Pseudobinary Alloys Research Articles

Mechanical properties of various thermomechanical processed Ti-Mo-Al-Zr and pseudo-binary (Ti-Zr)-Mo shape memory alloys for biomedical applications

Shape memory alloys (SMAs) have attracted much attention due to the great demand for biomedical materials. Among the SMAs, the Ti-based SMAs are promising materials owing to their high biocompatibility, non-toxicity, excellent functionalities, and proper mechanical properties. Concerning the Ti-based SMAs, adding other elements is an often-used strategy, and the combinations of the addition materials are unlimited. Among the various Ti-based alloy systems, the Ti-Mo-Al-Zr alloy is one fundamental alloy system, since Mo and Al are served as the specific metals for the calculations of the Mo equivalent and Al equivalent for the evaluation of the alloy stability. While Zr is a neutral element for fine-tuning the properties of the alloys. This fundamental quaternary alloy was thus chosen in this study. In this research series, it has been found that the Ti-5.5Mo-8Al-6Zr alloy performed proper mechanical properties. Therefore, this specific alloy was further subjected to various thermomechanical treatments to further improve its properties. In addition to the Ti-5.5Mo-8Al-6Zr alloy, pseudo-binary alloys of (Ti-Zr)-Mo were also investigated due to their intrinsic low phase transformation temperature compared to the pure Ti and Zr elements. Strategies for the development of these SMAs by conducting thermomechanical treatments have been proposed in this study.

Sputter deposition of ZnO–AlN pseudo-binary amorphous alloys with tunable band gaps in the deep ultraviolet region

ZnO–AlN pseudo-binary amorphous alloys (a-ZAON hereinafter) with tunable band gaps in the deep ultraviolet (DUV) region have been synthesized using magnetron sputtering. The miscibility gap between ZnO and AlN has been overcome using room-temperature sputtering deposition, leveraging the rapid quenching abilities of sputtered particles to fabricate metastable but single-phase alloys. X-ray diffraction patterns and optical transmittance spectra revealed that the synthesized films with chemical composition ratios of [Zn]/([Zn] + [Al]) = 0.24–0.79 likely manifested as single-phase of a-ZAON films. Despite their amorphous structures, these films presented direct band gaps of 3.4–5.8 eV and thus high optical absorption coefficients (105 cm−1). Notably, the observed values adhered to Vegard’s law for crystalline ZnO–AlN systems, implying that the a-ZAON films were solid solution alloys with atomic-level mixing. Furthermore, atomic force microscopy analyses revealed smooth film surfaces with root-mean-square roughness of 0.8–0.9 nm. Overall, the wide-ranging band gap tunability, high absorption coefficients, amorphous structures, surface smoothness, and low synthesis temperatures of a-ZAON films position them as promising materials for use in DUV optoelectronic devices and power devices fabricated using large-scale glass and flexible substrates.

Double Helix of Icosahedra Structure and Spin Glass Magnetism of the δ-Co2.5Zn17.5-xMnx (x = 0.4-3.5) Pseudo-Binary Alloys.

We have synthesized δ-Co2.5Zn17.5-xMnx (x = 0.4-3.5) pseudo-binary alloys of 10 different compositions by a high-temperature solid-state synthetic route, determined their crystal structures and the Mn substitution pattern, and estimated the existence range of the δ-phase. The alloys crystallize in two chiral enantiomorphic space groups P62 and P64, where the basic atomic polyhedron of the chiral structure is an icosahedron and the neighboring icosahedra share vertices to form an infinitely long double helix along the hexagonal axis (like in the δ-Co2.5Zn17.5 parent binary phase). The alloys are pure δ-phase up to the Mn content x ≈ 3.5. The Mn atoms partially substitute Zn atoms at particular crystallographic sites located on the icosahedra. The study of magnetism was performed on the Co2.5Zn17.1Mn0.4 alloy with the lowest Mn content. Contrary to the expectation that structural chirality may induce the formation of a nontrivial magnetic state, a spin glass state with no relation to the structural chirality was found. The magnetic sublattice contains all of the necessary ingredients (randomness and frustration) for the formation of a spin glass state. Typical out-of-equilibrium dynamic phenomena of a spin system with broken ergodicity were detected below the spin freezing temperature Tf ≈ 8 K.

DFT studies on electronic and structure properties of PbSe1-xSx alloys for thermoelectric materials using VCA and RS

In this work, Density Functional Theory (DFT) was employed to investigate the crystal structure and electronic properties of lead selenide (PbSe) and lead sulfide (PbS) semiconductors and their pseudo binary alloys PbSe1-xSx. The virtual crystal approximation (VCA) and randomly substituted solid models were employed to study these materials. In addition, the thermoelectric properties as function of the alloy composition were studied. Lattice parameters obtained using the generalized gradient approximation (GGA) were compared with theoretical and experimental results. The electronic bands were calculated for different sulfur compositions (0≤x ≤ 1, Δx = 0.1) using the Generalized Gradient Approximation of TB09LDA (MGGA). It was observed that the transition from the valence band to the conduction band takes place at the L point, which agrees with previous theoretical investigations. Slight deviations from Vegard's law were observed in the lattice parameters and bandgap of the alloys, especially for the sulfur-rich alloys. Effective band diagrams obtained from the unfolding of supercell band diagrams, reported for the first time for this system, show that the impacts of alloy disorder are low in the vicinity of the L point. The influence of the alloy composition on the transport properties was studied within the framework of Boltzmann's semiclassical theory. The electrical conductivity shows a thermally activated increase which influences the total thermal conductivity above T > 600–700 K, and the figure of merit ZT. Seebeck coefficient dependence with the chemical potential suggests an ambipolar behavior of the alloys, which present both n and p character. The alloys have the ZT maxima above 900 K influenced by the PbSe1-xSx alloy composition. Remarkably, the alloy with x = 0.5 present a maximum ZT value comparable to that of PbSe, which indicates that is promising to substituting selenium by sulfur atoms to tailor the thermoelectrical properties. This work shows the suitability of the VCA approximation and the band unfolding method, to describe the composition-dependent properties of the PbSe1-xSx pseudo binary alloys.

Preparation of high strength and electrical conductivity copper-chromium pseudobinary alloy by cold-rolling of a billet produced by laser additive manufacturing

A new method to prepare large Cu–Cr alloy with both high strength and high conductivity has been developed. Cu–Cr billets are produced efficiently by laser additive manufacturing, and the microstructure of the alloy is changed by severe plastic deformation caused by large cold rolling ratio. The strength of the alloy can be significantly increased to 677 MPa by eliminating pores, introducing texture and refining grain. The deformation twins caused by plastic deformation processing make up for the plasticity loss caused by grain refinement. With the increase of density and the deformation of Cr particles, the electrical conductivity of the alloy is increased to 28.7 MS/m. Our findings not only deepen the understanding of laser additive manufacturing of highly reflective metals, but also provide a new idea for the preparation of high-strength and high-conductivity Cu alloy workpieces.

A phase-field model of concurrent Suzuki segregation and partial dislocation glide

Co–Al–W-base superalloys with the classic γ−γ′ microstructure offer exciting high temperature property profiles. High temperature deformation in such alloys involves shearing of the γ′ phase by a a/3〈112〉 superpartial to create a superlattice intrinsic stacking fault (SISF) while the trailing a/6〈112〉 partial is pinned at the γ−γ′ interface. Experiments indicate that Suzuki segregation to such faults lowers their energy, which in turn lowers the resistance to partial dislocation glide. However, quantifying the extent of solute segregation and its impact on the dynamics of partial dislocation glide from experiments is challenging. In order to fulfill the purpose computationally, in this paper, we present a phase-field model of the phenomenon of concurrent solute segregation and partial dislocation glide. Our simulations reveal that under creep conditions in a representative pseudobinary alloy belonging to the Co–Al–W system, there is a marked increase in the partial dislocation velocity due to solute segregation. The rise in dislocation velocity due to segregation is found to be more significant for lower resolved shear stresses on the dislocation. Higher solute interdiffusivity also leads to enhanced partial glide velocities. Our model can be extended to multicomponent systems, which can, in turn, be used to accelerate the design of novel Co-base superalloys by predicting the kinetics of the displacive-diffusive shearing of the γ′ phase for prospective alloy systems.

Directly depositing highly densified and uniform Cu-Cr pseudobinary alloy

Cu-Cr pseudobinary alloys have excellent electrical properties and are widely used in many industries. Laser additive manufacturing can effectively avoid the shortcomings of traditional methods for preparing Cu-Cr alloys. However, the high reflection of Cu powder to laser energy brings difficulties to industrial practice. The assembled Cu powder is used as raw material to absorb more laser energy through the outer layer of Cr powder, thereby improving the melting efficiency of the powder and the quality of the molten pool. Laser remelting of unmelted Cr powder can inhibit the uneven nucleation and growth of precipitated Cr, and improve the uniformity of electrical conductivity and element distribution. This study provides a new idea for the preparation of high-performance Cu alloys.

Active site tuning based on pseudo-binary alloys for low-temperature acetylene semihydrogenation

The size of Ni–Ni ensembles can be finely tuned by Cu doping to the Ni sites of Ni3Ga. The (Ni0.8Cu0.2)3Ga/TiO2 catalyst exhibited outstandingly high catalytic activity, selectivity, and stability in acetylene semihydrogenation even at 150 °C.

Ti30Zr10Hf10Ni35Cu15 high-entropy shape memory alloy with tunable transformation temperature and elastocaloric performance by heat treatment

This work investigates the influence of heat treatments on a pseudo-binary Ti30Zr10Hf10Ni35Cu15 high-entropy shape memory alloy. Heat treatments on the alloy resulted in the formation of second phases and thus were able to adjust its transformation temperatures. This phenomenon results from the formation of H-phase and (Zr,Hf)7Cu10 phase during low-temperature and high-temperature aging, respectively. The superelasticity of solution-treated, 500 °C-aged and 700 °C-aged samples was tested under compression, and all samples exhibited nearly 5 % recoverable strain and 15 °C elastocaloric cooling capacity. Further cyclic compression tests confirmed their stability, with up to 75 % of the initial cooling capacity retained after 5000 compression cycles. Due to its high yield strength, the Ti30Zr10Hf10Ni35Cu15 high-entropy shape memory alloy showed great superelasticity and elastocaloric performance at various testing temperatures. Furthermore, with heat treatments, the austenitic transformation finishing temperature (Af) of the alloy was tunable to between −10 °C (furnace-cooled) and 60 °C (700 °C-aged) with promising functional performance. These features expand the application range of TiZrHfNiCu high-entropy shape memory alloys as potential superelastic and elastocaloric materials.

Alternations of hardness and tensile properties of the ultrasound-assisted aging treatments on the Al-Mg-Si alloy

Lightweight metals with appropriate strength are crucial materials among the critical future technologies and sustainable issues. The Al-Mg-Si alloys, which are processed by aging treatments, are considered promising candidates. Hence, the pseudo-binary Al-Mg2Si alloy with an excess Si addition was chosen in this study. In addition, to further manipulate the alloys, besides to the often-controlled two factors of aging temperature and aging time, ultrasound was introduced into the aging system as an additional third factor to further control the aging behaviors. One-step and two-step aging treatments were both conducted to verify the effect of the introduction of ultrasound. It was found that certain alternations of mechanical properties, such as micro Vickers hardness, which is a surface property, were obviously imposed. On the other hand, the tensile strength and fracture strain, which are bulk mechanical properties, showed limited changes between the ultrasound-applied and ultrasound-free specimens. Many possibilities have been proposed and discussed for the observed phenomenon. The cavitation would be the greatest factor in the alternation of the micro Vickers hardness. Microstructures observed by bright-field images were in good accordance with that of the observed mechanical properties.

AlYN Thin Films with High Y Content: Microstructure and Performance

Pseudobinary nitride alloys display enhanced piezoelectric properties compared to their nonalloyed counterparts enabling their wide application in high‐performance transducers and acoustic wave resonators. Their fabrication remains challenging because of their inherently stochastic nature, which requires in‐depth understanding of the film growth dynamics and the interplay of deposition parameters. Herein, thin Al1−xYxN films are produced with varied yttrium content in the range from x = 0.09 to 0.28 on a gradient seed layer on 200‐mm Si substrates and investigated via various X‐ray diffraction methods, high‐resolution scanning transmission electron microscopy, nanoindentation, and atomic force microscopy. Bulk acoustic wave resonators, solidly mounted on a multilayer acoustic isolation, are fabricated to analyze the piezoelectric performance of the films and to extract corresponding material parameters via fitting of the high‐frequency electrical response by 1D Mason's model. The trend of declining coupling is explained by the lattice softening and the increase in electron density, experimentally observed by monitoring reduced elastic modulus and dielectric constant values, respectively. The absence of expected enhancement of the piezoelectric modulus is interpreted by the presence of oxygen impurities, facilitating the inhomogeneous strain of the AlYN lattice, which effectively cancels the energy flattening phenomenon, found in III–V pseudobinary alloys.

Beyond phase-change materials: Pseudo-binary (GeTe)n(Sb2Te3)m alloys as promising thermoelectric materials

Exploring new materials with complex structures and excellent transport properties has always been a fascinating topic in thermoelectrics. Recently, (GeTe)n(Sb2Te3)m-based compounds (GSTs), a well-known family of phase-change materials, are found to be promising thermoelectric candidates. Rooted in but different from the parent GeTe and Sb2Te3 binary compounds, these pseudo-binary alloys exhibit special structures and good transport properties. Here in this review, we demonstrate some fundamental knowledge and recent progress on these GST materials for thermoelectric applications. The operation principle of phase-change memory, crystal structure, as well as the special metavalent bonding mechanism are introduced at first. Then the electrical and thermal transport properties are illustrated, which are associated with material structures and bonding features. Several strategies are discussed to enhance the thermoelectric performance of hexagonal GSTs. Then, this review extends to discuss a larger family of (AC)n(B2C3)m thermoelectric materials (A = Si, Ge, Sn, Pb; B = As, Sb, Bi; C = S, Se, Te), which share similar crystal structures and transport properties with hexagonal GSTs. Finally, some possible research directions are proposed for the future study on thermoelectric GSTs.

INVESTIGATION OF STRUCTURAL CHARACTERISTICS ON FERRITIC NODULAR CAST IRON

The linear form of graphite in gray cast iron is not favorable due to the weakening of the metal base and strong sources of stress concentration at the ends of the lamellae. Converting the lamellar form of graphite into nodular form is done by adding modifiers and pre-secreting smaller amounts of magnesium or cerium. In this way, the stress concentration due to graphite inclusions in nodular cast iron is significantly lower than in gray cast iron. “Nodular cast iron is a foundry pseudobinary alloy of iron and carbon, which was mostly excreted in the form of spherical graphite”. Depending on the structure of the metal base, the properties of strength and plasticity also depend, but certainly the shape, size and arrangement of graphite nodules has a significant influence. For these reasons, the size of graphite nodules is also determined, the highest values of the average nodule being from 50 to 10 μm. In this paper, a researched nodular cast iron with a ferrite structural base is given. The mentioned nodular casting was isothermally improved and tribologically tested, on a “pin and disc” tribometer. The obtained results are presented tabularly and diagrammatically.

Semisolid-Liquid Fabrication of Cu–Cr Pseudobinary Alloy by Laser-Directed Energy Deposition

Copper–Chromium (Cu–Cr) pseudobinary alloys are promising materials for electrical application. Nevertheless, their fabrication remains limited by traditional techniques, which are not suitable for manufacturing homogeneous Cu–Cr alloys with uniformly distributed elements. Recently, semisolid-liquid manufacturing method has emerged as a promising technique route to fabricate Cu–Cr alloys. In this work, the laser-directed energy deposition (L-DED) as one of the laser additive manufacturing (LAM) technology, was successfully introduced for semisolid-liquid fabricating the homogeneous Cu–30 mass%Cr alloys. The obtained Cu–Cr alloys are constituted by fully melted Cu metallurgically combined with semisolid-liquid Cr. The close combination of Cu and Cr is benefit to improve the electrical conductivity of the alloy.

Remarkable relation between melting entropy and kinetic viscosity in metallic glasses

There has been so far no consensus regarding the roles of melting entropy on glass formation. For this purpose, a study has been conducted on three compositions of the pseudo-binary alloys, Zr2Ni-Ti2Ni, viz., the eutectic compositions (Zr2Ni)0.206(Ti2Ni)0.794, (Zr2Ni)0.654(Ti2Ni)0.346, and the Laves compound (Zr2Ni)0.44(Ti2Ni)0.56. The study results of melting entropies, melting viscosities, and glass formabilities of the alloys unequivocally shows the fact that low melting entropy and high melting viscosity facilitate glass formation. From the data of different classes of systems, a unique relationship between melting entropy and melting viscosity has arisen in glass forming systems, which highlights the positive roles of low melting entropy on glass formation from a special perspective. This study of thermodynamics, kinetics, and glass formation highly suggests the melting entropy should be taken as a crucial reference for designing metallic glasses.

Study on the solutal convection during dendrite growth of superalloy under directional solidification condition

The solutal convection is able to affect the dendrite growth and solute distribution during directional solidification. The solutal convection is raised by the solute difference-caused buoyancy. When solutal convection becomes intensive, solute plumes will occur, which may cause freckle defects in directional solidification of superalloys. The onset of solutal plumes depends on the solidification condition. In this study, the dendrite growth with solutal convection during directional solidification of nickel-based superalloy was investigated by two-dimensional phase-field simulations. The lattice Boltzmann method was used to solve the flow field driven by solute difference caused-buoyancy force. The pseudo-binary alloy approximation was adopted for simplification of the multicomponent alloy. The effects of the temperature gradient, pulling velocity, and isotherm inclination angle on dendrite growth and solutal convection were investigated. The dendrite growth dynamics and solutal convection pattern under different solidification conditions were analyzed. Dendrite growth velocity oscillation was observed. The effect of pulling velocity on dendrite growth velocity oscillation was analyzed.

Optimized carrier concentration and enhanced thermoelectric properties in GeSb4-xBixTe7 materials

As the pseudo-binary alloys between GeTe and Sb2Te3, GeSbTe-based compounds are promising thermoelectric materials. Although Ge2Sb2Te5 and GeSb2Te4 have widely been studied, the thermoelectric properties of GeSb4Te7 have not been well understood yet. In this work, we design a series of GeSb4-xBixTe7 solid solutions and systematically study the variation in the crystal structure, electrical, and thermal transport properties. Alloying Bi effectively reduces the carrier concentration and, thus, enhances the Seebeck coefficient. Meanwhile, the thermal conductivity is greatly reduced via large mass fluctuations. A maximum zT of 0.69 at 550 K and an average zT value of 0.52 between 300 and 700 K have been achieved for GeSb1.5Bi2.5Te7. These findings will promote the understanding and development of GeSbTe-based thermoelectric materials.

Exploring the stable structures and photovoltaic properties of an ideal pseudo-binary alloy: Indium gallium phosphide

Pseudo-binary III-V semiconductor alloys are promising for applications in optical, photovoltaic and photoelectrochemical fields, for their tunable band gaps and band alignments. In this work, we carefully investigate structural and photovoltaic properties of indium gallium phosphide (InxGa1-xP; 0 < x < 1) alloys. Using evolutionary algorithm crystal structure prediction, we perform structure searches for indentifying potential crystal structures of InxGa1-xP alloys in nine chemical compositions at zero temperature and ambient pressure. We find that InxGa1-xP alloys can adopt zinc blende (ZB) and wurtzite (WT) structures and the former generally have lower energy than the latter at all compositions. Based on these predicted InxGa1-xP structures, we evaluated their spectroscopic limited maximum efficiencies (SLMEs) and find that InxGa1-xP alloys with high In concentrations (x ≥ 0.5) have higher SLME values than those of InxGa1-xP alloys with low In concentrations (x < 0.5). We also find that SLMEs of disordered InxGa1-xP alloys are larger than those of ordered alloys due to the enhanced oscillator strengths.

Inter-element miscibility driven stabilization of ordered pseudo-binary alloy

An infinite number of crystal structures in a multicomponent alloy with a specific atomic ratio can be devised, although only thermodynamically-stable phases can be formed. Here, we experimentally show the first example of a layer-structured pseudo-binary alloy, theoretically called Z3-FePd3. This Z3 structure is achieved by adding a small amount of In, which is immiscible with Fe but miscible with Pd and consists of an alternate L10 (CuAu-type)-PdFePd trilayer and Pd–In ordered alloy monolayer along the c axis. First-principles calculations strongly support that the specific inter-element miscibility of In atoms stabilizes the thermodynamically-unstable Z3-FePd3 phase without significantly changing the original density of states of the Z3-FePd3 phase. Our results demonstrate that the specific inter-element miscibility can switch stable structures and manipulate the material nature with a slight composition change.

Ternary platinum–cobalt–indium nanoalloy on ceria as a highly efficient catalyst for the oxidative dehydrogenation of propane using CO2

The oxidative dehydrogenation of propane using CO2 (CO2-ODP) is a promising technique for high-yield propylene production and CO2 utilization. Unfortunately the efficiency of existing catalysts is limited, and therefore, developing a highly efficient catalyst for CO2-ODP is of great importance for the chemical industry. Here we report a Pt–Co–In ternary nanoalloy on CeO2 that has a (Pt1−xCox)2In3 pseudo-binary alloy structure and exhibits very high catalytic activity, C3H6 selectivity, stability and CO2 utilization efficiency at 550 °C. Alloying platinum with indium and cobalt significantly improves the C3H6 selectivity and CO2 reduction ability, respectively. The cobalt species provide a high density of states near the Fermi level, which lowers the energy barrier of CO2 reduction. The stability of the catalyst is greatly enhanced by combining the strong CO2 activation ability of the alloy with the oxygen releasing ability of the CeO2 support, which facilitates Mars–van Krevelen-type coke combustion. The CO2-mediated oxidative dehydrogenation of propane is an attractive reaction for propylene production, although the selection of competent catalysts available for this process is scant. Now, the authors report a ceria-supported Pt–Co–In ternary alloy that achieves this transformation with high efficiency.