Fast Solidification Research Articles

Synthesis of inherently helical nanofibers: Effects of solidification of electrified jet during electrospinning

AbstractIn this paper, a helical fiber was fabricated through electrospinning by increasing the vapor pressure of the solvent, increasing the conductivity of the polymer solution and forming an uneven electrical field distribution around the jet. Fiber morphology during electrospinning of a dielectric polymer solution was observed to dramatically change from straight to helical due to rapid solidification of the jet as vapor pressure of the solvent increased. A similar effect was observed with conductive solutions prepared by adding large amounts of metal ion to the polymer solution. The addition of metal ion induced strong electrical stresses, causing the electrified jet to rapidly solidify in the early stage of electrospinning. Simulations revealed that the jet near the nozzle tip was subject to a strong electrical field due to increased charge density. The thickness of the emerging fiber was rapidly reduced with fast and simultaneous solidification, resulting in helical nanofibers. In addition, by using the asymmetric spinnerets, an uneven electric field distribution around jet was generated, maximizing the fiber curvature and increasing the helical fiber ratio.

Water-based polyurethane adhesive films with enhanced bonding strength capable of in situ and high-efficient deposition on metal surface

Producing high-efficient, low-cost, and green water-based adhesives with enhanced bonding performance still remains highly challenging. In this study, waterborne polyurethane (WPU) adhesive films with long-term stability are in situ fabricated on a metal substrate by a facile and high-efficiency preparation method known as demulsification-induced fast solidification (DIFS). The bonding strength of adhesive films was enhanced by constructing multiple cross-linked structures between polycarbodiimide (PCD) and WPU, which determines the cohesive force of the adhesive films. The bonding strength obtained for WPU-L/PCD-0.1 (L: polycaprolactone, 0.1 represents the PCD mass fraction to emulsion) adhesive film is>2.40 ± 0.21 MPa (stock-break failure mode) at room temperature for 120 d, satisfactory for stable connections. Moreover, the cross-linked adhesive film exhibits an excellent water-resistance performance because PCD and hydrophilic carboxyl groups of WPU form a cross-linking network to eliminate the hydrophilic carboxyl groups. We expect that this new type of adhesive film will be useful for metal bonding and metal protection coatings applications.

The Roles of Ni and Co in Dendritic Growth and Tensile Properties of Fe‐Containing Al–Si–Cu–Zn Scraps under Slow and Fast Solidification Cooling

Elementary correction of Al scraps contaminated with Fe has emerged as an alternative to existing recycling processes. The appropriate management of solidification parameters may regulate both the microstructure and the properties in a highly effective way. As shown in this article by José E. Spinelli and co-workers, number 2100822, this may allow for use in new applications with greater performance requirements.

NbB refining capability: Effects of slow and rapid solidification on dendritic spacings and grain sizes of a 6201 alloy

NbB inoculants are refiners that might be of interest to the Al industry. Grain size (GS) and secondary dendrite arm spacing (SDAS) are two important microstructural variables to consider when assessing a refiner's performance. Both of these attributes may have an impact on the alloy’s properties. The interplay of grain refiner and cooling rate on grain size, SDAS, and grain shape in the 6201 alloy is investigated in this article. It is demonstrated that GS associated with rapid solidification of the 6201 + NbB alloy was roughly 7 times smaller than that associated with slow solidification. Furthermore, regardless of the processing method (either slow or fast solidification), α-Al cells are generated for GS/SDAS ratio below and equal to 6.

Microstructure evolution and tensile property of TiAl alloy using continuous direct energy deposition technique

Attributing to the fast solidification and thermal cycling during additive manufacturing process, massive phase transformation could take place thus leading to the formation of unpredictable microstructures with large variation in mechanical properties. In this paper, a continuous direct energy deposition technique (CDED) is adopted to prepare TiAl alloy seceding from the thermal cycling, and the evolution of microstructure, microhardness and tensile properties of alloy are investigated. Results indicate that the microstructure of alloy composes of columnar grains with very fine (α2 +γ) lamellae, and no heat-affect band is observed. A heat transfer model is established to assist in explaining the solid-phase transformation and microstructure formation mechanism of TiAl alloy. Furthermore, a special duplex γ microstructure (DP γ) forms which composes of massive γ phase surrounded by feathery-like γ phase. By dissecting crystallographic orientation from EBSD results, the formation mechanism of DP γ is clarified as the result of sequential solid-state phase transition in (α + γ) phase region, in which the feathery-like microstructure forms firstly followed by the massive γ phases nucleating at the inter-phase boundaries of feathery-like γ. Tensile property of as-deposited alloy reveals of 535 MPa with 1% elongation, and the highest hardness of around 320HV is detected at the top region of alloy with the finest interlamellar spacing.

Microstructure and correlated mechanical properties study of Ni–(Fe, Co)–Mn–(Al, In) as-spun ribbons

The Ni–Mn–based shape memory alloys as a promising candidate of elastocaloric material has been reported in many literatures, especially on bulk samples. The as-spun ribbon, which has a larger surface area and is more efficient for heat transfer, is rarely studied and hence of importance. In the present work, we succeeded in producing very long as-spun Ni–Fe–Mn–(Al, In) ribbons, with around 300 mm in length. The microstructure and mechanical properties of these as-spun ribbons were thoroughly investigated by scanning electron microscopy and electron backscattered diffraction (SEM-EBSD), nanoindentation and 3-points bending experiments. Through SEM-EBSD analyses, the microstructure and texture of the as-spun ribbons were studied. A gradient in microstructure exists along the thickness direction (TD) of the ribbon, which is induced by the temperature gradient during fast rate solidification, resulting in fine equiaxed grains along the surface contacted with the rotating wheel in melt spinning process and elongated grains, respectively. Both equiaxed and elongated grains possess a strong {001} fiber texture (<001>//TD). Nanoindentation analyses show little variation of hardness between the two different microstructures. The ductility index of both Ni–Fe–Mn–Al and Ni–Fe–Mn–In ribbons are within the range of intermetallic materials. The substitution of In by Al allows to increase very slightly the ductility index, which can reach 0.75. The fine equiaxed grains show better tensile resistance than the elongated grains in 3-points bending test. The substitution of In by Al improves the maximum bending strain by a factor of 3. The maximum strain for Ni–Fe–Mn–Al as-spun ribbons can reach 3% before fracture. Fractography shows that, the intergranular fracture is the main damage mechanism in these as-spun ribbons.

Precipitation Mechanism in Ultra-Fine Grained Al-Mg-Si-Cu Alloy Fabricated by Fast Solidification and Hot Extrusion Processes

Precipitation Mechanism in Ultra-Fine Grained Al-Mg-Si-Cu Alloy Fabricated by Fast Solidification and Hot Extrusion Processes

Recent advancements in nanocomposite coating manufactured by laser cladding and alloying Technique: A critical review

This review article discusses about the development of nanocomposite coating on surfaces of metallic materials produced by laser surface cladding and alloying process. The purpose of coating is to deposit hard, wear and corrosion resistant layer on the surface of metallic material so that the materials can be used for manufacturing of engineering components operated in severe wear and corrosion environment. Nanocomposite coatings are having wide applications in automobile, chemical, aerospace and electronics industries due to its attractive properties like very high hardness, good tribological properties, excellent corrosion resistance and excellent oxidation resistance at high temperature. The various engineering materials upon which nanocomposite coatings can be fabricated are ferrous materials, aluminium alloy, titanium alloy, nickel based super alloy and magnesium alloy. The laser surface cladding and alloying process are widely used for fabrication of nanocomposite coating on metallic materials because of its excellent characteristics such as fast solidification and cooling rate, production of fine microstructure, highly flexible process, less dilution, narrow heat affected zone and highly automated process. The nanocomposite coating can be formed by transition metals, alloys, ceramics, and rare earth oxides. The formation of nanocomposite coating depends upon the laser process parameters and selection of nanoparticles during coating process. The various laser process parameters which control the formation of nanocomposite coating are laser power density, laser scanning speed, argon flow rate, feed rate of powder, wavelength of laser beam, frequency of laser, and laser spot diameter. The nanocomposite coated metallic materials can be used for manufacturing of mechanical components like turbine blades, friction devices and automobile parts applicable to severe wear and corrosive conditions. In this review paper the problem arises during laser processing for nanocomposite coating formation on various metallic materials and its control has been described.

Mechanical properties and strengthening mechanism of silty sands stabilized with steel slag-based geopolymer binder

Geopolymer binder has the advantages of early strength, fast solidification, high volume stability, and low permeability. It is beneficial to improve the mechanical performance of silty sands, saving cement consumption and being environmentally friendly. However, the strength improvement of silty sand stabilized with steel slag-based geopolymer was significantly controlled by their material composition and technical parameters. This study conducted a series of unconfined compression tests to investigate the material composition of steel slag-based geopolymer binders and their reasonable mixing ratio for silty sand stabilization. The optimum mixing ratio of precursor (steel slag) to alkaline activator (the combination of Na₂SiO₃ and CaO) and the optimum dosage of steel slag-based geopolymer for silty sand stabilization were explored. The strengthening mechanism of geopolymer-stabilized silty sands was discussed based on microstructural images and elemental concentrations of primary components observed by SEM and EDS. The results show that when the mass ratio of Slag : Na₂SiO₃ : CaO was 80:35:21, and the steel slag-based geopolymer material was 15%, the silty sand could achieve the best mechanical performance improvement. The microstructural characteristics of geopolymer-stabilized silty sands at different curing ages illustrated that the compactness and integrity of silty sand structures were enhanced over the curing age. The improving cementitious contact among particles and enlarging particle size was responsible for the strength improvement of silty sand. This research can provide a reference for applying steel slag-based geopolymer in silty sand stabilization in engineering practices.

Demonstration of temperature-sensitive paints with rigorously controlled thickness applied to variously shaped metal substrates with a highly stable connection based on a demulsification-induced fast solidification strategy

Temperature-sensitive paints with rigorously controlled thickness are in situ fabricated on metal surfaces based on the demulsification-induced fast solidification method.

Investigation on anisotropic behavior of additively manufactured maraging steel during orthogonal cutting

Laser powder bed fusion (LPBF) as an additive manufacturing (AM) process allows for sophisticated geometries to be produced. With optimized process parameters high densities of the metal parts can be achieved. The locally concentrated melting and fast solidification leads to a fine dendritic microstructure depending on the melt pool size. In this dendritic structure the layer wise build-up is still visible. It is well known that this leads to an anisotropic material behavior.In this paper the influence of the build-up orientation relative to the cutting vector on the cutting process is studied. For this objective, specimens out of maraging steel with different build-up directions are build and subsequently examined utilizing an orthogonal cut. During the cut, forces, vibrations and acoustic emission are used to investigate the cutting behavior. Furthermore, the chips are analyzed for the geometric characteristic values. With this, the anisotropic behavior could be demonstrated. Depending on the build-up orientation α, cutting force varies by up to 6 % and thrust force by up to 8. Chip thickness also varies depending on α by up to 18,6 %. Based on the findings, a regression model is developed which maps the specific material properties. This makes it possible to predict resulting cutting forces and chip volume, based on the layer penetration angle. Finally, this leads to a better understanding of the interactions between the additive subtractive process chain.

Significant strengthening effect in ultra-fine grained Al alloy made by fast solidification and hot extrusion processes

Grain refinement with a facile process without additional alloying is quite desired for strengthening the Al alloys. Using the melt spinning process, we obtained the ultra-fine grained foils of Al–Mg–Si–Cu alloy (AA6061), then the foils followed by hot extrusion to produce the rods for industrial applications. The yield strength of the extruded melt-spun rod is 102% higher than that of the extruded rods of the alloy by a conventional direct chill casting. The electron backscatter diffraction results reveal that the average grain diameter in the extruded melt-spun sample is only 1.35 μm, indicating that the sample is an ultra-fine grained alloy. Through the Hall–Petch relationship, the finer grains contribute to a 66.9% increase in yield strength of the extruded rod. Moreover, the <111> fiber texture occupied 68% of the volume fraction after hot extrusion, contributing to 30.5% improvement of the yield strength in the extruded melt-spun sample. This study shows that the ultra-fine grained Al–Mg–Si–Cu alloy rods have excellent mechanical properties, which provides a strong potential for industrial application.

Preface

Overview of the 18th International Scientific and Technical Conference Rapid Solidification Materials and Coatings A A Lozovan1 and D K Kostrin2 1Department of Materials and Materials Technology, Moscow Aviation Institute(National Research University) “MAI”, 121552, Orshanskaya, 3, Moscow, Russia 2Department of Electronic Instruments and Devices, Saint Petersburg Electrotechnical University “LETI”, 197376, Professora Popova, 5, Saint Petersburg, RussiaE-mail: alexandr.lozovan@yandex.ru . In this preface the main results of the 18th International Scientific and Technical Conference Rapid Solidification Materials and Coatings that was held on 19–20 October 2021 in Moscow, Russia are discussed.From 19 to 20 October 2021, the 18th International Scientific and Technical Conference Rapid Solidification Materials and Coatings (RSMC–2021) was held at the Moscow Aviation Institute (National Research University).Despite the difficulties associated with the coronavirus pandemic, more than 100 specialists from leading universities, the Russian Academy of Sciences and Russian enterprises, as well as scientists from Ukraine and Belarus, took part in the Conference. For the successful holding of the Conference in a pandemic, all the necessary measures were taken to ensure the implementation of sanitary rules and standards for the protection of Conference participants.At the Conference the results, which were obtained in the last year after the previous Conference, of the theoretical and experimental studies on the physics of condensed matter, low-temperature plasma physics, electronic and ion-plasma surface modification, physical methods of film deposition and other studies obtained over the last year after the previous Conference.The main objects of these studies were superficiality and superficial phenomena. Therefore, to the development and improvement of methods of surface modification and coatings deposition, as well as methods of their research and development of modern surface treatment equipment was paid the greatest attention at the Conference.During the Conference more than 70 reports were presented, which were heard in the following, traditional Conference sections (figure 1):• section 1 – Rapid solidification materials;• section 2 – Methods of coating application and research;• section 3 – Laser, electron-beam and ion-plasma methods of surface modification;• section 4 – Composite materials and permanent joints;• section 5 – Works of young scientists.The Conference was opened by Alexander Vladimirovich Bespalov, Co-Chairman of the Director of the Department of Materials Science and Materials Technology of the Moscow Aviation Institute (National Research University), who emphasized the importance of developing research in the field of physical and physicochemical methods of obtaining and processing new materials and coatings for the aerospace industry. He also noted the achievements of the Institute’s scientists in the field of laser coating and fast solidification materials.List of Organizing Committee, Program Committee, Photos are available in this pdf.

Effect of rare earth oxide additive in coating deposited by laser cladding: A review

In this paper, the effect of rare earth oxide additive on coating material deposited by laser cladding process on various engineering materials has been discussed. The purpose of rare earth oxide additive in the coating composition is to improve the various properties like mechanical, tribological, and chemical properties. The main rare earth oxides are La2O3, CeO2 and Y2O3, which are generally used in laser cladded coatings. The limited amount of addition of these rare earth oxide compound may leads to improvement in hardness, wear and corrosion resistance of coating. The attractive properties of rare earth oxide is grain refinement, conversion of coarse structure to fine dendritic structure, creating grain boundary movement hindrance of dislocation in the material which leads to its application as nutrients in the coating material. The main purpose of coating is to enhance the surface properties of material like hardness, corrosion resistance and wear resistance. When rare earth oxide are added to the coating then it creates extra enhancement in the above properties. The laser cladding is widely used in modern manufacturing technology due to its very attractive properties like good metallurgical bonding with substrate, less dilution, minimum distortion, less heat affected zone and fast solidification and high cooling rate. In this review article the coating developed by laser cladding on various conventional engineering materials like ferrous materials, magnesium alloys, titanium alloys, aluminium alloys and nickel based super alloys with rare earth oxide addition are described.

Nanostructuring of Nb-Si-Cr Alloys by Electron Beam Melting to Improve the Mechanical Properties and the Oxidation Behavior

Materials processed by additive manufacturing often exhibit a very fine-scaled microstructures due to high cooling rates in the process. In this study, single-layer surface electron beam melting is used to create very high cooling rates similar to additive manufacturing processes to investigate the resulting microstructure. In the case of Nb-Si-Cr in-situ composites, a nano-scaled eutectic microstructure is beneficial for improving the mechanical and oxidational properties. Fast solidification results in the formation of supersaturated phases of Nbss and Cr2Nb with phase diameters down to 10 nm as well as in the stabilization of the metastable Nb9(Cr,Si)5 phase at room temperature. After processing with different solidification rates, the decomposition of the Nb9(Cr,Si)5 phase has been studied in detail with atom probe microscopy. The stabilization of mixed silicide phases by electron beam melting shows a new pathway for improving hardness and enhancing oxidation resistance of nanostructured eutectic in-situ composites, by which the inherent weaknesses of Nb-Si-Cr can be overcome without further alloying elements.Graphical

Interface-Mediated Twinning-Induced Plasticity in a Fine Hexagonal Microstructure Generated by Additive Manufacturing.

The grain size is a determinant microstructural feature to enable the activation of deformation twinning in hexagonal close-packed (hcp) metals. Although deformation twinning is one of the most effective mechanisms for improving the strength-ductility trade-off of structural alloys, its activation is reduced with decreasing grain size. This work reports the discovery of the activation of deformation twinning in a fine-grained hcp microstructure by introducing ductile body-centered cubic (bcc) nano-layer interfaces. The fast solidification and cooling conditions of laser-based additive manufacturing are exploited to obtain a fine microstructure that, coupled with an intensified intrinsic heat treatment, permits to generate the bcc nano-layers. In situ high-energy synchrotron X-ray diffraction allows tracking the activation and evolution of mechanical twinning in real-time. The findings obtained show the potential of ductile nano-layering for the novel design of hcp damage tolerant materials with improved life spans.

Freeze-printing of pectin/alginate scaffolds with high resolution, overhang structures and interconnected porous network

We report herein the fabrication of a pectin-based scaffold (6 wt% pectin, 3 wt% alginate) with high resolution (small-diameter rods), small pores, and interconnected porosity using a low temperature 3D printing process known as freeze-printing. The ability to successfully print natural polymers has been a long-standing challenge in the field of additive manufacturing of polymeric tissue scaffolds. This is due to the slow evaporation rate of the aqueous solvent, which leads to unstable structures. This problem has been addressed by utilizing the fast solidification rate of the freeze-printing process. Scaffolds with a hgresolution (rod-diameter of 83 ± 14 µm), small pores (<250 µm), overhang structures, and an interconnected porous network (pore height of 319 µm in the z-direction) were obtained. The scaffolds were also found to support the viability of chondrocytes and their synthesis of type II collagen. This report investigates the processing-structure relationship and fundamental science of structurally stable scaffold structures produced by additive manufacturing of natural polymers. • A pectin-rich scaffold was fabricated with high resolution and 3D-interporosity. • The scaffold has a small rod-diameter at 83 ± 14 µm and small pores (<250 µm). • Rapid solidification by freeze-printing prevented broadening and collapse of the printed rods. • The dimension of the pores in the z-diection is adjustable.

Recrystallization kinetics, mechanisms, and topology in alloys processed by laser powder-bed fusion: AISI 316L stainless steel as example

Alloys manufactured by laser powder-bed fusion have intrinsic and hierarchical microstructural features inherited from the fast solidification (up to 104 K/s) and subsequent thermal cycles. This creates epitaxed grains, dislocation cell structures, and second-phase oxide nanoparticles. Epitaxed grains follow a pattern where finer grains are found in the melt pool centerline along the laser track. Upon further annealing, this characteristic microstructure has pronounced consequences on the recrystallization mechanisms and thus on grain topology. By changing the scanning strategy, we control the emerging grain patterns in a representative alloy (AISI 316L austenitic stainless steel) by creating linear strings for unidirectional scans, while a chessboard grain pattern arises by applying a 90°-rotation between layers. Upon post-processing annealing (at 1150 °C from 15 min to 8 h), we study the relationship between the as-built and recrystallized microstructures. Recrystallization starts with fine nuclei in regions with high dislocation density along the melt pool centerlines, resulting in early-stage linear impingement (linearly clustered nucleation), as revealed by microstructural path analysis. Recrystallization is sluggish, due to dynamic Zener-Smith pinning. This effect leads to jerky boundary motion due to periodic pinning and depinning from oxide particles, caused by their gradual coarsening. Lower nuclei number density slows kinetics for the case of unidirectional scanning, while twinning aids in the nucleation of grains with mobile grain boundaries. Our findings show that changes in the laser scanning strategy are a suitable design tool for tailoring recrystallization and thus microstructure.

Tomoscopy: Time-Resolved Tomography for Dynamic Processes in Materials.

The structure and constitution of opaque materials can be studied with X-ray imaging methods such as 3D tomography. To observe the dynamic evolution of their structure and the distribution of constituents, for example, during processing, heating, mechanical loading, etc., 3D imaging has to be fast enough. In this paper, the recent developments of time-resolved X-ray tomography that have led to what one now calls "tomoscopy" are briefly reviewed A novel setup is presented and applied that pushes temporal resolution down to just 1ms, that is, 1000tomograms per second (tps) are acquired, while maintaining spatial resolutions of micrometers and running experiments for minutes without interruption. Applications recorded at different acquisition rates ranging from 50 to 1000tps are presented. The authors observe and quantify the immiscible hypermonotectic reaction of AlBi10 (in wt%) alloy and dendrite evolution in AlGe10 (in wt%) casting alloy during fast solidification. The combustion process and the evolution of the constituents are analyzed in a burning sparkler. Finally, the authors follow the structure and density of two metal foams over a long period of time and derive details of bubble formation and bubble ageing including quantitative analyses of bubble parameters with millisecond temporal resolution.

The Roles of Ni and Co in Dendritic Growth and Tensile Properties of Fe‐Containing Al–Si–Cu–Zn Scraps under Slow and Fast Solidification Cooling

Studies of Fe‐contaminated Al‐based scraps have drawn attention for years. However, little has been researched about the effects of cobalt (Co) and nickel (Ni) additions to contaminated scraps both under slow solidification (directional solidification, DS) and fast solidification regime (copper mold centrifugal casting, CC). As such, the current study examines a representative low‐alloy Al–Si chemistry from industrial scraps, i.e., the Al–7%Si–0.6%Fe–0.35%Cu–0.25%Zn (% by weight). This alloy is changed independently using Ni and Co. It is observed that a mixture of uneven distributed α and β Fe‐bearing particles prevails for all tested alloys and solidification conditions. The coexistence of both phases agrees with the charts proposed by Gorny's work for the range of secondary dendritic spacing, λ 2, observed. Although the Fe‐containing particles are smaller for fast‐solidified samples, they still maintain the acute morphology and, in some cases, the Chinese script shape. This results in a reduction in ductility of the order of 65% for the nonmodified and Ni‐modified samples considering mean λ 2 varying from 20 μm (DS) to 6.5 μm (CC), despite improvements in mechanical strength. Furthermore, addition of Co results in a higher number of Fe‐based particles within the microstructure. In this case, the largest particle/α‐Al interfacial area results in slightly poor ductility (~6–8%) and higher strength (175–205 MPa), with less ductility loss when DS and CC samples are compared.