Nano-size Phases Research Articles

Design of a 2.7 GPa ultra-high-strength high Co–Ni secondary hardening steel by two-step nano-size precipitation tailoring

High Co–Ni secondary hardening steels are valuable in the field of aviation materials. With the increasing demand of lightweight, further enhancing its strength has received widespread attention. In this study, instead of using only M2C carbides as the reinforcements in the traditional high Co–Ni secondary hardening steels, nano-size NiAl phases were introduced to provide additional strength. To obtain the collaborative precipitation of these two reinforcements, systematically thermodynamic calculation, including the driving force, coarsening rate, etc., was made to quantitatively tailor the composition and the two-step aging parameters. The calculation results showed that adding 1 % Al into the standard composition of M54 is a plan with high potential and a second aging process at 450 °C should be added to promote NiAl precipitation. Based on the experimental validation, the target microstructure formed as the design. With the dual-phase strengthening of NiAl particles and M2C carbides, the yield and tensile strength are greater than 2.3 and 2.7 GPa, respectively, which increases the strength of M54 steel by >30 %, retaining sufficient elongation and relatively low cost. This new designed alloy increased the strength–ductility balance of high Co–Ni secondary hardening steels and aviation maraging steels from ∼12.5 to 13.5 GPa%.

The inhibition of MnO on Fe2Al5Znx growth and associated three-dimensional nested phase distribution in the galvanized coating of high-Al low-Si dual phase steel

Continuous hot-dip galvanizing is an important process for dual phase (DP) steel and other advanced high-strength steels (AHSSs). During this process, the formation of a Fe-Al inhibition layer and the selective oxidation of alloying elements will change the interfacial layer structure, and affect the galvanized coating structure. So far, the interfacial layer structure and its relationship with galvanized coating in high-Al low-Si DP steel are still unclear. In this paper, the interfacial layer and galvanized coating of hot-dip galvanized high-Al low-Si DP steel were characterized by electron microscopy. The results showed that there exists abundant nano-size MnO phases and Fe2Al5Znx phases inside the interfacial layer, and the galvanized coating consists of Fe3Zn10 nanophases and η-Zn phase. The competitive relationship between those interfacial phases strongly affects the phase distribution inside the galvanized coating adjacent to the interfacial layer. The MnO phases in the interfacial layer hinder the nucleation and growth of Fe2Al5Znx phases. As a result, the inhibition of the Fe-Zn reaction is weakened and the final galvanized coating exhibited a three-dimensional nested distribution of coexistence of Fe3Zn10 nanophases and η-Zn phase.

The effect of nano-size second phases on the tribological performance of TNTZ alloy

The tribological performance of Ti-29Nb-14Ta-4.5Zr (TNTZ) alloy reinforced by various nano-sized phases has been studied. The β-phase matrix was reinforced by the different nano-second phases (α′, α, and ω) during solution treatment and quenching in different media followed by aging at 500 °C and 300 °C for 48 hr. According to the EBSD results, no significant substructure development occurred beneath the wear track and the improvement in the tribological performance of TNTZ alloy is only due to the presence of well distributed-hard nanoscale precipitations in the β matrix. The tribological performances of the alloy reinforced by nano-ω/α precipitations are better than the two others by at least five times. The best tribological performance was found for the TNTZ alloy reinforced by nano-ω precipitations which introduce this structure as a promising high potential candidate for biomedical applications due to its superior tribological properties in the metal-to-metal contact condition.

Effects of Zn addition on the aging behavior and mechanical properties of Mg[sbnd]8Al[sbnd]2Sn wrought alloy

The effect of Zn (0–1 wt%) content on the aging behavior and mechanical properties of Mg8Al2Sn-xZn alloys have been investigated. The results indicated that addition of Zn promoted the age-hardening response and precipitation of the Mg17Al12 phases through high grain boundary migration and the increase of the nucleation rate of Mg17Al12 phases. The proportion of discontinuous precipitation zone in the Mg8Al2Sn1Zn alloy was 37%, which was two times larger than that in the Mg8Al2Sn alloy without Zn. The discontinuous precipitation phases grew fast and were not suppressed by nano-size Mg2Sn phases. Both continuous and discontinuous precipitates were refined in the as-aged alloys with the addition of Zn. According to the yield strength calculation, fine precipitates with high density more effectively enhanced the strength in Mg8Al2Sn1Zn alloy. The yield strength of the Mg8Al2Sn1Zn alloy was increased by 24% after the aging treatment. The peak-aged AZT812 alloy exhibited mechanical properties that included a yield strength, an ultimate tensile strength and an elongation of 296 MPa, 408 MPa and 7%, respectively.

Combination processes of diamond recovery from metasomatically altered kimberlite rocks

The article gives new experimental data on chemistry, phase composition, structure and physicochemical properties of surface of minerals composing metasomatically altered kimberlite rocks. The authors have determined formation conditions and basic genetic types of mineral micro- and nano-size phases on diamond surface in the form of aluminosilicate minerals, thin coats of clayey minerals, calcite and dolomite bound with carbonate cement, as well as their negative effect on recovery of diamonds by foam separation. The mechanisms and efficient methods of combined energy effects on the natural heterogeneous system of diamond and surface mineral phase are found to rupture hydrophilic mineral films on diamond surface, prevent their repeated formation and reduce diamond loss in processing of diamond-bearing kimberlites.

Sol–gel preparation, structural, thermal and spectroscopic analyses, and opto-electronic and photocatalytic activities of normal spinel nickel cobaltite nano-powder for photo-degradation of Reactive Red RB

Nickel cobaltite nano-composites have been prepared by a modified sol–gel process using nickel–cobalt acetates as precursors and citric acid-monoethylene glycol as stabilizers followed by calcination at 400 and 650 °C in air. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and thermogravimetry (TG-DTG), and energy dispersive X-ray (EDX), Fourier transform infrared (FTIR) and UV–Vis diffuse reflectance (UV–Vis DRS) spectroscopies were used for structural, thermal, and opto-electronic characterization of the prepared nano-powders. XRD results showed that using acetate as precursor and calcination at 400 °C results in a pure nickel cobaltite phase (NiCo2O4), while at 650 °C, nickel cobaltite with NiO impurity is produced. The nano-structured nickel cobaltite photocatalyst was composed of nano-size crystalline phases with an average size of 25 nm. The optical band gap energy of the nano-structured nickel cobaltite photocatalyst was 2.00 (640) and 3.20 eV (387.5 nm) from the UV–Vis DRS absorption spectra. The photo-catalytic activity of the synthesized nickel cobaltite nano-composite photo-catalysts for degradation of Reactive Red RB azo textile dye was examined. The nano-structured nickel cobaltite photocatalyst exhibited high photocatalytic activity for the photo-degradation of Reactive Red RB which is related to the optical absorption in the visible (640 nm) and UV (387.5 nm) irradiation, electron–hole separation and high surface area of the nano size particles (average size of 25 nm).

Nanomineralogy as a new dimension in understanding elusive geochemical processes in soils: The case of low-solubility-index elements

Abstract Nanomineralogical studies of mineral surface coatings in soils reveal insights into biogeochemical processes that heretofore were not known to exist. This is a new dimension in understanding past and present biogeochemical processes in soils, and in this study it is a way to better understand the behavior of low-solubility-index elements such as Al, Ti, and Zr. Soils were sampled from selected sites in Sudbury (Ontario, Canada) that have been affected by acidification and particulate matter emissions from base-metal smelters with subsequent remediation within the past century. These anthropogenic processes have affected an entire landscape, but are now recorded in assemblages of nano-size phases that can be only studied using a combination of focused ion beam technology (for sample preparation) and high-resolution analytical transmission electron microscopy (for phase identification). A first generation of clay minerals (pre-acidification phase), their partial replacement by nano-size hematite and amorphous silica (anthropogenic acidification), and a second generation of clay minerals (post-acidification, including soil remediation) are products of changes in soil biogeochemical processes during these natural and anthropogenic-induced weathering stages. Complex assemblages of nanophases formed prior to the second generation of clay minerals depict underlying mechanisms for the mobilization and sequestration of the low-solubility-index elements Zr and Ti under acidic conditions. The occurrence of baddeleyite (ZrO2), anatase (TiO2), and the Magneli phases Ti4O7 and Ti5O9 (all present at the nanoscale) suggest an influx of nanocolloidal Zr and Ti oxides during weathering of smelter-derived particulate matter. Kelyshite {NaZr[Si2O6(OH)]}, authigenic zircon (ZrSiO4), and kleberite [Fe3+Ti6O11(OH)5] are most likely products of the sequestration of the Zr- and Ti-bearing nanocolloids.

Changes in YBCO Single Grain Bulk Superconductor Exposed to Air Moisture

Changes in bulk single grain YBCO superconductor at exposition to air were studied. The increase of the sample weight caused by reaction with air moisture was observed by weighing the samples over two months period. Thermal analyses and mass spectrometry of the exposed samples has shown evolution of water and oxygen during sample heating. Observation with scanning electron microscope con rmed the formation of some nanosize phases at the inner sample surfaces. XPS spectra done on the freshly cleaved and on the air exposed (001) surfaces con rmed changes in Ba and Cu bonds. Observed structural changes did not caused systematic changes in measured trapped eld.

In situ growth of nanoparticles through control of non-stoichiometry

Surfaces decorated with uniformly dispersed catalytically active nanoparticles play a key role in many fields, including renewable energy and catalysis. Typically, these structures are prepared by deposition techniques, but alternatively they could be made by growing the nanoparticles in situ directly from the (porous) backbone support. Here we demonstrate that growing nano-size phases from perovskites can be controlled through judicious choice of composition, particularly by tuning deviations from the ideal ABO3 stoichiometry. This non-stoichiometry facilitates a change in equilibrium position to make particle exsolution much more dynamic, enabling the preparation of compositionally diverse nanoparticles (that is, metallic, oxides or mixtures) and seems to afford unprecedented control over particle size, distribution and surface anchorage. The phenomenon is also shown to be influenced strongly by surface reorganization characteristics. The concept exemplified here may serve in the design and development of more sophisticated oxide materials with advanced functionality across a range of possible domains of application.

Thermodynamics of Advanced Alloys Modification by Exogenous Nanophases

The thermodynamic analysis of a ceramic compound solubility was carried out for ceramic compounds which may be used for dispersion hardening of advanced nickel alloys. The thermodynamic description of stability conditions was completed for a disperse heterophase systems consists of metal melt – nanosize phases (NSP). For a thermodynamic criterion (К) of stability was selected the specific variation of a free energy of the process of a disperse system degradation (referred to change of unit of a surface phases contact). The analysis was executed in view of formation of thick and thin elastic wetting films and takes in account a disjoining pressure. The above definition of new thermodynamically rigorous criterions becomes physically real, if the isotherm of a disjoining pressure is measured. The derived criterions are simplified in the Young approximation. In this case the criterion are expressed through measurable interfacial performances - interfacial tension and wetting angles. The application of a stability condition gives a simple outcome: aggregation of NSP does not happen at a wetting angles ≤ 600. On a basis of own experimental data the evaluations are carried out for possibility of using of some compounds as exogenous modifiers of a nickel alloys. The example of dispersion hardening of high-temperature strength nickel alloy and improving its heat resisting properties is reduced.

Conversion of W2C to WC phase during mechano-chemical synthesis of nano-size WC–Al2O3 powder using WO3–2Al–(1 + x)C mixtures

Due to the weak properties of W2C phase, its formation during the process of WC synthesis should be prevented. The aim of the present study has been the mechano-chemical synthesis of a WC–Al2O3 composite powder free from undesirable W2C phase through the addition of excess carbon to the WO3–2Al–C initial mixture. Based on the thermodynamic calculations and results of the supplementary experiments in W–yC and W2C–C systems, the possibility of the conversion of W2C to WC phase through the addition of excess carbon has been investigated. It has been shown that production of a WC–Al2O3 composite powder by 360min mechano-chemical treatment of an initial mixture of WO3–2Al–1.8C is possible. TEM observations and Williamson–Hall calculation revealed that the obtained WC–Al2O3 powder contains macro-size agglomerates in which each agglomerate consists of nano-size phases.

Epitaxial self-assembly of multiferroic nanostructures

The morphology and structure of interfaces in PbTiO3–CoFe2O4 films on SrTiO3 substrates of various orientations are studied. It is found that for film with thickness more than 100 nm with columnar two-phase morphology, the average orientations of the interfaces between the phases reside on the {110}, {111}, and {112} planes for films normal to substrates oriented along ⟨001⟩, ⟨110⟩, and ⟨111⟩ correspondingly. These macroscopic interfaces consist of {111} nanofacets. The study of very thin film less than 30 nm shows that the interfaces between nanosize phases are {111} planes. Available theoretical results on morphology of multiferroic thin film nanostructure allow us to conclude that for thick films (>100 nm), two-phase columnar morphology (shape of constituent phases, their arrangement, and average crystallographic orientations of the interfaces) is essentially determined by the trend for minimization of elastic energy, while the trend to minimize the energy of interfaces results in faceting interfaces along the {111} planes. Possibility of long range ordering in phase arrangement is discussed.