Fine Grain Research Articles

Microstructure and Mechanical Properties of Mg-8Li-3Al-0.3Si Alloy Deformed Through a Combination of Back-Extrusion and Spinning Process

In this work, the Mg-8Li-3Al-0.3Si (LAS830) alloy was prepared by the vacuum melting method. The as-cast alloy was subjected to backward extrusion at 250 °C and then spun at 250 °C. The microstructure and mechanical properties of the alloy during deformation were studied. The results showed that the LAS830 alloy primarily consisted of α-Mg and β-Li phases, and the AlLi, MgLi2Al, and Mg2Si phases were dispersed. After backward extrusion, the grains and AlLi phase were refined, the β-Li phase recrystallized, and the fine MgLi2Al phase precipitated. The spinning of the extruded alloy tubes resulted in the lamellar distribution of an α/β duplex microstructure, with even finer grains and more dispersed precipitates. The combined deformation significantly enhanced the alloy’s strength and ductility, with the ultimate tensile strength reaching 235.4 MPa and an elongation of 15.74%. In addition, the average hardness of the α/β phase increases after backward extrusion, but the average hardness of the β-Li phase increases further after spinning. The as-cast LAS830 alloy exhibited a high work hardening rate but a low softening rate. With reverse extrusion, the work hardening rate decreased and the softening degree increased. Compared with backward extrusion, the work hardening rate and softening degree of the LAS830 alloy was reduced after spinning due to the combined effect of the lamellar distributed duplex microstructure and the dispersed second phases in the alloy, while its softening rate increased.

Functionally Graded Oxide Scale on (Hf,Zr,Ti)B2 Coating with Exceptional Ablation Resistance Induced by Unique Ti Dissolving.

Multicomponent Ti-containing ultra-high temperature ceramics (UHTCs) have emerged as more promising ablation-resistant materials than typical UHTCs for applications above 2000 °C. However, the underlying mechanism of Ti improving the ablation performance is still obscure. Here, (Hf,Zr,Ti)B2 coatings are fabricated by supersonic atmospheric plasma spraying, and the effects of Ti content on the ablation performance under an oxyacetylene flame are investigated. The (Hf0.45Zr0.45Ti0.10)B2 coating shows superior ablation resistance and cycling reliability at ≈2200°C. A functionally graded oxide scale comprising an outer dense layer and an underlying fine granular layer formed. The former is a better oxygen barrier owing to fewer cracks and the latter has high strain tolerance due to finer grain size. The uniform dissolving of ≈4 mol% Ti in the inner layer results in grain refinement via sluggish diffusion and thus stress release. For the outer layer, Ti segregation at the nanoscale leads to a metastable cubic (Hf,Zr,Ti)O2 and local severe lattice distortion, inhibiting the propagation of cracks. Ti ions' unique dissolving in the oxide scale enables a strong oxygen diffusion barrier with high strain tolerance, which is responsible for superior performance. This study provides new insights into the ablation behavior of Ti-containing multicomponent UHTCs.

TIG Welding of EN AW-6082 Al Alloy: A Comparative Analysis of Filler Rods on Microstructural and Mechanical Performance

This study investigates the impact of different filler wires (ER5356, ER4043, and ER4047) on the microstructural and mechanical properties of EN AW-6082 Al alloy joints produced by tungsten inert gas (TIG) welding. Butt-welded samples with a single V-groove joint configuration were prepared using optimized welding parameters. The welded samples were subjected to visual inspection, microstructural analysis, hardness testing, tensile testing, and impact toughness evaluation. The results showed that all the welds were free of visible defects. Microstructural examination revealed that the ER5356 filler produced the finest grain structure of 18.03 ± 3 μm, while ER4047 resulted in the coarsest grains of 36.07 ± 5 μm. Correspondingly, the joints made with ER5356 exhibited the highest tensile stress of 278 ± 6 MPa, yield stress of 219 ± 5.4 MPa, hardness values of 72.7 ± 5 HV, and welding efficiency of 86.07%, whereas those made with ER4047 produced the lowest values. The hardness in the weld region was lower than that in the parent metal and heat-affected zone for all samples. However, ER4047 welds demonstrated superior impact toughness and strain-hardening capacity. The findings underscore the importance of filler metal selection in tailoring mechanical properties for high-performance applications.

Comparative Study on Combined Addition of Gd-Ce and Gd-Y on the Mechanical Properties and Electrochemical Behavior of Mg-Zn-Mn-Ca Alloys

This study presents a comparative analysis of the influence of Ce-Gd and Gd-Y additions on the microstructural evolution, mechanical properties, and electrochemical behavior of extruded Mg-3Zn-Mn-Ca alloy rods. Despite the frequent incorporation of Gd, Y, and Ce as alloying elements in magnesium alloys, the systematic examination of their combined effects on Mg-Zn alloys has been limited. Our findings reveal that both Gd-Ce and Gd-Y additions significantly enhance the mechanical properties of Mg-3Zn-Mn-Ca alloy, although through differing mechanisms. Specifically, the Mg-3Zn-1Mn-0.5Ca-1Gd-0.5Ce(ZMXE3101(GdCe)) alloy exhibited a yield strength of 304.5 MPa and an elongation of 15%, achieved through dynamic recrystallization and enhanced basal texture. The grain refinement and texture strengthening resulting from the coarse second-phase particles formed by Ce-Gd played a significant role in increasing the yield strength. In contrast, the Mg-3Zn-1Mn-0.5Ca-1Gd-0.5Y (ZMXE3101(GdY)) alloy demonstrated a yield strength of 305 MPa and an elongation of 20%. The finer grains and elongated unrecrystallized grains formed by Gd-Y contributed to the elevation in yield strength. While the ductility of this alloy was slightly lower than that of Mg-3Zn-Mn-Ca without rare earth additions, it still exhibited commendable overall mechanical properties. The electrochemical test results indicate that the addition of both Gd-Ce and Gd-Y enhances the corrosion current density of Mg-3Zn-Mn-Ca alloy, attributable to the generation of numerous rare earth phase particles that function as cathodes. Compared to the ZMXE3101(GdY) alloy, ZMXE3101(GdCe) exhibits a higher equilibrium potential and significantly lower corrosion current density. This is due to the formation of a protective film during the corrosion process by Gd-Ce.

Microstructure and Tensile Behaviors of Laser-Arc Hybrid Welds Comparing to Submerged Arc Welds of High-Manganese Steel for Cryogenic Applications

The weldability and the relationship between microstructure and tensile properties at 298 and 110 K produced by laser-arc hybrid welding (LAHW) in high-Mn steel welds were thoroughly investigated. In the laser zone of LAHWs using filler wire, more Mn vaporization in the laser zone was observed than at the arc zone of LAHWs. The arc zone showed a decrease in Mn content of ~0.6 wt%, while the laser zone showed a decrease of ~0.9 wt%. The arc and laser zones of the LAHWs showed stacking fault energies (SFEs) of 17.8 and 17.3 mJ/m², respectively. The tensile deformation of LAHWs at 298 K was conducted with a deformation twins mode, while it was shifted to deformation twins + ε-martensite transformation at 110 K. The yield strength was slightly higher in the laser zone, which had a finer grain size compared to the arc zone. The formation of ε-martensite with deformation twins preceded necking during tensile testing, therefore increasing the yield strength at 110 K. In terms of performance, the LAHW process demonstrated a 25% increase in productivity compared to the conventional submerged arc welding (SAW) process, with a yield strength exceeding 400 MPa, comparable to that of SAW. These findings indicate that LAHW is a highly effective welding method for high-Mn steels, particularly in cryogenic applications.

Improvement of microstructure and mechanical properties for Al7075 aluminium reinforced with hybrid graphite and SiC particles via a combination of mechanical alloying and stir casting

Abstract This research focuses on the fabrication of Al7075 composites reinforced with varying amounts of nano-sized SiC particles (1.0, 1.5, and 2.0 wt%) combined with 0.5 wt% graphite (Gr), employing a hybrid process of mechanical alloying and semi-solid stir casting. The study investigates the influence of SiC content, nanoparticle feeding method, and the role of Gr on the microstructures, mechanical characteristics, and machinability of the composites. Microstructural analysis revealed that integrating milled powders into the molten Al7075 alloy produced a uniform dispersion of nanoscale SiC particles within the α-Al matrix, avoiding the particle agglomeration observed with the conventional method. Higher SiC content resulted in finer grains and improved mechanical performance. The Al7075-0.5Gr-2.0SiC composite exhibited a 16% increase in hardness relative to the unreinforced Al7075 alloy. The inclusion of nanoscale SiC particles notably enhanced tensile strength, while the presence of Gr acted as a lubricant, improving surface roughness.

Effect of feedstock bimodal powder design and cold isostatic pressing on the mechanical behavior of binder jetting additive manufactured Inconel 718 superalloy

Densification of metallic and ceramic materials within the context of binder jetting additive manufacturing (BJAM) presents a considerable technical challenge. This study leveraged a bimodal feedstock powder design, in conjunction with cold isostatic pressing (CIP), to optimize the green density of BJAMed Inconel 718 (IN718) superalloy. This approach consequently elevated the sintered density and the attendant mechanical properties to their highest potential. Supplementary to this, a pair of heat treatment methodologies were executed: a solid solution-dual aging process (HT-1) and a dual aging process (HT-2), aimed at augmenting the mechanical properties of the alloy. The investigation revealed that the bimodal feedstock powder configuration, with a 10:1 mass ratio of coarse to fine particles (D50 29.1 μm and D50 11.4 μm, respectively), outperformed the unimodal powder design regarding relative density, dimensional precision, and mechanical integrity. Furthermore, the CIP process was identified as an essential step for enhancing the relative density and mechanical behavior of the BJAMed IN718 superalloy. The synergistic effect of the bimodal powder design and CIP treatment significantly improved densification, achieving a relative density of 98 %, and enhanced mechanical properties, with an ultimate tensile strength reaching 1105 MPa, even under the conditions of a relatively low sintering temperature of 1285 °C and a brief dwell time of 60 min. When juxtaposed with the as-sintered and HT-2 treated IN718 samples, the HT-1 treated IN718 displayed a finer grain structure within the γ matrix, which translated to superior mechanical properties, with an ultimate tensile strength of 1206 MPa.

Effects of rapid infrared radiation heating on the warping deformation and mechanical properties of selective laser melted Co-Cr dental alloy.

Infrared radiation heating (IRH) technology has been innovatively applied to the annealing of selective laser melted (SLM) cobalt chromium (Co-Cr) frameworks. However, previous studies have not reported the effects of IRH on the warping deformation and mechanical properties of these frameworks. The purpose of this in vitro study was to investigate the effects of IRH on the warping deformation and mechanical properties of dental SLM Co-Cr alloy and to evaluate its potential applications in dental restorations. Two types of specimens, bone-shaped tensile specimens and warping deformation specimens (cantilever beam structures), were fabricated by SLM, followed by annealing using IRH and general furnace heating (GFH). The specimens were divided into 4 groups (n=6) based on the applied heat treatment method and build direction (IRH-XY; IRH-Z; GFH-XY; GFH-Z). The cantilever beam support structure of the warping deformation specimen was cut using wire cutting, and the warping deformation was measured using a digital image correlation optical extensometer. Tensile tests were used to evaluate mechanical properties, with the fracture characteristics being observed using a scanning electron microscope (SEM). A micro-Vickers hardness tester was used to measure the microhardness. The microstructures were analyzed using a metallographic microscope. All data were analyzed using a 1-way ANOVA and the Tukey Honestly Significant Difference test (α=.05). The surfaces of the SLM Co-Cr warping deformation specimens treated with IRH showed slight oxidation, while those treated with GFH exhibited a dark black appearance. No significant difference was found in deformation between the IRH group (0.412 ±0.039 mm) and the GFH group (0.379 ±0.070 mm) (P>.05). The elongation of the longitudinally built specimens was significantly higher than that of their transversely built counterparts (P<.05), while the yield strength showed an opposite trend. The longitudinally built specimens demonstrated ductile fracture characteristics, while the transversely built specimens displayed quasi-cleavage fractures. The specimens treated with IRH exhibited comparable tensile strength and microhardness with the GFH-treated specimens, with no statistically significant differences (P>.05). IRH treatment resulted in finer grains in the SLM Co-Cr alloy. Many fine second-phase particles precipitated from the matrix in the longitudinally built specimens, while few were observed in the transversely built specimens. The SLM Co-Cr specimens treated with IRH achieved comparable warping deformation and mechanical properties with those of the GFH-treated specimens. The IRH technology holds great potential for application to dental restorations.

Effect of Post-Processing on the Microstructure of WE43 Magnesium Alloy Fabricated by Laser Powder Directed Energy Deposition

Additive manufacturing of magnesium (Mg) alloys is of interest for the fabrication of complex-shaped lightweight materials. This study evaluates the microstructure of WE43 Mg alloy deposited using laser powder directed energy deposition (LPDED) additive manufacturing technique in as-deposited and post-processed conditions. As-deposited samples exhibited roughly 2% porosity, which was reduced to below 0.1% after hot isostatic pressing. Despite limited grain growth after heat treatment, some grains experienced abnormal grain growth, likely due to Zener pinning and non-uniform dissolution of grain boundary precipitates. Moreover, as-deposited specimens contained Nd-rich grain boundary precipitates which dissolved during post-processing. Additionally, during heat treatment. a fine distribution of needle-like β1 or β precipitates formed. Overall, the precipitate size and distribution following heat treatment was non-uniform, likely because of the non-uniform response of the LPDED material to heat treatment, owing to the variation in local- and global-temperature profiles during deposition. Furthermore, arc-shaped phases with a high concentration of Y, O, and Zr were present for all processing conditions and are associated with the passivation of the feedstock powder prior to deposition. Moreover, an equiaxed-grain structure with a random orientation and a finer grain size in the regions adjacent to the arc-shaped phases was observed in all processing conditions.

Advanced machine learning for optimal parameter prediction in friction stir processing of Al-6061 alloy with alumina nanoparticle reinforcement

This study investigates the effects of friction stir processing (FSP) on Al-6061 aluminium alloy, reinforced with aluminium oxide nanoparticles. Using a CNC milling machine, various processing factors such as feed rate, number of passes, and rotational speed were explored to understand their influence on the ultimate and yield strengths, natural frequencies, and damping ratios of the samples. The processed data properties were predicted using a sophisticated machine learning technique called SRS-optimized long short-term memory (LSTME). Friction stir processing significantly enhances damping characteristics by refining the grain structure. Increasing rotational speed and traverse speed improve damping properties and mechanical characteristics. The addition of alumina nanoparticles further enhances the dampening capabilities of the material. The highest level of damping efficiency was seen when the rotational speed was set at 900 rpm for all measured passes. With an increasing number of passes as an FSP parameter, there is a decrease in the shear modulus and natural frequency, while the loss factor and damping ratio experience an increase. Higher rotational speeds generate additional thermal energy, resulting in stronger materials due to grain breakdown and increased resistance to deformation. This finer grain structure, resulting from higher rotational speeds, leads to stronger materials and higher yield strength. The developed machine learning model achieved impressive R2 values: 0.911 for ultimate strength (UTS), 0.951 for yield strength (YS), 0.953 for natural frequency, and 0.985 for damping ratio. Higher rotational speeds result in stronger materials, with a significant increase in yield strength attributed to finer grain structures.

Effect of Peening Media Type on the High‐Cycle Tensile–Tensile Fatigue Properties of Ti‐6Al‐4V Alloy by Ultrasonic Shot Peening

ABSTRACTThis study investigates the effect of ultrasonic shot peening (USP) on Ti‐6Al‐4V samples using cast steel and zirconia ceramic shots at the same intensity. The surface integrity of the samples before and after treatment was characterized, and tensile–tensile fatigue tests were conducted under various stress amplitudes to compare the improvements in fatigue performance. The mechanisms underlying the enhancement of fatigue properties were analyzed by examining microstructural changes and fracture morphologies. The results show that, compared to steel shot, zirconia ceramic shot leads to lower surface roughness, finer surface grains, and more significant work hardening and plastic deformation. These factors contribute to a more pronounced improvement in the fatigue performance under tension–tension loading of Ti‐6Al‐4V under USP treatment. The superior performance of ceramic shot can be attributed to low density combined with high hardness of the ceramic shot.

Cross-checking OSL ages from different grain sizes to improve chronological reliability in deltaic environments: an example from the Yangtze River Delta

The Yangtze River Delta has experienced intricate sedimentary and environmental changes throughout the Holocene, driven by the interplay of fluvial and marine forcings. This study presents quartz optically stimulated luminescence (OSL) ages and luminescence sensitivity data from a Holocene sediment core MQ, analyzed across four grain-size fractions, ranging from silt to sand. The results reveal substantial variability in OSL ages and sensitivity among grain sizes, with the medium-grain (45–63 μm) fraction yielding the most consistent and reliable results. In contrast, finer and coarser grains tend to overestimate ages due to incomplete bleaching, with the accurate dating of coarser grains requiring more aliquots or single-grain measurements. The variability in luminescence sensitivity reflects changes in sediment provenance and depositional conditions between estuarine and deltaic environments. OSL ages indicate that the sedimentary evolution of the Yangtze River Delta progressed through distinct phases: rapid accumulation during the early Holocene (10–7 ka) driven by rising sea level and valley infilling; reduced sedimentation during the middle Holocene (7–3 ka) related to a dry climate in the catchment; and accelerated deposition in the late Holocene (3 ka–present) associated with enhanced fluvial input linked to intensified human activities. This study highlights the importance of selecting suitable appropriate grain sizes and carefully comparing different fractions in OSL analysis to reconstruct deltaic chronologies accurately. The finding that the medium-grain fraction yields more reliable OSL ages than finer and coarser fractions should be tested in similar settings elsewhere. The results provide valuable insights for future research on complex depositional environments and contribute to a better understanding of long-term environmental changes.

Effect of tool pin profile on mechanical and microstructural properties of cooling assisted friction stir welding of AA6063-T6 weld joint

ABSTRACT Experiments have been performed in air and cooling-assisted condition with three tool pin profiles i.e. square, triangular and threaded cylinder. In this study, an effort has been made to comprehend how the mechanical characteristics, micro-hardness, and microstructure of friction stir welded AA6063-T6 joints are affected by in-process cooling, tool profiles, tool dimensions, and process parameters. For friction stir welding with cooling assistance, process parameters were optimised. For higher tensile and impact strength, a square tool profile with a shoulder to pin diameter ratio of 3:1 is found to be the most effective. The most important welding parameter was found to be rotations per minute (rpm). Microstructural analysis reveals finer grain size and a significant increase in microhardness in the weld nugget zone with cooling assisted FSW.

The Influence of Grain Size on the Abrasive Wear Resistance of Hardox 500 Steel

High-strength martensitic steels with boron are among the leading materials widely recognized for their exceptional resistance to abrasive wear. These steels exhibit some of the highest strength indices among bulk steels, a result of their specific chemical composition, thermomechanical rolling processes at the steel mill, and the use of pure, high-quality ores. With hardness values ranging from 400 to 650 HBW, they are ideal for demanding applications such as excavator buckets, plow blades, shafts, wear-resistant bars, and container liners. One critical microstructural property contributing to their high mechanical performance is the prior austenite grain size (PAG). A finer grain structure is associated with enhanced plasticity, and plastic deformation plays a significant role in abrasive wear mechanisms. However, this relationship between grain size and wear resistance is not well-documented in the literature, with few studies providing specific quantitative data. To address this gap, the authors conducted a study to examine the effect of prior austenite grain size on wear resistance when exposed to loose abrasive electrofused alumina no. 90. The findings indicate that applying targeted heat treatment can increase hardness by 58 Brinell units compared to the as-delivered condition. Moreover, as grain size increases from 18 µm to 130 µm, the relative abrasive wear resistance coefficient Kb decreases from 1.00 (for Hardox 500 steel in its as-delivered state) to 0.80 for austenitized material treated at 1200 °C.

Analysis of Mechanical Properties and Fatigue Resistance in Laser Welded WAAM Ultra-High-Strength Steel

The examination of WAAM UHS steel laser welds revealed effective material penetration, with desirable geometry showcased by a nearly I-shaped structure. Minor deficiencies were observed at the weld face, while excessive penetration was evident at the weld's root. Cross-sectional analysis indicated no discernible porosity or defects within the weld. Microstructural analysis highlighted fine-grained structures with dispersed precipitates in the WAAM UHS steel base material. Laser welding induced changes in the grain structure, resulting in finer grains and a mixture of ferrite and martensite in the weld zone. Significant increases in hardness were observed in the weld metal and HAZ near the fusion line, attributed to martensite prevalence induced by rapid cooling rates. The hardness of the base material measured around 294 HV, significantly rising in the weld metal, exceeding 401 HV. Mechanical properties altered post-welding, with yield strength decreasing from 749 MPa to 732 MPa. Laser welded WAAM UHS steel had 4% higher tensile strength compared to base material. However, ductility reduced from 27% to 22.5%. Bending fatigue tests revealed a considerable reduction in fatigue limit for laser-welded samples (80 MPa) compared to the base material (419 MPa), with fractures originating from the fusion line between the HAZ and the base material. Notably, the notch sensitivity of ultra-high-strength steels significantly reduces fatigue resistance.

A comparative study on BCTW-GIA and T-DW deposition processes

ABSTRACT To address the problem of mutual constraints between heat input and efficiency in arc additive manufacturing, a BCTW-GIA process is proposed. In this paper, components are manufactured using the BCTW-GIA and T-DW methods. The macroscopic morphology, cooling process, microstructure and properties of the components are analysed. According to the results, the BCTW-GIA method achieves a deposition efficiency of 15.46 kg/h, which is a 123% improvement compared to the T-DW method. The addition of the main wire in the BCTW-GIA method consumed some of the heat, resulting in less heat being applied to the member, and the maximum and average temperatures were reduced by 26% and 13%, respectively, compared to the T-DW method. The BCTW-GIA components have a finer grain size and an average microhardness of 197.17 HV. The BCTW-GIA specimens had higher transverse and longitudinal tensile strengths, which increased by 7% and 10% respectively over the T-DW specimens.

Investigation of the microstructural characteristics of laser-cladded Ti6Al4V titanium alloy and its corrosion behavior in simulated body fluid

Laser cladding technology has a wide range of potential industrial applications in the surface strengthening, repair and reuse of orthopedic implants. By employing this technique to conduct same-material surface restoration and enhancement on titanium alloys, it demonstrates significant developmental potential. However, the microstructure of laser additively manufactured titanium alloy differs significantly from that of traditional titanium alloys, which affects its corrosion resistance in human body fluids. To compare the corrosion resistance differences between the cladding layer and the substrate, this study investigates the microstructure of multi-pass laser cladding Ti6Al4V (TC4) titanium alloy and analyzes the corrosion morphology and corrosion products of the cladding layer in simulated body fluids (SBF). By comparing the electrochemical corrosion behavior of laser cladding with that of traditionally manufactured TC4, this research reveals the differences in corrosion resistance between the two titanium alloys. The research demonstrates that the microstructure of cladding primarily consists of prior-β grains and continuous grain boundary α phase, along with a complex basketweave structure composed of fine acicular α phase and lamellar α phase. Additionally, due to the complex thermal cycling process, the acicular α' colonies within the prior-β grains. These features enhance the cladding layer’s resistance to plastic deformation and increase microhardness, though with some uneven distribution. Interestingly, the TC4 cladding layer forms a porous passivation layer after corrosion, primarily composed of a TiO2 passivation film and deposits of hydroxyapatite and other phosphates. Due to the lower β-phase content, finer grains with higher energy states, and a greater proportion of high-angle grain boundaries (HAGBs) in the cladding layer, it exhibits higher electrochemical activity. As a result of these microstructural differences, the corrosion resistance of the TC4 cladding layer in SBF is inferior to that of TC4 manufactured using traditional techniques.

Controlled and Safe Hydrogen Generation from Waste Aluminum and Water, a New Approach to Hydrogen Generation.

A new method is proposed to generate hydrogen in situ at low pressure from powder-pressed recycled aluminum turnings activated with small amounts of NaOH and drops of water. The contribution of this system is that the user can obtain small flows of high-purity hydrogen (>99%) to charge their portable electronic devices in remote places, in a simple, controlled, and safe way, since only water is used. Test tubes that contain tiny amounts of NaOH on their surface can be transported and used without contact. In addition to being a safer system, a smaller amount of NaOH and water is needed compared to other systems, there is no need to preheat the water, and the system can even generate heat. As the feeding is drop by drop, the hydrogen flow can be easily controlled by manual or automatic dosing. The waste obtained is solid and contains mostly aluminum hydroxide with some NaOH and impurities from the waste of origin, which are easy to sell and recycle. A study has been carried out to optimize the type of test tubes and establish critical parameters. The results show that a constant and controllable flow rate of hydrogen can be obtained depending on the drip frequency where the chemical reaction predominates over diffusion, that the optimal amount of NaOH is 20 wt%, that a finer grain size can increase the H2 yield with respect to the stoichiometric value but reduces the instantaneous flow with respect to that obtained with larger grains, and that it is very important to control the density and the impurities to increase porosity and therefore water diffusion. The estimated cost of the hydrogen produced is 3.15 EUR/kgH2 and an energy density of 1.12 kWh/kg was achieved with a test tube of 92% aluminum purity and 20 wt% NaOH.

Study on structure and electrical properties of BNBT-La2/3ZrO3 ceramic

BNT-based energy storage dielectric material is a new type of multifunctional material with environmental friendliness, high energy storage density, and excellent temperature stability. It is a research hotspot where different components are introduced into BNT-based ceramics to obtain ceramic materials with high energy storage density. In this study, 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (BNBT) was selected as the substrate and doped with La2/3ZrO3 (LZ). Through the modification of La3+/Zr4+ at A/B sites, wider optical bandgap and finer grains with exceptionally large electrical breakdown strength and relatively strong relaxation behaviors in the appropriate range were obtained. Ultimately, an ultra-high energy storage density of 6.48 J/cm3 was attained at 480 kV/cm with a La2/3ZrO3 concentration of 0.07 mol%. In addition, the BNBT-LZ ceramics exhibited a good frequency-stabilized dynamic range (Wrec = 3.29 ± 6.7 % J/cm³, 10–200 Hz) and temperature stability (Wrec = 3.63 ± 9.9 % J/cm³, 20–160 °C), together with excellent charge-discharge performance(t0.9 = 3.36 μs). All these characteristics demonstrate that the modification of BNT-based ceramics by La3+/Zr4+ has a significant effect on the energy storage density. The results show that the BNBT-LZ system can be used as a promising dielectric material for high energy storage density capacitors.

Sintered Nd-Fe-B magnets from gas-atomized powders and the effect of lubricants

The production of sintered Nd-Fe-B magnets currently relies on alloys solidified via strip casting. However, the spacing of Nd2Fe14B lamellae in the strip-cast alloys is not optimal for obtaining monocrystalline powders with a mean particle size significantly smaller than 3 μm. Magnets made of finer monocrystalline powder are expected to have smaller grains and a higher coercivity, which would reduce current reliance on scarce and expensive heavy-rare-earth elements. Because of finer Nd2Fe14B grains, gas atomized Nd-Fe-B alloys generally yield more homogeneous fine powders than the strip-cast alloys. In this study, sintered Nd-Fe-B magnets were prepared from gas-atomized alloy and their properties were compared with those of magnets made from the strip-cast alloy of the same chemical composition. The gas-atomized alloy was found to contain an additional metastable phase of the TbCu7-type structure. As compared to the strip-cast alloy, the gas-atomized alloy yielded a jet-milled powder with smaller mean particle diameter and sintered magnets with finer grains and a higher coercivity. The metastable phase specific to the gas-atomized alloys was eventually eliminated during the sintering process without damaging the magnetic properties. Treatment of the new ultrafine powders prior to their compaction in a magnetic field with lubricants ensured a higher degree of the crystallographic alignment and lead to a higher coercivity while still maintaining high remanence. In particular, a magnet prepared from the gas-atomized alloy treated with methyl octanoate exhibited a remanence of 1.38 T, a coercivity of 1278 kA/m, and a maximum energy product of 359 kJ/m3. The results indicate that a simultaneous utilization of the gas-atomized alloys and appropriate lubricants may reduce the need for the heavy rare earths, making the magnets more sustainable.