Positive Enthalpy Of Mixing Research Articles

A Study on the Structural, Wear, and Corrosion Properties of CoCuFeNiMo High-Entropy Alloy

This study investigates the structural properties, wear resistance and corrosion behavior of a CoCuFeNiMo equiatomic high-entropy alloy. The alloy was prepared using a vacuum arc melting device, and its structural properties were analyzed through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Wear tests were conducted using a pin-on-disc machine against 4140 stainless steel at different loads. Corrosion behavior was evaluated through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5wt% NaCl solution. The results indicated the presence of a major face-centered cubic (FCC) phase and a minor (µ) phase. The alloy exhibited segregation of Cu, attributed to positive mixing enthalpy. The coefficient of friction exhibited stability under lower loads but fluctuated under higher loads, possibly due to inhomogeneity in the microstructure caused by Cu segregation. Wear rates increased linearly with applied loads, indicating a direct relationship between load and wear properties. The worn surfaces displayed characteristics of mild abrasive wear, with delaminations, ploughing, and abrasive wear tracks. Pitting corrosion was observed, and the corrosion process was explained as the attack of Cl- ions leading to galvanic corrosion between different phases. In the corrosion analysis, the Ecorr value was -0.616V, and the icorr value was found to be 2.22 × 10-5 A/cm2.

Microstructures and hydrogen evolution reaction performance of Ru-M(M=Cu, Ni and Nb) system by magnetron sputtering: The mixing enthalpy effect

Nanostructured hydrogen evolution reaction (HER) electrocatalysts were prepared by magnetron sputtering. With increasing sputtering power of the Ru target, the catalytic performance of Cu-Ru system improved. Pure Ru sample shows the best performance, due to the larger electrochemical surface area, better hydrophily and smaller electron transfer impedance. No Cu-Ru interaction to improve the catalytic property was observed. This can be attributed to the formation of Cu and Ru nanograins rather than CuRu alloys, due to the repulsive force between Ru and Cu resulted by the positive mixing enthalpy. For Ni-Ru system with a mixing enthalpy close to 0, nanocrystalline NiRu alloys formed. Ru1Ni3 showed a high HER performance close to pure Ru due to the synergistic effect. Nb-Ru also shows synergistic interaction to improve the HER performance. Though the active area is smaller than pure Ru, Nb1Ru1 sample achieves an overpotential of 39 mV at a current density of 10 mA/cm2, lower than that of pure Ru. The main reason can be attributed to the formation of amorphous/crystalline heterojunction due to the negative mixing enthalpy. This promotes the charge transfer at the interface, leading to a smaller electrochemical impedance. The Nb1Ru1 sample also shows better stability for 100 h test with an increasing of only 6 mV of the overpotential at 10 mA/cm2.

Computational investigation of the interaction mechanisms of low‐density polyethylene (LDPE)/polyurethane and low‐density polyethylene (LDPE)/hexane systems as absorbents for oil spill remediation: A DFT study

AbstractThe escalating frequency of oil spill incidents and industrial wastewater discharges necessitates the development of effective remediation strategies. In this study, we conduct a comprehensive computational investigation using density functional theory (DFT) to elucidate the interaction mechanisms within polyethylene (PE) combined with polyurethane (PU) and hexane. The study focuses on adsorption energies, intermolecular interactions, miscibility, and electronic properties, providing a molecular‐level understanding crucial for designing advanced absorbent materials. The investigation reveals that the low‐density polyethylene/polyurethane (LDPE/PU) system exhibits significantly higher adsorption energies (−12.87 kcal/mol) compared to PE/hexane (−7.66 kcal/mol), indicating a robust binding affinity. This discrepancy underscores the superior performance of PE/PU as an absorbent material. The enthalpy results, with ∆H values of −55.75 kcal/mol for PE/hexane‐n‐hexadecane and −66.11 kcal/mol for PE/PU‐n‐hexadecane complexes at 298.15 K, support exothermic adsorption. The more exothermic ∆H for PE/PU indicates stronger interactions during oil absorption than PE/hexane. Additionally, Gibbs free energy change (∆G) values affirm a more favorable process for PE/PU, exhibiting a lower ∆G (−42.54 kcal/mol) compared to PE/hexane (−34.79 kcal/mol). Non‐covalent interaction (NCI) studies confirm the importance of van der Waals forces in both systems, validating their role in the adsorption process. Miscibility studies indicate limited interactions, with PE/PU showing positive enthalpy of mixing. Electronic study demonstrates PE/PU's higher energy gap of 9.19 eV, correlating with superior performance. This research contributes to the fundamental understanding of oil absorption processes and informs the design and optimization of environmentally sustainable and efficient oil‐absorbing materials for remediation applications.Highlights DFT explores polymeric systems, PE/PU and PE/hexane, for oil absorbent. PE/PU excels with −12.87 kcal/mol adsorption energy, surpassing PE/hexane (−7.66 kcal/mol). NCI validates van der Waals forces in both systems, crucial for effective adsorption. Miscibility studies reveal limited interactions. PE/PU's superior 9.19 eV energy gap signifies enhanced absorbent performance. PE/PU excels as an oil‐absorbent material, underlining its overall superiority.

Performance of Fluxgate Magnetometer with Cu-Doped CoFeSiB Amorphous Microwire Core.

In this study, we investigated the effects of Cu doping on the performance of CoFeSiB amorphous microwires as the core of a fluxgate magnetometer. The noise performance of fluxgate sensors primarily depends on the crystal structure of constituent materials. CoFeSiB amorphous microwires with varying Cu doping ratios were prepared using melt-extraction technology. The microstructure of microwire configurations was observed using transmission electron microscopy, and the growth of nanocrystalline was examined. Additionally, the magnetic performance of the microwire and the noise of the magnetic fluxgate sensors were tested to establish the relationship between Cu-doped CoFeSiB amorphous wires and sensor noise performance. The results indicated that Cu doping triggers a positive mixing enthalpy and the reduced difference in the atomic radius that enhances the degree of nanocrystalline formation within the system; differential scanning calorimetry analysis indicates that this is due to Cu doping reducing the glass formation capacity of the system. In addition, Cu doping affects the soft magnetic properties of amorphous microwires, with 1% low-doping samples exhibiting better soft magnetic properties. This phenomenon is likely the result of the interaction between nanocrystalline organization and magnetic domains. Furthermore, a Cu doping ratio of 1% yields the best noise performance, aligning with the trend observed in the material's magnetic properties. Therefore, to reduce the noise of the CoFeSiB amorphous wire sensor, the primary goal should be to reduce microscopic defects in amorphous alloys and enhance soft magnetic properties. Cu doping is a superior preparation method which facilitates control over preparation conditions, ensuring the formation of stable amorphous wires with consistent performance.

Enhancing Microstructural and Mechanical Properties of Ferrous Medium-Entropy Alloy through Cu Addition and Post-Weld Heat Treatment in Gas Tungsten Arc Welding.

This study investigates the impact of a high-entropy alloy filler metal coated with copper (Cu) and post-weld heat treatment (PWHT) on the weldability of a ferrous medium-entropy alloy (MEA) in gas tungsten arc welding. The addition of 1-at% Cu had an insignificant effect on the microstructural behaviour, despite a positive mixing enthalpy with other elements. It was observed that a small amount of Cu was insufficient to induce phase separation into the Cu-rich phase and refine the microstructure of the as-welded specimen. However, with an increase in the PWHT temperature, the tensile strength remained mostly consistent, while the elongation significantly increased (elongation of as welded, PWHT700, PWHT800, and PWHT 900 were 19, 43, 55 and 68%, respectively). Notably, the PWHT temperature of 900 °C yielded the most desirable results by shifting the fracture location from the coarse-grained heat-affected zone (CGHAZ) to base metal (BM). This was due to significant recrystallisation and homogenised hardness of the cold-rolled BM during PWHT. However, the CGHAZ with coarse grains induced by the welding heat input remained invariant during the PWHT. This study proposes a viable PHWT temperature (900 °C) for enhancing the weldability of cold-rolled ferrous MEA without additional process.

Impact of 3d TM elements on Cu segregation in CrCuTiV-based high entropy alloys and their mechanical properties

As Cu segregation is commonly known to negatively impact the comprehensive mechanical properties of Cu-containing high entropy alloys (HEAs), this study investigated the effects of transition elements on Cu segregation by adding X (X = Fe, Co, and Ni) into the precursor HEA, CrCuTiV. Cu segregation was observed in the cases of X = Fe or Co, but not for X = Ni or none (i.e., without element addition). Analysis indicates that Cu segregation results from the moderate valence electron concentration and positive mixing enthalpy in the X = Fe and Co alloys, which enhance the strength via solid solution strengthening but reduce the plasticity by promoting crack formation and propagation. In contrast, the precursor alloy CrCuTiV demonstrated an exceptional combination of yield strength (1456 MPa), plasticity (21.2%), and specific yield strength (218.3 kPa m3/kg). The study sheds light on the influence of similar 3d elements on Cu segregation and its impact on the mechanical properties, which may aid in the design and development of Cu-containing HEAs with optimized mechanical properties for various industrial applications.

Correlated microstructure and magnetic properties of Ce-substituted sintered Nd-Fe-B magnets: Role of various phases at triple junctions and grain boundaries

We report the investigation of the microstructure and magnetic properties of a sintered (Nd,Pr)30.3-xCexFebalM1.4B0.92 (in wt.%, xCe = 0) magnet with varying Ce substitutions (xCe = 2, 4, 6, 8). Structure analysis revealed a lattice contraction with Ce addition of up to xCe < 6, and the further increase in the Ce content to 6 wt.% led to a suppression in lattice contraction. The magnetic properties showed a notable deviation from the linear trend in coercivity and remanent magnetization for the magnets with Ce content of xCe > 4. The detailed microstructure analysis revealed that the magnets with xCe > 4 exhibit the REFe2 phase at the expense of a reduced mass fraction of a REOx phase, suggesting that the generation of the REFe2 phase suppressed the formation of the REOx phase. The site occupancy and valence state of Ce, analyzed using atomic-resolution energy dispersive spectroscopy and electron energy loss spectrometry, established that the suppressed lattice contraction is accompanied by a preferential site occupation of Ce from a random case to a 4f-centric site, along with a valence change from a mixed state to a trivalent state, inferring that Ce3+ ions are rejected from the 4g site of the RE2Fe14B phase to occupy the 4f site with a subsequently reduced number of Ce4+ ions due to the magneto-volume and chemical bonding effects. These findings display a new phase formation pathway of the REFe2 phase from a valence state perspective, i.e., the part of Ce4+ ions is considered to be rejected from the RE2Fe14B phase to nucleate the REFe2 phase, which is later found to separate chemically into RE-rich and Fe-rich regions. Further, a bi-layer interfacial structure, composed of Fe-rich and RE-rich layers, is formed in between the RE2Fe14B and the REFe2 phases due to the weak wettability of the REFe2 phase and a slightly positive mixing enthalpy between Ce and Fe. The deviation in magnetic properties is discussed based on the structural and microstructural results. These findings provide structural insight for developing low-cost and high-performance Ce-substituted Nd-Fe-B magnets.

Large Decrease in the Melting Point of Benzoquinones via High-n Eutectic Mixing Predicted by a Regular Solution Model.

Decreasing the melting point (Tm) of a mixture is of interest in cryopreservatives, molten salts, and battery electrolytes. One general strategy to decrease Tm, exemplified by deep eutectic solvents, is to mix components with favorable (negative) enthalpic interactions. We demonstrate a complementary strategy to decrease Tm by mixing many components with neutral or slightly positive enthalpic interactions, using the number of components (n) to increase the entropy of mixing and decrease Tm. In theory, under certain conditions this approach could achieve an arbitrarily low Tm. Furthermore, if the components are small redox-active molecules, such as the benzoquinones studied here, this approach could lead to high energy density flow battery electrolytes. Finding the eutectic composition of a high-n mixture can be challenging due to the large compositional space yet is essential for ensuring the existence of a purely liquid phase. We reformulate and apply fundamental thermodynamic equations to describe high-n eutectic mixtures of small redox-active molecules (benzoquinones and hydroquinones). We illustrate a novel application of this theory by tuning the entropy of melting, rather than the enthalpy, in systems highly relevant to energy storage. We demonstrate with differential scanning calorimetry measurements that 1,4-benzoquinone derivatives exhibit eutectic mixing that decreases their Tm, despite slightly positive enthalpies of mixing (0-5 kJ/mol). By rigorously investigating all 21 binary mixtures of a set of seven 1,4-benzoquinone derivatives with alkyl substituents (Tm's between 44 and 120 °C), we find that the eutectic melting point of a mixture of all seven achieves a large decrease in Tm to -6 °C. We further determine that the regular solution model shows improvement over an ideal solution model in predicting the eutectic properties for this newly investigated type of mixture composed of many small redox-active organic molecules.

Effect of Ag microalloying on the magnetic properties and microstructure of Fe–P–C amorphous alloys

In this work, a series of Fe80−xAgxP13C7 (x = 0, 0.4, 0.6, and 1.0 at. %) amorphous/nanocrystalline alloys with high saturation magnetization (Ms) and excellent bending ductility were produced through melt spinning. The effect of Ag microalloying on the thermostability, microstructure, and soft magnetic properties was then investigated in detail. We observed that the doping of Ag could increase the value of Ms, without significantly deteriorating the coercive force. The increase in Ms was due to the precipitation of α-Fe nanocrystals, caused by Ag, which had a positive mixing enthalpy and immiscibility with iron, resulting in phase decomposition and acting as sites for α-Fe nanocrystalline nucleation. This work offers a promising method for preparing soft magnetic materials with amorphous/nanocrystalline structures and good bending ductility, without annealing.

Structural heterogeneity, β relaxation and magnetic properties of Fe-Zr-B amorphous alloys with Si and Cu additions

Despite numerous studies on β relaxation of amorphous alloys, the relationship between structural heterogeneity and β relaxation and the effect on magnetic properties of Fe-based amorphous alloys is still unknow. In this work, the structure and magnetic properties of Fe84-xZr6B10Mx (M = Si, Cu; x = 0, 0.6, 1 at%) amorphous alloys were investigated. With the increase of Si content, the negative value of average chemical affinity (∆Hchem) of the alloys is increased, leading to the synergetic enhancement in structural heterogeneity and β relaxation. In addition to this, the increase of liquid-like regions (LLRs) reduces saturation magnetic flux density (Bs) and increases coercivity (Hc). However, the addition of Cu element decreases the negative value of ∆Hchem of the alloys, resulting in weakening of structural heterogeneity and β relaxation synergetically. The reduction of LLRs has resulted in increase in Bs. Moreover, Fe-Cu atom pairs with positive enthalpy of mixing increases the local density of quasi dislocation dipoles (QDDs), resulting in the increase of Hc.

Effects of Cu additions on microstructure and mechanical properties of as-cast CrFeCoNiCux high-entropy alloy

The influences of Cu additions on the microstructural evolution and room-temperature tensile properties of the as-cast CrFeCoNi were investigated in detail. The results revealed that the structure of the alloy changed from a FCC single-phase to FCC1 plus FCC2 dual-phase by adding Cu element. The FCC2 phase was determined to be Cu-rich phase existing in the inter-dendrite region, and its volume fraction increased with the increase of Cu additions. The formation of Cu-rich inter-dendrite was mainly ascribed to the liquid-phase separation induced by the large positive mixing enthalpy between Cu and other metallic elements. The yield and ultimate tensile strengths against the Cu content displayed a positive correlation due to the enhancement of short-range obstacles to dislocations slip, while the more significant superposition of stress field produced by the dislocation piling-ups at grain boundaries of Cu-containing high-entropy alloys led to a small fracture strain.

Structural evolution of MgO layer in Mg-based composites reinforced by Metallic Glasses during the SPS sintering process

The SPS sintering process is used in this study to create 50 wt % micro-sized spherical Fe-based metallic glass powders reinforced magnesium matrix composites (FMGP). The release of trace amounts of Cr in Fe-based metallic glass particles due to a positive mixing enthalpy with Mg not only improves the mechanical suitability of the interface between the metallic glass and the matrix but also contributes to the solution to the increasing problem of fracture toughness of the composite. Following the inclusion of metallic glass particles (50 wt %), the tensile strength (23%), yield strength (50%), and plasticity (more than 8%) were significantly increased. The Cr diffused to the interface and dissolved into the MgO in the form of replacement, forming the oxidation transition layer with the MgO and α-Mg at the interface and distributed among a discontinuous form, according to the analysis of the high-resolution transmission diagram of the composites and the calibration of the diffraction spots of the magnesium matrix at the interface. This enhances mechanical interface matching and transforms the composite's fracture process from inter-crystalline to quasi-destructive, increasing the material's fracture toughness. Once established, the model's first-principles computation and analysis are consistent with the test results.

Effects of Cu and Ag Elements on Corrosion Resistance of Dual-Phase Fe-Based Medium-Entropy Alloys.

The effect of adding elements to promote phase separation on the functional properties of medium-entropy alloys has rarely been reported. In this paper, medium-entropy alloys with dual FCC phases were prepared by adding Cu and Ag elements, which exhibited a positive mixing enthalpy with Fe. Dual-phase Fe-based medium-entropy alloys were fabricated via water-cooled copper crucible magnetic levitation melting and copper mold suction casting. The effects of Cu and Ag elements microalloying on the microstructure and corrosion resistance of a medium-entropy alloy were studied, and an optimal composition was defined. The results show that Cu and Ag elements were enriched between the dendrites and precipitated an FCC2 phase on the FCC1 matrix. During electrochemical corrosion under PBS solutions, Cu and Ag elements formed an oxide layer on the alloy's surface, which prevented the matrix atoms from diffusing. With an increase in Cu and Ag content, the corrosion potential and the arc radius of capacitive resistance increased, while the corrosion current density decreased, indicating that corrosion resistance improved. The corrosion current density of (Fe63.3Mn14Si9.1Cr9.8C3.8)94Cu3Ag3 in PBS solution was as high as 1.357 × 10-8 A·cm-2.

Atomic transport in amorphous Mo-Cu and Ta-Cu immiscible systems

Metastable binary systems with positive enthalpy of mixing have practically no diffusional data in literature. Experimental data on Cu diffusion in amorphous immiscible systems such as Mo-Cu and Ta-Cu are presented in this study. These studies were conducted in sputtered Ni/Mo1−xCux/Ni and Ni/Ta1−xCux/Ni tri-layers, where the nanocrystalline Ni layers acted as effective sinks for Cu atoms located in the amorphous layers. The secondary neutral mass spectrometry (SNMS) technique allowed us to observe the out-diffusion of Cu into the Ni sink layer at temperatures between 100 °C and 250 °C. Additionally, high-resolution transmission electron microscopy (HR-TEM) and energy dispersive spectroscopy (EDX) was used to characterize Mo-Cu and Ta-Cu layers. As a result of a coupled diffusion equation being solved for both amorphous (source) and polycrystalline (sink) layers, we were able to construct best-fit concentration profiles and calculate Cu diffusion parameters for both layers. We assumed bulk diffusion in amorphous films, while transport along moving grain boundaries was assumed in polycrystalline Ni layers. With this model, we were able to replicate the observed profile features at the amorphous/polycrystalline interface. Based on these evaluations, the pre-exponential factors and activation energies are 5 × 10−14 m2/s, 55.3 ± 12 kJ/mol in Mo-Cu and 1.2 × 10−12 m2/s, 76 ± 19 kJ/mol in Ta-Cu systems.

Thermodynamic and structural variations along the olivenite–libethenite solid solution

Abstract. Many natural secondary arsenates contain a small fraction of phosphate. In this work, we investigated the olivenite–libethenite (Cu2(AsO4)(OH)–Cu2(PO4)(OH)) solid solution as a model system for the P–As substitution in secondary minerals. The synthetic samples spanned the entire range from pure olivenite (Xlib=0) to libethenite (Xlib=1). Acid-solution calorimetry determined that the excess enthalpies are non-ideal, with a maximum at Xlib=0.6 of +1.6 kJ mol−1. This asymmetry can be described by the Redlich–Kister equation of Hex= Xoli⋅Xlib [A+B(Xoli−Xlib)], with A=6.27 ± 0.16 and B=2.9 ± 0.5 kJ mol−1. Three-dimensional electron diffraction analysis on the intermediate member with Xlib=0.5 showed that there is no P–As ordering, meaning that the configurational entropy (Sconf) can be calculated as -R(Xoliln⁡Xoli+Xlibln⁡Xlib). The excess vibrational entropies (Svibex), determined by relaxation calorimetry, are small and negative. The entropies of mixing (Sconf+Svibex) also show asymmetry, with a maximum near Xlib=0.6. Autocorrelation analysis of infrared spectra suggests local heterogeneity that arises from strain relaxation around cations with different sizes (As5+ / P5+) in the intermediate members and explains the positive enthalpies of mixing. The length scale of this strain is around 5 Å, limited to the vicinity of the tetrahedra in the structure. At longer length scales (≈15 Å), the strain is partially compensated by the monoclinic–orthorhombic transformation. The volume of mixing shows complex behavior, determined by P–As substitution and symmetry change. A small (0.9 kJ mol−1) drop in enthalpies of mixing in the region of Xlib=0.7–0.8 confirms the change from monoclinic to orthorhombic symmetry.

Effect of Cu content on the microstructure and mechanical properties of FeNiMnCuxAl0.1Ti0.1 (x = 0.5,1.0 and 1.5) high entropy alloy system

Investigation of the microstructure and mechanical properties of FeNiMnCuxAl0.1Ti0.1 (x = 0.5, 1.0, & 1.5) high entropy alloys (HEAs) with increasing Cu content has been carried out. As-cast alloys were subjected to solutionization treatment at 1000 °C for 24 h to achieve a single-phase and then cold rolled to a thickness reduction of 85%. As-cast HEAs consist of two FCC phases, i.e., Fe-rich dendritic phase & Cu-rich interdendritic FCC phase and a small number of intermetallic particles. The presence of these phases was correlated using ThermoCalc calculations, X-ray diffraction (XRD), and scanning electron microscopy (SEM) studies. Phase separation is due to the positive enthalpy of mixing of Cu and Fe elements in the alloy. After the heat treatment, the Cu-rich inter-dendritic phase dissolved and formed a single FCC phase. The yield strength and tensile strength of the cold-rolled HEAs are found to increase with the increase in Cu content. Tensile strength of the HEAs increases from 708 to 900 MPa with the increase of Cu content from 0.5 to 1.5, respectively. Strain hardening was observed in the alloys before failure due to the hindrance of dislocation motion by the presence of the massive number of dislocations accumulated during cold rolling and from the intermetallic particles.

Role of mixing thermodynamic properties on the Soret effect.

We demonstrate that the modified Kempers model, a recently developed theoretical model for the Soret effect in oxide melts, is applicable for predicting the composition dependence of the Soret coefficient in three binary molecular liquids with negative enthalpies of mixing. We compared the theoretical and experimental values for water/ethanol, water/methanol, water/ethylene glycol, water/acetone, and benzene/n-heptane mixtures. In water/ethanol, water/methanol, and water/ethylene glycol, which have negative enthalpies of mixing across the entire mole fraction range, the modified Kempers model successfully predicts the signchange of the Soret coefficient with high accuracy, whereas, in water/acetone and benzene/n-heptane, which have composition ranges with positive enthalpies of mixing, it cannot predict the signchange of the Soret coefficient. These results suggest that the model is applicable in composition ranges with negative enthalpies of mixing and provides a framework for predicting and understanding the Soret effect from the equilibrium thermodynamic properties of mixing, such as the partial molar volume, partial molar enthalpy of mixing, and chemical potential.

Microstructure and mechanical properties of as-cast (CuNi)100−xCox medium-entropy alloys

Microstructure and mechanical properties of non-equiatomic (CuNi)100−xCox (x=15, 20, 25 and 30, at.%) medium-entropy alloys (MEAs) prepared by vacuum arc-melting were investigated. Results show that all the as-cast MEAs exhibit dual face-centered cubic (fcc) solid-solution phases with identical lattice constant, showing typical dendrite structure consisting of (Ni, Co)-rich phase in dendrites and Cu-rich phase in inter-dendrites. The positive enthalpy of mixing among Cu and Ni-Co elements is responsible for the segregation of Cu. With the increase of Co content, the volume fraction of (Ni, Co)-rich phase increases while the Cu-rich phase decreases, resulting in an increment of yield strength and a decrement of elongation for the (CuNi)100−xCox MEAs. Nano-indentation test results show a great difference of microhardness between the two fcc phases of the MEAs. The measured microhardness value of the (Ni, Co)-rich phase is almost twofold as compared to that of the Cu-rich phase in all the (CuNi)100−xCox MEAs. During the deformation of the MEAs, the Cu-rich phase bears the main plastic strain, whereas the (Ni, Co)-rich phase provides more pronounced strengthening.

Interfacial Characteristics and Mechanical Properties of CuSn15/HT250 Prepared via Additive Manufacturing Combined with an Inconel 718 Interlayer

Tremendous discrepancies in the positive enthalpy of mixing and the coefficient of thermal expansion emerge between the copper alloy and the gray cast iron, accounting for numerous pores and cracks in the interfacial region during the metallurgical bonding process. To enhance the interfacial bonding properties of these two refractory materials, laser-directed energy deposition was applied to fabricate the CuSn15 alloy on the HT250 substrate; meanwhile, Inconel 718 alloy, acting as the interlayer, was added to their bonding region. Firstly, the effect of the deposition process on deposition layer quality was investigated, and then the effects of Inconel 718 addition on the interfacial morphology, element distribution, phase composition, bonding strength, microhardness were studied. The results showed that a substrate (HT250) without cracks and a deposition layer (CuSn15) free from pores could be obtained via parameter optimization combined with preheating and slow cooling processes. Adding the Inconel 718 interlayer eliminated the interfacial pores and cracks, facilitated interfacial element (Cu, Fe, Ni) diffusion, and enhanced interfacial bonding strength. The interface between HT250 and CuSn15 mainly contained the FeSn2 phase, while the interfaces of the CuSn15-Inconel 718 and the Inconel 718-HT250 were mainly composed of the Ni3Sn4, Cr5Si3, FeSi2, Cr7C3. The microhardness and fracture morphology of the interfacial region in the samples with and without the interlayer were also studied. Finally, CuSn15 was also successfully deposited on the surface of the HT250 impeller with large size and complex structure, which was applied in the root blower.

Microstructural Stability of the CoCrFe2Ni2 High Entropy Alloys with Additions of Cu and Mo

New High Entropy Alloys based on the CoCrFe2Ni2 system have been developed by adding up to 10 at. % of Cu, Mo, and Cu + Mo in different amounts. These alloys showed a single face-centred cubic (FCC) structure after homogenization at 1200 °C. In order to evaluate their thermal stability, aging heat treatments at 500, 700, and 900 °C for 8 h were applied to study the possible precipitation phenomena. In the alloys where only Cu or Mo was added, we found the precipitation of an FCC Cu-rich phase or the µ phase rich in Mo, respectively, in agreement with some of the results previously shown in the literature. Nevertheless, we have observed that when both elements are present, Cu precipitation does not occur, and the formation of the Mo-rich phase is inhibited (or delayed). This is a surprising result as Cu and Mo have a positive enthalpy of mixing, being immiscible in a binary system, while added together they improve the stability of this system and maintain a single FCC crystal structure from medium to high temperatures