Cu-rich Regions Research Articles

Study on the damage of Zr63.5Cu23Al9Fe4.5 amorphous and crystalline alloys by Fe, He ions beam irradiation

In order to study the physical mechanism of the effect of complex fusion irradiation environment on Zr-based amorphous alloys, simultaneous irradiation with Fe and He ions was performed on Zr63.5Cu23Al9Fe4.5 amorphous and crystalline alloys at room temperature. Single Fe ions irradiation and single He ions irradiation were used for comparison to investigate the influence of synergistic effects as well as intrinsic structural differences on irradiation-induced microstructural evolution and mechanical properties. It was been found that the irradiated amorphous alloys maintained its amorphous structure without nanocrystallization or elemental segregation. However, the irradiated region of the crystalline alloys experienced full amorphization, forming amorphous structure with bright contrast (Al-rich) and dark contrast (Cu-rich or Fe-rich). Under single He ions irradiation and simultaneous Fe+He ions irradiation conditions, He bubbles generated in both amorphous and crystalline alloys, where He bubbles in amorphous alloys distributed homogeneously, while the Cu-rich region of crystalline alloys exhibited larger sizes of He bubbles. Compared to single He ions irradiation, the size of He bubbles was larger, the atomic arrangement was more disordered (for amorphous alloys) and the element distribution was more homogeneous (for crystalline alloys) after simultaneous irradiation. Compared to single Fe ions irradiation, simultaneous irradiation induced slightly greater swelling. After irradiation, obvious softening was observed in both alloys, and the hardness of amorphous alloys was as follows: unirradiated > single He ions irradiation ≈ single Fe ions irradiation ≈ simultaneous Fe+He ions irradiation, while that of crystalline alloys was as follows: unirradiated > single He ions irradiation > single Fe ions irradiation ≈ simultaneous Fe+He ions irradiation. The serrated flow behavior of amorphous alloys weakened and the deformation was more homogeneous. As a result of irradiation-induced amorphization, serrated flow phenomenon also occurred in crystalline alloys, however, this type of inhomogeneous amorphous structure showed much weaker serrated flow behavior than the homogeneous amorphous structure. This study provides a deeper understanding of the irradiation damage mechanism of Zr-based amorphous alloys in complex irradiation environments.

Morphological Characteristics of W/Cu Composite Nanoparticles with Complex Phase Structure Synthesized via Reactive Radio Frequency (RF) Thermal Plasma

The W/Cu binary system is characterized by its mutual insolubility and excellent wettability, making W/Cu composite materials ideal for managing thermal and electrical properties in electronic components. To optimize material properties, control over the microstructure is crucial, and nanocomposites with uniform dispersion offer significant advantages. In this study, W/Cu composite nanoparticles were synthesized by feeding a blended feedstock of tungsten trioxide (WO3) micro-powder and cupric oxide (CuO) micro-powder into a reactive radio frequency (RF) argon–hydrogen thermal plasma system. Cu-coated W nanocomposite particles were obtained through the vaporization, reduction, and condensation processes. The resulting nanocomposite particles were composed of body-centered cubic (BCC) α-W, A15 β-W, and face-centered cubic (FCC) Cu phases, with a chemical composition closely matching theoretical calculations. The phase evolution and morphological changes of the synthesized particles were analyzed as a function of heat treatment temperatures up to 1000 °C in a reducing atmosphere. Up to 600 °C, the phase composition and morphology remained stable. At 800 °C, localized diffusion and coalescence of Cu led to the formation of particulate Cu, and a significant phase transformation from metastable β-W to α-W was observed. Additionally, extensive Cu segregation due to long-range diffusion resulted in distinct Cu-rich and Cu-depleted regions. In these regions, notable sintering of W particles and the complete disappearance of β-W occurred. The results showed that the temperature-dependent redistribution of Cu plays a crucial role in the phase transformation of W and the morphology of W/Cu composite particles.

Fabrication of porous high-entropy Mn-Fe-Co-Ni-Cu-Zn alloys by vapor phase dealloying

Porous multicomponent 3d transition-metal (TM) alloys were fabricated by eliminating Zn from rapidly quenched ribbons with distinct compositions, TM7Zn93 and TM4Zn96 (TM – a mixture of Mn, Fe, Co, Ni, and Cu) using vapor phase dealloying (VPD). Phase composition and microstructure of the ribbons in an as-quenched state and resulting porous materials were investigated in detail by S/TEM-EDS, XRD, SEM, and EDXRF methods. In the as-quenched state, the majority of the alloy is composed of the CoZn13 type structure (C2/m space group). Atomically resolved EDS mapping clarified the chemical site occupancy of the TM elements in the structure. The resulting fabricated porous high-entropy alloys (HEA) have a spongy microstructure with a bimodal pore size and their surface area was estimated at 2–4 m2/g. Analysis of pore size distribution revealed their macro-mesoporous structure. The formation of the solid solution with the FCC (Fm3̅m space group) crystal structure during VPD was confirmed by XRD data. STEM-EDS analysis revealed the existence of several FCC solid solution phases within the porous HEA. A nanoscale elemental/phase separation into Co- and Cu-rich FCC solid solution regions with coherent interfaces across the individual crystalline grains has been found. A general route to prepare porous HEA using rapid solidification and vapor phase dealloying has been discussed.

Tailored gradient nanocrystallization in bulk metallic glass via ultrasonic vibrations

To advance materials with superior performance, the construction of gradient structures has emerged as a promising strategy. In this study, a gradient nanocrystalline-amorphous structure was induced in Zr46Cu46Al8 bulk metallic glass (BMG) through ultrasonic vibration (UV) treatment. Applying a 20 kHz ultrasonic cyclic loading in the elastic regime, controllable gradient structures with varying crystallized volume fractions can be achieved in less than 2 s by adjusting the input UV energy. In contrast to traditional methods of inducing structural gradients in BMGs, this novel approach offers distinct advantages: it is exceptionally rapid, requires minimal stress, and allows for easy tuning of the extent of structural gradients through precise adjustment of processing parameters. Nanoindentation tests reveal higher hardness near the struck surface, attributed to a greater degree of nanocrystal formation, which gradually diminishes with depth. As a result of the gradient dispersion of nanocrystals, an increased plasticity was found after UV treatment, characterized by the formation of multiple shear bands. Microstructural investigations suggest that UV-induced nanocrystallization originates from local atomic rearrangements in phase-separated Cu-rich regions with high diffusional mobility. Our study underscores the tunability of structural gradients and corresponding performance improvements in BMGs through ultrasonic energy modulation, offering valuable insights for designing advanced metallic materials with tailored mechanical properties.

Anomalous two-step repair mechanism of Al–Cu alloy regulated by the surroundings during E-beam irradiation

Understanding the repair mechanisms of defects is essential for gaining insight into improving the quality and enhancing the performance of materials. While new structures and elemental segregation always exist around defects, the influence of the surroundings on the repair mechanism has rarely been investigated on the atomic scale. Here, by tracking the morphological and microstructural evolution of Al2Cu nanopores with and without Cu-rich phases in the vicinity under electron beam irradiation, our in-situ transmission electron microscopy (TEM) study revealed a surrounding-dependent repair behavior. In contrast to the Al2Cu nanopores without Cu-rich neighborhoods, which display an isotropically shrinking from all directions, the Al2Cu nanopores with Al4Cu9 nearby exhibit an anomalous two-step repair mechanism. First, new Al4Cu9 structures nucleated from the Cu-rich region and evolved to fill the nanopores. Second, Al4Cu9 reacted with Al atoms and gradually transformed into Al2Cu. High-resolution TEM (HRTEM) images and strain maps demonstrate that the repair is imperfect as the eventual repaired region contains both Al4Cu9 and Al2Cu. This is caused by the simultaneous sputtering and depositing effects of electron beams (E-Beam). Our findings provide critical insights into the modulatory function of surroundings on the nanopore repair mechanism.

Metal Scrap to Hydrogen: Manufacture of Hydroreactive Solid Shapes via Combination of Ball Milling, Cold Pressing, and Spark Plasma Sintering.

Two sorts of tablets were manufactured from ball-milled powder (aluminum scrap and copper) by cold pressing and spark plasma sintering. Their microstructure, phase, and elemental compositions were investigated via scanning electron microscopy, X-ray diffraction analysis, and energy-dispersive X-ray spectroscopy. New phases, Al2Cu and MgCuAl2, were detected in the samples. Their microstructure was formed by welded scrap particles, the intermetallides, and Cu-rich regions located majorly along 'interparticle boundaries' and, to a lesser extent, within small, micro- and nanosized 'intraparticle spots'. The tablets were sealed with adhesive, so only the top surface was exposed to the environment, and tested in a chlorine aqueous solution for hydrogen generation performance. For both sample sorts, hydrogen yields of nearly 100% were achieved. The sintered tablets reacted faster than the cold-pressed ones: at 60, 70, and 80 °C, their entire 'conversion into hydrogen' took ~80, 40, and 30 min. vs. ~220, 100, and 70 min. The experimental kinetic curves were fitted with a contracting geometry equation, and those for the sintered samples were approximated with higher precision. The key effect of the additive was to enhance hydrogen evolution through the galvanic corrosion of Al in the regions adjacent to the intermetallic inclusions and Cu-rich spots.

Nucleation and growth of Cu6Sn5 during the aging process of Cu/Sn interface in electronic packaging-by in-situ TEM

The rapid nucleation of Cu6Sn5 during the soldering process, as well as its growth at the solid-state interface system (Cu/Sn) during chip service, present significant challenges. To study this, we introduced a small amount of Co element into the Cu-Sn system in order to reduce the formation energy of Cu6Sn5. Through transmission electron microscopy, we performed in situ observations of the nucleation and growth of Cu6Sn5 at the Cu/Sn solid phase interface. Our experimental findings confirm that the diffusion of Cu element at the interface plays a dominant role in the nucleation and growth process of Cu6Sn5. During this diffusion process, once the local concentration of Cu surpasses a threshold, Cu6Sn5 begins to nucleate around the Cu-rich region. The driving force behind this phase transition arises from two factors: non-uniformity of atomic flux at grain boundaries leading to stress accumulation, and localized bonding between a pair of valence electrons on Cu and adjacent Sn atoms, resulting in the formation of a shared orbital. Based on the curvature of the nucleation solid interface, three distinct growth modes have been observed: spiral growth, layer-layer growth, and island growth. These variations stem from changes in the dynamic mechanism associated with the morphology coefficient linked to the interface arc length. The nucleation and growth of Cu6Sn5 are governed by anisotropic attachment kinetics, with the growth process transitioning to diffusion-controlled continuous growth.

Impact of local chemical ordering on deformation mechanisms in single-crystalline CuNiCoFe high-entropy alloys: a molecular dynamics study

High-entropy alloys (HEAs), composed of multiple constituent elements with concentrations ranging from 5% to 35%, have been considered ideal solid solution of multi-principal elements. However, recent experimental and computational studies have demonstrated that complex enthalpic interactions among constituents lead to a wide variety of local chemical ordering (LCO) at lower temperatures. HEAs containing Cu typically decompose by forming of Cu-rich phases during annealing, thus affecting mechanical properties. In this study, CuNiCoFe HEA was chosen as a model with a tendency for Cu segregation at low temperatures. The formation of LCO and its impact on the deformation behaviors in the single-crystalline CuNiCoFe HEA were studied via molecular dynamics simulations. Our results demonstrate that CuNiCoFe HEA decomposes by Cu clustering, in agreement with prior experimental and computational studies, owing to insufficient configuration entropy to compete against the mixing enthalpy at lower temperatures. A softening in ultimate stress in the LCO models was observed compared to the random solid solution models. The softening is due to the lower unstable stacking fault energy, which determines the nucleation event of dislocations, thereby rationalizing the dislocation nucleation in the Cu-rich regions and the softening of the overall ultimate strength in the LCO models. Additionally, the inhomogeneous FCC–BCC transformation is closely associated with concentration inhomogeneity. CuNiCoFe HEA with LCO can be regarded as composites, consisting of clusters with different properties. Consequently, concentration inhomogeneity induced by LCO profoundly impacts the mechanical properties and deformation behaviors of the HEA. This study provides insights into the effect of LCO on the mechanical properties of CuNiCoFe HEAs, which is crucial for developing HEAs with tailored properties for specific applications.

Unlocking the Potential of CuAgZr Metallic Glasses: A Comprehensive Exploration with Combinatorial Synthesis, High-Throughput Characterization, and Machine Learning.

In this work, the CuAgZr metallic glasses (MGs) are investigated, a promising material for biomedical applications due to their high strength, corrosion resistance, and antibacterial activity. Using an integrated approach of combinatorial synthesis, high-throughput characterization, and machine learning (ML), the mechanical properties of CuAgZr MGs are efficiently explored. The investigation find that post-deposition oxidation in inter-columnar regions with looser packing causes high oxygen content in Cu-rich regions, significantly affecting the alloys' mechanical behavior. The study also reveals that nanoscale structural features greatly impact plastic yielding and flow in the alloys. ML algorithms are tested, and the multi-layer perceptron algorithm produced satisfactory predictions for the alloys' hardness of untested alloys, providing valuable clues for future research. The work demonstrates the potential of using combinatorial synthesis, high-throughput characterization, and ML techniques to facilitate the development of new MGs with improved strength and economic feasibility.

Microstructure and mechanical properties of wire arc additive manufactured ZL205A alloy

The evolution of grain structure, precipitates and mechanical properties of the ZL205A alloy prepared by wire arc additive manufacturing were investigated. The results show that the as-deposited alloy consists of equiaxed and columnar grains in the bottom region. As the deposition height increases, the alloy mainly consists of equiaxed grains. The evolution of columnar to equiaxed grains is explained by the solidification theory. The needle-like θ′-Al2Cu precipitates in Cu-rich regions surrounding the α-Al+θ-Al2Cu eutectics. As the part deposited first is subjected to multiple cycles of heating by the subsequently deposited layers, the volume fraction and average size of θ′ precipitates gradually decrease with the increase of deposition heights. The microhardness of the as-deposited alloy fluctuates in the range of 74.6–84.5 HV. The mechanical properties of the horizontal specimens at different heights are affected by the combination of grain structure, precipitates and pores, and that of the specimens in the middle region are optimal. The mechanical properties of the horizontal and vertical specimens show isotropic. Attributed to the grain boundary strengthening and precipitation strengthening, the yield strength (132.9 MPa) and elongation (15.9%) of the as-deposited alloy are approximately 31.3% and 211.8% higher than that of the as-cast alloy, respectively.

Synthesis of Tungsten Carbides in a Copper Matrix by Spark Plasma Sintering: Microstructure Formation Mechanisms and Properties of the Consolidated Materials.

In this study, the synthesis of tungsten carbides in a copper matrix by spark plasma sintering (SPS) is conducted and the microstructure formation mechanisms of the composite materials are investigated. The reaction mixtures were prepared by the high-energy mechanical milling (MM) of W, C and Cu powders. The influence of the MM time and SPS temperature on the tungsten carbide synthesis in an inert copper matrix was analyzed. It was demonstrated that the milling duration is a critical factor for creating the direct contacts between the W and C reactants and increasing the reactive transformation degree. A WC-W2C-Cu composite was fabricated from the W-C-3Cu powder mixture milled for 10 min and subjected to SPS at a temperature of 980 °C for 5 min. The formation of unconventional microstructures with Cu-rich regions is related to inter-particle melting during SPS. The WC-W2C-Cu composite showed a promising combination of mechanical and functional properties: a hardness of 300 HV, an electrical conductivity of 24% of the International Annealed Copper Standard, a residual porosity of less than 5%, a coefficient of friction in pair with a WC-6Co counterpart of 0.46, and a specific wear rate of the material of 0.52 × 10-5 mm3 N-1 m-1.

Co-evolution of the atomic/nano scale structural heterogeneities and magnetic properties of Fe-Si-B-Cu metallic glass during relaxation with composition fluctuations

The metallic glass (MG) exhibits composition fluctuation or chemical heterogeneity during relaxation. However, the influence of this factor on the evolution of the intrinsic structural heterogeneity of MGs remains unclear. In this study, we systematically examined the co-evolution between atomic and nano-scale structural heterogeneities of Fe-Si-B-Cu MGs during relaxation. We discovered that, despite some degree of fluctuation in composition during the relaxation of Fe-Si-B-Cu MGs, it does not prevent the reduction of structural heterogeneities at the atomic/nano scale. The results demonstrate an overall increase in the number density and number of types of densely packed clusters with a high degree of local five-fold symmetry and a decrease in the number density and number of types of loosely packed clusters with a low degree of local five-fold symmetry. Furthermore, a certain degree of compositional fluctuation during relaxation of Fe-Si-B-Cu MGs facilitates the formation of uniformly distributed Fe-rich regions and Cu-rich regions.

Solidification Microstructures in 3d-Transition Metal High Entropy Alloys with Cu Element

In this study, high-entropy alloys (HEAs) with Cu as the main constituent element were investigated, focusing on the distribution of Cu in the ingots. Based on the taxonomy of HEAs, those with Cu as the casting material were classified as (1) HEAs whose main constituent elements were 3d transition metals, such as Co, Cr, Fe, Mn, Ni, and Cu (3d-HEAs), and (2) high-entropy (HE) brasses based on the Cu-Zn alloy system and HE bronzes based on Cu-Sn and/or Cu-Al alloy systems. In the case of 3d-HEAs with Cu, the distribution of Cu in the ingots exhibited the following tendency: (1-1) segregation from the dendrite to the residual liquid, resulting in the formation of Cu-rich interdendritic regions in the ingots; (1-2) liquid-phase separation resulting in the formation of a Cu-rich liquid, which formed a macroscopically phase-separated structure; and (1-3) the dispersion of fine Cu precipitates embedded in the solid solution matrix.

Macroscopic tensile properties of AlxCoCrCuFeNi (x = 0.3 and 1) before and after heat treatment

The relationship between morphology (grain-size order) and mechanical properties of AlxCoCrCuFeNi (x = 0.3 and 1) was evaluated. Both alloys were prepared using the arc-melting method. Crystal structures with x = 0.3, face-centered cubic (FCC), and body-centered cubic (BCC) structures were observed for x = 1, the typical crystal structures of AlxCoCrCuFeNi. The alloys prepared via arc melting exhibited two different microstructures: a Cu-rich region (area I) and an equiatomic region (area II). Microstructures of the as-fabricated specimen were homogenized through heat treatment at 600 and 1000 °C for 5 h. Although the homogenization of the microstructure proceeded, areas I and II remained after the heat treatment. In particular, the area I composition was inconsistent with the predicted phase diagram. Tensile tests for these alloys revealed that the tensile strength of x = 1 (∼310–1100 MPa) is higher than that of x = 0.3 (∼320–660 MPa), whereas the fracture strain of x = 1 (∼0.03–0.09) is lower than that of x = 0.3 (∼0.06–0.26). These results indicate that the increase in Al content caused an increase in strength and brittle fracture because it also caused an increase in the formation of the BCC and B2 phases, which required higher stresses for the movement of dislocations than the FCC phase. Because the tensile properties of AlxCoCrCuFeNi are comparable to those of conventional alloys, such as Ti alloys and steels, a design with a moderate composition for stronger and tougher AlxCoCrCuFeNi is required to apply high entropy alloys to structural materials.

Microstructure evolution and shearing behaviour of δꞌ/θꞌ/δꞌ precipitates in an aged Al-Cu-Li-Mg aluminium alloy

We report here on the microstructure evolution and the strengthening behaviour of the δꞌ/θꞌ/δꞌ precipitates in the aged Al-Cu-Li-Mg aluminium alloy by atomic high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and in-situ TEM compression straining. On the chosen zone axis, atomic HAADF-STEM images reveal the in-situ microstructure evolution of the δꞌ/θꞌ/δꞌ precipitates. A monolayer GP(θꞌ) zone, grown on the (001)Al plane, evolves from the Cu-rich region. After the transformation of the GP(θꞌ) zone to θꞌ phase, the boundaries of the θꞌ phase are coated with the δꞌ phases, forming a matured δꞌ/θꞌ/δꞌ precipitate. Additionally, the growth of δꞌ phases on the two sides of θꞌ is not affected by the inclined boundaries of θꞌ and the hard impingement of the thin T1 precipitate. During the in-situ TEM compression straining on the peak-aged nanopillar, the deviated slip band structures and the large displacement bursts are presumably associated with the dislocation-precipitate interaction of the T1 and δꞌ/θꞌ/δꞌ precipitates. Furthermore, evidence from atomic HAADF-STEM images shows that dislocations can cut the δꞌ/θꞌ/δꞌ precipitate, producing the stacking fault layers within the θꞌ phase of the sheared δꞌ/θꞌ/δꞌ precipitate.

Shock compression and spall damage of dendritic high-entropy alloy CoCrFeNiCu

Plate impact experiments are conducted on a dendritic dual face-center cubic phase high-entropy alloy (HEA) CoCrFeNiCu, consisting of Cu-lean dendritic (DR) and Cu-rich interdendritic regions (ID). Free surface velocity histories are obtained along with microstructure characterizations. The Hugoniot equation of state and spall strength at different shock stresses are determined. Dislocation slip is the main deformation mode for CoCrFeNiCu HEA, and the dislocation density of the Cu-rich interdendritic regions increases more significantly during shock compression. Both ductile and brittle damage modes are observed. With increasing impact velocity, the Cu-rich interdendritic regions with severe strain localizations and more defects provide more damage nucleation sites. The spall strength increases firstly, reaches its maximum at a peak shock stress of 5.8 GPa, and then decreases. Molecular dynamics simulations reveal that the abnormal dependence of spall strength on peak shock stress is a result of strain localization and thermal softening in the Cu-rich regions.

Elucidating laser directed energy deposition based additive manufacturing of copper-stainless steel functionally graded material: Processing and material behavior

Copper (Cu)-stainless steel (SS 304L) multi-material is enduring research topic for various engineering applications such as tooling industry, aerospace, power-generation and cryogenic applications. Laser directed energy deposition (LDED) based additive manufacturing is a one of the promising technologies for fabricating Cu-SS multi-material component. However, LDED of Cu-SS is difficult due to the significant difference in thermo-physical properties and poor solubility of Cu and Fe. One of the methods to overcome this issue is adopting a functionally graded material (FGM) approach. In this pretext, the fabrication of Cu-SS FGM using the LDED process is taken up in the present study with three different Cu compositional grading approaches, such as direct (GD100Cu), 50 % (GD50Cu) and 20 % (GD20Cu). The LDED process windows for single tracks and bulk deposition of Cu-SS FGM are identified by varying the laser power, scan speed and composition of Cu and SS304L. Subsequently, the identified process window is used to deposit bulk structures of Cu-SS FGM. The LDED-built Cu-SS FGMs are characterized in terms of build quality, chemical composition, microstructural evolution and mechanical behavior. Microscopic analysis reveals, the defect-free deposition of GD100Cu and GD50Cu, at identified process parameters. For GD20Cu, the micro-crack formation in the graded region and inter-layer porosity in the Cu-rich region are two competing phenomenon, and it is observed that layer-wise increase in laser power and interlayer delay leads to minimum crack density and lower porosity. Further, increase in Cu content leads to significant change in microstructural morphology from columnar dendrites to fine cellular morphology. In Cu-SS FG structures, the chemical composition and mechanical properties are found to be changing gradually. Further, obtained ultimate tensile strength (UTS) of GD100Cu and GD50Cu is found higher than GD20Cu and the mode of failure is found to be ductile. The improved UTS in GD100Cu and GD50Cu in comparison with pure Cu arises due to formation of nano precipitate of Cu in the inter-dendritic zone of Fe rich phase. This establishes the suitability of LDED for building FG Cu-SS components at GD50Cu over GD20Cu.

Primary and secondary phase separation in Cu–Zr–Al bulk metallic glass by control of quenching conditions

Here, we report primary and secondary nanoscale phase separation in Cu46Zr46Al8 (at.%) bulk metallic glass (BMG) achieved by altering the casting temperature. The BMG rods were cast by using the melting currents of 160 A and 220 A which provide, respectively, higher and lower cooling rates. The transmission electron microscopy and energy-dispersive X-ray analysis revealed that the higher cooling rate conditions brings a primary phase separation of nanoscale Cu-rich amorphous regions which are evenly dispersed in the Cu-depleted amorphous matrix phase. However, lower cooling rates results in a bimodal microstructure comprising coarsened primary-separated nanograins and very fine secondary-separated nanograins throughout the amorphous matrix containing nanocrystals of smaller than 5 nm in size. This unique microstructure developed under lower cooling rates gives lower relaxation enthalpy, higher short-range ordering, and enhanced strain-hardening. Our study emphasizes the significant role of casting temperature on controlling the morphology of nanoscale phase separation in BMGs.

PTBP1 controls intestinal epithelial regeneration through post-transcriptional regulation of gene expression.

The intestinal epithelial regeneration is driven by intestinal stem cells under homeostatic conditions. Differentiated intestinal epithelial cells, such as Paneth cells, are capable of acquiring multipotency and contributing to regeneration upon theloss of intestinal stem cells. Paneth cells also support intestinal stem cell survival and regeneration. We report here that depletion of an RNA-binding protein named polypyrimidine tract binding protein 1 (PTBP1) in mouse intestinal epithelial cells causes intestinal stem cell death and epithelial regeneration failure. Mechanistically, we show that PTBP1 inhibits neuronal-like splicing programs in intestinal crypt cells, which is critical for maintaining intestinal stem cell stemness. This function is achieved at least in part through promoting the non-productive splicing of its paralog PTBP2. Moreover, PTBP1 inhibits the expression of an AKT inhibitor PHLDA3 in Paneth cells and permits AKT activation, which presumably maintains Paneth cell plasticity and function in supporting intestinal stem cell niche. We show that PTBP1 directly binds to a CU-rich region in the 3' UTR of Phlda3, which we demonstrate to be critical for downregulating the mRNA and protein levels of Phlda3. Our results thus reveal the multifaceted in vivo regulation of intestinal epithelial regeneration by PTBP1 at the post-transcriptional level.

On the Evolution of Nano-Structures at the Al-Cu Interface and the Influence of Annealing Temperature on the Interfacial Strength.

Molecular dynamics (MD) simulations are invoked to simulate the diffusion process and microstructural evolution at the solid–liquid, cast-rolled Al–Cu interfaces. K-Means clustering algorithm is used to identify the formation and composition of two types of nanostructural features in the Al-rich and Cu-rich regions of the interface (i.e., the intermetallic Al2Cu near the Al-rich interface and the intermetallic Al4Cu9 near the Cu-rich interface). MD simulations are also used to assess the effects of annealing temperature on the evolution of the compositionally graded microstructural features at the Al–Cu interfaces and to characterize the mechanical strength of the Al–Cu interfaces. It is found that the failure of the Al–Cu interface takes place at the Al-rich side of the interface (Al2Cu–Al) which is mechanically weaker than the Cu-rich side of the interface (Cu–Al4Cu9), which is also verified by the nanoindentation studies of the interfaces. Centrosymmetry parameter analyses and dislocation analyses are used to understand the microstructural features that influence deformation behavior leading to the failure of the Al–Cu interfaces. Increasing the annealing temperature reduces the stacking fault density at the Al–Cu interface, suppresses the generation of nanovoids which are precursors for the initiation of fracture at the Al-rich interface, and increases the strength of the interface.