Nanometric Grain Research Articles

Ethanolamine ices: Experiments in simulated space conditions

Laboratory experiments on the interactions between complex organic molecules, interstellar dust, and ultraviolet (UV) radiation are crucial to understanding the physicochemical mechanisms that lead to the synthesis of the observed interstellar complex organic molecules (iCOMs), and to search for new molecular species not yet observed in the gas phase of the interstellar medium (ISM). We aim to study the role of a new, recently discovered interstellar molecule, ethanolamine (EtA, NH CH CH OH), in surface chemistry in the ISM. In the laboratory, thanks to a combination of temperature programmed desorption (TPD) experiments and electron ionization (EI) mass spectrometry analyses, we studied the thermal desorption of pure ethanolamine and its mixture with water from nanometric amorphous olivine grains cooled down to 10 K, with or without UV irradiation. Ethanolamine was found to be stable, even in the presence of water, when irradiated with UV light. The presence of olivine grains strongly modified the TPD curves, trapping the molecule up to about 295 K, meaning that the precursors of some biological molecules could be retained on the grains even in the innermost parts of protoplanetary disk. We then identified a series of products formed when the molecule was irradiated onto the dust substrate. Of particular interest is the fact that irradiation of ice containing ethanolamine, a molecule known to be present in the ISM, can produce more complex and astrobiologically interesting species. Furthermore, our results further our understanding of existing observational data.

Comparative Microstructure Characteristics of Synthesized PbS Nanocrystals and Galena

Lead sulfide (PbS) on the nanoscale was synthesized via a chemical route at room temperature using lead nitrate {Pb(NO3)2} and sodium sulfide (Na2S). The Na2S was prepared at ~105 °C using sodium hydroxide (NaOH) and sulfur (S) powder. The produced PbS, denoted as Lab-PbS, was compared with a high-concentration PbS phase of galena. The produced Na2S and Lab-PbS were examined using scanning electron microscopy and energy dispersive X-ray spectroscopy for microstructural and chemical analysis. The results confirmed a high-purity PbS compound (>99%) with a nanoscale particle size. The results showed that ultrasonic agitation was vital for obtaining the nanoparticle size of the Lab-PbS. Furthermore, thin films from the synthesized Lab-PbS and galena were successfully thermally evaporated on glass, quartz, and silicon substrates. The formation of nanometric grains was confirmed by scanning electron microscopy (SEM). XRD and FTIR spectroscopy were carried out for the Lab-PbS, galena fine powders, and galena thin films. The average crystal diameter was calculated for the galena thin films and was found to be approximately 26.6 nm. Moreover, the UV–Visible transmission curve was measured for the thin films in the wavelength range of 200–1100 nm in order to calculate the bandgap energy (Eg) for the thin films. The values of Eg were approximately 2.65 eV and 2.85 eV for the galena and Lab-PbS thin films, respectively. Finally, the sintering of the Lab-PbS and galena powders was carried out at ~700 °C for 1 h under vacuum, achieving relative densities of ~98.1% and ~99.2% for the Lab-PbS and galena, respectively.

Understanding the lower fracture resistance of cold sintered ceramics

The cold sintering process (CSP) enables densification of ceramics at unprecedented low temperatures, unlocking unique opportunities in microstructural design. However, the mechanical behaviour of cold sintered ceramics remains unexplored. This study aims to compare the mechanical strength and fracture resistance of cold sintered (140°C) with conventionally sintered (1000°C) ZnO. The effect of grain size is investigated in samples sintered using conventional, cold and rapid sintering. It was found that cold sintered ZnO exhibits ∼50 % lower strength compared to conventionally sintered parts (∼120 vs. ∼240 MPa). This is explained by the lower fracture toughness of the former (0.57 vs. 1.15 MPa·m1/2), resulting from a grain size effect that favours intergranular fracture along nanometric grains. This grain size effect is supported by the higher hardness measured on cold vs. conventionally sintered ZnO (4.5 vs. 1.8 GPa). The lower toughness of cold sintered ceramics is demonstrated to be related to their nanocrystalline nature.

Effect of Mg/Ag co–doping on crystal structure, optical, and transport properties of SnO2 compound

The attempt to search for novel materials for optoelectronics material has become a highly debated and intensively investigated field of study. Within the scope of this investigation, Sn0.94Ag0.06-xMgxO2 (0 ≤ x ≤ 0.06) polycrystalline samples were produced using the traditional solid–state reaction method, and their crystalline structure, micro–structure, Raman spectroscopy, optical, and transport characteristics were investigated. Confirmation of a single rutile phase with a tetragonal crystal structure through XRD (X–ray diffraction) analysis is revealed. The morphology study by scanning electron microscopy indicated the formation of nanometric grains. All elements are evenly distributed throughout the structure, as seen by the elemental color mapping. The successful incorporation of Mg/Ag to the SnO2 lattice is evidenced by two prominent peaks in the Raman spectra of these compounds, with wavenumbers of 634 and 775 cm−1, which correspond to the A1g and B2g Raman modes, respectively. The UV–Vis spectrophotometer facilitated the acquisition of absorbance and transmittance data, which revealed that the optical band gap exhibited an expansion when the quantity of Mg/Ag co–doping increased in the SnO2 material. The transmittance value was also shown to increase from 80 % to 90 % with increased Mg co–doping concentration. The Maxwell–Weigner model has been employed to fully understand how the dielectric constant (εr), loss tangent (tan δ), complex impedance, and ac conductivity of Mg/Ag co–doped SnO2 compounds behave depending on frequency. The current–voltage (I–V) characteristics of the sample were measured using a Keithley 6517b electrometer in two–probe mode with a Tin metal pressure contact. The properties of I–V exhibited an Ohmic behavior. A study on the room temperature resistivity reveled that the materials are highly resistive in the nature.

Investigation of isothermal entropy change, relative cooling power, and refrigerant capacity of GdCoAl nanocomposite thin film by changing the Al ratio at low magnetic fields of 100 Oe and 1000 Oe

There are two challenges with magnetocaloric materials (MCMs): the production of low-cost materials and the applicability of MCMs at low magnetic fields. Due to the abundance of Al, the effects of Al composition in GdCoAl nanocomposite thin film alloys were investigated by fabricating Gd19.60Co20.00Al60.40 and Gd38.62Co28.43Al32.95 alloys. Nanometric grains were seen in the surface images with different grain dimensions by changing the Al ratio. With an increase in the Al ratio, the Z-height dimension decreased. The grains were homogeneous and small for the ternary thin film with a high Al ratio. It was established that the alloy with a higher amount of Al had a higher Curie temperature at a lower (100 Oe) magnetic field; it performed worse when compared to the low Al ratio sample regarding RCP and RC due to the small full width at half maxima. However, Gd19.60Co20.00Al60.40 at a higher magnetic field intensity of 1000 Oe, performed better.

Study of helium diffusion in yttria: A multiscale approach based on the density functional theory and kinetic Monte Carlo, with transmission electron microscopy and thermo-desorption spectroscopy

A known issue for future nuclear reactors is helium accumulation inside the steel structure materials, responsible for structural issues such as embrittlement and cracking. One possible solution is using new types of reinforced steel, such as oxide dispersion strengthened (ODS) steel. It consists of adding oxide nanoparticles to the Fe-based material, especially yttrium oxide (yttria, Y2O3), improving its properties. Therefore, one first step is understanding the helium diffusion inside this system. Very little is known about helium inside yttria, with most studies being theoretical ones. Based on this context, this work proposes a combined theoretical and experimental multiscale approach to investigate helium diffusion inside yttria.The theoretical approach starts with the density functional theory, used to model the atomic yttria cell and determine helium insertion sites. The transitions between the sites were described using the Nudged Elastic Bond (NEB) method. Kinetic Monte Carlo was then employed to obtain the interstitial diffusion coefficient expression for the first time for this material. It showed a limited diffusion at temperatures below 600 K, which may indicate a tendency for He to be blocked in the oxide. Then, the charged vacancies were explored. It showed that the vacancy further reduces helium diffusion. Finally, it was demonstrated that helium spreads across different vacancies and interstitial sites.The experimental part involved implanting helium ions at 50 keV in samples with nanometric or micrometric grains. Then, the specimens were characterised with transmission electron microscopy (TEM) and thermo-desorption spectroscopy (TDS) techniques. TEM did not evidence detectable bubbles even at the highest studied fluence (1 × 1016 cm−2). The TDS highlighted different mechanisms for helium diffusion and the grain size's role, providing a novel model for diffusion coefficient calculation based on interstitial diffusion.

Spherical Lignin-Derived Activated Carbons for the Adsorption of Phenol from Aqueous Media.

In this work, a synthesis and activation path, which enabled the preparation of spherical activated carbon from a lignin precursor, characterized by high adsorption capacity in the removal of phenolic compounds from water, was successfully developed. Two industrial by-products, i.e., Kraft lignin and sodium lignosulfonate, were used to form spherical nanometric lignin grains using pH and solvent shift methods. The obtained materials became precursors to form porous activated carbons via chemical activation (using K2CO3 or ZnCl2 as activating agents) and carbonization (in the temperature range of 600-900 °C). The thermal stabilization step at 250 °C was necessary to ensure the sphericity of the grains during high-temperature heat treatment. The study investigated the influence of the type of chemical activator used, its quantity, and the method of introduction into the lignin precursor, along with the carbonization temperature, on various characteristics including morphology (examined by scanning electron microscopy), the degree of graphitization (evaluated by powder X-ray diffraction), the porosity (assessed using low-temperature N2 adsorption), and the surface composition (analyzed with X-ray photoelectron spectroscopy) of the produced carbons. Finally, the carbon materials were tested as adsorbents for removing phenol from an aqueous solution. A conspicuous impact of microporosity and a degree of graphitization on the performance of the investigated adsorbents was found.

The Crystallization Behavior of a Na2O-GeO2-P2O5 Glass System: A (Micro)Structural, Electrical, and Dielectric Study.

Sodium-phosphate-based glass-ceramics (GCs) are promising materials for a wide range of applications, including solid-state sodium-ion batteries, microelectronic packaging substrates, and humidity sensors. This study investigated the impact of 24 h heat-treatments (HT) at varying temperatures on Na-Ge-P glass, with a focus on (micro)structural, electrical, and dielectric properties of prepared GCs. Various techniques such as powder X-ray diffraction (PXRD), infrared spectroscopy-attenuated total reflection (IR-ATR), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were employed. With the elevation of HT temperature, crystallinity progressively rose; at 450 °C, the microstructure retained amorphous traits featuring nanometric grains, whereas at 550 °C, HT resulted in fully crystallized structures characterized by square-shaped micron-scale grains of NaPO3. The insight into the evaluation of electrical and dielectric properties was provided by Solid-State Impedance Spectroscopy (SS-IS), revealing a strong correlation with the conditions of controlled crystallization and observed (micro)structure. Compared to the initial glass, which showed DC conductivity (σDC) on the order of magnitude 10-7 Ω-1 cm-1 at 393 K, the obtained GCs exhibited a lower σDC ranging from 10-8 to 10-10 Ω-1 cm-1. With the rise in HT temperature, σDC further decreased due to the crystallization of the NaPO3 phase, depleting the glass matrix of mobile Na+ ions. The prepared GCs showed improved dielectric parameters in comparison to the initial glass, with a noticeable increase in dielectric constant values (~20) followed by a decline in dielectric loss (~10-3) values as the HT temperatures rise. Particularly, the GC obtained at @450 stood out as the optimal sample, showcasing an elevated dielectric constant and low dielectric loss value, along with moderate ionic conductivity. This research uncovers the intricate relationship between heat-treatment conditions and material properties, emphasizing that controlled crystallization allows for precise modifications to microstructure and phase composition within the remaining glassy phase, ultimately facilitating the fine-tuning of material properties.

Nanostructured Cu12+xSb4S13 tetrahedrites prepared by solvothermal synthesis in 1-(2-aminoethyl)piperazine for efficient thermal energy harvesting

Intrinsically low lattice thermal conductivity and the earth-abundant nature of elements make tetrahedrites very promising sulfur-based materials for thermoelectric applications. Although the thermoelectric performance of lightweight sulfides is usually restricted due to high lattice thermal conductivity, nanoengineering may effectively enhance the energy conversion performance of tetrahedrites by disturbing phonon transport. In this work, we modified our unique solvothermal synthesis method with 1-(2-aminoethyl)piperazine as a solvent and pure elements as reagents to obtain both copper-rich and copper-poor tetrahedrites with nanometric grain sizes ranging from 40 to 300 nm. The powders obtained were densified by the PECS method at T = 573 K and p = 40 MPa. The structural and thermal properties of the fabricated materials were systematically investigated as a function of temperature to revisit the phase evolution of the Cu-Sb-S system in the vicinity of the tetrahedrite compounds. The Seebeck coefficient of the investigated materials changes from 150 µVK−1 up to 400 µVK−1 at 300 K due to the effective tuning of the carrier concentration. In turn, the nanocrystalline nature of the prepared tetrahedrites, which influences the strong phonon scattering at grain boundaries, results in an ultralow lattice thermal conductivity of around 0.25 Wm−1K−1 at 300 K. As a result of the tuned electronic transport and ultralow lattice thermal conductivity, the highest ZT parameter of 0.9 at 596 K was achieved for the nominal composition Cu13Sb4S13. This is one of the best values reported to date for low-cost and environmentally friendly tetrahedrites at this temperature. The resultant nanomaterials can be used as components in novel inorganic and organic-inorganic composites for direct conversion of heat to electricity.

BN6BT ceramics via cold‐sintering with annealing: Effects of grain size of precursor powders and annealing temperature

AbstractIn this work, (Bi0.5Na0.5)0.94Ba0.06TiO3 (BN6BT) lead‐free ceramics were prepared via cold‐sintering followed by annealing, and effects of grain size of precursor powders and annealing temperature on microstructure, dielectric, and ferroelectric properties of the ceramics were studied. The precursor powders for cold sintering were obtained by mixing the powders with sub‐micrometer (average grain size, AGS = 0.26 μm) and nanometer (AGS = 73 nm) grains in various mass ratios (1:0, 1:1, 1:2, and 1:4). The precursor powders were mixed with deionized water and cold sintered at 180°C for 1 h under 500 MPa. The cold‐sintered samples were then annealed at temperatures between 800 and 1000°C for 2 h. For the ratios of 1:2 and 1:4, the corresponding ceramics annealed at 950°C exhibit dielectric and ferroelectric properties similar to those of the BN6BT ceramics sintered at 1170°C via the solid‐state sintering method. The present BN6BT ceramics exhibit dense microstructure with finer grains with AGS = 280 nm, higher breakdown strength (BDS = 160 kV· cm−1) compared to the solid‐state sintered BN6BT ceramics with AGS = 1.6 μm and BDS = 75 kV· cm−1. The results demonstrate that the cold‐sintering followed by annealing is effective in preparing BN6BT ceramics with fine grains and excellent dielectric and ferroelectric properties at relatively low temperatures.

The Role of Grain Size in the Mechanical Properties of Metals

It is now well established that the grain size is the fundamental microstructural feature of all polycrystalline materials. In practice, a very wide range of grain sizes will be needed in order to fully evaluate the effect of grain size on the mechanical properties of metals. For many years this was a significant limitation because it was not possible to use conventional thermomechanical processing to produce materials with submicrometer or nanometer grain sizes. Recently, this problem has been addressed by developing alternative processing techniques based on the application of severe plastic deformation. This overview demonstrates that, although the flow stress increases with decreasing grain size at low temperatures and decreases with decreasing grain size at high temperatures, this clear dichotomy in behavior may be adequately explained by using a single theoretical flow mechanism based on the occurrence of grain boundary sliding.

Design and coherent strengthening of ultra-high strength refractory high entropy alloys based on laser additive manufacturing

The WNbMoTa-based refractory high entropy alloy (RHEA) is expected to become a new generation of high-temperature materials due to its high thermal stability, which can be used in aerospace, nuclear energy and other fields. In this paper, TN10 (TN is the abbreviation of Ti and Ni elements), TN15, TN20 and TN25 non-equimolar WNbMoTa-based RHEAs were designed based on phase engineering and formed by laser powder bed fusion (LPBF) technology. The solidification thermodynamics, microstructure and mechanical properties (compressive strength at 25 °C) of the four alloys were analyzed, and the strengthening mechanism of TN20 alloy was studied. The compressive yield strength of the four alloys exceeds 2050 MPa, the ultimate compressive strength exceeds 2550 MPa, and the elongation exceeds 9%. The compressive yield strength of TN20 alloy is 2513 MPa, the ultimate strength is 3127 MPa, and the elongation is 11.38%. The room temperature (25 °C) compressive yield strength of TN20 alloy is the highest among the high entropy alloys studied so far. TN20 alloy is composed of BCC matrix phase and grain boundary phase containing three different structures, which are B2 TiNi phase, Ni55Nb25Ti15Ta5 phase generating stacking faults and Ni70Ti20Nb10 secondary precipitated phase. The micrometer matrix phase and nanometer grain boundary phase of TN20 alloy show a network distribution in fine crystal region. After the matrix phase cracks due to high thermal stress, the flow TiNi-rich grain boundary phases precipitate to fill the cracks. The grain boundary phase with high proportion in this region is enhanced by the secondary phase and its nanoprecipitated phase. In other regions, stacking faults are generated by the Ni55Nb25Ti15Ta5 phases, which convert the thermal stress that induces crack into lattice defects of the crystal. On the other hand, the content of B2 phase is the highest in grain boundary phase, and the grain boundary between B2 phase and matrix phase is a coherent grain boundary, which realizes the high quality combination of grain boundary phase and matrix phase. The design and strengthening of WNbMoTa-based non-equimolar RHEAs are studied in this paper, which is expected to provide a reference for the design of a new generation of high entropy alloy.

Ultra-rapid debinding and sintering of additively manufactured ceramics by ultrafast high-temperature sintering

In recent years, additive manufacturing (AM) of ceramics has significantly advanced in terms of the range of equipment available, printing resolution and productivity. Most techniques involve the use of ceramic powders embedded in an organic binder which is typically removed through a slow thermal debinding process.Herein, we prove for the first time that ultra-rapid debinding and sintering are possible for complex 3YSZ components produced using material extrusion technology. The printed components were first chemically debinded in acetone thus removing about one-half of the binder, and then thermally debinded and densified by ultrafast high-temperature sintering (UHS) in a single-step process (30–120 s). Fully dense components were obtained with tailored microstructure and nanometric grain size. The sintered artefacts were crack-free even at the microscopic level.This approach paves the way for rapid processing (debinding and sintering) of additively manufactured ceramics with reduced energy consumption and carbon footprint.

Review on Grain Size- and Grain Boundary Phenomenon in Unusual Mechanical Behavior of Ultrafine-Grained Al Alloys

In the last three decades, several severe plastic deformation (SPD) procedures have been developed and applied in materials science to create bulk, ultrafine-grained (UFG) structures. As a consequence of the SPD, not only submicron and even nanometer grain sizes can be obtained, but also new grain boundaries with non-equilibrium structures in a material may be formed. Therefore, both the strength and ductility of the UFG materials can change significantly compared to the coarse-grained counterparts. This review is focused on unusual mechanical behaviors of UFG Al and Al alloys, associated with grain boundary structure and segregations which are responsible for the modification of the Hall-Petch relationship and the so-called size-effect for UFG structure. Unusually high strain rate sensitivity, intensive grain boundary sliding and superplasticity at low temperature are described and surveyed. In addition, innovation potential of these phenomena is also briefly considered.

Ball Milling and Consolidation Process of Al-Cr Powder Mixture—Microstructural Characterization

The interest in studying the synthesis of an Al–Cr alloy system by non-equilibria processes is due to the formation of metastable or quasicrystalline phases when rapid solidification has been utilized. Similarly, the formation of quasicrystals has been reported to a much lesser extent when the mechanical alloying technique was applied. In the present research, a mixture of powders of Cr and Al (both elements with a purity of 99.99%) with compositions of Al-5 and 7.5 at. % Cr was subjected to a ball milling process. Afterwards, the powder mixture was subjected to a consolidation process, conducted by pressing and sintering processes. The X-ray diffraction analyses revealed that during 20 h of milling there was no formation of metastable or quasicrystalline second phases detected. In addition, the X-ray diffraction peaks revealed that as milling time increased, the nanometric grain size decreased, and once the sintering treatment was applied, the crystallite size decreased following the same tendency. The dislocation density was estimated using the size of nanometric grains; this computation revealed that the dislocation density grew throughout the ball milling process; even after sintering, the multiplication of dislocations prevailed following the same tendency.

A closer look into slickensides: Deformation on and under fault surfaces

Accurate descriptions of natural fault surfaces and associated fault rocks are important for understanding fault zone processes and properties. Slickensides--grooved polished surfaces that record displacement and wear along faults-- develop measurable roughness and characteristic microstructures during fault slip. We quantify the roughness of natural slickensides from three different fault surfaces by calculating the surfaces power spectra and height distributions and analyze the microstructures formed below the slickensides. Slickenside surfaces exhibit anisotropic self-affine roughness with corresponding mean Hurst exponents in directions parallel-- 0.53 ± 0.07-- and perpendicular --0.6 ± 0.1-- to slip, consistent with reports from other fault surfaces. Additionally, surfaces exhibit non-Gaussian height distributions, with their skewness and kurtosis roughness parameters having noticeable dependence on the scale of observation. Below the surface, microstructural analyses reveal that S–C–C′ fabrics develop adjacent to a C-plane-parallel principal slip zone characterized by a sharp decrease in clast size and a thin (≤100 μm) nanoparticulate-rich principal slip surface (PSS). These microstructures are present in most analyzed samples suggesting they commonly form during slickenside development regardless of lithology or tectonic setting. Our results suggests that 1) PSS likely arise by progressive localization along weaker oriented fabrics 2) deformation along PSS's is energetic enough to comminute the rocks into nanometric grains, and 3) fault geometry can be further characterized by studying the height distributions of fault surfaces, which are likely to impact stress distributions and frictional responses along faults.

Breaks in the Hall–Petch Relationship after Severe Plastic Deformation of Magnesium, Aluminum, Copper, and Iron

Strengthening by grain refinement via the Hall–Petch mechanism and softening by nanograin formation via the inverse Hall–Petch mechanism have been the subject of argument for decades, particularly for ultrafine-grained materials. In this study, the Hall–Petch relationship is examined for ultrafine-grained magnesium, aluminum, copper, and iron produced by severe plastic deformation in the literature. Magnesium, aluminum, copper, and their alloys follow the Hall–Petch relationship with a low slope, but an up-break appears when the grain sizes are reduced below 500–1000 nm. This extra strengthening, which is mainly due to the enhanced contribution of dislocations, is followed by a down-break for grain sizes smaller than 70–150 nm due to the diminution of the dislocation contribution and an enhancement of thermally-activated phenomena. For pure iron with a lower dislocation mobility, the Hall–Petch breaks are not evident, but the strength at the nanometer grain size range is lower than the expected Hall–Petch trend in the submicrometer range. The strength of nanograined iron can be increased to the expected trend by stabilizing grain boundaries via impurity atoms. Detailed analyses of the data confirm that grain refinement to the nanometer level is not necessarily a solution to achieve extra strengthening, but other strategies such as microstructural stabilization by segregation or precipitation are required.

Effect of the annealing treatment on structural and transport properties of thermoelectric Sm y (Fe x Ni1−x )4Sb12 thin films

The crystallographic and transport properties of thin films fabricated by pulsed laser deposition and belonging to the Sm y (Fe x Ni1-x )4Sb12 filled skutterudite system were studied with the aim to unveil the effect exerted by temperature and duration of thermal treatments on structural and thermoelectric features. The importance of annealing treatments in Ar atmosphere up to 523 K was recognized, and the thermal treatment performed at 473 K for 3 h was selected as the most effective in improving the material properties. With respect to the corresponding bulk compositions, a significant enhancement in phase purity, as well as an increase in electrical conductivity and a drop in room temperature thermal conductivity, were observed in annealed films. The low thermal conductivity, in particular, can be deemed as deriving from the reduced dimensionality and the consequent substrate/film interfacial stress, coupled with the nanometric grain size.

Microcrystallization Effects Induced by Laser Annealing in Cr-Al-C Ion-Beam-Sputtered Films.

The microcrystallization effects induced by the real-time laser annealing in Cr-Al-C ion-sputtered films with an off-stoichiometric composition are studied. The laser annealing has been performed during Raman experiments with tunable laser power densities. Morphostructural changes induced during laser annealing were investigated by scanning electron microscopy. It has been proven that real-time laser annealing in the high-laser-power-density mode promotes quite clearly the formation of nanograins through surface microcrystallization. Detailed Raman analysis allowed for the observation of the optical modes that unequivocally identifies the low-symmetry 211 MAX phase in both low- and high-power-density modes. Such findings confirming the microcrystallization as well as the stabilization of the grain boundaries by carbon nanoclustering are confirmed by X-ray diffraction results, where the single-phase hexagonal 211 was unequivocally proven to form in the high-laser-power-density mode. The microcrystallization via laser annealing was also found to be beneficial for the elastic behavior, as the hardness values between 16 and 26 GPa were found after laser annealing, accompanied by a significantly high Young's bulk modulus. Such large values, larger than those in bulk compounds, are explicable by the nanometric grain sizes accompanied by the increase of the grain boundary regions.

Positron annihilation spectroscopic study of intrinsic and ion-irradiation induced vacancy defects in Zr-containing ODS steels with and without Al

The oxide dispersion strengthened (ODS) ferritic steels containing Zr are synthesized with and without Al addition and found to possess homogeneous distribution of nanoprecipitates and nanometric grain sizes. Positron lifetime measured in both alloys indicate trapping in dislocations and vacancy clusters respectively. Room temperature irradiations with 1.6 MeV Fe+ ions induced stable vacancy type defects in both the alloys whereas high temperature irraditaions at 340 °C show the recombination of vacancies and interstitials. In room-temperature irradiated specimens, the onset of defect production in Zr-ODS is delayed owing to its superior sink strength caused by the smaller sized, higher number densities of dispersoids compared to Al-ODS.