Ductile Phase Research Articles

Peculiarities of deformation and destruction of porous titanium nickelide alloys at stretching, compression and bending

The analysis of experimental data obtained during quasi-static tension, compression and bending of anisotropic and structurally inhomogeneous porous titanium nickelide alloys obtained by the method of self-propagating high-temperature synthesis (SHS) is carried out. It is shown that the studied porous titanium nickelide alloy near room temperature is in a pre-martensitic state and experiences a reversible martensitic transformation (MT) under the action of an external load. The influence of geometric anisotropy on the deformation behavior under tension and bending is shown. By means of quasi-static tension and three-point bending to failure of lamellar samples of porous titanium nickelide with a porosity of 60–70%, it was shown for the first time that all obtained strain curves are qualitatively self-similar and contain a basic block of two linear hardening sections and a yield section between them. It is shown for the first time that a decrease in the effective cross section and a decrease in the degree of geometric anisotropy of the deformation zone lead to the appearance of an additional yield region on the deformation curves of quasi-static tension. This indicates a significant dependence of the contribution of reversible martensitic deformation to the total deformation on the geometric anisotropy of porous titanium nickelide. An analysis of fracture surfaces showed the effect of the type and rate of loading on the ratio of brittle martensitic and ductile austenite phases in a multiphase matrix of a porous titanium nickelide alloy. The research was carried out with financial support of the Russian Science Foundation under the Grant No. 22-72-10037, https://rscf.ru/project/22-72-10037/.

Compressive vs. tensile yield and fracture toughness behavior of a body-centered cubic refractory high-entropy superalloy Al0.5Nb1.25Ta1.25TiZr at temperatures from ambient to 1200°C

The microstructure of high-entropy alloys with refractory elements and Al as constituents can be considered to be analogous to superalloys. These so-termed refractory high-entropy superalloys (RHSAs) can show remarkable compressive strength up to temperatures exceeding 1200 °C. Here, we examine the microstructure and properties - compressive, tensile, and fracture toughness - of a precipitation-hardened, body-centered cubic, RHSA, Al0.5Nb1.25Ta1.25TiZr, at ambient temperature (RT) to 1200 °C. Two dual-phase microstructures comprising ordered B2 (brittle) and disordered A2 (ductile) phases were produced in this alloy - one with B2 as the matrix, the other with A2 - for evaluation of the mechanical properties. Under compression, both microstructures display RT compressive strengths above 1.5 GPa and considerable ductility exceeding 40% at elevated temperatures; the alloy with the A2 matrix has ∼15% compressive ductility even at RT. However, properties are very different under tensile loading; at all temperatures, both microstructures fail predominately in an intergranular mode in the elastic regime at a fracture stress less than 200 MPa and ductility below 0.15%. The microstructure with the A2 matrix has a KIc fracture toughness of ∼15 MPa√m at RT, although at all temperatures above 800 °C, measured KIc values for both dual-phase microstructures are less than 5 MPa√m. In this study, we investigate the microstructural origin of these mechanical properties, and emphasize the importance of evaluating these alloys in tension.

Multiscale modeling of the mechanical behavior of brazed Ni-based superalloy sheet metals

The elastic–plastic behavior of brazed Ni-based superalloys used in abradable turbomachinery sealing systems is analyzed by means of numerical simulations. A sequential multiscale modeling approach is employed to analyze the relevant effects on the mechanical behavior of a layered composite consisting of the braze metal and the joining partners. The focus of the investigations lies on the role of the multiphase microstructure within the brazing layer and the significance of microscopic parameters such as, for example, the volume fraction of the phases compared to macroscopic parameters (e.g., the brazing layer thickness). A representative volume element is employed on the microscale, and a layered composite is modeled on the macroscale to capture all relevant effects on both length scales during mechanical loading of the layered material composite. Virtual tensile tests at different temperatures and strain rates are chosen as a controlled testing environment that captures the characteristic loading conditions during a rubbing event in a turbomachinery. The parameter on the microscale with the highest influence on the mechanical behavior is the volume ratio of the brittle and ductile phases. It also has a significant effect on the macroscopic mechanical behavior. To reduce the risk of damage, it is advised to minimize the fraction of brittle phases in the brazing layer. According to the simulation results, this can be even more effective than reducing the overall thickness of the brazing layer. Additionally, an improvement of an existing analytical model for the estimation of the flow stress in the ductile phase of a dual-phase microstructure is proposed. By increasing the order of the root function in the analytic model, the effect of stress distribution between brittle and ductile phases can be incorporated in an empirical manner. This reduces the deviation between the analytical and the numerical approaches significantly.

Ceramic composites toughened by vat photopolymerization 3D printing technology

High strength and high toughness are mutually exclusive in structural materials. In ceramic materials, increasing toughness usually depends on the introduction of a ductile phase that reduces the strength and high-temperature stability of the material. In this work, vat photopolymerization 3D printing technology was used to achieve toughening of ceramic composite material. The friction sliding of the 3D-printed ceramic macrolayer structure results in effective energy dissipation and redistribution of strain in the whole structure, and macroscale toughening of the ceramic material is realized. In addition, the bridging and elongation of the crack in situ amorphous ceramic whiskers were significant microscopic toughening results, coupled with the toughening of the crack tip of nano-ZrO2. Multiscale collaborative toughening methods based on 3D-printed ceramics should find wide applications for materials in service at extreme high temperatures.

New insight into tailorable eutectic high entropy alloys with remarkable strength–ductility synergy and ample shaping freedom fabricated using laser powder bed fusion

Eutectic high entropy alloys (EHEAs) are typical heterostructured materials comprising ductile and hard phases that can be easily tailored to fabricate components with desirable structures and properties. Herein, an AlCoCrFeNi 2.1 EHEA with dual-phase nanolamellar structure and high strength and ductility (yield strength ( σ YS ) = 1210 MPa, ultimate tensile strength ( σ UTS ) = 1414 MPa, and elongation ( ε ) = 16%) was produced using laser powder bed fusion (LPBF). The AlCoCrFeNi 2.1 EHEA presented fine-grain structure with nanoprecipitates (L1 2 and BCC phases) embedded within alternating FCC and B2 nano-scale lamellae. We demonstrated that the high strength of the EHEA originated primarily from the high back stress strengthening of fine grains and high-density heterophase interfaces, and high dislocation density caused by rapid solidification as well as dispersed nanoparticles provided extra strengthening. Furthermore, the cellular structure comprising nearly square FCC cells and surrounding B2 phases was observed, which was induced by the presence of oxides on the surface of the feedstock powder. AlCoCrFeNi 2.1 EHEA with two-hierarchical dual-phase structure, that is, a mixture of lamellar and cellular structures, was obtained. Such heterogeneous structure presented outstanding strength–ductility synergy ( σ YS = 1042 MPa, σ UTS = 1303 MPa, and ε = 26%). These results promote the development of high-performance materials with manufacturing flexibility using additive manufacturing approaches to tailor their multiscale microstructure.

Modeling Deformation and Fracture of Boron-Based Ceramics with Nonuniform Grain and Phase Boundaries and Thermal-Residual Stress

A phase field framework of elasticity, inelasticity, and fracture mechanics is invoked to study the behavior of ceramic materials. Mechanisms addressed by phase field theory include deformation twinning, dislocation slip, amorphization, and anisotropic cleavage fracture. Failure along grain and phase boundaries is resolved explicitly, whereWeibull statistics are used to characterize the surface energies of such boundaries. Residual stress incurred by mismatching coefficients of thermal expansion among phases is included. Polycrystalline materials of interest are the ultra-hard ceramics boron carbide (B4C) and boron carbide-titanium diboride (B4C-TiB2), the latter a dual-phase composite. Recent advancements in processing technology enable the production of these materials via spark-plasma sintering (SPS) at nearly full theoretical density. Numerical simulations invoking biaxial loading (e.g., pure shear) demonstrate how properties and mechanisms at the scale of the microstructure influence overall strength and ductility. In agreement with experimental inferences, simulations show that plasticity is more prevalent in the TiB2 phase of the composite and reduces the tendency for transgranular fracture. The composite demonstrates greater overall strength and ductility than monolithic B4C in both simulations and experiments. Toughening of the more brittle B4C phase from residual stress, in addition to crack mitigation from the stronger and more ductile TiB2 phase are deemed advantageous attributes of the composite.

Strong and Tough Alumina Ceramic from the Particle‐Stabilized Foam

Strength and toughness are two vital and contradictory properties, especially in alumina structural ceramics. This mutual exclusion limits the widespread application of advanced alumina ceramics in harsh environments. To deal with this issue, self‐toughening alumina bulk ceramics without any ductile phase and with a unique combination of excellent toughness and reliable strength by combining the foam ceramics with hot‐pressing sintering are prepared. Foam ceramics with honeycomb cellular structures are prepared by particle‐stabilized foaming. Then, the foam ceramics is directly hot pressed sintered, in which the cellular structure is fractured into fragments and completely dense under pressure. Equiaxed grains that constituting the fragments grow anisotropically into plate‐like grains with a large diameter–thickness ratio during hot‐pressing sintering. Plate‐like grains improve the material's fracture toughness by exerting a toughening mechanism similar to that of fibers. The self‐toughening alumina ceramics exhibit a unique combination of high flexural strength (874 ± 31 MPa) and high fracture toughness (6.2 ± 0.1 MPa m1/2). The Vickers hardness also can reach 21 GPa. Herein, a new strategy with relatively simple processing to fabricate high‐performance ceramics based on the widespread ceramic processing techniques are provided.

Enhanced cyclability of superelasticity and elastocaloric effect in Cu and B co-doped Co-Ni-Ga shape memory alloys

A< 001 > B2 preferentially oriented Co-Ni-Ga alloy with Cu and B co-alloying is synthesized. It contains two kinds of ductile secondary phases precipitated in the columnar grain interior and grain boundaries, respectively. This textured Co-Ni-Ga-Cu-B heterostructural alloy presents remarkable mechanical properties with a high yield strength of ~1203 MPa and an appreciable failure strain of ~8.8%. It also offers exceptional superelasticity with a fully recoverable strain of 2.5%, a low driving force of 99 MPa and narrow stress hysteresis of 33.5 MPa. Excellent mechanical cyclic stability for 20,000 cycles after cyclic training is also successfully achieved. With the advantages of its superior mechanical responses, an excellent room-temperature elastocaloric effect is demonstrated with a moderate adiabatic temperature change of −3.2 K at a small transformation strain of 1.5%, which is observed over 20,000 cycles without any apparent degradation. More importantly, the fatigue resistance of the superelasticity and the elastocaloric effect is much more enhanced relative to the reported single-crystal counterparts. The great performances of the superelasticity and the elastocaloric effect of the optimized Co-Ni-Ga alloy imply a promising candidate for advanced superelastic and solid-state refrigeration applications. The collaborative designing approach may be exploited to other intermetallic-type shape memory alloys. • The mechanical property of Co-Ni-Ga alloy was improved by doping Cu and B. • Stable superelasticity was achieved for 20,000 cycles in the doped Co-Ni-Ga alloy. • The elastocaloric effect shows good cyclic stability over 20,000 cycles.

Study the Properties of High-Density Polyethylene with Nano Particles Silica Composite

In this research work high density polyethylene (HDPE) and silica nanoparticles (SiO2 NPs) were studied. Samples having 0-10 % composition variation were prepared by injection molding. HDPE and Sio2 NPs constituents were combined at microscopic level and they are insoluble into each other. This phase is called as “Reinforcing” Phase. Soft and ductile phase is called Matrix phase. Matrix phase provides base support to the reinforcing phase and it is protecting the reinforcing phase from the hot environment against the degradation of Polymer Matrix Composites (PMC). Silica dioxide Particle in the form of powder was examined by Electron microscopic method (46.69% silica &amp;53.31% oxygen) with size 2-20 nm. It has large specific surface area/surface energy. Sample of HDPE/SiO2 NPs composites were characterized by mechanical and thermal analysis. It was concluded that the including the SiO2 NPs into HDPE resulted in higher tensile and flexural properties. It has increased the impact strength of composite by 23.58% (5% by wt. addition of silica nanoparticles) and 46.42% (10% by wt. addition of silica nanoparticles).

Petrographic and Kinematic Analysis of the Itombwe Synclinorium Formations Exposed at Tshondo and Bugoy (South-Kivu region, Democratic Republic of the Congo)

The purpose of this study is to investigate the Itombwe synclinorium formations that were affected by the late Pan-African orogenesis in the nordeastern Congo. A variety of controversies surround Tshondo and Bugoy's tectonic evolution and associated metasedimentary formations. A field-based approach combined with paleostress inversion techniques and petrographic analyses were conducted on 190 structural measurements and 6 rock samples used in this study. The results reveal the presence of four major petrographic facies: conglomeratic facies (conglomerate and diamictite), carbonate facies (travertine), greenschist facies (graphitic black shale and pelite), as well as quatzitic facies (quartzite and sandstone). The mineral assemblages consisting of high contents (&gt;70%) of muscovite/sericite and biotite albite, plagioclase, quartz, and some opaque minerals. With the assistance of Win-Tensor software, the kinematic analysis reveals two major deformation phases, (1) a ductile deformation phase (D1-2), which is associated with isoclinal folds and strike-slip faults, and (2) a submeridian brittle deformation phase (D2), which generated extensive faults trending NNW-SSE to NE-SW directions, while reactivating bedding surfaces (NE-SW) in a series of secondary faults. The findings of this research may assist geologists in conducting core logging operations and provide a baseline for understanding the relationship between rock, minerlization, and tectonics in mineral-rich areas.

High Pressure Study of New Type of MAX Phases: Hf2AB2 (A = In, Sn)

This study carries out density functional theory (DFT)‐based simulation in order to observe the effect of pressure (up to 120 GPa) on the various physical properties of boron (B) containing new MAX compounds Hf2InB2 and Hf2SnB2. Structural parameters in ambient conditions show excellent concordance with prior experimental and theoretical data. A decreasing trend of lattice parameters with pressure is observed. The stability of the phases under pressure is determined by calculating the elastic constant using the Born stability criteria, and is found stable within the studied pressure range. Pressure's effect on the various elastic moduli is considered, and a linear response with pressure is observed. The brittle/ductile behavior under pressure is investigated, and a brittle to ductile phase transition is found. An opposite trend of elastic moduli with pressure is observed for Vickers hardness. The nonlinear variation of Vickers hardness with pressure has been interpreted in terms of Pugh ratio and density of states (DOS). A decreasing trend of the anisotropic indices is observed for Hf2InB2, while an increasing trend is observed for Hf2SnB2. The electronic and optical properties are also significantly influenced by the pressure. The results obtained at zero GPa have been compared with previous results and show significant agreement.

Effect of the addition of ductile phase on mechanical properties of Alumina/nano SiC ceramic composite

ABSTRACT Silicon carbide reinforcement in Alumina possess better physical and mechanical properties at elevated temperature. However, addition of second phase ceramic to matrix enhances the strength and hardness but it moderately improves the fracture toughness. The reason is due to lack of plastic deformation. Addition of ductile metallic phase helps in bridging the advancing crack in the matrix. In the present study, Alumina/nano SiC ceramic composite is toughened by the addition of copper metal particles. The influence of these metallic particles on behavior and mechanical properties of Alumina/SiC ceramic composite have been studied. The composite is processed using microwave hybrid sintering technique (2800 Watt) for one hour at 1400℃ and 1500℃. After sintering, microstructure of sample, grain size, relative densification, hardness and toughness have been examined. Highest densification of 93% and hardness of 1590 HV is achieved at 1400℃ sintering temperature while highest fracture toughness of 3.9 MPa m1/2 is achieved at temperature of 1500℃ with coarsening of alumina grains. The ductile phase in ceramic has proven to be effective for better bonding. It creates ceramic-metal bonds, which act as a tiny metal matrix between ceramic particles and contribute to ductile phase toughening in developed (Alumina/5% nano SiC/5%Cu) ceramic composite.

On the influence of specimen size and geometry on the fracture toughness of tungsten heavy metal alloys

We previously showed that commercial tungsten (W)-based heavy metal alloy (WHA) composites containing 90 to 97 wt% W, reinforced with 3 to 10 wt% of a NiFe ductile phase (DP), have room temperature (RT) maximum load elastic-plastic fracture toughness (KJm) values from 69 to 110 MPa√m. This is far higher than for monolithic RT W toughness (≈ 8 ± 4 MPa√m). In all cases, fracture took place by stable crack growth. However, these results were based on very small (16/3.3/1.65 mm) pre-cracked bend bar tests, which naturally raises the question of size effects on the measured KJm. While they are best thought of as being composites, here we experimentally assess size and geometry effects on the KJm of WHA, in the broad context of validity criteria that have been developed for both cleavage and ductile tearing, R-curve fracture in steels. Specifically, we examine the relation between KJm and a dimensionless elastic-plastic zone small scale yielding deformation limit criterion, M ≥ σobo/Jm. Here σo is the flow stress, Jm is the measured J at maximum load, and bo is the initial unbroken ligament dimension. Tests on specimens from 3x to 8x larger than the original small (1x) bend bars show only weak or no size effect up to 95W with KJm ≈ 82 ± 5 MPa√m. However, 3x 97W alloy fractured elastically at KIm ≈ 38 ± 4 MPa√m. The corresponding average for the 1x specimens was KJm 100 ± 15 MPa√m for the 90–95W and 69 ± 12 MPa√m for the 97W alloys. The approximately constant KJm for 3–8x specimen sizes suggests that the M required for constraint-related size independence is ≈ 200. However, DP fraction also plays a role, and there are additional effects of compact tension versus bend bar specimen geometries.

Novel processing route for design and manufacturing of metal toughened nanoceramics: Al–Al2O3 nanocermets

Monolithic alumina is a highly brittle ceramic with a very low fracture toughness, making it an unreliable material for mechanical and structural applications. Ceramic-metal composites (cermets) are the subject of intensive interest to obtain materials which can address the intrinsic brittleness of ceramics without compromising their high strength and light weight. In the present investigation, aluminium-alumina (Al–Al 2 O 3 ) nanocermets were developed. The nanocermets possessed the toughness of Al phase and the strength of reinforced nano Al 2 O 3 particles. The nanocermets green bodies were prepared such that upon sintering each adjacent Al 2 O 3 grain was conformally coated with a continuous Al film. Mechanical milling via a combination of cryo-milling and ball-milling was used to prepare Al–Al 2 O 3 nano-powder mixture. Spark plasma sintering was used to consolidate the green nanocermets. Results show that specimens prepared from 35 h milled powders exhibited superior mechanical properties as compared to other nanocermets, with an improvement in microhardness, elastic modulus, compressive strength, and flexural strength by 88%, 78%, 69% and 40% with respect to sintered pure Al. The indentation toughness of 35 h milled nanocermet showed an increment of 12.5% with respect to sintered pure Al 2 O 3 . Characterization techniques such as XRD, SEM, HR-TEM, X-ray tomography were employed to investigate the phase evolution and structural morphology, while FEM simulations were performed for understanding the crack propagation mechanisms in nanocermets. Figure Description: A novel processing route devised from the combination of cryo-milling and ball-milling of elemental Al and Al 2 O 3 powders, followed by spark plasma sintering (SPS) for the development of toughened and strengthened Al–Al 2 O 3 nanocermets (metal-ceramic nano-systems). An attempt has been made to utilize the favourable physical and mechanical attributes of ductile metal phase and brittle ceramic phase to fabricate nanocermets with enhanced mechanical properties. These nanocermets will find use in structural applications requiring components with high strength to weight ratio, such as automotive parts, ballistic armours and jet propulsion systems. • Al 0.2 -(Al 2 O 3 ) 0.8 nanocermets possessing the toughness from ductile Al and strength from brittle Al 2 O 3 are developed. • A combination of cryo-milling and ball-milling is used for the preparation of nanosized Al-Al 2 O 3 powder mixtures. • An optimized cryo-milling of 10 h transforms micron-sized Al particles into nanometric thin sheets. • Enhanced wettability of Al and Al 2 O 3 at the grain boundary interface is achieved for metal-ceramic nano-systems. • Toughening of brittle Al 2 O 3 by metallic Al phase transforms the inter-granular fracture into trans-granular mode.

Process optimization and thermodynamic modeling of weld zone in nickel powder-added dissimilar pulsed-laser NiTi/ASS joint

Dissimilar joining of NiTi alloys to stainless steel has attracted abundant consideration. In this research, pure nickel powder diluted in PVA adhesive was added to the joint area with different concentrations to eliminate or minimize the brittle intermetallic compounds. Also, thermodynamic concepts of phase stability employing the quaternary CALPHAD method were used to calculate the weld zone's phase stability. The results indicated that laser welding combined with 30% nickel powder addition did not have a noteworthy effect on detracting the content of Fe2Ti in the weld zone. In contrast, adding nickel powder with a concentration of 50% reformed the chemical composition and changed the Fe2Ti primary solidifying phase to more ductile phases of Ni3Ti and γ. The results of equilibrium thermodynamic calculations also predicted that Ni3Ti, γ, and B2-(Fe,Ni)Ti phases are possible to form in this condition. In laser welding with 70% nickel powder, unmixed nickel areas and gas porosities were observed in the weld zone. The superlative mechanical properties were obtained for the samples with 50% nickel powder addition. The microhardness results revealed a diminution of the weld zone's average hardness from 667 HV (without nickel powder addition) to 325 HV (50% nickel powder addition). Evaluation of joint strength revealed the twofold increase in 50% nickel powder added joints compared with conventional samples; the fracture strength and fracture strain reached 310 MPa and 2.9%, respectively. Therefore, Ni powder addition is an effective process for improving the mechanical properties of dissimilar joints of these two alloys.

Corrosion and mechanical behavior of amorphous-nanocrystalline NiCrMo coatings

To develop a high-performance coating for marine engineering equipment, we successfully designed amorphous-nanocrystalline NiCr0.25Mox (x = 0, 0.02, 0.05, 0.1, 0.2, 0.4) alloy coatings via direct current (DC) magnetron sputtering. The compositional, microstructural, corrosion and mechanical properties, specifically the relationship between the coating structure and performance were discussed in detail. The results showed that the amorphous phase sharply alleviated grain boundary corrosion, and the addition of Cr and Mo was beneficial to improve repassivation ability with the formation of a dense passive film. In the nanoindentation and micro-scratch tests, the nanohardness and adhesion strength of the coatings first increased remarkably with Mo content and then declined due to the formation of an amorphous phase. The enhancement of strength was caused by nanocrystals hindering the formation of shear banding, while the addition of Mo improved the tendency of amorphous formation due to the difference in atomic size and lattice distortion. Most importantly, the NiCr0.25Mo0.1 coating exhibited excellent corrosion performance and mechanical behavior through the formation of a dense passivation film composed of Cr2O3 and Cr(OH)3. These ductile solid solution crystalline phases promoted homogeneous plastic deformation and decelerated crack propagation during the scratching process.

Microstructure and mechanical properties of NbC–Ni cermets prepared by microwave sintering

Abstract This study shows the application of microwave sintering (MS) on preparing NbC–10Ni and NbC–12Ni cermets, as well as the effect of its microstructure, phase formation, and mechanical properties. Results indicated that NbC–Ni cermets with a fine and uniform structure can be obtained by MS in a relatively short time. And the sintering temperature greatly influenced the microstructure and mechanical properties of NbC–Ni cermets, whereas the effect of dwell time is relatively small. With the increase of the sintering temperature, the microstructure of NbC–Ni cermets experienced sintering densification and grain growth. The strength and toughness increased first and then decreased, and the hardness increased with the increase of sintering temperature. According to the comprehensive mechanical properties, the optimized sintering process is 1,390°C and the dwell time is 15 min. At this time, no new phase formed, but the diffraction peak of the Ni phase shifted. Through analysis, it is found that the improvement mechanisms for comprehensive mechanical properties of NbC–Ni cermets mainly include grain refinement, crack deflection and bridging, and energy absorption of the ductile phase of Ni.

Design of NbNiTaTi refractory high-entropy alloy via NiTi eutectic phase

Refractory high-entropy alloys (RHEAs) hold far reaching application potential in high temperature structural materials fields due to their high melting points and excellent softening resistance. However, the trade-off between strength-ductility and oxidation resistance of RHEAs has become a critical problem for their processing and application. In this work, we reported a strategy to enhance ductility of NbNiTaTi RHEA by applying the eutectic reaction of NiTi shape memory alloys. Experimentally, NbNiTaTi RHEA exhibited BCC phase and eutectic structure composed of IM phase and NiTiB2 phase. The RHEA showed a compressive strength of 2140 ± 30 MPa and a compressive plastic strain of 34 ± 2% at room temperature. Actually, the ultrafine eutectic structure with ductile NiTiB2 phase and hard IM phase could greatly enhance the ductility of NbNiTaTi RHEA while ensuring its strength. Meanwhile, The BCC phase with high solidification temperature remedied the weakness of high temperature stability of RHEA after adding non-high melting point elements. Besides, NbNiTaTi RHEA showed good corrosion resistance and its passive film remained stable across a wide range of potential. These results provided theoretical guidance for the application of ductile phase in RHEA field.

Structural, electronic, mechanical and thermodynamic properties of antiperovskites Ti3InX (X=C and N) ceramics: A first-principles study

The mechanical and thermodynamic properties of Ti3InX (X = C and N) ceramics are investigated by the first-principles calculations. The structural and mechanical parameters are in good agreement with the available theoretical and experimental results. The results show that Ti3InX ceramics are thermodynamics stable. The stiffness and hardness of Ti3InC ceramics are higher than those of Ti3InN ceramics, but its strength is weaker than that of Ti3InN ceramics at 0K. Ti3InC and Ti3InN ceramics belong to brittle phase and ductile phase, respectively. Ti3InC and Ti3InN ceramics exhibit normal thermal expansion behavior at 0–1830K and 0–1640K, respectively, and belong to medium expansion materials and high expansion materials, respectively. The Grüneisen constants of Ti3InC and Ti3InN ceramics are 1.49–1.67 and 1.49–1.88, respectively. The thermal conductivity of Ti3InN ceramics is obviously lower than that of Ti3InC ceramics. The adsorption energy of O on Ti3InC(100) surface is lower than that on Ti3InN(100) surface, indicating that Ti3InC(100) surface is more sensitive to oxygen. Meanwhile, the melting temperature, hardness and Debye temperature of Ti3InX ceramics are also estimated.

Phase Prediction, Microstructure and Mechanical Properties of Fe–Mn–Ni–Cr–Al–Si High Entropy Alloys

The selection of high-entropy alloys (HEAs), which are relatively lightweight and have unique mechanical properties, remains a substantial challenge. In this study, six new HEAs were designed from the relatively low-cost Fe–Mn–Ni–Cr–Al–Si system using Thermo-Calc software, and then manufactured using a casting process. The effects of the atomic ratio of the alloying elements on the microstructures and mechanical properties of these alloys in the as-cast condition were systematically investigated. Brittle body-centered cubic BCC/B2 and silicide phases were found in relatively large amounts in the form of dendritic structure within large equiaxed grains with fine needle-shaped phases in the Fe30Mn15Ni20Cr15Al10Si10 and Fe35Mn15Ni20Cr15Al10Si5 alloys, in addition to the face-centered cubic (FCC) phase. When the contents of Mn and Ni were increased in the Fe35Mn25Ni15Cr15Al5Si5 and Fe35Mn20Ni20Cr15Al5Si5 alloys, the amounts of brittle phases were reduced; however, the ductile FCC phase is not significant. The FCC phase amount, which appeared as a honeycombed structure, was more than enough when the Si content was decreased to 3%. Broad relationships between the chemical composition of the alloys, especially the Si content, and the hardness and compression properties’ measurements were established. As the Si content decreased, both the hardness and compression properties of the resulting alloy also decreased. The experimental observation of the six HEAs matched the equilibrium phases predicted by the Thermo-Calc calculations.