Homogeneous Microstructure Research Articles

Strengthened solid solution and homogenized eutectic structure of Al-based multi-component alloy via electromagnetic stirring

Macro-segregation and coarse intermetallic compounds (IMCs) are common problems in lightweight multi-component alloys (MCAs), in this work, electromagnetic stirring treatment (EST) and mixed eutectic strategy were proposed to tune the solidified microstructure of Al-based MCA. For the studied MCA, the positive and negative segregation of solute elements (except for Si) were found both lower than 5 % in the ingot, and the macro-segregation was reduced by approximately 50 % after the EST utilized. Also, the dispersion of the fine eutectic β-Mg2Si phase was significantly promoted by applying EST, specifically, its size at the edge of the ingot was ranged in 2–4 μm. Consequently, the alloy prepared by EST present superior strength-plasticity synergy at room temperature (RT), with the ultimate compressive strength reaching 724 MPa at the edge of the ingot and the strain reaching 15.1 % at the center of the ingot. Moreover, EST was determined enhance the content of solid-solutioned Al atoms in the eutectic β-phase, thus varied its crystal structure and reduced its hardness and Young's modulus, and futher enhanced the deformation coordination between the IMCs and the matrix, thereby improving the mechanical properties of the alloy. This study elaborated the underlying mechanism of microstructural homogeneity regulation, the obtained results could offer guidance for fabricating large-sized Al-based MCAs with excellent mechanical properties.

Friction Stir Welding of AZ31 Mg Alloy: Microstructure, Micro hardness and Electrochemical Behavior

In this investigation, rolled plates of AZ31 Mg alloy were successfully friction-stir welded. It was found that the process leads to the microstructural refinement in the NZ due to the dynamic recrystallization with a global microstructural heterogeneity through the weld. The maximum microhardness values were attributed to the finest microstructure. The obtained results revealed that the cathodic behavior of the grain boundaries improves the corrosion resistance of the NZ. Thus, the corrosion resistance enhancement was ascribed to the most homogeneous microstructure and the finest grains.

Microstructure, mechanical properties and corrosion behavior of W-B-Ni-Fe shielding cermets synthesized by reactive boride sintering

In this work, a novel type of nuclear shielding material capable of shielding γ rays and neutrons, W-B-Ni-Fe cermets, was synthesized using W, NiB, and Fe powders by reactive boride sintering. The cermets possessed a constant (Ni + Fe)/B atomic ratio of 1.50 and various W/B atomic ratio (ARWB) of 8.26, 3.25, 1.88 and 1.24, respectively. Microstructure and mechanical properties were characterized and analyzed, and corrosion behavior was discussed using electrochemical method in 1.0 M H2SO4 aqueous solution. After sintering, the cermets were composed of orthorhombic W2(Ni,Fe)B2 hard phase, W phase and Ni based binder phase. The homogeneous microstructure with both fine W2(Ni,Fe)B2 and W particles was obtained when ARWB was 3.25. At room temperature (RT), the hardness increased monotonically with ARWB decreasing, while the compressive and bending strengths peaked when ARWB was 3.25 due to the cooperativeeffect of hard-phase and grain-refinement strengthening. At high temperature (500 ℃), the presence of ductile W phase enabled an increase of bending strength compared to that at RT. The corrosion of cermets in 1.0 M H2SO4 solution began with active dissolution of Ni based binder phase, and then the passivation process occurred with the formation of blue WO3-x phase. With ARWB decreasing, Icorr was first sharply decreased and then sharply increased. The impedance value of cermet was lowest when ARWB was 3.25 which is due to the relatively lower forming ability of passive film.

Study on microstructure evolution mechanism and inhomogeneous characteristic of 2219 aluminum alloy in hot flow forming

In order to reveal the evolution mechanism of the deformation microstructure of 2219 aluminum alloy tube under compression-shear stress, in this paper, flow forming tests and their numerical simulations were carried out, respectively, at temperatures from 250 °C to 400 °C. Meanwhile, a midrange layer index was proposed to analyze the gradient of deformation microstructure. The results show that multiple recrystallization mechanisms of the 2219 aluminum alloy are presented simultaneously during hot flow forming. The shear stress during forming is the main factor that generated the microstructure gradient along the thickness direction, and the recrystallization level is higher with higher shear strain. In addition, it is beneficial to improve microstructure homogeneity and mechanical properties by increasing thickness reduction or decreasing the temperature. This study provides guidance for microstructure control of the 2219 aluminum alloy tube flow forming process.

Atom Probe Tomography Investigation of Clustering in Model P2O5-Doped Borosilicate Glasses for Nuclear Waste Vitrification.

Atom probe tomography (APT) has been utilized to investigate the microstructure of two model borosilicate glasses designed to understand the solubility limits of phosphorous pentoxide (P2O5). This component is found in certain high-level radioactive defence wastes destined for vitrification, where phase separation can potentially lead to a number of issues relating to the processing of the glass and its long-term chemical and structural stability. The development of suitable focused ion beam (FIB)-preparation routes and APT analysis conditions were initially determined for the model glasses, before examining their detailed microstructures. In a 3.0 mol% P2O5-doped glass, both visual inspection and sensitive statistical analysis of the APT data show homogeneous microstructures, while raising the content to 4.0 mol% initiates the formation of phosphorus-enriched nanoscale precipitates. This study confirms the expected inhomogeneities and phase separation of these glasses and offers routes to characterizing these at near-atomic scale resolution using APT.

Achieving Homogeneous Microstructure and Superior Properties in High-N Austenitic Stainless Steel via a Novel Atmosphere-Switching Method

Powder metallurgy is widely used to fabricate high-nitrogen, nickel-free austenitic stainless steel. However, after sintering and nitriding, additional solution treatment is typically required to achieve uniform nitrogen distribution and a homogeneous austenite phase. This work proposes a novel method to eliminate the need for lengthy and high-temperature solution treatment by switching the nitrogen atmosphere to argon during the cooling process. The effects of different N2-Ar atmosphere-switching temperatures (750–1320 °C) on the phase composition, element distribution, microstructure, mechanical properties, and corrosion resistance of the studied steels were systematically investigated. Results show that cooling in the N2 atmosphere initially transforms the matrix to a fully austenitic structure enriched with nitrogen. Excessive nitrogen infiltration leads to Cr2N precipitation, inducing partial austenite decomposition and forming a multiphase structure comprising austenite, α-Fe, and Cr2N. Strategic switching from N2 to Ar reverses this reaction, yielding a high-nitrogen, chemically uniform austenitic structure. Specifically, switching at 1150 °C, the steel exhibits excellent mechanical properties and corrosion resistance, with a yield strength of 749 MPa, an ultimate tensile strength of 1030 MPa, an elongation of 38.7%, and a corrosion current of 0.06 mA/cm2, outperforming the steels cooled solely in N2 and subsequently solution-treated. This novel method offers advantages in cost reduction, energy saving, and operational effectiveness, highlighting its potential for broad industrial application.

New Insights into the Ingot Breakdown Mechanism of Near-β Titanium Alloy: An Orientation-Driven Perspective

The ingot breakdown behavior of a typical near-β titanium alloy, Ti-55511, was investigated by various multi-pass upsetting processes. Particular emphasis was placed on the breakdown mechanism of the ultra-large β grains. The results showed that the upsetting far above the β-transus yielded uniform and refined macrostructure with relatively coarse grain size. In contrast, subtransus deformation within the (α + β) dual-phase field caused severe strain localization and macroscale shear bands. It was found that the static recrystallization during the post-deformation annealing was determined by the preferential grain orientations, which were closely related to the processing conditions. During β-working, the stable <001>-oriented grains were predominant and fragmentized mainly via a so-called “low-angle grain boundary merging” mechanism, even under a fairly low deformation. However, the vast <001> grain area was unbeneficial for microstructural conversion since it provided minor nucleation sites for the subsequent annealing. In contrast, the α/β-working produced the majority <111>-orientated grains, which were strongly inclined to strain localization. Highly misoriented deformation/shear bands were massively produced within the <111> grains, providing abundant nucleation sites for static recrystallization and, hence, were favorable for microstructural refinement. Furthermore, the intrinsic causes for deformation nonuniformity were discussed in detail, as well as the competition between microstructural homogeneity and refinement.

Experimental investigation on characterization of friction stir processed AZ31-based composite

Present study has been conducted to characterize the Mg alloy namely AZ31-based composite joined by Friction stir processing (FSP) technique. This study deals with the effect of single and double passes in FSP of AZ31 Mg alloy. The single pass run in FSP is followed at tool rotation speed (N) of 1000 to 1400 rpm. Also, the double pass run in FSP was followed at these speeds without using reinforcements. The feedstock particles namely SiC, Al2O3, Cr, and Si powders were used in fabrication process. The hardness, impact strength, and tensile strength characteristics were assessed in the stir region zone, and the results indicated significant improvement in these properties. The highest values of mechanical strength were seen in the FSPed area with N = 1000 rpm at a constant transverse speed (r) of 40 mm/min. Also, the tensile strength of the two passes FSPed plates is much higher than that of the single section without any reinforcement, as revealed in previous study also. The Scanning electron microscopy (SEM) analysis is done at two different magnifications for the Silicon carbide, Alumina, Chromium, and Silicon powder reinforced composites fabricated at speed of 1000 rpm. The microstructure shows that reinforced particles were uniform dispersed into FSPed region and agglomerated with Mg matrix. Si powder produces finer microstructure as compare to SiC, Al2O3, Cr. FSP decreases the grain size of processed material. Optical Microscopy results revealed that the reinforcement particle produced a homogenous microstructure and, a refined grain and equally dispersed in matrix material without split to the particle.

First report of Sansabaina acicula, an organic-cemented siliceous agglutinated foraminifera from the Early Permian glaciomarine Pebbley Beach Formation, Southern Sydney Basin, southeastern Australia

A ca 6 cm-thick microfossil coquina bed dominated by plastically deformed and siliceous tubular test fragments is described for the first time from the Lower Permian (Artinskian) Pebbley Beach Formation of coastal and glacial marine origin in the southern Sydney Basin, southeastern Australia. The test fragments are mostly very large, straight, smooth, nearly cylindrical in shape, and the test walls are composed mainly of homogenous microcrystalline quartz grains. This homogeneous siliceous test-wall microstructure is interpreted to have resulted from diagenetic alteration of what might have been originally organic-cemented, flexible (not rigid) and siliceous agglutinated walls. As such, this microscopic tubular test is identified as Sansabaina acicula, an organic-cemented siliceous-agglutinated foraminifera originally described from the Kungurian Quinnanie Shale in the Carnarvon Basin of Western Australia. The discovery of Sansabaina acicula supports the previous interpretation of the studied strata being deposited in a stressed marine shelf environment. G. R. Shi [guang@uow.edu.au], Sangmin Lee* [lsam@uow.edu.au], Paul F. Carr [pcarr@uow.edu.au] and Brian G. Jones [briangj@uow.edu.au], School of Earth, Atmospheric and Life Sciences, University of Wollongong, Northfields Avenue, NSW 2522 Australia David W. Haig [david.haig@uwa.edu.au], Oceans Institute, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia.

Simultaneously enhancing mechanical and anti-corrosion properties of aluminum through electrodeposition of supersaturated Al(Fe) solid solutions

The heterogeneous microstructure in bulk aluminum (Al) alloys or coatings, comprising an α-Al solid solution matrix and coarse intermetallic compounds (IMCs), poses a challenge in balancing mechanical and anti-corrosion properties. This challenge is particularly pronounced in Al alloys with high iron (Fe) content. Here, supersaturated Al(Fe) solid solutions with a single phase have been electrodeposited using imidazolium chloroaluminate ionic liquids (ILs). Ferrous chloride (FeCl2) dissolved in Lewis-acidic ILs is assumed to form Cl-bridged [Fe(AlCl4)4]2−, which, together with the well-known Al2Cl7− species, supports the reduction and deposition of Al(Fe) alloy coatings. The supersaturated Fe solutes significantly strengthens the Al matrix, with the hardness of Al(Fe, 6.6 at.%) reaching up to 3.43 GPa, surpassing that of any commercial Al alloys and other binary Al-based solid solutions. Moreover, the Al(Fe) deposits demonstrate superior anti-corrosion performance compared to pure Al. The homogeneous microstructure and extended Fe solubility within Al(Fe) solid solutions inherently contributes to a simultaneous improvements in mechanical and anti-corrosion properties. The nanograined and compact structure also benefit these properties. Accordingly, the combination of electrodeposition techniques and Al(Fe) alloys offers a promising approach for providing effective mechanical and chemical protection on metal surfaces.

Physicochemical quality improvement of dried rice noodles by direct heat-moisture treatment during the drying process

In view of the advantage of heat-moisture treatment (HMT) in modifying the properties of starchy materials, the purpose of this study was to explore the effects of directly applying HMT during the drying process on the properties of dried rice noodles. As attained to prescribed moisture content (20%–35%), the rice noodles were subjected to HMT at 110 °C for 2 h. By HMT, the dried rice noodles exhibited greater structural orderliness and thermal resistance. The relative crystallinity increased from 8.73% to 11.50% and the short-range order (the absorbance ratio of 1047 cm−1/1022 cm−1) increased from 0.57 to 0.72. On the contrary, the lamellar thickness, the radius of gyration, and the mass fractal dimension and pasting viscosities were lowered. Then, HMT induced dried rice noodles with restricted starch leaching during rehydration and reduced cooking loss. HMT increased microstructure homogeneity and texture properties of the cooked rice noodles. Notably, the heat-moisture treated rice noodles at 20% moisture content showed a significant higher cooking yield, about threefold of extensibility, and 1.68 folds of chewiness than the control. Our findings, if generally applicable to the processing of rice noodles, could offer a streamlined approach to increasing the quality of dried rice noodles.

Relation between Tensile Strut and Compressive Foam Deformation Behaviour: Failure Mechanisms and the Influence of Dendritic Versus Globular Grain Structure in an AlSi7Mg0.3 (A356) Precision‐Cast Open‐Cell Foam

Open‐cell aluminum foams are gaining importance for the design of lightweight structures and as electrodes in lithium‐ion batteries. AlSi7Mg0.3 foams were produced by a modified investment‐casting process. By tuning the mold temperature, a change from the usual nearly monocrystalline dendritic to a polycrystalline globular grain structure was achieved. Tension and compression tests on single struts and foam specimens, respectively, were combined with digital image correlation, scanning electron microscopy, and phase‐contrast enhanced micro‐computed tomography in a synchrotron facility to correlate the mechanical properties and the failure mechanisms with the microstructure. The “globular” foams exhibited a lower strength and a less pronounced subsequent stress drop than the “dendritic” foams, and the deformation mechanism changed from shear‐band dominated failure to a layer‐by‐layer collapse, because of the lower strength and higher ductility of the “globular” struts. The “dendritic” struts have a more homogeneous microstructure, while the “globular” struts often contain silicon agglomerates in their central region. Accordingly, the latter struts exhibit a higher degree of scatter for the fracture strain. Thus, the arrangement of the silicon particles and the eutectic determines the mechanical properties on the strut level and thereby the failure behavior on the foam level.This article is protected by copyright. All rights reserved.

Investigating the Microstructural Evolution and Homogeneity in Al 6061 Alloy Processed through Multi-directional Forging at Cryogenic Temperature

Investigating the Microstructural Evolution and Homogeneity in Al 6061 Alloy Processed through Multi-directional Forging at Cryogenic Temperature

High cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing

In this work, the high cycle fatigue behavior of bulk 6061Al prepared by cold spray-friction stir processing composite additive manufacturing (CFAM) was studied for the first time. The microstructure and fatigue fracture morphology of CFAM sample were characterized by scanning electron microscopy equipped with electron backscattering diffraction. The stress versus number of cycles of failure (S-N) curve for CFAM sample was established, and the fatigue crack growth behavior of CFAM sample was analyzed. The results showed that the microstructure of CFAM sample was denser and more homogeneous compared with cold spray (CS) sample, and the average grain size was refined to 3.3 μm due to dynamic recrystallisation. The dense, homogeneous and fine microstructure delayed the initiation and growth of fatigue cracks, and thus resulted in a 178% increase in fatigue strength in the CFAM sample over CS sample. The fatigue surface of the CFAM sample could be divided into fatigue source zone, crack growth zone, and transient fracture zone, showing typical fatigue fracture characteristics. The fatigue crack growth rate in the CFAM sample was significantly lower than that of CS sample for the same stress intensity factor range (ΔK). This was because the fine grains uniformly distributed in CFAM sample increased the proportion of grain boundaries and hindered the fatigue cracks growth. Therefore, CFAM is a promising technology for preparing bulk 6061 Al with excellent fatigue properties.

Digestion of mixed protein gels using elderly static in vitro digestion model: Impact of microstructure on bioaccessibility of vitamins B12 and D3

The intake of food products that provide adequate amounts of nutrients is a strategy to deal with the changes in physiological functions that occur during aging that can lead to malnutrition. In this work heat-set mixed protein gels (MPG) composed of soy protein isolate (SPI) and whey protein isolate (WPI) are developed, with different SPI:WPI ratios (15 g protein isolate/100 g gel) and enriched with vitamins D3 and B12. Different protein ratios formed gels with different microstructures and rheological properties. The gel containing 70 % of WPI had a more homogeneous microstructure. The influence of the MPG microstructure on the digestion and bioaccessibility of proteins and vitamins using elderly static in vitro digestion was evaluated. An important result is that mixing SPI and WPI increased the proteolysis. Regarding vitamins bioaccessibility, vitamin D3 became more bioaccessible after the intestinal phase, and there was no difference in vitamin B12 concentration in the intestinal and gastric phases. Therefore, mixing SPI and WPI to produce MPG resulted in improved digestion of proteins, as well as higher bioaccessibility of the vitamins. The results indicated the MPG are promising protein matrices to be used in food products for the elderly.

The influence of sintering additives on densification and phase composition of ZrB2 – HfB2 composite

This work deals with the preparation of composites from the ZrB2-HfB2-MeX system (where: MeX = SiC, B4C, WC, MoSi2 and CrSi2). Three pressure-assisted sintering techniques were used to obtain the composites, i.e. hot-pressing (HP), spark-plasma sintering (SPS) and high pressure-high temperature (HPHT) sintering. Hot-pressing was selected as the most favourable sintering technique. The composites obtained via hot-pressing were characterized by high density and homogeneous microstructure. The work did not undermine or justify the need to reduce passivating oxide layers on boride grains. In the case of silicides, especially chromium silicide, there was a significant reduction in the sintering temperature of the ZrB2-HfB2 composites by about 500–600°C. In composites with the addition of silicides, there is a tendency to create complex solid solutions, which is visible as core-shell microstructures.

Microstructure and mechanical properties of a porous ceramic composite with needle‐like mullite and zirconia

AbstractPorous mullite ceramics have good properties for high‐temperature applications, but porosity gives place to ceramics with low mechanical strength, which restricts the service life in their potential applications. Therefore, performing modifications at the microscale to increase the mechanical strength has become a current challenge to expand its application fields. This work describes the properties of a porous mullite–zirconia composite produced by ceramic processing, using industrial kaolin and stabilized zirconia as raw materials. The growth of mullite needle‐like grains to reinforce the ceramic was promoted by the addition of a molybdenum oxide precursor. The effect of zirconia on the composite was analyzed through an experimental multi‐technique approach and considering a pure mullite sample, identically processed, as a reference. The novel composite has a porosity of about 50%, and presents a homogeneous microstructure, with interlocked mullite needle‐like grains and dispersed rounded zirconia grains. This morphology restricts the mullite tendency to shrink during sintering, giving the material a higher stiffness. In particular, the presence of zirconia in the composite improves both the flexural strength and the apparent Young modulus of the material (about 20% and up to 600%, respectively). These results encourage further investigations to establish this composite for different technological applications.

Investigations on kaolin mixtures: Impact on mullite formation kinetics and microstructure evolution

AbstractThis study evaluates Algerian kaolin (Djebel Debbagh (DD1) and Tamazart (KT2)) as potential substitutes for commercial kaolin (Lab) in the production of mullite‐based ceramics. Three compositions were prepared by incorporating the appropriate percentage of alumina to each calcined kaolin to achieve stoichiometric mullite precursors. The phase evolution of individual kaolin powders, as well as their mixtures with alumina, depends strongly on the calcination temperature and kaolin impurities. The differential scanning calorimetry combined with thermogravimetric analysis (TGA) showed lower secondary mullite formation temperature for the KT2‐based mixture. However, X‐ray diffraction revealed a complete mullitization in DD1 mixture. The K2O hindered cristobalite formation and reduced secondary mullite formation rate. Microstructure analysis showed lath‐shaped primary mullite and equi‐axed secondary mullite particles. After sintering at 1600°C, The KT2‐based sample (M3) exhibited higher density (3.013 g/cm3) and hardness (9.9 GPa), whereas the DD2‐based sample (M2) showed moderate densification (2.91 g/cm3) and higher flexural strength (159.42 MPa). Impurities (mainly Fe2O3, and K2O) promoted liquid phase sintering, resulting in greater densification in M3, whereas M2 showed more homogeneous microstructure, refined grains, and lower glassy phase content, contributing to enhanced strength.

Achieving High-Strength Ductility Property in a Microstructure Homogenization Al-Zn-Mg-Cu Alloy by Electroshock Treatment

Achieving High-Strength Ductility Property in a Microstructure Homogenization Al-Zn-Mg-Cu Alloy by Electroshock Treatment

Material extrusion: A promising tool for processing CoCrMo alloy with excellent wear resistance for biomedical applications

CoCrMo is a prevalent alloy in prosthesis manufacturing, characterized by its favorable biocompatibility, high resistance to corrosion and high wear-resistance. Material Extrusion (MEX) Additive Manufacturing allows control over microstructural homogeneity, minimizing material waste and enabling the selection of the geometry and size of the parts, key features in the biomedical field. Granule-based MEX has been recently developed and uses a granulated metal-polymer composite as starting material that is extruded to fabricate complex parts. The binder is eliminated and the final part is obtained after sintering. This research aims to investigate the potential of MEX as a promising route for fabricating CoCrMo parts for prosthesis manufacturing. A feedstock based on Paraffin Wax and High-Density Polyethylene as binder, was prepared with optimized solid loading, then screw based MEX printing parameters, in terms of printing temperature and extrusion flow, were explored to maximize density after sintering. The microstructure development was evaluated based on carbon content, shrinkage, density, grain size, and hardness and wear performance of the optimized samples investigated. Almost fully dense parts with a microstructure free of carbides and secondary phases has been developed, which enables an excellent wear response in terms of wear rate and wear coefficient.