both the fibrils in solution as well as the low concentration monomers. Spectroscopic simulations of the PSMα3 monomer and fibers were performed on previously reported PDB structures (PDB identification: 5i55) (3) (Fig. 1).Open in a separate windowFig. 1.PDB structures of PSMα3 (A) monomers and (B) cross-α fibers extended along the screw axis. (C) FTIR spectra of 0.5 mM monomeric PSMα3 (blue) compared to the 10 mM PSMα3 fibril (red) in D₂O upon aggregation.     

Effect of Minor Er Additions on the Microstructures and Mechanical Properties of Cast Al-Cu-Mg-Ag Alloys

The microstructures and mechanical properties of novel cast Al-Cu-Mg-Ag alloys with and without minor additions of Er (0.09 and 0.2 wt %) are investigated by Vickers hardness tests, tensile tests, optical metallographic examination, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results reveal that the Er addition decreases the hardness value of peak-aged Al-Cu-Mg-Ag alloy but has little influence on the time required for achieving the peak aging condition. Meanwhile, the Ω phase is suppressed in Er-added alloys, leading to a lower tensile strength at room temperature, which causes the (Mg, Ag, Er, V, Ti)-rich phase in the matrix in Er-added alloys. This blocky phase consumes available Mg and Ag atoms for Ω nucleation, leading to the low number density of Ω plates. The strength properties of Er-added alloys at 300 °C are found to be enhanced, which benefits from the pinning effect of the Al₈Cu₄Er phase on grain boundaries. Meanwhile, the brittle fracture of Er-added alloys at room temperature is directly associated with the Al₈Cu₄Er phase and the blocky (Mg, Ag, Er, V, Ti)-rich phase, which acts as the source of microcracks during deformation. In addition, no obvious grain refinement effect can be observed in Er-added alloys.     

Effect of Heat Treatment on the Mechanical and Corrosion Properties of Mg–Zn–Ga Biodegradable Mg Alloys

Mg alloys have mechanical properties similar to those of human bones, and have been studied extensively because of their potential use in biodegradable medical implants. In this study, the influence of different heat treatment regimens on the microstructure and mechanical and corrosion properties of biodegradable Mg–Zn–Ga alloys was investigated, because Ga is effective in the treatment of disorders associated with accelerated bone loss. Solid–solution heat treatment (SSHT) enhanced the mechanical properties of these alloys, and a low corrosion rate in Hanks’ solution was achieved because of the decrease in the cathodic-phase content after SSHT. Thus, the Mg–4 wt.% Zn–4 wt.% Ga–0.5 wt.% Y alloy after 18 h of SSHT at 350 °C (ultimate tensile strength: 207 MPa; yield strength: 97 MPa; elongation at fracture: 7.5%; corrosion rate: 0.27 mm/year) was recommended for low-loaded orthopedic implants.     

Simulation of the θ′ Precipitation Process with Interfacial Anisotropy Effects in Al-Cu Alloys

The effects of anisotropic interfacial properties and heterogeneous elasticity on the growth and ripening of plate-like θ′-phase (Al₂Cu) in Al-1.69 at.% Cu alloy are studied. Multi-phase-field simulations are conducted and discussed in comparison with aging experiments. The precipitate/matrix interface is considered to be anisotropic in terms of its energy and mobility. We find that the additional incorporation of an anisotropic interfacial mobility in conjunction with the elastic anisotropy result in substantially larger aspect ratios of the precipitates closer to the experimental observations. The anisotropy of the interfacial energy shows comparably small effect on the precipitate’s aspect ratio but changes the interface’s shape at the rim. The effect of the chemo-mechanical coupling, i.e., the composition dependence of the elastic constants, is studied as well. We show that the inverse ripening phenomenon, recently evidenced for δ’ precipitates in Al-Li alloys (Park et al. Sci. Rep. 2019, 9, 3981), does not establish for the θ′ precipitates. This is because of the anisotropic stress fields built around the θ′ precipitates, stemming from the precipitate’s shape and the interaction among different variants of the θ′ precipitate, that disturb the chemo-mechanical effects. These results show that the chemo-mechanical effects on the precipitation ripening strongly depend on the degree of sphericity and elastic isotropy of the precipitate and matrix phases.