Desired Microstructure Research Articles

Processing Map and Mechanism of Hot Deformation of a Corrosion-Resistant Nickel-Based Alloy

Hot deformation behavior of a corrosion-resistant nickel-based alloy was studied in temperature range of 1050-1200 °C and strain rate range of 0.001-10 s−1 by employing hot compression tests. An approach of processing map was used to reveal the hot workability and microstructural evolution during the hot deformation. The results show that different stable domains in the processing map associated with the microstructure evolution can be ascribed to different dynamic recrystallization (DRX) mechanisms. The discontinuous dynamic recrystallization (DDRX) grains evolved by the necklace mechanism are finer than those evolved by the ordinary mechanism, respectively, arising from the strong nucleation process and the growth process. If subjected to low temperature and high strain rate, the flow instability domain occurs, due to the continuous dynamic recrystallization (CDRX) based on the evolution of deformation micro-bands within the deformed grains. Based on the processing map, a DRX mechanism map is established, which can provide an idea for designing desired microstructure.

Could the 3D Printing Technology be a Useful Strategy to Obtain Customized Nutrition?

Within the concept of personalized nutrition we want to introduce the terms of "customized food formula" which refers to the preparation (at home) or the production (at industrial level) of new food formulations having nutrients and functional compounds necessary to prevent diseases or to reduce the risk for each subject (or subjects category) who exhibit a susceptibility to diseases. Three-dimensional (3D) printing is a group of technologies of growing interest able to produce, slice by slice, materials with any desired shape, dimension, and structure properties. The application of 3D printing in food science, as called "3D food printing," is a pioneering technology that could allow to build personalized foods by depositing nutrients and functional compounds or soft-materials obtained by their mixture. Also by 3D food printing it is expected to obtain personalized food formula having desired shape, dimension, and microstructure. This would be useful for people having swallowing problems. In this paper we analyzed the first examples of 3D food printing available in literature as well as we reported our results focused on the production of 3D printed wheat-based snacks enriched with insect powder (Tenebrio molitor) with the aim to improve the quality and the content of proteins.

Acicular ferrite nucleation as a diffusion controlled process in high strength low alloyed (HSLA) steel weld metal

Abstract Acicular ferrite is a desirable microstructure in high strength low alloy steel weld metal. This is due to its improved toughness and the enhanced mechanical properties of the weld metal. Although the nucleation of acicular ferrite has been studied by many researchers, the exact mechanisms of its nucleation and growth are still under discussion and remained unclear. In this research work, the mechanism of acicular ferrite formation in the weld metal as cast structure has been clarified as diffusion controlled solid state phase transformation. This is based on the classic theory of nucleation and growth which can contribute to possible increase of nucleation sites and growth of intergranular ferrite in HSLA steel weld metal. Therefore, it could be considered that inclusions are not acting as a nucleation site for the intergranular acicular ferrite. Consequently, our results revealed that, in austenite transformation to pro-eutectoid and acicular ferrite, manganese as an austenite stabilizer alloying element is playing an important role in the nucleation and growth of the ferrite grains. It should be added that cooling rate accompanied with the presence of other alloying elements has influenced the type and morphology of the final ferrite microstructure and constituent products.

Microstructure evolutions and nucleation mechanisms of dynamic recrystallization of a powder metallurgy Ni-based superalloy during hot compression

Dynamic recrystallization (DRX) has been of great concern throughout the manufacturing processes, and it deeply affects in-service performance of powder metallurgy Ni-based disk components. Understanding the underpinning mechanisms of DRX is vital to produce the desired microstructure and mechanical properties of the superalloys. In this article, microstructure evolutions and nucleation mechanisms of DRX of an advanced Ni-based superalloy during hot deformation were studied using high resolution EBSD and TEM. The experimental results show that low angle grain boundaries were formed at low temperature and readily evolved to high angle grain boundaries with temperature increasing and/or strain rate decreasing. Effects of strain amount on DRX were examined and significant DRX was detected when the strain increased to 0.5 under conditions of 1050°C/0.01s−1. Three different nucleation mechanisms were found under different deformation parameters. Nucleation of DRX was strongly related to the bulged-original boundaries, which acted as the interaction barrier with mobile dislocations at relatively low temperature and strain rate of 0.1s−1. In contrast, twining boundaries were identified as the nucleation sites at a higher temperature and strain rate of 0.01s−1. At 1100°C and low strain rate of 0.001s−1, coalesced γ′ was encompassed by bulged-original boundary, where nucleation of DRX was detected.

Sn-doped few-layer MoS2/graphene hybrids with rich active sites and their enhanced catalytic performance for hydrogen generation

A facile hydrothermal method has been adopted to fabricate Sn-doped MoS2/graphene hybrids and their electrocatalytic properties toward hydrogen evolution reaction (HER) are also investigated. It is found that the incorporation of graphene and Sn-doping can efficiently suppress the stacking of MoS2 layers to form few-layer (1–3 layers) MoS2 nanosheets with rich active sites. Moreover, the few-layer Sn-MoS2 nanosheets are well implanted in the flexible and highly conductive graphene network. Such the desirable microstructures endow the hybrids with greatly enhanced HER performances including a smaller onset potential, larger exchange current density, smaller Tafel slope as well as higher turnover frequency than those of the bare MoS2.

Three-Dimensional Printing of Highly Conductive Carbon Nanotube Microarchitectures with Fluid Ink

Moving printed electronics to three dimensions essentially requires advanced additive manufacturing techniques yielding multifunctionality materials and high spatial resolution. Here, we report the meniscus-guided 3D printing of highly conductive multiwall carbon nanotube (MWNT) microarchitectures that exploit rapid solidification of a fluid ink meniscus formed by pulling a micronozzle. To achieve high-quality printing with continuous ink flow through a confined nozzle geometry, that is, without agglomeration and nozzle clogging, we design a polyvinylpyrrolidone-wrapped MWNT ink with uniform dispersion and appropriate rheological properties. The developed technique can produce various desired 3D microstructures, with a high MWNT concentration of up to 75 wt % being obtained via post-thermal treatment. Successful demonstrations of electronic components such as sensing transducers, emitters, and radio frequency inductors are also described herein. We expect that the technique presented in this study will facilitate selection of diverse materials in 3D printing and enhance the freedom of integration for advanced conceptual devices.

Microstructure and corrosion resistance of Ni-Al2O3-SiC nanocomposite coatings produced by electrodeposition technique

Ni–Al2O3–SiC nanocomposite coatings were electro-deposited on steel in a typical Watt's bath containing Al2O3 and SiC nanoparticles. Afterwards, the effect of the nanoparticle concentration in the electrolyte bath (ranging from 0 g/L to 40 g/L) on the microstructure and corrosion performance was evaluated. To investigate the microstructural changes and surface morphology of the coatings, as well as the nanoparticle distribution in the deposits, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy was utilized. Also, transmission electron microscopy was performed to further investigate the microstructure and to confirm the production of the nanocomposite coating. The electrochemical corrosion behavior of the prepared coatings was investigated in a 3.5 wt % NaCl solution by a potentiostat-galvanostat device. It was found that desirable structure of the protruding crystallite morphology with no detectable cracks and pores can be achieved at the medium concentrations of the reinforcement (e.g. 20 g/L). It was also found that the corrosion resistance of the coatings is considerably improved by adding the Al2O3+SiC nanoparticles to the Ni matrix. The optimum concentration of the nanoparticles in the electrolyte bath to attain the nanocomposite coating with a desirable microstructure and consequently a desirable corrosion resistance was 20 g/L.

Effect of step quenching on microstructures and mechanical properties of HSLA steel

Step quenching and tempering (SQT) for HSLA multi-phases steel was designed to obtain the desirable multi-phases microstructure with the superior mechanical properties. Quenching and tempering (QT) and intercritical quenching and tempering (IQT) was also conducted as controls. Besides, Effects of austenitizing temperature for the different treatment routes on microstructural characteristics and mechanical properties were also investigated. Due to the cooperation of the “soft” ferrite/pearlite and “hard” martensite, the samples undergoing SQT possess the relatively high tensile strength and impact toughness, and the lowest yield ratio. Increase of austenitizing temperature results in the coarse austenite grains, and thus significantly decrease of tensile strength and impact energy, in spite of the heat treatment paths. Higher austenitizing temperature also leads to lower density of dislocations and higher grain size, which reduces the yield ratio for all samples.

Hardening Baja AISI 1045 Menggunakan Gel Aloe Vera Sebagai Media Pendingin

Quenching is a cooling method of heat treatment for metal hardening. Quenching refers to the process of rapidly cooling metal parts from the austenitizing or solution treating temperature, typically from within the range of 815 to 970 °C for steel. The selection of a quenchant medium depends on the hardenability of the particular alloy, the section thickness and shape involved, and the cooling rates to achieve the desired microstructure. The liquid quenchants of oil is commonly used in industrial manufacture. But, oil is not environmental . Th e aim of this research research is to find new quenchant for change oil as quenchant to more environmental. Gel aloe vera is purposed for it. The m aterial used in this study is AISI 1045 steel . Cooling curve and cooling rate is measured by finite element model, ANSYS APDL 14.5. True experimental is done to view microstructure and measure hardness of steel. Simulation result shown that gel aloe vera has almost similar cooling curve and cooling rate with oil. Microstructure result of steel for gel aloe vera as quenchant is martensite in surface, bainite in center, and pearlite in between surface and center. Hardness number of steel for gel aloe vera as quenchant is 189.63 HVN in surface, 182.566 HVN in center, and 162.866 HVN in between surface and center. By simulation and true experimental analisys concluded that gel aloe vera has opportunities to change oil as quenchant for hardening process.

Hydrothermal synthesis of selenium-doped graphene-like molybdenum disulfide/graphene hybrid as an efficient electrocatalyst for hydrogen evolution

Se-doped graphene-like MoS2/graphene hybrid (Se-GL-MoS2/G) has been synthesized by an ionic liquid-assisted hydrothermal method and is also evaluated as an electrochemical catalyst for hydrogen evolution reaction (HER). The results indicate that Se-doped MoS2 nanosheets are characteristic of monolayers with rich exposed active edges and are well dispersed in the highly conductive graphene networks. Consequently, the desirable microstructures endow the Se-GL-MoS2/G hybrid with significantly enhanced catalytic activity for HER compared with the bare MoS2.

Effect of Mo Content on Microstructure and Property of Low-Carbon Bainitic Steels

In this work, three low-carbon bainitic steels, with different Mo contents, were designed to investigate the effects of Mo addition on microstructure and mechanical properties. Two-step cooling, i.e., initial accelerated cooling and subsequent slow cooling, was used to obtain the desired bainite microstructure. The results show that the product of strength and elongation first increases and then shows no significant change with increasing Mo. Compared with Mo-free steel, bainite in the Mo-containing steel tends to have a lath-like morphology due to a decrease in the bainitic transformation temperature. More martensite transformation occurs with the increasing Mo, resulting in greater hardness of the steel. Both the strength and elongation of the steel can be enhanced by Mo addition; however, the elongation may decrease with a further increase in Mo. From a practical viewpoint, the content of Mo could be ~0.14 wt. % for the composition design of low-carbon bainitic steels in the present work. To be noted, an optimal scheme may need to consider other situations such as the role of sheet thickness, toughness behavior and so on, which could require changes in the chemistry. Nevertheless, these results provide a reference for the composition design and processing method of low-carbon bainitic steels.

Sensor‐controlled bainitic transformation and microstructure formation of forgings during the cooling process

Bainitic steels are increasingly employed for manufacturing high‐performance forged components because they provide several advantages over martensitically hardened and tempered steels and can obtain their desired microstructure directly from the forging heat. However, especially during the heat treatment from the forging heat, many process parameters influence the microstructure formation in the component's surface and core regions, so that reliable predictions about the transformations using continuous cooling transformation diagrams and computational simulations are challenging.Within the framework of the project “EcoForge” a measuring system was developed, that non‐destructively monitors the materials transformation as well as the phase and microstructure formation in situ during cooling from the austenite. The onset of the transformation, the current transformation level and the end of the transformation is reliably detected, so that process times can be optimised. Using characteristic signal profiles it is also possible to differentiate and classify the formation of microstructures, e.g. bainite and martensite, to regulate the cooling parameters and specifically set the component's properties. Owing to its robustness and the potential for evaluating the measured signal profiles online in real time, the testing system is also suitable for online‐quality control in industrial forging and heat treatment lines.

Effects of hot rolled microstructure after twin-roll casting on microstructure, texture and magnetic properties of low silicon non-oriented electrical steel

In this work, a 0.71wt%Si+0.44wt%Al as-cast strip was produced by novel twin-roll casting. Some as-cast samples were respectively reheated and hot rolled at different temperatures in order to obtain different microstructure prior to cold rolling and annealing. The effects of the hot rolled microstructure on microstructure, texture evolution and magnetic properties were investigated in detail. A coarse deformed microstructure with λ-fiber texture was formed after hot rolling at 850–1050°C, finally leading to an inhomogeneous recrystallization microstructure with strong λ-fiber, Goss and extremely weak γ-fiber texture. By contrast, a fine transformed microstructure was formed after hot rolling at 1150–1250°C, finally leading to a fine and homogeneous recrystallization microstructure with stronger α-fiber, γ-fiber and much weaker λ-fiber texture. It should be noted that both the magnetic induction and core loss non-monotonically decreased or increased according to the hot rolling temperature. The unfavorable α-fiber and γ-fiber textures in the annealed sheets were much weaker than those of the conventional products regardless of the hot rolling temperature, thus contributing to a much higher magnetic induction. However, the average grain size in the annealed sheets was much lower than those of the conventional products regardless of the hot rolling temperature, thus leading to a higher core loss except the case of 1050°C. Hence, it is underscored that better integrated magnetic properties than those of the conventional products can be obtained by optimizing the hot rolled microstructure to produce final desirable recrystallization microstructure and texture.

Preparation of nanocrystalline Al3Ti/Al13(Fe,Ni)4 intermetallic compound by means of melt spinning and subsequent annealing

In present study, the fabrication and structural characterization of nanocrystalline Al3Ti/Al13(Fe,Ni)4 intermetallic compound by means of melt spinning and subsequent annealing has been performed. For this purpose, melt spinning process was done in Al80Fe10Ti5Ni5 (at%) alloying system at different wheel speeds in the range of 20–50 m/s. To achieve the desired microstructure, the melt spun ribbons were annealed at temperatures between 300 and 600 °C. The prepared samples were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), differential scanning calorimetry (DSC) and nano-indentation (NI) techniques. During the melt spinning with a wheel speed of 50 m/s, a fully amorphous phase was formed in the Al80Fe10Ti5Ni5 alloying system. By annealing the produced amorphous phase, Al3Ti and Al13(Fe,Ni)4 intermetallic phases precipitated from the amorphous matrix. The fully amorphous phase has a hardness about 4.5 GPa, which increased to about 6.2 GPa after annealing process.

An inverse design framework for prescribing precipitation heat treatments from a target microstructure

The computer-aided materials design process is highly iterative in nature and as such requires flexible tools that have the ability to link processing, properties, and performance not only in the usual forward direction but also in the inverse direction more associated with a goal-oriented/design framework of Integrated Computational Materials Engineering (ICME). While many computational techniques exist that relate properties to performance in both forward/inverse directions, tools that prescribe a process when given a desired microstructure have not been developed in detail. This research fills that gap by coupling physics-based precipitation models with “mesh adaptive direct search” optimization techniques as a strategy to develop (inverse) microstructure-processing relations. This framework is demonstrated by prescribing heat treatments in Ni-rich NiTi shape memory alloys that will result in a desired size distribution of Ni4Ti3 precipitates. This prescriptive technique provides a rigorous strategy for the identification of materials processing schedules—provided the forward models connecting processing and microstructure are available—that yield specific microstructural features and that can significantly reduce the experimental search space that needs to be explored, accelerating the materials development process.

Development and design of microstructure based coated electrode for ballistic performance of shielded metal arc welded armour steel joints

Joining of high strength armour steel plate developed for lighter armour vehicles using both austenitic and ferritic type of electrode/filler wire could show inferior ballistic performance of the welds. Combination of hard facing electrode and softer Austenitic Stainless Steel electrodes, though provided improved ballistic performance, might not satisfy main design criteria such as strength and toughness due to non-homogeneous microstructure of weld metal. In order to satisfy improved ballistic performance as well as other design parameters, it is highly desirable to develop coated electrode which will attribute more homogeneous microstructure in weld metal similar to high strength armour steel plate.The present investigation has attempted to obtain martensite, bainite and some amount of retained austenite in the weld metal by proper design of alloying elements in the coating of SMAW electrode based on metallurgical index. Three different electrodes attributing different combination of microstructural constituents in armour steel weld metals exhibited excellent ballistic performance combined with other design criteria such as strength and toughness at −40°C. However, among the different microstructural constituents lower bainite along with retained austenite showing maximum toughness both at room temperature and at −40°C could be considered as most desirable microstructure in armour steel weld metal.

Effects of Coiling Temperature after Hot Rolling on Microstructure, Texture, and Magnetic Properties of Non-Oriented Electrical Steel in Strip Casting Processing Route

Low silicon non-oriented electrical steel is produced using a novel strip casting processing route. The focus is on investigating the effects of coiling temperature after hot rolling on microstructure, texture evolution, and magnetic properties. A fine microstructure with weak λ-fiber texture is formed after coiling at 650 °C. By contrast, a much coarser microstructure with a much stronger λ-fiber texture is produced after coiling at 750 °C. After cold rolling and annealing, a fine and inhomogeneous recrystallization microstructure dominated by mild λ-fiber, α-fiber, and γ-fiber recrystallization texture is formed in the case of coiling at 650 °C. By contrast, a coarse and inhomogeneous recrystallization microstructure characterized by strong Goss, α-fiber, and weak λ-fiber together with extremely weak γ-fiber recrystallization texture is formed in the case of coiling at 750 °C. Much lower iron loss and higher magnetic induction are obtained in the latter case as a result of the more desirable recrystallization microstructure and texture. It underscores that the relatively higher temperature of coiling has a similar effect as the conventional hot-band normalizing. Hence, the hot-band normalizing might be omitted in the fabrication of high-performance non-oriented electrical steels using this novel and compact strip casting production route.

Electron Beam Melting of Ti-48Al-2Nb-0.7Cr-0.3Si: Feasibility investigation

In this work, carried out within the European project TIALCHARGER, TiAl-based powders of Ti-48Al-2Nb-0.7Cr-0.3Si, were used to fabricate specimens and prototypes of hollow turbocharger turbines by Electron Beam Melting (EBM). This additive manufacturing technology uses an electron beam to generate parts by selectively melting the powders layer by layer according to CAD data. Components produced with these powders were characterized in terms of residual defects and resulted appropriate both in terms of overall residual porosity and maximum defect size. Furthermore the microstructure of the as produced material was investigated and heat treatments were set up in order to obtain the desired microstructure. This is an essential point for these materials because their mechanical properties are extremely sensitive to microstructure. Chemical composition of powders and massive materials were analysed. Loss of Al was observed, while the levels of impurities were very low and similar for both the powder and the part. Mechanical tests were performed on the heat treated samples and the results are in well agreement with literature data for this TiAl alloy for the desired automotive application.

A Novel Manufacturing Route for Automobile Parts through Two-Wire-Arc Thermal Spray Process

The present work deals with a novel manufacturing route that can be used to fabricate automobile sheet parts such as bonnet/bumper by metal alloy coating through two-wire-arc thermal spray (TWATS) process. Later the coating is supported with fiber through cladding process and becomes a freestanding composite coating. The coating has a metallic look and is free from oxidation. This novel manufacturing process is rapid and customized. A case study, where aluminum alloy wire was used to produce freestanding coating, was performed by response surface method optimization of the two-wire-arc spray process factors: the voltage, current, spray distance, gas pressure, and selection of mold/substrate material that was used to fabricate automobile bonnet. Initial experiments were performed on the four different substrates materials, viz., steel, aluminum, ceramic, and graphite; the graphite substrate showed some promising results and was selected to run the experimental array to optimize the process parameters. Spray distance more than 150 mm, voltage 30 V, current 250 A, and primary atomizing gas (nitrogen) pressure 100 psi (0.689 MPa) may be used. The freestanding aluminum coating was evaluated analyzing its performance, in terms of desirable microstructure and mechanical properties.

Melt-cast microfibers of Cu-based shape memory alloy adopt a favorable texture for superelasticity

Continuous production of shape memory alloy (SMA) fibers and microfibers is a non-trivial task due to the challenges associated with their undeformed memory and, for many copper-based SMAs, brittleness in non-engineered forms. Here we demonstrate the direct continuous casting of super-meter-scale Cu-based SMA microfibers into a desirable oligocrystalline microstructure that is not brittle. The melt-casting process used here develops a favorable texture as well, leading to large superelastic strains (above 8%), beyond what is typical for non-single-crystal SMAs.