Elements In Solid Solution Research Articles

Effects of solute alloying elements on solid solubility of TiC in austenite

Solute elements in microalloying steel affect the solid solubility of microalloying elements, and thus affect the second phase precipitation in steels. In this work, the influences of solid solution elements, especially Si and Al, on the solubility product of TiC in austenite were studied using the two-sublattice model. The results show that both Al and Si additions reduced the solubility product of TiC in the austenite region, and the reduction degree of TiC solubility product with Al addition was increased with increasing temperature, while it was decreased with Si addition. In addition, Mn, Mo and Cr additions all increased the solubility product of TiC in the austenite region, and the increment degree of TiC solubility product with Mo addition was decreased with increasing temperature, while it changed slightly with Mn or Cr addition with temperature. The model of solubility product of TiC without alloying additions in austenite was modified, and the calculating result was highly consistent with findings of literatures. Finally, a calculation model of TiC solubility product considering the influence of alloying elements was established.

Mn-controlled martensitic variant selection significantly affects the strength and toughness of 2.3 GPa ultra-high strength spring steel

In this study, the microstructure and mechanical properties of 55SiCrVNb ultra-high strength spring steel with 0.7 and 1.5 wt.% Mn were systematically investigated. The results show that 0.7Mn steel exhibited higher strength and toughness. The morphology and content of retained austenite, content of element in solid solution and the type and quantity of precipitates were basically the same in 0.7Mn and 1.5Mn steels. Hence, the variant reconstruction, as a unique perspective, was used to unravel the strengthening and toughening mechanisms governing the evolution of variants across varying Mn contents. Compared with the 1.5Mn steel, the decrease in Mn content deteriorated the variant selectivity (decreased variant frequency over 50 %), which led to a more uniform distribution of close-packed plane (CP) and Bain groups in 0.7Mn steel, thus refining the block size and improving the grain refinement strengthening (σp). The 0.7Mn steel with a higher density of high angle grain boundaries (HAGBs) effectively constrained dislocation slip, thereby enhancing dislocation strengthening (σd). As the Mn content decreased, the block size decreased from 0.24 to 0.14 μm, and the contribution of σp and σd increased by about 107 and 96 MPa, thus improving the yield strength. In addition, the increased HAGBs, which were dominated by the highly selective V1/V2, V1/V3(V5) and V1/V6 variant pairs, and the uniform CP and Bain group also contributed to inhibiting crack deflection and enhancing the impact toughness. Moreover, the higher Schmid factor with high geometrically necessary dislocation of 0.7Mn steel improved the deformation resistance of variants and strength. This work provided a new mechanism of strengthening and toughening dominated by variants.

Electrical conductivity of binary magnesium alloys: Integrating first-principles and machine learning studies

The electrical conductivity is the fundamental physical property of Mg alloys and the basic information for the design of comprehensive high-performance Mg alloys. In this work, the electrical conductivity of 29 Mg-based binary alloys has been calculated using the first-principles methods and the main factors have been analyzed by machine learning. It is found that the electrical conductivity values of the binary alloys containing elements located in the s region and p region of the periodic table are bigger than others of alloys contain alloying elements in the f region and d region. The results of machine learning show that the difference ratio of volume (∆V/VMg), extra-nuclear electron configuration and difference of valence () play the main controlling role, followed by solid solubility and electronegativity of the alloying element. For solid solution elements in Mg-based binary alloys, the impact weight on the electrical conductivity is: difference ratio of volume > number of extra-nuclear electron vacancy > difference of valence.

The effects of refractory elements on mechanical properties in CoCrNiFe concentrated solid solution alloys across different temperatures

Mo, W and Re are all important strengthening elements in either single phase solid solution (SS) alloys or the SS phases in precipitation-strengthened Ni/Co-based superalloys, of which the compositions are usually complicated. To directly compare the effects of Mo, W and Re on the mechanical properties of concentrated SS alloys, a model CoCrNiFe concentrated SS alloy as the base and three alloys with 3 at.% Mo, W and Re additions are fabricated and their mechanical properties are examined in both quasi-static tensile and creep tests at room and two high temperatures. Experimental and modeling results demonstrate that at room and low temperatures, the order of strengthening effect is W > Mo > Re, in accordance with solid solution strengthening model and thermal activation analysis. On the other hand, Re can significantly decrease the minimum creep rate at 1273 K, primarily due to the reduced diffusivity as confirmed from the diffusion couple analysis.

Quantitative analysis of microstructural evolution in cold-sprayed CuCrZr: Understanding heat transfer mechanisms from room temperature to 600°C

Cold-sprayed CuCrZr coating offers interesting multifunctional properties with a combination of high mechanical property, good thermal stability and substantial deposition thickness. Despite these advantages, the incorporation of solid solution elements and the deposit’s unique microstructure often result in suboptimal heat transfer capabilities. This study delved into the thermal conductivity of cold-sprayed CuCrZr coatings over a temperature range from room temperature to 600 °C. Furthermore, it quantitatively analyzed their microstructural evolution post-thermal testing and its correlation with thermal properties, employing techniques such as FESEM, EBSD, TEM, and XRD. Findings indicate the CuCrZr coating exhibits significant thermal sensitivity, with conductivity increasing from 65.83±1.79 W/(m∙K) at 25 °C to 198.42±0.63 W/(m∙K) at 600 °C. The annealing effect during thermal testing significantly enhances the coatings’ room temperature thermal properties, chiefly through the enhancement of interparticle metallurgical bonding, grain enlargement, solid solution precipitation, and a reduction in dislocation density. The thermal conduction across the coating/substrate interface is intricately influenced by the interplay between electrons and phonons, with impediments at the interface becoming markedly pronounced beyond 300 °C. The investigation pinpointed interparticle interfaces as the predominant barriers to heat transfer, contributing to 73.77 % of the total resistance. Meanwhile, the effects of solid solution elements, grain boundaries, and dislocations on thermal conductivity were comparatively minor, contributing 9.36 %, 1.04 %, and 0.44 %, respectively. However, it is also noted that the annealing effect can induce the coalescence of microcracks into pores and promote the precipitation or oxidation of Cr at the interfaces, which, in turn, limits the potential for further enhancements in thermal conductivity.

Mechanical property and strengthening mechanism of ZrC nanoparticle dispersion-strengthened Mo containing FeCrAl alloys

Poor mechanical strength at high temperature is the key problem to limit the application of FeCrAl alloys as the candidates for the accident tolerant fuel (ATF) cladding in LWRs. Fe-13Cr-5Al (wt %) alloys were strengthened by adding solid solution element Mo and nanosized ZrC particles, and the strengthening mechanism was assessed by microstructure characterizations including TEM and EBSD. Fe-13Cr-5Al-2Mo-1ZrC alloy has the highest ultimate tensile strength (UTS) and an acceptable ductility at each tested temperature (Room temperature, 400 °C or 800 °C). Especially at 800 °C, the UTS of Fe-13Cr-5Al-2Mo-1ZrC alloy is about 124 MPa, which is 125 % and 34.7 % higher than that of raw Fe-13Cr-5Al (55 MPa) and Fe-13Cr-5Al-1ZrC alloys (89 MPa), respectively. Fe-13Cr-5Al-2Mo-1ZrC alloy has the highest hardness of 306.3 HV, which is 12.8 % higher than that of Fe-13Cr-5Al and 3.7 % higher than that of Fe-13Cr-5Al-1ZrC alloys, respectively. Furthermore, Fe-13Cr-5Al-2Mo-1ZrC samples maintain high strength and favorable ductility after annealing at 1000 °C for 20 h indicating their superior thermal stabilities. The excellent mechanical properties and superior thermal stabilities of Fe-13Cr-5Al-2Mo-1ZrC alloy were not only attributed to the dispersion strengthen by nanosized ZrC particles, the solid solution strengthening by Mo elements, but also the grain refinement structure promoted by the synergistic effects of Mo and ZrC additions.

Structural modeling of high-entropy oxides battery anodes using x-ray absorption spectroscopy

High-entropy oxides (HEOs) are single phase solid solutions where five or more metals share the same sublattice, giving rise to unexpected features in various fields of applications. Recently, HEOs have emerged as an alternative conversion electrode anode material for next-generation Li-ion batteries, where the combination of several different elements in a single solid solution can synergistically act to overcome some of its main drawbacks, improving performance. Due to their chemical complexity, x-ray absorption spectroscopy (XAS) emerges as an appropriate technique to study the electronic (x-ray absorption near edge structure, XANES) and local structure (extended x-ray absorption fine structure, EXAFS) of these compounds as a function of cycling. This work aims to highlight the capabilities of XAS as an element-specific probe to understand a material’s structure at the atomistic level through EXAFS modeling of (MgFeCoNiCuZn)O high-entropy system and how to extract valuable information about the bond distance, number of near neighbors, and local disorder, which are crucial to a full understanding of the electrochemical reaction mechanisms of such battery electrodes.

Modeling solute drag during austenite–ferrite transformation with ab initio binding energies

The solute drag effect can have a considerable impact on the austenite to ferrite transformation. Most models describing the solute drag effect require knowledge of solute binding energies, which due to lack of accurate data typically are treated as fit parameters. In this study we use density functional theory (DFT) calculations to estimate the effective binding energies of the substitutional alloying elements in an ultra low carbon steel. For the first time these energies are used to calculate the solute drag effect considering site competition for the austenite to ferrite phase transformation. The depletion of elements in solid solution as a result from precipitation is computed and the solute drag contribution of each element is calculated. Comparison of the binding energies with the resulting solute drag effect to literature data shows reasonable agreement. The outlined approach points the way to future alloy development based on interface-controlled integrated computational materials engineering. Another field of application is given by the circular economy driven transition in the steel industry from the BF/BOF- to the EAF-based production route with increased utilization of scrap material introducing new tramp elements.

High-performance Ni-based superalloy 718 fabricated via arc plasma directed energy deposition: effect of post-deposition heat treatments on microstructure and mechanical properties

Ni-based superalloy 718 fabricated via arc plasma direct energy deposition (IN718 AP-DED) exhibit a limited response to heat treatment due to its coarse primary microstructure and interdendritic segregation, which may prevent its use in high-integrity applications. Thus, dedicated heat treatments for IN718 AP-DED must possess a homogenization temperature as high as possible to significantly dissolve the eutectics and increase the γ′′-former elements in solid-solution. The present work proposed heat treatments for IN718 AP-DED (homogenization – 1050, 1100, 1142, and 1185 °C / 2 h – followed by aging – 718 °C / 8 h, cooling at 56 °C / h, and 621 °C / 8 h). The as-built IN718 AP-DED showed the typical coarse and oriented (cube texture) microstructure with eutectics (Laves and MC-typical carbides) in the interdendritic region, which were significantly dissolved during the homogenization, promoting a high-volume fraction of hardening phase (γ′′ and γ′) and outstanding quasi-static mechanical properties after the aging step. The present work showed that IN718 AP-DED mechanical properties can be optimized through dedicated heat treatments, meeting the ductility and yield strength requirements (room temperature) of AMS 5662. Furthermore, the heat treatments did not alter the grain morphology and texture aspect, inducing a lower Young’s modulus compared to the non-oriented material.

Development of potassium doped tungsten plate for fusion reactor applications

Since fusion reactors including DEMO and beyond are expected to be operated for a longer period of time than ITER, plasma-facing materials (PFM) will suffer by longer term heat load and non-negligible neutron irradiation damage. Therefore, for tungsten (W) materials as PFM, improvement of low temperature brittleness and suppression of recrystallization embrittlement and neutron irradiation embrittlement are required. To address these issues, various modified W materials have been developed by applying alloying with solid solution elements and second-phase dispersion techniques such as solid particles and bubbles. As a result, potassium-doped W (K-doped W), in which K bubbles are dispersed, was found to be effective for all of the above issues. However, the materials used in these evaluations were relatively small and not large enough to fabricate, for example, ITER divertor monoblocks (12 mm thick). In the present study, K-doped W plate with a sufficient thickness (more than 12 mm) for application to fusion reactor components like divertor monoblocks were developed and the fundamental properties were evaluated.

Creation of Multi-Principal Element Alloy NiCoCr Nanostructures via Nanosecond Laser-Induced Dewetting.

The multi-principal element alloynanoparticles (MPEA NPs), a new class of nanomaterials, present a highly rewarding opportunity to explore new or vastly different functional properties than the traditional mono/bi/multimetallic nanostructures due to their unique characteristics of atomic-level homogeneous mixing of constituent elements in the nanoconfinements. Here, the successful creation of NiCoCr nanoparticles, a well-known MPEA system is reported, using ultrafast nanosecond laser-induced dewetting of alloy thin films. Nanoparticle formation occurs by spontaneously breaking the energetically unstable thin films in a melt state under laser-induced hydrodynamic instability and subsequently accumulating in a droplet shape via surface energy minimization. While NiCoCr alloy shows a stark contrast in physical properties compared to individual metallic constituents, i.e., Ni, Co, and Cr, yet the transient nature of the laser-driven process facilitates a homogeneous distribution of the constituents (Ni, Co, and Cr) in the nanoparticles. Using high-resolution chemical analysis and scanning nanodiffraction, the environmental stability and grain arrangement in the nanoparticles are further investigated. Thermal transport simulations reveal that the ultrashort (≈100ns) melt-state lifetime of NiCoCr during the dewetting event helps retain the constituent elements in a single-phase solid solution with homogenous distribution and opens the pathway to create the unique MPEA nanoparticles with laser-induced dewetting process.

A facile synthesis of 2D bimetallic solid solution nitrides for robust stability in lithium-ion battery

Nanostructured transition metal nitrides (TMNs) demonstrate immense promise for lithium-ion battery applications owing to their outstanding conductivity and high theoretical capacity. However, challenges such as the expansion of volume, aggregation concerns, and rapid capacity decay still need to be effectively addressed. Herein, a facile synthesis of 2D nitrides, including TiVN, NbVN and TiNbN, is achieved through nitriding their corresponding MXenes. The distinct 2D layered structure enables them fast lithium-ion transport and inhibits volume variation, thereby improving rate performance and stability. Moreover, the incorporation of bimetallic elements in solid solution induces lattice distortion, creating lattice vacancies and increasing lithium storage capacity. Atomic-level interactions within solid solutions, confirming by the shifts of binding energy, contribute to improved structural stability and accelerated charge transfer. The theoretical calculation further proves that the bimetallic solid solution structure elevates the d-band center and increases the Li+ adsorption energy. Consequently, the synthesized TiVN, NbVN and TiNbN demonstrate remarkable lithium storage performance. Especially, NbVN with a porous morphology stands out by achieving a specific capacity of 216.6 mAh/g after 1,400 cycles at 1 A/g, significantly outperforming Nb4N5 and VN. This work may provide valuable insights for the efficient synthesis and electrochemical applications of two-dimensional solid-solution nitrides.

Microstructure and Wear Resistance of Grx-Ti-BN Composite Coating on TC4 by Argon Arc Cladding

The TC4 (Ti-6Al-4V) alloy has problems such as low material hardness, poor wear resistance, and abnormal sensitivity to adhesive wear and fretting wear. In this study, we used graphene-reinforced Ti/BN composite coatings prepared on the surface of the TC4 alloy by argon arc cladding technology. We explored the optimal content of graphene to improve its hardness and wear resistance. The physical phases and microstructures of the coatings were analyzed using an X-ray diffractometer, metallurgical microscope, and scanning electron microscope. Microhardness and wear properties of the cladding coating were measured by a Vickers hardness tester and a universal friction and wear tester. The incorporation of graphene resulted in a transformation of the reinforcing phase in the coating from TiN to Ti(N, C). The C element in the molten pool was substituted with the N element in an unending solid solution, resulting in the formation of Ti(N, C) through intermittent nucleation. As the amount of graphene in the molten pool increases, the concentration of carbon (C) also increases. This leads to the continuous growth of Ti(N, C) particles, resulting in a coarser coating structure and a decrease in coating performance. When the graphene content is 5 wt.%, the microstructure refinement of the coating is the most obvious, the microhardness is 900 HV0.2, which is 3 times higher than that of the matrix, and the wear rate is 4.9 × 10−5 mm3/(N·m), which is 4.9 times higher than that of the matrix. The wear mechanism of the coating is primarily abrasive wear with some slight adhesive wear.

Effect of solid solution elements on cracking susceptibility of Ni-based superalloys during additive manufacturing

Alloy composition design usually contributes to eliminating cracking in Ni-based superalloys during additive manufacturing (AM). However, a detailed understanding of each solid solution element in the cracking susceptibility of Ni-based superalloys during AM is still missing. Thirteen newly designed alloys are considered to investigate the combined effect of solid solution elements on cracking susceptibility. The behaviors of solidification cracking, liquation cracking, and solid-state cracking were analyzed by the microstructural characterization and thermodynamic calculations. The results showed that W and Mo cause the formation of high melting-point carbides at grain boundaries (GBs), which increase solidification cracking susceptibility. Moreover, W and Mo lead to a slightly higher solidification cracking index (SCI) compared to Co, Cr, and Re. In the successive solidification and remelting process, the borides enriched in W, Mo, and B around GBs will cause grain boundary segregation and liquation cracking. W and Re extend the freezing range (FR) and exacerbate the segregation of Al and Ti in the inter-dendritic regions, contributing to the formation of eutectics. Similarly, complete or partial melting of the eutectic can induce liquation cracking during the thermal cycling in AM. The solid-state cracking susceptibility can be reduced by solid solution elements, especially Re and Co. In summary, compared to Co, Cr, and Re, W and Mo exacerbate the cracking susceptibility.

Self‐lubricating effect of solid solution elements on tribological performance of Ti3AlC2 over a wide temperature range

AbstractThis study explores the feasibility of tribological self‐lubricating over a wide temperature range by doping Si and Sn solid solution components on the A‐sites of Ti3AlC2 to adapt to the severe circumstances. The specimens were sintered at 1450°C for 120 min under a pressure of 30 MPa in a vacuum environment, and their dry sliding tribological capabilities against Al2O3 at temperatures ranging from ambient temperature to 800°C were investigated using a rotational ball‐on‐disk tribo‐tester. The findings demonstrated a constantly decreased friction coefficient of Ti3Al0.8Si0.2Sn0.2C2 throughout the temperature range and admirable antifriction at higher temperatures where wear rates were 1–2 orders of magnitude lower than those at room temperature, which was superior to earlier reported Ti3AlC2. The predominant friction surface self‐adaptability mechanisms after solid solution treatment were determined to be tribo‐oxidation wear and tribo‐chemical reactions that played a vital role by examining the microstructural evolutions and tribo‐chemical phase composition on friction surfaces at various temperatures. The tribo‐oxidation‐induced generated lubricant film consisting of TiO2, Al2O3, SnO2 mixture oxide phases, and aluminosilicates was responsible for the decreased friction coefficient and wear rate.

Adsorption and diffusion behavior of oxygen atoms on Ti3SiC2 (0001) surface

Ti3SiC2 is the most typical 312 MAX phase, which has attracted more attentions in many fields. In this paper, the (0001) plane of Ti3SiC2 was built. The adsorption energy and diffusion path of oxygen atom at different sites were calculated by first principles. There are three different adsorption sites for oxygen atom on Ti3SiC2 (0001) surface. By calculating the adsorption energy of the three adsorption sites, it was found that the adsorption energy of the oxygen atom at the center site is the lowest. The diffusion path of the oxygen atom was simulated and showed that oxygen atom located at the center of Ti-Si tetrahedron after the diffusion into the bulk phase. The effects of solid solution elements on the diffusion activation energy of oxygen atoms were calculated. suggesting that the solid solution of V, Mo and W will greatly increase the energy barrier, thus preventing the inward diffusion of oxygen atoms.

Cryo-compression and annealing hardening of 7075 aluminum alloy

7075 aluminum alloy, as a lightweight, high-strength, and corrosion-resistant structural material, is widely used in the aviation industry. Because 7075 aluminum alloy is commonly used in structural components, its plastic processing ability is highly required by the usage environment. Recent studies have shown that 7075 aluminum alloy exhibits better deformation ability under low temperature conditions. In this paper Cryo-compression experiments on 7075 aluminum alloy under different compression rates (0.001 s-1-0.5 s-1) in a low-temperature environment (soaked in liquid nitrogen for 30 minutes) has been discussed. Annealing process research was conducted on the low-temperature compressed samples, and the optimal annealing process parameters (400Co, insulation for 15 minutes) and optimal deformation amount (16%) were obtained through comparison of microstructure and properties. And it was found that 7075 aluminum alloy exhibited annealing hardening phenomenon when annealed at 250 Co, and the reason was the diffusion segregation of solid solution elements formed during low-temperature forming, which led to the precipitation of the second phase MgZn2 during low-temperature annealing.

Effect of compositional heterogeneity on the mechanical properties of a single-phase Cu-9Al alloy with different grain sizes

Recent investigations have indicated that compositional heterogeneity, which is compositional undulation of alloying elements in single-phase solid solutions, can enhance the strength without sacrificing ductility, similar to cluster strengthening, of single-crystal nano-pillars and bulk nanocrystalline metallic materials. However, the impact of compositional heterogeneity on the mechanical properties of coarse-grained metallic materials is not yet fully understood. In this study, we examine the influence of compositional heterogeneity on the tensile mechanical properties of a Cu-9Al (at.%) alloy with a coarse-grained structure fabricated using wire arc additive manufacturing and with an ultrafine-grained structure after further processing. Our results demonstrate that the effects of compositional heterogeneity depend significantly on the grain size. Specifically, in ultrafine-grained samples, there is a remarkable improvement in strength with only a slight reduction in ductility. However, as grain size increases, the strengthening effect of compositional heterogeneity diminishes, resulting in softening with a significant loss of ductility. These phenomena can be attributed to the behaviour of dislocations in the materials. Overall, this study highlights the importance of understanding the relationship between compositional heterogeneity, grain size, and mechanical properties in metallic materials, which can inform the design of new materials with improved strength and ductility.

Microstructures and mechanical properties of novel MoTaVW refractory high-entropy alloys

Refractory high-entropy alloys (RHEAs) containing multiple principal alloying elements have created a growing interest in exploring superalloys applications due to their high melting points and excellent softening resistance. The room-temperature brittleness and oxygen sensitivity greatly restrict their further processing and application. Here, utilizing the unique high strength of Vanadium (V) among alloy elements and cocktail effect of HEAs, we designed a MoTaVW RHEAs with equal atomic ratio, that exhibit multiphase phases (Ta-rich, Mo-rich and V-rich phase) with different composition at different sintering temperatures and the alloy elements in BCC solid solution tend to be uniformly distributed as the increased sintering temperature. Exploring the room-temperature compressive properties and underlying deformation mechanisms, the MoTaVW RHEAs exhibit the yield strength (σy) of 1420 MPa and the plastic strain (εp) of 18 %, that achieved good combination of strength and plasticity compared with other most known BCC RHEAs, which are attributed to high solid solution strengthening caused by lattice distortion and the cross slip of screw dislocations on the close-packed plane that can enhance the synergistic effect of strength and plasticity. These results reveal the MoTaVW RHEAs is a very promising materials for compositional space in RHEAs.

Density functional study of atomic arrangements in CrMnFeCoNi high-entropy alloy and their impact on vacancy formation energy and segregation

Using the density functional theory-coupled Monte Carlo approach, we explored the chemical short-range order (SRO) and element segregation in equimolar CrMnFeCoNi alloy. We found that state-of-the-art approximation of random element distribution is only applicable at > 1100 K close to the melting temperature, while the Cr-Cr repulsion driving the system stabilization and accompanying the formation of cubic Cr sublattice, and mild Ni-Ni attraction are the most prominent pair interactions at lower temperatures. Chemical potential and vacancy formation energy calculations indicate that Cr is most sensitive to the local chemical environment, making Cr atoms most stabilized when the preferred SRO is introduced. While the vacancy formation is predicted equally probable among five constituting elements in the random solid solution, Cr and Ni atoms show the lowest vacancy formation energies in the structure with SRO. Furthermore, distinct element segregation was predicted in the vicinity of planar defects, including symmetric tilt grain boundary and stacking fault, which we correlated to the site- and chemistry-dependent atomic volume and bond lengths. It suggests that the local mechanical strain and bond energy induce the SRO development and element segregation: Namely, the system takes advantage of segregation of Ni atoms having large atomic volume or Cr-Cr pairs having elongated bond lengths to fill in the excess volume at defects that relaxes the mechanical strain field and optimizes bond energy distribution. The correlation between the SRO and properties of CrMnFeCoNi alloy needs further investigations, which is expected to greatly help understand and control the properties of high-entropy alloys.