Direct Casting Research Articles

A simple route for preparation of TRIP-assisted Si–Mn steel with excellent performance using direct strip casting

A simple route for preparation of TRIP-assisted Si–Mn steel with excellent performance using direct strip casting

Shape memory and superelasticity in polycrystalline ceria-stabilized zirconia honeycombs

Shape-memory and superelastic materials undergo a reversible martensitic transformation that allows them to return to their original state after deformation, either on the application of heat or the removal of stress. While zirconia-based ceramics can undergo this martensitic transformation, the volume expansion that accompanies the transformation can cause mismatched stresses at grain boundaries in polycrystalline systems, leading to cracking and premature failure. To increase the surface area to volume ratio, and thus circumvent this premature failure, this work uses directional freeze casting to incorporate columnar pores into ceria-stabilized zirconia ceramics, thereby producing honeycomb-like structures. These ceramics can be subjected to stresses up to 45 MPa and, depending on the ceria content, exhibit either shape-memory or superelastic behavior under uniaxial compression. The studies highlight the use of X-ray diffraction and Raman spectroscopy to track the extent of the martensitic transformations over different collection volumes and explore that behavior over multiple cycles. Furthermore, in-situ Raman spectroscopy coupled with conventional uniaxial compression and diamond anvil cell loading confirm, for the first time, superelastic behavior in bulk-scale, polycrystalline, porous zirconia ceramics.

Development of High Temperature Materials for Aero Engine Hot End Components: An Overview

The present paper overviews the development of materials and superalloys for aero engine hot end components to meet the increasing trend of turbine inlet temperature. Requirement of higher and higher thrust is steadily increasing the turbine inlet temperature and the development of nickel-chromium superalloys in early 1940s could not fulfil the material capability for long. Various nickel-base superalloys developed in 1950s and 1960s could increase the life of hot end components by retaining strength and resisting oxidation at extreme temperatures. In the 1960s and 1970s, with almost stagnation in high temperature alloy development, metallurgists changed focus from alloy chemistry to alloy processing which evolved the directional solidification and single crystal casting technologies. At present, almost all fighter class engines and high bypass commercial engines are using nickel and cobalt base superalloys for hot end components and single crystal superalloys particularly for turbine blades. This paper covers the developmental phases of superalloys and casting technologies for engine hot end components. This paper will be an invaluable asset for the researchers as well as for designers of future gas turbine engines.

Anisotropic cellulose-based phase change aerogels for acoustic-thermal energy conversion and management

Porous materials are usually used as sound-absorbing materials to alleviate noise pollution problems. However, the heat energy conversed from the acoustic energy is wasteful. Herein, anisotropic cellulose-based phase change aerogels (MXene/CNF-C/PEG aerogels) are fabricated by facile directional freeze casting method with anisotropic porous structure, efficient sound wave absorption, acoustic-thermal conversion and thermal management capability. MXene/CNF-C/PEG aerogels with shape stability are formed by hydrogen bonding forces between carboxylated cellulose nanofibers (CNF-C) and PEG without chemical crosslinking. The addition of MXene not only increases thermal conductive performance to 150 % but also enhances acoustic-thermal conversion ability effectively. Moreover, the directional porous MXene/CNF-C/PEG aerogels (DMCPs) possess high energy storage density (143.0 J/g) and acoustic-thermal conversion performance, which open up broad application prospect in the field of acoustic to heat energy conversion and storage.

Microstructure and mechanical behavior in a spherical L12 nanoprecipitates strengthened Ni35Co27.5Cr27.5Al5Ti5 high-entropy alloy fabricated by direct casting and heat treatment

Intricate thermomechanical processing (TMP) including casting, homogenization, cold rolling, annealing and aging, has been widely used to achieve L12-strengthened CoCrNi-based medium- and high-entropy alloys (MEAs/HEAs). However, a large number of parts are usually manufactured by direct casting. We fabricated a non-equiatomic Ni35Co27.5Cr27.5Al5Ti5 HEA consisting of spherical L12 nanoprecipitates and FCC matrix using casting, homogenization and aging. Notably, both the homogenized and aged Ni35Co27.5Cr27.5Al5Ti5 HEA samples exhibit equiaxed grains, with the latter showcasing uniformly distributed spherical L12 nanoprecipitates in the FCC matrix. The average size and volume fraction of these nanoprecipitates in the aged HEA are ∼10.9 nm and ∼41.9 vol%, respectively. Mechanical testing reveals remarkable improvements in the aged HEA, with a yield strength of ∼916 MPa, an ultimate tensile strength of ∼1220 MPa, and a total elongation of ∼21.5 %. The observed enhancement is primarily attributed to precipitation strengthening mechanism. Digital image correlation (DIC) analysis of tensile deformation demonstrates uniform strain distribution in both the homogenized and aged HEA samples. In addition, electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) examinations unveil a complex interplay of deformation mechanisms, including multiple planar slip, dislocation shearing coherent L12 precipitates, superpartials, stacking fault (SF) networks, and Lomer-Cottrell (L-C) locks. These mechanisms collectively impede dislocation motion, thereby contributing to the excellent strain-hardening ability and outstanding strength-ductility synergy of the HEA.

Effects of squeeze casting on microstructure and mechanical properties of Al–5Cu–1Mn–0.3Ti alloy

In this work, the microstructure and mechanical properties of the Al–5Cu–1Mn–0.3Ti alloy prepared by different casting processes were investigated. The results showed that direct squeeze casting can further refine the grain and θ-Al2Cu phase, which is favourable to the uniform distribution of the θ-Al2Cu phase. The fluffy θ-Al2Cu/α-Al interface was caused by the severe pressure loss during the indirect squeeze casting process. The strength and elongation of direct squeeze casting alloy are 508 MPa and 18.5%, which are 40.3% and 123% higher than those of the alloys of indirect squeeze casting. The in situ tensile experiments revealed that the crack initiation mechanism of the indirect squeeze casting alloy is the debonding of the θ-Al2Cu phase at the grain boundaries.

Developing Porous Fibrin Scaffolds with Tunable Anisotropic Features to Direct Myoblast Orientation.

Functional regeneration of anisotropically aligned tissues such as ligaments, microvascular networks, myocardium, or skeletal muscle requires a temporal and spatial series of biochemical and biophysical cues to direct cell functions that promote native tissue regeneration. When these cues are lost during traumatic injuries such as volumetric muscle loss (VML), scar formation occurs, limiting the regenerative capacity of the tissue. Currently, autologous tissue transfer is the gold standard for treating injuries such as VML but can result in adverse outcomes including graft failure, donor site morbidity, and excessive scarring. Tissue-engineered scaffolds composed of biomaterials, cells, or both have been investigated to promote functional tissue regeneration but are still limited by inadequate tissue ingrowth. These scaffolds should provide precisely tuned topographies and stiffnesses using proregenerative materials to encourage tissue-specific functions such as myoblast orientation, followed by aligned myotube formation and recovery of functional contraction. In this study, we describe the design and characterization of novel porous fibrin scaffolds with anisotropic microarchitectural features that recapitulate the native tissue microenvironment and offer a promising approach for regeneration of aligned tissues. We used directional freeze-casting with varied fibrin concentrations and freezing temperatures to produce scaffolds with tunable degrees of anisotropy and strut widths. Nanoindentation analyses showed that the moduli of our fibrin scaffolds varied as a function of fibrin concentration and were consistent with native skeletal muscle tissue. Quantitative morphometric analyses of myoblast cytoskeletons on scaffold microarchitectures demonstrated enhanced cell alignment as a function of microarchitectural morphology. The ability to precisely control the anisotropic features of fibrin scaffolds promises to provide a powerful tool for directing aligned tissue ingrowth and enhance functional regeneration of tissues such as skeletal muscle.

Squeeze casting of 4032 aluminum alloy and the synergetic enhancement of strength and ductility via Al-Ti-Nb-B grain refiner

The 4032 aluminum alloy is a high-Si deformation aluminum alloy, that is commonly generated through forging due to the difficulties involved in its direct casting. In this work, the 4032 aluminum alloy is innovatively prepared via a squeeze casting process, and the Al-6Nb-1.5Ti-0.5B refining agent is incorporated to enhance its mechanical properties. A range of analytical techniques are subsequently employed to analyze the grain refinement mechanism of Al-6Nb-1.5Ti-0.5B under squeeze casting conditions. It was found that the microstructure of the aged 4032 aluminum alloy after refinement treatment was mainly composed of α-Al grains measuring <100 μm in size, in addition to a eutectic Si phase, that is accompanied by stacked dislocations and diffusely distributed Q′-Al5Cu2Mg8Si6 and θ′-Al2Cu phases. The yield strength of the alloy reached 340 MPa, its tensile strength was 404 MPa, and the elongation was 4.1 %. In the presence of the Al-6Nb-1.5Ti-0.5B refiner, the generation of nucleation cores (e.g., MAl3(M = Ti, Nb)) in the melt led to a significant reduction (∼50 %) in the α-Al grain size of the aged 4032 aluminum alloy (i.e., 95.1 ± 21.0 μm), compared with the standard alloy. After the T6 heat treatment of the refined 4032 aluminum alloy, the size of the precipitation phase was reduced by 36.8 %, and fine silicon particles with a spherical morphology and a more random distribution were observed. No obvious selective orientation was detected, and the fracture morphology improved significantly, thereby leading to a synergistic improvement in the strength and toughness of the alloy.

Influence of silicon and tramp elements on the high-temperature oxidation of steel in direct casting and rolling processes

Influence of silicon and tramp elements on the high-temperature oxidation of steel in direct casting and rolling processes

Designing interconnected passages by “legs-to-head” directional U-shape freeze casting to boost solar-driven self-pumping oil spill recovery

Solar-heating siphon-assisted oil recovery is promising as an eco-friendly strategy for oil spill mitigation due to its spontaneous, continuous, and renewable operation.

Achieving exceptional strength-ductility combination in a novel L12 nanoparticles-strengthened high-entropy alloy via conventional casting

A novel L12 precipitation-strengthened Co51.3Ni19.5Cr19Al6.4Ti3.4Nb0.4 medium-entropy alloy (MEA) with excellent combination of large ductility and high strength was prepared via direct casting. The coherent ultrafine L12 precipitates particles (∼30 nm) with a volume fraction of 65% formed uniformly in the FCC matrix after heat-treatment, which endows this newly-designed MEA with superior tensile properties, i.e., a yield strength of ∼710 MPa, an ultimate tensile strength of ∼1045 MPa and a uniform elongation of ∼31.3%, respectively. The blocking effect of ultra-fine L12 precipitates significantly contributes to the high strength of the Co51.3Ni19.5Cr19Al6.4Ti3.4Nb0.4 MEA. In addition, deformation-induced nano-spaced stacking-fault networks, nano-twins and high-density Lomer-Cottrell locks facilitate the high work-hardening capacity, leading to excellent tensile ductility. This alloy design strategy can potentially be applied to many other alloys and open new avenues for designing strong yet ductile materials for engineering applications.

3D Printing of Robust High-Performance Conducting Polymer Hydrogel-Based Electrical Bioadhesive Interface for Soft Bioelectronics.

Electrical bioadhesive interface (EBI), especially conducting polymer hydrogel (CPH)-based EBI, exhibits promising potential applications in various fields, including biomedical devices, neural interfaces, and wearable devices. However, current fabrication techniques of CPH-based EBI mostly focus on conventional methods such as direct casting, injection, and molding, which remains a lingering challenge for further pushing them toward customized practical bioelectronic applications and commercialization. Herein, 3D printable high-performance CPH-based EBI precursor inks are developed through composite engineering of PEDOT:PSS and adhesive ionic macromolecular dopants within tough hydrogel matrices (PVA). Such inks allow the facile fabrication of high-resolution and programmable patterned EBI through 3D printing. Upon successive freeze-thawing, the as-printed PEDOT:PSS-based EBI simultaneously exhibits high conductivity of 1.2 S m-1, low interfacial impedance of 20 Ω, high stretchability of 349%, superior toughness of 109kJ m-3, and satisfactory adhesion to various materials. Enabled by these advantageous properties and excellent printability, the facile and continuous manufacturing of EBI-based skin electrodes is further demonstratedvia 3D printing, and the fabricated electrodes display excellent ECG and EMG signal recording capability superior to commercial products. This work may provide a new avenue for rational design and fabrication of next-generation EBI for soft bioelectronics, further advancing seamless human-machine integration.

74 µm PEEK‐Reinforced Sulfonated Poly(phenylene sulfone)‐Membrane for Stable Water Electrolysis with Lower Gas Crossover and Lower Resistance than Nafion N115

AbstractPolymer electrolyte membrane (PEM) water electrolysis is a crucial technology for green hydrogen production. Hydrocarbon membranes are drawing a lot of attention due to potentially superior properties and the fact that common fluorinated polymers might face a potential ban. This study introduces a sulfonated poly(phenylene sulfone) (sPPS) membrane, reinforced with a poly(ether‐ether‐ketone) (PEEK) mesh. The reinforced membrane induces a drastic increase in dimensional stability, enabling direct anode casting—an essential step toward industrial manufacturing. It further exhibits a significant reduction in water uptake (115% vs 294% for pure sPPS) and a 40% lower H2‐crossover (0.18 mA cm−2) compared to the industry standard N115 (0.31 mA cm−2). Due to the lower thickness (74 vs 127 µm) and higher ion exchange capacity (IEC)(1.92 vs 0.89 mmol g−1), the PEEK‐sPPS membrane displays a substantially lower resistance (70 vs 159 mΩ cm2 for N115). This directly translates into a voltage reduction of ≈90 mV at 1 A cm−2 or ≈180 mV at 2 A cm−2, both typical operating current densities. Finally, PEEK‐sPPS exhibits the longest lifetime shown for hydrocarbon membranes with almost 650 h at 1 A cm−2 and a low degradation rate (80 µV h−1).

Multilayer composite membranes composed of carbon molecular sieve membranes sandwiched between stacked zeolite nanosheets

This study proposes a novel method for fabricating composite membranes with a unique multilayer structure comprising Mobil-type five (MFI) zeolite nanosheets and carbon molecular sieve (CMS) membranes. The proposed fabrication method involves direct solution casting of a nanosheet/polymer composite onto porous alumina supports and subsequent carbonization, thereby eliminating the necessity for intermediate layers, typically required in most conventional supported CMS membranes. The fabricated membranes exhibit clear molecular sieving separation attributes, demonstrating the efficiency of the proposed method in preparing membranes without intermediate layers. Furthermore, the membranes exhibit an intriguing morphological configuration, wherein the CMS layers occupy the interstitial spaces between the stacked zeolite nanosheets. Therefore, compared with conventional CMS membranes without nanosheets, the fabricated CMS membrane with MFI nanosheets contain a significant proportion of sp2 bonded carbon atoms. The distinct physical and chemical structures of the composite membrane considerably improve its stability against structural densification associated with physical aging. A marginal H2 permeance reduction is observed for the 6 and 10 wt% loading samples of the composite membrane after aging for 100 d at 180 °C. Moreover, the H2/CO2 selectivity of the 6 wt% loading sample of the aged membrane increased from approximately 4 to 21, surpassing the upper bound of the corresponding gas pair. Thus, the proposed method can be used for fabricating molecular sieve membranes owing to its advantages such as ease of membrane preparation and gas-separation performance and structural stability enhancements of the fabricated membranes.

Microstructure evolution of porous calcium hexaluminate compacts during first heating

Porous calcium hexaluminate (CaAl12O19 or CA6) structures show long-term stability at high temperatures, high refractoriness, low thermal conductivity, and excellent chemical resistance, thus being Taylor-made for thermal insulation. Previous works attained porous structures from in situ formation of CA6 combining CaO and Al2O3 sources in solid-state reactive sintering. Although the approach is time-and-energy-saving regarding the production of large parts of complex shapes, it faces considerable difficulties related to the expansive formation of calcium aluminates. To overcome such drawbacks, pre-formed porous CA6 aggregates improve the system's dimensional stability before sintering. Despite the straightforward processing, few studies have investigated such materials systemically. This article addresses the combination of pre-formed porous CA6 aggregates and organic and inorganic binders for the production of porous structures by two shaping processes, namely, uniaxial pressing and direct casting of aqueous suspensions. After drying, the samples' microstructure and physical properties evolution were investigated up to sintering (1100-1500 °C) through total porosity, Young's modulus, compression strength, pore diameter, and thermal conductivity measurements, dilatometric analyses, and scanning electron microscopy. Reference samples of coarse calcined alumina were tested under the same conditions to highlight the impacts of CA6 particles' morphology. Compared to them, the CA6-containing samples showed almost no variation in total porosity and average pore size levels during thermal treatments, although their strength and rigidity increased significantly after sintering. Their microstructure remained practically unchanged after drying, showing clusters of large asymmetrical CA6 crystals bonded to each other by their edges, and surrounding a large fraction of 1.8–2.2 μm pores. According to the results, although water content, processing method, and compacting levels are important parameters, particles' microstructure, ratio of intra-particle pores, and asymmetrical shape are key variables for the development of physical properties. Such characteristics strongly contributed to their densification resistance and lower thermal conductivity after exposure to high temperatures.

Charging-for-Recycling Business Model and Consumer Adoption of Recyclable Electronics

High costs of recycling operations have kept recycling rates low for many consumer electronics. Meanwhile, increasing the adoption of more recyclable electronics among consumers remains a challenge. Motivated by Best Buy’s decision to charge consumers a flat fee to accept their used TVs/monitors for recycling, we study how charging for recycling would influence consumer adoption of recyclable electronics. Through experimental studies, and building on relevant behavioral insights (nudging and the theory of planned behavior), we compare the charging for recycling scenario with free recycling and recycling tax as current baselines. We find that, compared to the baselines, charging for recycling increases the adoption of recyclable electronics as long as consumers are not in emergency purchase situations. Our results suggest a potential alternative to unsuccessful direct green marketing and cast doubt on prohibiting retailers from charging for recycling.

The Role of TiO2 on ZnAl2O4 Spinel Prepared by Direct Coagulation Casting Method: Physico-mechanical, Optical, Structural and Antimicrobial Properties

This work represents the shaping of alumina–zinc oxide (AZ) samples with the direct coagulation casting method. The effect of zinc oxide (0, 10, 20, 30, and 40 wt%) and the firing temperatures on the phase composition, microstructure, physical properties, and mechanical properties of the AZ samples were studied. The effect of titanium oxide (2, 5, and 7 wt%) and the firing temperatures on the phase composition, microstructure, physical properties, and mechanical properties of the AZ sample with 40 wt% of zinc oxide were studied. Furthermore, the optical properties, magnetic properties, and antimicrobial activity were measured. The results indicate that the increase in zinc oxide enhances the formation of zinc aluminate, which has a gahnite phase. Moreover, increasing the zinc oxide increases the apparent porosity and decreases the grain size and bulk density at various firing temperatures. On the other hand, the addition of 5 wt% titanium oxide increases the bulk density to 3.5 g/cm3 compared to 1.72 g/cm3 with no titania. The apparent porosity and compressive strength reached 5% and 69.2 MPa after 5 wt% TiO2 addition; respectively, compared to 59% and 27.2 MPa with no titania addition. The prepared samples show promising optical band gap of 2.98–3.97 eV, a mixed magnetic behavior, and favorable antibacterial activity against E. coli, S. aureus, B. cereus strains.

Porous mullite fiber-based ceramics inspired by biomimetic natural pine wood

How to further improve the strength of fiber porous ceramics has always been the focus of researchers. Herein, inspired by the unique microstructure of natural woods which exhibit excellent mechanical and thermal insulation properties, a high strength mullite fiber-based porous ceramic with wood-like microstructure was successfully designed and fabricated. The wood-like porous ceramics were mainly composed of two kinds of layered structures that are perpendicular to each other. The horizontally oriented lamellar structure was constructed by assembling the fiber membranes layer by layer, and the vertically oriented lamellar structure perpendicular to the fiber layer was constructed by the directional freeze casting method. The results indicated that as to the mullite fiber-based porous ceramics with the similar density (∼0.36 g/cm3), the compressive strength along the X-axis direction of porous ceramics with wood-like microstructure prepared by the directional freeze casting method (3.4 MPa) was much higher than that of porous ceramics prepared by the non-directional freeze casting method (1.04 MPa), owing to the formation of silica lamellar structure perpendicular to the fiber layers. In addition, the wood-like mullite fiber-based porous ceramics also exhibited excellent thermal insulation performance along the X direction due to existence of a large number of pores in the fiber layers. This study provides a new strategy for the preparation of a high-strength thermal insulating fiber-based porous ceramic.

Hierarchical microstructure enables high strength and good ductility in as-cast Fe27Ni35Cr18.25Al13.75Co2Ti2Mo2 high-entropy alloy

As-cast alloys often require complex thermomechanical processing to obtain a hierarchical structure to achieve a good combination of strength and ductility. Here in this work, a novel hierarchical Fe27Ni35Cr18.25Al13.75Co2Ti2Mo2 high-entropy alloy (HEA) with ultra-high tensile strength and excellent ductility was fabricated by direct casting. The as-cast alloy exhibits hierarchical structure with an ultrafine lamellar microstructure (ULM), ultrafine rhombus microstructure (URM), ultrafine vermicular microstructure (UVM), nanosized precipitates and spinodal decomposition (SP) that develops during casting and cooling. The incompatibility of face-centered cubic (FCC) and body-centered cubic (BCC) phases in the deformation process leads to heterogeneous deformation-induced (HDI) hardening, which brings the alloy a tensile yield strength (YS) of ∼1056 MPa, an ultimate tensile strength (UTS) of ∼1526 MPa and a total elongation (El) of ∼15.6%. Additionally, the numerous interfaces generated by the hierarchical structure absorb the energy during deformation, effectively retarding the dislocation motion and causing strong work-hardening.

High aspect-ratio sub-500 nm UV-PDMS bilayer stamps by means of hybrid thermal-ultraviolet curing for resonant nanopillars fabrication through soft UV-NIL

A novel protocol for the fabrication of bilayer stamps for soft UV-NIL is presented. The patterned layer is composed of a commercially available UV-curable PDMS, while a quartz backplane acts as support layer. The pattern reproduced in the stamp through direct casting comes from a hard template and is composed of nanopillar arrays with 250–300 nm of diameter and 300–400 nm in height. The master template with nanoholes is treated with a self-assembled monolayer before pattern reproduction for improved separation of UV-PDMS layer. The hybrid cross-linking protocol includes a thermal and a UV process, and parameters of the former are investigated for best results. The pattern was reproduced in a resist on a Si sample by means of soft UV-NIL, and the imprinted nanohole arrays show dimensions coherent with the stamp. Finally, its application in the fabrication of resonant nanopillars for sensing purposes is briefly described. This is, to the best of our knowledge, the first time a hybrid thermal-ultraviolet curing of UV-PDMS has been reported and that protruding nanostructures with aspect-ratio higher than 1 in soft UV-NIL stamps have been demonstrated.