Intermetallics最新文献

The microstructure and tensile mechanical properties of novel FeNiCrAl_xTi_y medium-entropy alloys (MEAs) were investigated. The results showed that the microstructure of the MEAs undergoes a transformation from FCC single-phase to FCC + BCC dual-phase with increasing Ti and Al content. The addition of Ti and Al significantly increases the strength while maintaining appropriate ductility. Specifically, the (FeNiCr)₉₄Ti₂Al₄ exhibits excellent combinations of yield strength (∼1.2 GPa and ∼1.5 GPa) and tensile ductility (13 % and 19 %) at both 298 K and 77 K. Microstructural analysis reveals that the excellent cryogenic mechanical properties are attributed to the co-existing multiple strengthening mechanisms. This work provides a simple route for designing low-cost MEAs with excellent cryogenic tensile properties.

Based on the problems of micro defects (cracks, pores, etc.), uneven distribution of strengthening particles, and poor bonding between strengthening particles and metal matrix in practical engineering applications, the new AlCrFeNiMo_0.5-x(WC) (x = 0, 5, 15, 30 wt%) composite coatings have been designed, and further prepared using laser cladding. Their micro-structures, micro-hardness and dry sliding wear properties were deeply explored. They exhibited the dendritic morphologies and consisted of BCC1, BCC2, and carbide phases. The AlCrFeNiMo_0.5-30 wt%(WC) coating had the highest hardness (772 HV), which was approximately 5 times that of Q235 steel substrate. With the increase of WC content, dry sliding wear properties showed an increasing trend, that is, AlCrFeNiMo_0.5-30 wt%(WC) coating had the lowest friction coefficient (0.50) and wear rate (9.23 × 10⁻⁶ mm³/(N · m)), exhibiting excellent tribological properties, which was attributed to the coupling effect of hard carbide and ductile BCC phases. It would be a promising wear-resistant coating material under dry sliding environment. This study not only has significant theoretical significance for understanding the failure patterns and performance evolution of new high entropy alloy/WC composite coating materials in dry sliding environments, but also demonstrates important value for expanding the application of new high entropy alloy/WC composite coating materials in practical engineering.

As is widely recognized, the Long Period Stacking Ordered (LPSO) phase is an important strengthening phase in the rare earth magnesium alloys. The LPSO phase not only enhances the strength of the alloy, but also improves its plasticity, thereby effectively addressing the strength-ductility trade-off phenomenon. Therefore, the preparation of metallic materials containing LPSO phase provides a new idea for designing a new generation of high-strength and high-toughness alloys. In present study, A novel nano-sized LPSO phase is observed and characterized for the first time in GH4169 nickel-based alloy. The results show that the stacking sequence of the LPSO phase is ABCBCBA, which indicates that this LPSO phase has a 6H structure. Meanwhile, the orientation relationships between LPSO phase and the Ni matrix are (11–1)_γ//(0006)_LPSO and [011]_γ//[2-1-10]_LPSO.

A quaternary Ni₅₀Fe₂₀Cr₂₀Zr₁₀ eutectic alloy was designed based on the Ni–Fe–Cr alloy, and the gradient ultrafine lamellar γ+Ni₅Zr eutectic was achieved by means of electromagnetic levitation coupled with fall casting (EML-FC). The temperature field, the process of interface migration, microstructural characteristics and the nanoindentation creep property of the alloy were systematically analyzed. During the rapid solidification, since the conical surface served as the main heat dissipation channel, the solid-liquid interface moved from the conical surface towards the top of the cone axis. The gradual decrease in cooling rate from 10⁵ to 10³ K s⁻¹ along this direction led to the formation of the gradient ultrafine lamellar γ + Ni₅Zr eutectic with the size from 59 ± 12 to 140 ± 36 nm. The nanoindentation creep behavior and mechanism were analyzed by estimating the strain rate sensitivity and activation volume. As the interlamellar spacing of the eutectic decreased, the nanohardness and creep resistance of the alloy gradually increased owing to an increase in grain boundary density and the enhancement of coupling effect between dislocation and grain boundary. In addition, the creep behavior of alloy was sensitive to the loading rate. Increasing the loading rate led to an increase in strain rate sensitivity from 7.69 × 10⁻³ to 18.89 × 10⁻³ and a decrease in activation volume from 29 to 12 b³. This special eutectic structure and its improved nanohardness and creep resistance properties offered a potential opportunity to explore a new generation of alloys for the hot-end components of 972 K ultra-supercritical fossil-fired power plants.

To enhance the wear resistance of nickel-based superalloys and broaden their applications, we investigated the microstructural organization and wear properties of IN718 composites reinforced with graphene nanoparticles fabricated through selective laser melting. The optimal parameters for printing were obtained by combining experiments and simulations, and their wear patterns were subsequently explored at different sliding speeds (250–350 r/min) and loads (4N–8N). Based on the composite TEM images combined with experiments, it was found that the homogeneous dispersion of graphene nanoparticles in the 3D-printed GNPs/IN718 composites acted as dislocation reinforcement and load reinforcement. The average microhardness of the GNPs/IN718 composites increased by 24.2 % compared to the IN718 alloy. In the friction test, GNPs acts as a lubricating phase, resulting in a significant increase in the friction wear performance of the composite. The average coefficient of friction decreased by 33.8 % and the wear rate decreased by 51.3 %. The wear state of the composites change from abrasive wear to delamination wear and a combination of delamination wear and oxidative wear as the speed and load are increased, respectively. This paper provides potential guidance for further improving the wear performance of additively manufactured nickel-based superalloys.

The effect of grain boundary diffusion on the magnetic properties and microstructure of Nd-Fe-Co-B sintered magnets is investigated using Dy₇₀Al₁₀Cu₂₀ alloy as the diffusion source. After the secondary annealing of the Nd-Fe-Co-B sintered magnet (H_cj = 7.94 kOe), its coercivity is substantially increased to 13.10 kOe. Following post-diffusion annealing, the coercivity of the sintered magnet significantly increased to 20.86 kOe. Microstructure analysis revealed that after the second annealing, the main phase grains in the magnet were connected but lacked thin intergranular phases. The distribution of Co was uneven, with an abundance of soft magnetic phases rich in Co, which was not conducive to improving coercivity. After diffusion, Dy formed a shell structure with high magnetic crystal anisotropy on the outer side of the main phase grains, leading to a significant increase in coercivity. Al and Cu entered the interior of the magnet, reducing the melting point of the grain boundary phase and promoting the uniform distribution of Co through the flow of the liquid phase. A large amount of thin continuous intergranular phase is generated inside the magnet, which helps reduce the exchange coupling between hard magnetic grains. The experimental results indicate that the Dy-Al-Cu alloy can effectively enhance the grain boundary structure of Nd-Fe-Co-B magnets, reduce the abundance of Co-rich phases, and improve the coercivity of the magnet.

Dealloying is a proficient technique in the fabrication of nanostructured metals, particularly nanoporous materials, with promising potential for diverse applications. However, the development of robust and self-standing nanostructured metal foils through dealloying presents significant challenges. By generating an alloy layer on the surface of the metal foil, nanostructures can be generated on the metal foil surface through subsequent dealloying. This approach utilizes the inherent flexibility and ductility of the metal foil to ensure self-support. It also allows for the tailoring of the structure and composition of the dealloyed nanostructured metal by manipulation of the phase constitution in the surface alloy layer. In this study, we report a strategy for generating alloy layers on metal foil surfaces through the thermal evaporation of magnesium (Mg) followed by annealing. Upon dealloying the surface alloy layer, we successfully obtain self-supported nanostructured metal foils. Employing copper (Cu) as an example, we demonstrate that Mg can form a Mg–Cu alloy layer on the surface of a Cu foil, where the control over the alloy layer's phase composition and thickness is achieved by adjusting the annealing duration. Furthermore, we investigated the feasibility of this method on nickel (Ni) substrates, including Ni foils and Ni foams. Moreover, by further functionalizing the resulting nanostructured Ni foil, we transformed it into Ni(OH)₂/Ni foil and explored its performance in the electrocatalytic oxygen evolution reaction (OER). The resulting catalyst achieved a current density of 10 mA cm⁻² at a potential of only 349 mV in a 1 M KOH solution, exhibiting a Tafel slope of 84.52 mV dec⁻¹. Following 10 h of stability testing, the catalyst exhibited negligible degradation in performance. This study provides a convenient and versatile pathway for preparing self-supported nanostructured metals.

Nanocrystalline multi-main-phase (MMP) Nd-Ce-Fe-B magnet can effectively suppress the magnetic dilution effect of Ce. However, its low coercivity and poor thermal stability have not been adequately overcome. In this work, a novel low-melting-point Gd₆₀Y₁₀Cu₁₅Al₁₅ alloy was introduced into MMP Nd-Ce-Fe-B magnet through intergranular addition for simultaneously enhancing its coercivity and thermal stability. The results show that the intrinsic coercivity H_cj is obviously improved, and its maximum increment is ∼12.3 % at 4 wt% Gd₆₀Y₁₀Cu₁₅Al₁₅ alloy. Especially, the increase in H_cj is more significant, and an abnormally increase in the maximum energy product (BH)_max occurs at high temperature of 150 °C. Meanwhile, the reversible temperature coefficients of H_cj (β) and B_r (α) are improved simultaneously. These findings imply the enhanced thermal stability for the MMP magnet with Gd₆₀Y₁₀Cu₁₅Al₁₅ addition. The microstructural characterizations, compositional analyses and micromagnetic simulations reveal that the competitive effects of the formed non-ferromagnetic grain boundary (GB) phase and Y or Gd diffusion into the main phase lead mainly to a synergistic improvement in the coercivity and thermal stability of the magnet. This work is expected to provide a promising cost-effective approach for developing the high-performance thermally-stable Nd-Ce-Fe-B magnet and explore more possibilities for effective utilization of Y or Gd rare-earth resources.

This study employs density functional theory (DFT) using Wien2k to comprehensively analyze the essential properties of two half-Heusler alloys, KCrSi and KCrGe. Our findings demonstrate that the ferromagnetic Type 2 configuration exhibits superior stability over non-magnetic and antiferromagnetic states for all KCrZ (Z = Si, Ge) alloys. These alloys exhibit complete spin polarization and half-metallic character, with calculated magnetic moments of 3 μB for both KCrSi and KCrGe. The Curie temperature (T_C) is determined using the mean field approximation. Mechanical stability is assessed through second-order elastic constants (SOECs), and electronic properties are analyzed using local spin density approximation (LSDA), Perdew-Burke Generalized Gradient Approximation (PBE-GGA), and Tran-Blaha modified Becke-Johnson (TB-mBJ) schemes, confirming the retention of the half-metallic nature. The negative enthalpy of formation (ΔH) suggests material stability. The use of semi-classical Boltzmann theory, incorporated through the sophisticated scheme of BoltzTraP, explores transport coefficients. High pressures and temperature discrepancies in thermodynamics are considered by implementing the quasi-harmonic Debye approximation to illustrate stability. Finally, optical properties are summarized to assess the applicability of this alloy for optoelectronic applications. The overall characteristics of these particular alloys suggest potential applications in sustainable thermoelectric and optoelectronic features.

In order to reveal the discharge and ignition mechanism of high-entropy alloy under quasi-static compression load, the stress, potential and ignition evolution process of high-entropy alloy with prefabricated cracks were tested. The atomic structure and dislocation evolution of high-entropy alloy during crack propagation and compression were determined by molecular dynamics simulation, and the discharge mechanism of crack tip was analyzed at the micro level. Based on the calculation of Gibbs free energy, the products in the ignition reaction process were predicted. The results of mechanical/thermal/electrical characteristics induced by compressive load show that the discharge usually occurs near the ignition moment of specimen fracture, and the maximum potential signal can reach 34.2 V. The formation of crack group, crack propagation, local stress concentration, charge accumulation and release at the crack tip jointly induce the generation of discharge signals. With the propagation of cracks, a large number of stacking faults appear and a diamond-shaped failure zone is formed. The increase of disordered atoms leads to fracture. During the compression process, a large number of dislocations induce the separation of charges, which aggravates the discharge at the crack tip. In the Hf-Zr-Ti-Ta-Nb-Cu high-entropy alloy system, the reaction product Ta₂O₅ is preferentially generated, while in the Ti–Zr-Hf-Cu system, Ti₂O₃ is preferentially generated. The tip discharge and chemical bond fracture during crack propagation induce ignition, and the chemical bond recombines with energy release.