Amorphization and nanocrystal formation in a Pd–Ni–Cu–P alloy after cooling under different conditions

Structure formation during solidification of a Pd–Ni–Cu–P melt is studied. It is demonstrated that changes in the heat transfer conditions lead to a nonlinear change in the characteristics of the structure. The article presents the regimes of cooling the samples and the results of their structure and composition studies. It is found that a decrease in the cooling rate of the alloy leads to an increase in the size, proportion and composition of nanoinclusions in an amorphous matrix. X-ray diffraction method, electron probe microanalysis, transmission microscopy and scanning calorimetry are used for samples characterization. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.

SPECIFIC STRUCTURE OF EFFECTIVE MEMBRANE ALLOYS BASED ON NIOBIUM, VANADIUM AND ZIRCONIUM

Аморфные, нанокристаллические мембранные сплавы на основе элементов V группы с уникальными механическими и функциональными свойствами и с матричной дуплексной микроструктурой активно способствуют развитию водородной энергетики. Имеются еще не вполне разрешенные проблемы для этих новых сплавов -их низкая термическая стабильность, недосточная механическая прочность (пластичность, твердость), а также охрупчивание интерметаллидное и гидридное. Для эффективного применения разрабатываются сплавы с тройным составом - в которые помимо элементов V группы входят и легирующие металлы никель и титан. Получают не только аморфные и нанокристаллические сплавы, применимые в электронике и электроэнергетике, а также мембранные сплавы с дуплексной матричной структурой, объединяющей аморфные, так нано- и квазикристаллические дендритно упрочняющие фазы, как упрочняющие аморфную матрицу. В специализируемых мембранных тройных сплавах формируются соединения NiTi и NiTi, стабилизирующие и предохраняющие нано- и кристаллические мембраны от хрупкого разрушения. Установлено, что интенсивное образование гидридов в этих альтернативных мембранных сплавах столь же не желательно, как и для традиционных сплавов на основе палладия. Рассматриваемые сплавы действительно позволяют получить газообразный водород высокой чистоты с применением новых составов взамен дорогостоящих мембран на основе сплавов Pd - Au / Ag / Cu. With unique mechanical and functional properties, amorphous, nanocrystalline and matrix duplex microstructure membrane alloys based on group V elements actively contribute to the development of hydrogen energy. There are still not completely resolved problems for these new alloys - their low thermal stability, insufficient mechanical strength (plasticity, hardness), and intermetallic and hydride embrittlement. For effective use, alloys with a triple composition are being developed - which, in addition to the elements of group V, also include nickel and titanium as alloying metals. Not only amorphous and nanocrystalline alloys are obtained that are applicable in electronics and power engineering, as well as membrane alloys with a duplex matrix structure that combines amorphous, nano-and quasicrystalline dendritic-hardening phases strengthening the amorphous matrix. In specialized membrane ternary alloys, NiTi and NiTi compounds are formed, which stabilize and protect nano-and crystalline membranes from brittle destruction. It has been found that the intense formation of hydrides in these alternative membrane alloys is as undesirable as for palladium-based compounds. The alloys under consideration actually make it possible to obtain high-purity gaseous hydrogen using new compositions instead of expensive membranes based on Pd - Au / Ag / Cu alloys.

Structure and Magnetic Properties of Thermodynamically Predicted Rapidly Quenched Fe85-xCuxB15 Alloys

In this work, based on the thermodynamic prediction, the comprehensive studies of the influence of Cu for Fe substitution on the crystal structure and magnetic properties of the rapidly quenched Fe85B15 alloy in the ribbon form are performed. Using thermodynamic calculations, the parabolic shape dependence of the ΔGamoprh with a minimum value at 0.6% of Cu was predicted. The ΔGamoprh from the Cu content dependence shape is also asymmetric, and, for Cu = 0% and Cu = 1.5%, the same ΔGamoprh value is observed. The heat treatment optimization process of all alloys showed that the least lossy (with a minimum value of core power losses) is the nanocomposite state of nanocrystals immersed in an amorphous matrix obtained by annealing in the temperature range of 300–330 °C for 20 min. The minimum value of core power losses P10/50 (core power losses at 1T@50Hz) of optimally annealed Fe85-xCuxB15 x = 0,0.6,1.2% alloys come from completely different crystallization states of nanocomposite materials, but it strongly correlates with Cu content and, thus, a number of nucleation sites. The TEM observations showed that, for the Cu-free alloy, the least lossy crystal structure is related to 2–3 nm short-ordered clusters; for the Cu = 0.6% alloy, only the limited value of several α-Fe nanograins are found, while for the Cu-rich alloy with Cu = 1.2%, the average diameter of nanograins is about 26 nm, and they are randomly distributed in the amorphous matrix. The only high number of nucleation sites in the Cu = 1.2% alloy allows for a sufficient level of grains’ coarsening of the α-Fe phase that strongly enhances the ferromagnetic exchange between the α-Fe nanocrystals, which is clearly seen with the increasing value of saturation induction up to 1.7T. The air-annealing process tested on studied alloys for optimal annealing conditions proves the possibility of its use for this type of material.

Observation of a Broadened Magnetocaloric Effect in Partially Crystallized Gd60Co40 Amorphous Alloy

To investigate the effect of crystallization treatment on the structure and magnetocaloric effect of Gd60Co40 amorphous alloy, the melt-spun ribbons were annealed at 513 K isothermally for 20, 40 and 60 min. The results indicate that, with increasing annealing time, the Gd4Co3 (space group P63/m) and Gd12Co7 (space group P21/c) phases precipitated from the amorphous precursor in sequence. In particular, in the samples annealed for 40 and 60 min, three successive magnetic transitions corresponding to the phases of Gd4Co3, Gd12Co7 and remaining amorphous matrix were detected, which induced an overlapped broadened profile of magnetic entropy change (|ΔSM|) versus temperature. Under magnetic field changing from 0 to 5 T, |ΔSM| values of 6.65 ± 0.1 kg−1·K−1 and 6.44 ± 0.1 J kg−1·K−1 in the temperature spans of 180–196 K and 177–196 K were obtained in ribbons annealed for 40 and 60 min, respectively. Compared with the fully amorphous alloy, the enhanced relative cooling power and flattened magnetocaloric effect of partially crystallized composites making them more suitable for the Ericsson thermodynamic cycle.

Facile and reproducible method of stabilizing $$\hbox {Bi}_2\hbox {O}_3$$ phases confined in nanocrystallites embedded in amorphous matrix

Bismuth sesquioxide ($$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 ) draws much attention due to wide variety of phases in which it exists depending on the temperature. Among them, $$\delta$$ δ phase is specially interesting because of its high oxide ion conductivity and prospects of applications as an electrolyte in fuel cells. Unfortunately, it is stable only in a narrow temperature range ca. 730–830 $$^{\circ }$$ ∘ C. Our group has developed a facile and reproducible two-stage method of stabilizing $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 crystalline phases confined in nanocrystallites embedded in amorphous matrix. In the first stage, glassy materials were obtained by a routine melt-quenching method: pure $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 powders were melted in porcelain crucibles and fast-cooled down to room temperature. In the second step, the materials were appropriately heat-treated to induce formation of crystallites of $$\beta$$ β , $$\delta$$ δ or $$\gamma$$ γ $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 phases confined in a glassy matrix, depending on the process conditions. It was found out that the vitrification of the initial $$\hbox {Bi}_2\hbox {O}_3$$ Bi 2 O 3 and the subsequent nanocrystallization were unexpectedly possible due to the presence of some Al, and Si impurities from the crucibles. Systematic DTA, XRD, optical, Raman and SEM/EDS studies were carried out to investigate the influence of the syntheses processes and allowed us to determine conditions under which the particular phases appear and remain stable down to room temperature.

Effect of Transition Elements on the Thermal Stability of Glassy Alloys 82Al–16Fe–2TM (TM: Ti, Ni, Cu) Prepared by Mechanical Alloying

In the present study, the thermal stability and crystallization behavior of mechanical alloyed metallic glassy Al82Fe16Ti2, Al82Fe16Ni2, and Al82Fe16Cu2 were investigated. The microstructure of the milled powders was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The results showed remarkable distinction in thermal stability of the alloys by varying only two atomic percentages of transition elements. Among them, Al82Fe16Ti2 alloy shows the highest thermal stability compared to the others. In the crystallization process, exothermal peaks corresponding to precipitation of fcc-Al and intermetallic phases from amorphous matrix were observed.

Investigation of Fiber-Driven Mechanical Behavior of Human and Porcine Bladder Tissue Tested Under Identical Conditions

The urinary bladder is a highly dynamic organ, that undergoes large deformations several times a day. Mechanical characteristics of the tissue are crucial in determining the function, and dysfunction, of the organ. Yet, literature reporting on the mechanical properties of human bladder tissue is scarce and, at times, contradictory. In this study, we focused on mechanically testing tissue from both human and pig bladders using identical protocols, to validate the use of pigs as a model for the human bladder. Furthermore, we tested the effect on tissue mechanical properties of two treatments, elastase to digest elastin fibers and oxybutynin to reduce smooth muscle cells spasticity, as well as of the anatomical direction of testing. We also implemented two different material models to aid in the interpretation of the experimental results. We found that human tissue behaves similarly to pig tissue at high deformations (collagen-dominated behavior) while we detected differences between the species at low deformations (amorphous matrix-dominated behavior). Our results also suggest that elastin could play a role in determining the behavior of the collagen fibers network. Finally, we confirmed the anisotropy of the tissue which reached higher stresses in the transverse when compared to the longitudinal direction.