Intermetallics最新文献

In this study, two Mo₂FeB₂-type multiple rare-earth-containing MRE₂Cu₂In (MRE = Dy_1/3Ho_1/3Er_1/3 and Ho_1/3Er_1/3Tm_1/3; space group P4/mbm, No. 127) compounds are prepared via arc-melting method and systematically determined regarding their structural and magnetic properties, magnetic phase transition (MPT), and magnetocaloric (MC) performances. They undergo typical second-order MPT at low temperatures. The MC effect and MC performances of the present MRE₂Cu₂In compounds at low temperatures are assessed using magnetic entropy changes, refrigerant capacity, and temperature-averaged entropy changes. The values of these parameters are comparable to most updated candidate materials for low-temperature magnetic cooling, making the present MRE₂Cu₂In compounds considerable for practical applications.

To clarify the initial microstructure dependent γ′-coarsening behavior, a corrosion-resistant Ni-based superalloy with the varied γ′-size were prepared by changing the primary aging heat treatment temperature. The microstructural evolution was investigated during long term thermal exposure (up to 3000 h) at 900 °C and 1000 °C, respectively. It was found that Cr, Co, and Mo preferentially partition to γ-matrix, while Ta, Ti, Al, Ni, and W partition to the γ′-phase. The abnormal partition of W to the γ′-phase can be attributed to the low content of Ta in CM247 LC alloy. Furthermore, the γ′-coarsening behavior can be divided into two stages. During the early stage of coarsening (<1000 h), the coarsening rate obeys the classical LSW model with the cube rate law. As the increase of the initial γ′-size, the γ′-coarsening rate obviously increases, which can be mainly attributed to the increased solute diffusion capability in the γ-matrix and the higher γ'/γ interfacial energy. By contrast, there is an apparent γ′-coalescence during the later stage of coarsening (1000 h–3000 h). The temperature plays a more dominant role on the γ′-coarsening rate than the duration times during thermal exposure.

Nb silicide coatings modified with active elements have good oxidation resistance, but there is a lack of systematic research on their oxidation behavior at high temperatures above 1250 °C. The aim of this work is to investigate the oxidation behavior of an Al–Y modified silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C. After oxidation at 1250 °C, the scale displays a typical layered structure consisting mainly of a TiO₂ outer layer, an amorphous SiO₂ matrix layer embedded with TiO₂ and ZrSiO₄, and an inner layer consisting of SiO₂ and Cr₂O₃. Above 1350 °C, the evaporation reaction of Cr₂O₃ into CrO₃ (g) is significantly accelerated and Cr₂O₃ disappeared gradually with temperature or time. The TiO₂ layers covering on the scales formed at 1250–1500 °C grow along the crystallographic orientation of [100]. The micropores formed on the surface of TiO₂ should be attributed to the further oxidation of Cr₂O₃ into volatile oxide CrO₃ (g). The scales exhibit a similar structure consisting mainly of a SiO₂ glass matrix embedded with ZrSiO₄ and a surface TiO₂ layer until 1500 °C. Above the eutectic temperature of SiO₂–TiO₂ system, the scale is mainly composed of a matrix layer of SiO₂–TiO₂ eutectic embedded with block TiO₂ particles, and a thin SiO₂ interface layer at 1560 °C. The degeneration path of the (Nb,X)Si₂ coating is (Nb,X)Si₂ → (Ti,Nb)₅Si₄ → γ-(Nb,X)₅Si₃.

In this investigation, we explore the impact of the Nb–Al ratio on the microstructural and mechanical properties of high-entropy superalloys (HESAs), focusing on hierarchical microstructures. Utilizing a series of HESAs with varying Nb–Al ratios, our study employs advanced characterization techniques, including differential scanning calorimetry (DSC) for thermal analysis, electron probe micro-analyzer (EPMA) for compositional analysis for the design of a homogenization treatment at 1500 K/24 h. Transmission electron microscopy (TEM) reveals that the increasing Nb–Al ratio refines the γ' precipitates and influences the size and volume fraction of embedded hierarchical γ particles. ThermoCalc equilibrium phase analysis and Vegard's-law calculations reveal a minimal lattice misfit between these phases, highlighting the interplay between Nb–Al ratio and phase stability. The increasing Nb–Al ratio inhibits the formation of hierarchical γ particles. We observe an enhancement in hardness from 433 HV to 492 HV with an increasing Nb–Al ratio. This study provides valuable insights into the role of Nb and the Nb–Al ratio in HESAs with hierarchical microstructures, demonstrating its significant influence on γ particle formation within γ' precipitates and mechanical strength. The findings advance our understanding of alloy design and pave the way for developing advanced HESAs for high-temperature applications.

A novel Fe₈₇Pr₁₁B₂ metallic glass that exhibits outstanding magnetocaloric effect near room temperature was prepared into the shape of amorphous ribbons. The ribbon exhibits soft magnetic properties and high saturation magnetization at 200 K, which is much lower than its Curie temperature at 325 K. No obvious spin-glass-like behavior was found above 200 K. The almost highest maximum magnetic entropy change (−ΔS_m^peak) among Fe-based metallic glasses near the hot end of a residential magnetic refrigerator is most likely attributed to the high concentration of Pr and low content of B in the Fe₈₇Pr₁₁B₂ amorphous ribbon. The high −ΔS_m^peak, large refrigeration capacity (RC) and adiabatic temperature rise (ΔT_ad) make the Fe₈₇Pr₁₁B₂ amorphous alloy better candidate for the potential component of a refrigerant working in a high-efficiency residential magnetic refrigerator.

Presently, interfacial intermetallic compounds play a vital role in determining the reliability of solder joints due to their intrinsic mechanical property. Especially for Zn–Al solder joints, the interfacial Cu–Zn IMCs grow significantly without diffusion barriers. This work comprehensively investigated the mechanical properties of interfacial IMCs in Zn–Al solder joints with and without the Ni–W–P diffusion barrier by nanoindentation tests and first-principles calculations. The nanoindentation results show that the elastic moduli of CuZn₄, Cu₅Zn₈, CuZn and Al₃Ni₂ were 68.45 ± 1.4 GPa, 142.6 ± 2.3 GPa, 94.7 ± 1.16 GPa, and 221 ± 18.9 GPa, respectively. Their corresponding hardness were 1.03 ± 0.04 GPa, 5.98 ± 0.23 GPa, 1.38 ± 0.16 GPa, and 17.7 ± 0.16 GPa. Through first-principles calculations, the bulk modulus of CuZn and Cu₅Zn₈ exhibits isotropic behaviour, while CuZn₄ and Al₃Ni₂ demonstrate anisotropy. In addition, the bulk modulus, shear modulus, Young's modulus and hardness values of Al₃Ni₂ are considerably higher when compared to those of Cu–Zn intermetallic compounds.

Oxidation behavior of a Ni–Co-based superalloy prepared by vacuum induction melting (VIM) plus electron beam smelting layered solidification technology (EBSL) and VIM plus electro slag remelting (ESR) at 1180 °C was investigated. The predominant oxides from the outer layer to the inner layer are TiO₂, Cr₂O₃, (Al, Ti)-rich oxide and Al₂O₃, respectively. The (Al, Ti)-rich oxide is considered to be Al₂Ti₄O₉, which is formed by TiO₂ and Al₂O₃. At high temperature, the external oxides experienced significant spalling, particularly in ESR-alloy, which indicated that the EBSL-alloy is more preferable in terms of oxidation resistance. This can be attributed to the presence of finer grains in EBSL-alloy, which facilitates the diffusion of elements and promotes the rapid formation of oxidation scales on the surface of the alloy. Additionally, the presence of a TiO₂ layer cover on Cr₂O₃ reduces the degree of spalling of oxides in EBSL-alloy.

The CoCrFeMnNi high entropy alloy thin films with crystalline (solid solution) structure or amorphous state were fabricated by magnetron sputtering process at different target powers and different substrate bias. Effects of the target power and substrate bias on the characteristics of the CoCrFeMnNi thin films such as microstructures, morphology and surface topography, as well as mechanical properties and corrosion behavior were studied. Phase prediction was calculated by using thermodynamic and kinetic criteria under various deposition conditions. The enthalpy, entropy, $\delta$ and Ω parameters, and electronegativity differences influenced the solid solution stability of thin films. These parameters led to the formation of solid solutions with crystalline or amorphous structures under specific limits, which corresponded to the practical XRD and TEM analysis results. Using a substrate bias in the deposition of CoCrFeMnNi thin film changed the amorphous structure to a crystalline (solid solution (BCC + FCC)) at higher target powers (200 and 300 W). On the other hand, the film structure was entirely amorphous at all sputtering target powers without the substrate bias. The mechanical properties, such as hardness, Young's modulus, film strength, and fracture toughness of CoCrFeMnNi thin film, can be enhanced by using the substrate bias and increasing the sputtering power. The potentiodynamic polarization test in 3.5 wt% NaCl aqueous solution indicated that the deposition of CoCrFeMnNi thin films at different sputtering powers and without substrate bias could increase the corrosion resistance of 304 stainless steel substrate. Using the substrate bias of −100 V in the fabrication of CoCrFeMnNi thin film decreased the corrosion current density and increased its polarization resistance.

A face-centered cubic nanocrystalline (NC) Ni–Fe alloy was fabricated by adjusting electrodeposition parameter. By evaluating the hardness of NC Ni–Fe via nanoindentation at the selected strain rates from 0.005 s⁻¹ to 0.2 s⁻¹, a transitional point of strain rate sensitivity index (m) was exhibited, contrary to the constant value that reported in other works. Based on X-ray diffraction and transmission electron microscopy analysis, which evidenced the apparent lattice expansion as much more Fe solutes dissolved in intragrain rather than grain boundary (GB), we attributed the unexpected enhancement of m value at lower strain rates to pronounced GB-mediated plasticity facilitated by residual dislocations near GBs, whilst the lower m value at higher strain rates mainly to the intragranular dislocation motions. This work contributes directly to understanding the profound effect of alloying on the mechanical behaviors of NC materials.

Multi-principal element alloys have attracted extensive attention as a new alloy design concept. In particular, the CoCrFeNi alloys with low stacking fault energy have excellent tensile plasticity and fracture toughness at both low and room temperature, and good phase stability at high temperatures, considered a new type of structural material with great potential. Multi-principal element alloys exhibit plastic instability termed serrated flow, at certain strain rates and temperature ranges. The serrated flow stress is usually closely related to dynamic strain aging, which reflects dislocation and barrier processes and impacts the mechanical properties of alloys. In the present study, CoCrFeNi alloys were selected as the research object, and the impact of grain size and the addition of Re elements on the serrated flow stress behavior was investigated. The results showed that in the tensile tests at 600 °C, the serrated flow stress behavior occurred in the fine-grain specimen only at a lower strain rate. The tensile curves of the coarse-grain specimen at different strain rates all show serration. Overall, the serrated type changes with the decreasing grain size, the increasing strain rate, and the addition of Re element, all of which result in a decrease in the magnitude and number of serrations and a weakening of the serrated behavior.