Spinodal Structure Research Articles

Adaptive attenuation of hierarchical composition fluctuations augments the plastic strain of a high entropy steel

A body-centred cubic (BCC) high entropy steel with a spinodal-like nanopattern and atomic-scale local chemical fluctuations exhibits controlled attenuation of its chemical complexity with deformation. Changes in the chemical composition of the spinodal structure measured using energy dispersive X-ray spectroscopy reveal that the average composition peak-to-peak amplitude decreases by 67% from 4.9 at.% to 1.6 at.% with increasing strain. On the other hand, the short-range chemical fluctuations, assessed with atomic strain mapping, displays a 48% decrease in the average strain peak-to-peak amplitude from 3.03 at.% to 1.59 at.% under mechanical loading. The reduction in local strain brought about by increased chemical homogeneity at both levels enables more uniform, steady deformation leading to extended ductility (13.7±1.9%), all the while maintaining ultrahigh strength (2.92±0.36 GPa, placing it among the highest values reported). The interactions between dislocations and concentration waves are identified and found to be responsible for this compelling effect on the newly created steel.

Refinement strengthening, second phase strengthening and spinodal microstructure-induced strength-ductility trade-off in a high-entropy alloy

The strength-ductility trade-off of high-entropy alloy (HEA) is a major factor affecting its potential application. In this work, the mechanical properties and deformation mechanisms of as-cast and cold rolled-annealed (RA) Fe23Co24Ni24Cr21Al8 (at%) HEA samples were comparatively investigated. Compared with as-cast sample, the cold-rolled and annealed sample possessed higher yield strength (725 ± 12 MPa), ultimate strength (1042 ± 23 MPa) and sustained good ductility (46.7 ± 4.5%), suggesting excellent strength-ductility combination was achieved in RA sample. The as-cast and RA samples both possessed dual phases including FCC and BCC, but the volume fraction of BCC in as-cast sample was very few. The RA sample exhibited significantly decreased grain size and more volume fraction of BCC compared with as-cast sample, indicative of the refinement strengthening and second phase strengthening. Meanwhile, a high density of dislocation walls and spinodal decomposition structure were observed in RA sample, which contributed to the outstanding ductility.

Crystal structure determination of a new LaPO4 phase in a multicomponent glass ceramic via 3D electron diffraction

A glass ceramic from the MgO–Al 2 O 3 –SiO 2 system containing additives of ZrO 2 , TiO 2 , La 2 O 3 and P 2 O 5 was investigated. Via x-ray powder diffraction (XRPD) and Transmission electron microscopy(TEM) the crystalline phases present could be identified as MgAl 2 O 4 (Spinel), orthorhombic ZrTiO 4 and a polymorph of LaPO 4 with a previously unknown crystal structure. The crystal structure of this LaPO 4 phase was solved ab initio via 3D ED Data. The polymorph occurs in a distorted barite structure type in the same space group (P2 1 /n) as the stable monazite type polymorph, however the density is higher and the La has a higher coordination number. Furthermore the LaPO 4 is present in a spinodal relict microstructure. Potential explanations for the presence of this metastable polymorph are pressure due to residual stresses from the crystallization or surface effects due to the high surface area resulting from the spinodal relict structure.

Tailoring the magnetic properties and microstructure of Alnico 8 magnets by various Ti contents and processing conditions

Shape anisotropy, developed as a result of spinodal decomposition (SD) is the basis for the hysteresis behavior of Alnico magnets. The SD process is sensitive to processing conditions and constituent elements. In this paper, the development of spinodal structure and its effects on magnetic properties and serviceability of Alnico 8 alloys are investigated. The Ti-content is varied between 2.5 and 7.5 wt%. The magnets are fabricated by conventional casting, homogenization, magnetic field annealing and tempering treatments. The magnetic properties of intrinsic coercivity, Hcj = 30 kA/m, remanence, Br = 0.53 T and maximum energy density, (BH)max = 6.03 kJ/m3 for 2.5 wt% Ti are increased to Hcj = 150 kA/m, Br = 0.0.88 T and (BH)max = 29.3 kJ/m3 for 6.5 wt% Ti alloy. These magnetic properties are 100% reversible up to 800 K. Furthermore, an alloy with 5.5 wt% Ti is directionally solidified and magnetic properties of Br = 1.01 T and (BH)max = 58.9 kJ/m3 are obtained. The evolution of mosaic nano structure, the mechanism of magnetic hardening and the interactions of various phases have been investigated.

Compositional interpretation of high elasticity Cu–Ni–Sn alloys using cluster-plus-glue-atom model

The D022 or L12-γ′ phase strengthened Cu–Ni–Sn alloys possesses a characteristic microstructure, exhibiting the distribution of precipitated phase with smaller size on a spinodal decomposition structure, which leads to that the composition of the precipitated phase and Cu matrix cannot be precisely measured and restriction of the accurate compositional design of the alloys. The present work initials to introduce the cluster-plus-glue-atom model for compositional interpretation of the industrial Cu–Ni–Sn alloys, and then optimizing the cluster formula according to the measured composition of the relevant precipitated phases. Moreover, the solid solution content of Ni or the precipitation content of Sn are calculated based on the optimized cluster formula, and establishing the relationship between the alloy composition and properties. It indicates that the strength mainly relays on the precipitation content of Sn while the conductivity depends on the solid solution content of Ni, which is also suitable for the Cu–Ni–Sn–Zn (Co) alloys or Cu–Ni–Al alloys with similar characteristics. Additionally, the ratio of strength/resistivity increases in the alloys as the increasing Sn content under the premise of close to 3 of Ni/Sn (or (Ni + Co)/Sn) atomic ratio, but the discontinuous precipitation is easily to generate. Therefore, the improved properties of the alloys cannot be attained via the reducing ratio of Ni/Sn (or (Ni + Co)/Sn) atomic ratio solely. Based on the above, this work provides theoretical support and application methods for the compositional design and performance prediction of coherent D022 or L12-γ′ phase strengthened alloys.

Microstructure evolution and mechanical properties of AlCrFe2Ni2(MoNb)x high entropy alloys

The AlCrFe2Ni2(MoNb)x multiphase high entropy alloys were designed, prepared and characterized. The synergistic effect of Mo and Nb alloying on microstructures and mechanical properties of AlCrFe2Ni2-based high entropy alloy were investigated. By synergistic alloying with Mo and Nb, the volume fraction of the BCC phase increased, and a novel Laves phase with hexagonal close-packed(HCP) structure was formed. With the increase of Mo and Nb content, the alloys dramatically transformed from equiaxed grain with multiple phases to dendrites with the spinodal decomposition structure of the A2 phase and B2 phase, as well as inter-dendrites with the eutectic structure of the FCC phase and Laves phase. Furthermore, the solidification behavior of the alloys varied considerably as the increase of Mo and Nb content. The coexisting solidification microstructure of the eutectic structure and spinodal decomposition structure in the AlCrFe2Ni2(MoNb)0.3, AlCrFe2Ni2(MoNb)0.5 and AlCrFe2Ni2(MoNb)0.7 alloys have hardly been observed in other HEAs. The increase of Mo and Nb elements tends to segregate in the front of the liquid–solid interface, which hinders the growth of the FCC phase and leads to the formation of fine rod-like morphology. The synergistic effect of the fine grain strengthening and the solid solution strengthening resulted in high yield strength and fracture strength of 878 MPa and 2830 MPa, maintaining high plastic strain of 43.7%. Further increasing the content of Mo and Nb would lead to the increase of brittle Laves phase, with the second phase strengthening becoming the dominant strengthening mechanism, resulting in an increase in yield strength to 1549 MPa and a decrease in plastic strain to 8.6%. The investigation results would provide a guide for strengthening the macroscopic mechanical properties of eutectic high entropy alloys through synergistic alloying effect.

Comprehensive characterisation of tribo-layer in a Cu-15Ni-8Sn alloy during dry sliding wear

The detailed characteristic of the tribo-layer in an age-hardening Cu-15Ni-8Sn alloy was studied with advanced analysis techniques. A comprehensive picture of the tribo-layer was drawn from nanoscale to macroscale. The characterisation was done for the oxide layer (OL) that is easy to scaling off during the preparation of metallographic samples, showing a homogeneous mixture of oxide and nanocrystalline particles with a thickness of several micrometers. The mechanically mixed layer (MML) is a multi-layer structure. In addition, the spinodal structure and ordered intermetallic precipitates existing in the matrix were gradually transformed or disappeared in OL and MML. Furthermore, there is a nanocrystalline transformation on the top of plastically deformed layer (PDL), where thin twin-matrix lamellar structure and equiaxed nanocrystallines were formed.

Structure and magnetic properties of spinodal decomposed Cu60Ni20Fe10Co10 ribbons with hard magnetism

The spinodal decomposed Cu-Ni-Fe alloy can possess both hard magnetic properties and excellent plastic toughness, corrosion resistance, and cold workability. Cu60Ni20Fe10Co10 ribbons are prepared by melt-spinning and annealing methods, and their phase composition, microstructure, and magnetic properties are studied. The results show that the as-spun ribbons are composed of equiaxed grains. Through the decomposition of γ → γ1 + γ2 inside the grains, the spinodal structure is formed, which endows the ribbons with the hard-magnetic properties. Also, the maximum coercivity of 679.3 ± 149.1 Oe and saturation magnetization of 72.0 ± 2.7 emu/g are obtained in the ribbons annealed at 435 °C for 30 min and 835 °C for 30 min, respectively. The shape anisotropy of γ1 and γ2, the concentration of Fe, Co, Ni in the γ2 phase, and the content of the α phase are the main factors to determine the magnetic properties. At the same time, the corresponding microstructure evolution models are proposed.

Spinodal Decomposition Stabilizes Plastic Flow in a Nanocrystalline Cu-Ti Alloy

A combination of high strength and reasonable ductility has been achieved in a copper-1.7 at.%titanium alloy deformed by high-pressure torsion. Grain refinement and a spinodal microstructure provided a hardness of 254 ± 2 Hv, yield strength of 800 MPa and elongation of 10%. The spinodal structure persisted during isothermal ageing, further increasing the yield strength to 890MPa while retaining an elongation of 7%. This work demonstrates the potential for spinodal microstructures to overcome the difficulties in retaining ductility in ultra-fine grained or nanocrystalline alloys, especially upon post- deformation heating where strain softening normally results in brittle behavior.

Structure and magnetic properties of alnico 8 ribbons

Alnico 8 ribbons were prepared by melt-spinning and annealing, and the effects of melt-spinning speeds on the structure and magnetic properties were investigated. The results show that all the as-spun ribbons are composed of the α-Fe(Co)-type α1 and the AlNi-type α2. With speed reducing from 40 m/s to 15 m/s, the <100> preferred orientation enhanced, the grain size and the α2 content increased. The as-spun ribbons show the weak hard magnetic properties. Annealing improves the spinodal structure consisting of the strip-like α1 and α2. The annealed ribbons melt-spun at 15 m/s achieve the optimal magnetic properties with the coercivity of 1558.3 Oe and the maximum magnetic polarisation density of 11.3 kGs, which are codetermined by the shape anisotropy of the strip-like α1 phase and the pinning mechanism of the α2 phase to the α1 domains.

Temperature effects on microstructure and mechanical properties of sintered high-entropy equiatomic Ti20V20Al20Fe20Cr20 alloy for aero-gear application

This work presented an upgraded high-entropy alloy by the addition of chromium to the conventional Ti-10V-2Fe-3Al alloy to fabricate equiatomic Ti20V20Al20Fe20Cr20 high-entropy alloy via spark plasma sintering powder processing at different temperature of 700 °C, 800 °C, 900 °C, 1000 °C, and 1100 °C respectively under a constant heating rate of 100 °C /min, the pressure of 40 MPa, and holding time of 5 min. The microstructure and phase transformation of the sintered alloyed were studied with a scanning electron microscope equipped with energy dispersive spectroscopy. The constituent phases present in the sintered high-entropy alloy were analyzed by X-ray diffraction and were found to show increased development of body-centered cubic solid solution alloys across the temperature gradients. The mechanical properties over a temperature range of 700 ≤ T °C ≤ 1100 generally show an increase in hardness from 3363 to 8480 MPa, tensile strength from 1097.17 to 2766.58 MPa, and yield strength from793.61 to 2001.13 MPa respectively. The SEM-EDS of Ti20V20Al20Fe20Cr20 equiatomic high-entropy alloys show the existence of a nano-net-like spinodal structure at the optimum temperature of 1100 °C, which are rich in body centered cubic structure. At this elevated temperature, the presence of strong body-centered cubic–forming elements such as Cr, Fe, and Al was established from the corresponding EDS. Ti20V20Al20Fe20Cr20 high-entropy equiatomic alloy has been successfully fabricated by spark plasma sintering. The effects of temperature on microstructural and mechanical properties of the sintered Ti20V20Al20Fe20Cr20 alloy demonstrated a general improvement of the alloys at the elevated region.

Effects of porosity and pore microstructure on the mechanical behavior of nanoporous silver

The tensile strength of nanoporous silver (AgNPs) is investigated by experiments and molecular dynamic analysis. Effects of sintering temperature on the porosity and ultimate strength of AgNPs are studied. The tensile properties of AgNPs with different micro structures and porosities are determined. The phase field method is adopted to develop the spinodal decomposition open-cell porous microstructure. AgNPs with cube, gyroid, and sphere pores generally show brittle fracture in tension, while AgNPs with spinodal decomposition structure show brittle fracture at low porosity and ductile fracture at high porosity. The influences of porosity on the Young’s modulus and ultimate strength are studied. The predicted stress-strain curves are validated by the Gibson-Ashby model and experimental data. The microstructure is investigated by common neighbor analysis and dislocation extraction algorithm. It is found that the dislocation nucleation sites are concentrated near the pore surfaces, the evolution of strain-stress curve is related to the dislocation density. Molecular dynamics simulations reveal that the uniaxial tensile deformation is accompanied by accumulation of stacking faults in ligaments, as well as the formation of Lomer–Cottrell locks at the junctions of dislocation. The influences of porosity and pore surface to the dislocation nucleation and tensile strength are discussed.

Design and characterization of FeCrCoAlMn0.5Mo0.1 high-entropy alloy coating by ultrasonic assisted laser cladding

In this work, FeCrCoAlMn 0.5 Mo 0.1 high-entropy alloy (HEA) coating was successfully synthesized on 316L stainless steel by ultrasonic assisted laser cladding. The effect of dilution rate on the phase composition of FeCrCoAlMn 0.5 Mo 0.1 coatings was investigated by thermodynamic calculation, solidification simulation and microstructure characterization. The mechanical properties, tribological behavior and corrosion resistance of FeCrCoAlMn 0.5 Mo 0.1 coating prepared under optimal dilution rate were also characterized in detail. The results show that the increase of dilution rate results in the transition of single solid solution (BCC) into dual-phase solid solution (FCC and BCC) of FeCrCoAlMn 0.5 Mo 0.1 coating. The TEM analysis reveals that FeCrCoAlMn 0.5 Mo 0.1 coating with optimal dilution rate (∼27.3%) is virtually composed of disordered BCC phase and ordered BCC (B2) phase. The spinodal decomposition structure and numerous dislocations were found in the grains. The average microhardness of FeCrCoAlMn 0.5 Mo 0.1 coating is ∼624.1 HV, which is more than 2.6 times higher than that of the substrate. The wear resistance of FeCrCoAlMn 0.5 Mo 0.1 coating was found significantly improved almost 4 times than that of 316L stainless steel. The passive current density of FeCrCoAlMn 0.5 Mo 0.1 coating is reduced by an order of magnitude compared with that of 316L stainless steel, proving the better corrosion resistance of FeCrCoAlMn 0.5 Mo 0.1 coating. • A new FeCrCoAlMn 0.5 Mo 0.1 HEA coating without defects was successfully prepared by ultrasonic assisted laser cladding. • Excessive dilution will result in phase transition of FeCrCoAlMn 0.5 Mo 0.1 HEA coating. • The spinodal decomposition structure and numerous dislocations are found in the coating. • FeCrCoAlMn 0.5 Mo 0.1 HEA coating shows good wear resistance and corrosion resistance.

Subnano Ruthenium Species Anchored on Tin Dioxide Surface for Efficient Alkaline Hydrogen Evolution Reaction

Summary Single-atom catalysts with unique electronic structures are drawing increasing attention as compared with nano-catalysts. However, subnano-catalysts, falling between the two categories, may match the demands of catalytic reactions better due to their tunable electronic structure, but they have rarely been studied. Here, we report a subnano-ruthenium species anchored on nano-SnO2 (Ru@SnO2). Although rutile SnO2 and RuO2 are isostructural and tend to form a spinodal structure in bulk materials, the Ru@SnO2 nano-structure is successfully prepared by our newly developed micro-etching technique. The optimized sample displays high activity for alkaline hydrogen evolution reaction with low overpotential and flat Tafel slope, superior to commercial Pt/C (20 wt%), while density functional theory investigations on the hydrogen-binding energy and Gibbs free energy are consistent with these results. The inherent design and synthesis strategies reported herein may open a new avenue for further catalyst development.

Phase Transition Mechanism and Mechanical Properties of AlCrFe2Ni2 High‐Entropy Alloys with Changes in the Applied Carbon Content

To understand the effect of carbon addition on dual‐phase high‐entropy alloys (HEAs), the mechanism of phase transition and mechanical properties of AlCrFe2Ni2Cx (x = 0, 0.06, 0.12, 0.18, 0.24) are investigated systematically. The results show that carbon addition induced the growth and aggregate of disordered noodle‐like face‐centered cubic (FCC) phases. The volume fraction of the FCC phase increases from 33.2% to 51.2% as the C content increases. The Al and Ni in the alloys are segregated at the phase boundaries. Disappearance of the spinodal decomposition structure compose of a disordered body‐centered cubic (BCC) structure and an ordered BCC structure (B2). The BCC phase transform into a spherical B2 phase with increasing C content. The experimental mechanical properties show that the yield strength of the HEAs is closely related to the volume fraction of BCC phase as the C content increases. The ε phase (Cr, C carbonization) precipitate in an FCC phase when the C content is above 2.0 at%. The hardness of the HEAs increases from 310 to 357 HV as the C content increases. The compressive strength and the fracture strain of the alloy decreases as the C content increases.

Structure and magnetic properties of Alnico8 alloy thermo-magnetically treated under a 10 T magnetic field

The structure and compositions of spinodal phases in Alnico8 alloy isothermally treated at 830 °C under external magnetic field (Hext) up to 10 T were investigated by transmission electron microscopy (TEM). Under ultra-high magnetic field (10 T), the spinodal structure of Alnico8 alloy presents interesting diversity for the shapes of α1 phase particles, namely, Π-shape, H-shape and Ш-shape apart from regular rod-shape. Composition analysis shows that the Fe was mainly distributed in the α1 phase. The Co content in the α1 phase was lower than that in the α2 phase as evidenced by the point analysis results, and Co content inα1 phase of the alloy treated without magnetic field was higher than that of the alloy treated with a magnetic field. In contrast, the Ni, Al, Cu and Ti were concentrated in the α2 phase. The average hyperfine field of the alloy treated without magnetic field was about 301.3 kOe. While the alloy treated under magnetic field, it was slightly decreased, which was about 292.0 and 296.1 kOe under 0.7 and 10 T, respectively. Magnetic properties of the alloy treated under a 10 T magnetic field were the best, which were about 1.09T, 396Oe and 9.5 kJ/m3 for Br, Hc and (BH)max respectively. Especially for the coercivity, which was mainly contributed by the anisotropy of the α1 phase induced by the high magnetic field.

Spinodal Decomposition and Mechanical Response of a TiZrNbTa High-Entropy Alloy.

In this study, the effects of spinodal decomposition on the microstructures and mechanical properties of a TiZrNbTa alloy are investigated. The as-cast TiZrNbTa alloy possesses dual phases of TiZr-rich inter-dendrite (ID) and NbTa-rich dendrite (DR) domains, both of which have a body-centered cubic (BCC) structure. In the DRs of the as-cast alloy, the α and ω precipitates are found to be uniformly distributed. After homogenization at 1100 °C for 24 h followed by water quenching, spinodal decomposition occurs and an interconnected structure with a wavelength of 20 nm is formed. The α and ω precipitates remained in the structure. Such a fine spinodal structure strengthens the alloy effectively. Detailed strengthening calculations were conducted in order to estimate the strengthening contributions from the α and ω precipitates, as well as the spinodal decomposition microstructure.

Excellent magnetic properties determined by spinodal decomposition structure of Alnico alloy doped SmCo5-based ribbons

5 wt% Alnico5 doped Sm(Co0.9Cu0.1)5 ribbons were prepared by melt spinning at 40 m/s, and the effects of magnetic field heat treatment (MHT) and annealing on the phase composition, microstructure and magnetic properties of the ribbons were investigated. The results show that all three ribbons consist of Co-rich SmCo5-and Sm-rich CeCo5-type phases with a spinodal structure. Annealing increases the content of SmCo5-type phase, enlarges the component differences between the two types of Sm(Co,M)5 phases and accumulates Alnico alloying elements into 3 g site of CeCo5-type phase. MHT narrows the ingredient differences between them, prompting the Alnico alloying elements to diffuse simultaneously into 2c and 3 g sites of two Sm(Co,M)5 phases, and concentrates the CeCo5-type phase on grain boundaries of the SmCo5-type phase to pin the magnetic domain movement. The as-spun ribbons present the magnetic properties of Hc = 32.0 kOe, Mr = 46.2 emu/g and Ms = 59.1 emu/g, while MHT increases them by 10.0%, 10.2% and 19.5%, respectively. These results can contribute to disclose the multi-element doping mechanism for improving the magnetic properties of SmCo5-based or similar alloys.

Effects of Al addition on structural evolution and mechanical properties of the CrCoNi medium-entropy alloy

In this study, we synthesized a series of (CoCrNi)100-xAlx (x = 0–30 at.%) medium-entropy alloys (MEAs), investigated alloying effects of Al element on microstructure and mechanical properties of CrCoNi MEA, then analyzed the strengthen mechanism caused by Al element. Microstructural evolutions were evaluated by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The microstructures of (CoCrNi)100-xAlx MEAs evolved from single face-centered cubic (FCC) (x < 12 at.%), to duplex FCC plus body-centered cubic (BCC) (12 ≤ x < 22 at.%), then to double BCC (x ≥ 22 at.%) structures with Al content increase. When Al content increase to 16 at.%, BCC phase decomposed into plate-like intervened structure with ordered and disordered BCC phases (B2 and A2 structure) by spinodal decomposition mechanism. When Al content higher than 22 at.%, spinodal structure evolve from plate-like intervened structure to spherical particles dispersed in matrix structure. The hardness of Alx alloys increased from HV170 to the maximum of HV700 and the compressive yield strength rose form 204 MPa–1792 MPa. The solid-solution strengthening of Al element and formation of hard BCC phase were the two main factors contributing to the strengthening effect in this alloy system. Experimental results showed that the duplex FCC plus BCC structure can significant enhanced the strength-ductility synergy of CrCoNi MEA. It is especially noted that Al19 alloy which consist of 40% volume fraction FCC and 60% volume fraction BCC exhibits the most attractive properties accompany with compromise compressive yield strength, fracture strength and facture strain of 1226 MPa, 2542 MPa and 21.97%, respectively, and the corresponding hardness of 494 HV.

Evolution of Microstructures and Properties in AlxCrFeMn0.8Ni2.1 HEAs

The microstructures, compression and corrosion behaviors of the as-cast AlxCrFeMn0.8Ni2.1 high-entropy alloys (0 ≤ x ≤ 2.3) were investigated in this paper. It was found that the crystal structure changed from initial dual FCC structure to mixed FCC and BCC structure, then to BCC structure as the increasing of Al content. Al0.8CrFeMn0.8Ni2.1 alloy exhibited a typical spinodal structure consisting of alternating two phases microstructure. Moreover, sunflower-like microstructure was obtained in the as-cast AlxCrFeMn0.8Ni2.1 alloys (1.0 ≤ x ≤ 2.0). With the increasing of Al, the macrohardness increased while the plasticity decreased in the alloys. The addition of an appropriate amount of Al could improve the compressive fracture strength of the alloys. In addition, the corrosion resistance deteriorated slightly with the increasing of Al in 1 mol/L NaCl solution.