The intermetallic phase control is a promising strategy to optimize the physicochemical properties of ordered intermetallic compounds and engineer their performance in various (electro)catalytic ...reactions. However, the intermetallic phase‐dependent catalytic performance is still rarely reported because of the difficulty in synthesizing ordered intermetallics with precisely controlled phase structures at atomic level, especially having ordered mesoscopic structure/morphology. Here, we successfully reported a precise synthesis of two phase‐pure mesoporous intermetallic gallium‐platinum (meso‐i‐Ga‐Pt) nanoparticles, including meso‐i‐Ga3Pt5 with an orthorhombic space group and meso‐i‐Ga1Pt1 with a non‐symmorphic chiral cubic space group. The intermetallic phase control of ordered meso‐i‐Ga‐Pt nanoparticles was realized by carefully tuning the induced Ga salts with different anions that optimized the free energies during the synthesis. The intermetallic phase‐dependent catalytic performance of ordered meso‐i‐Ga‐Pt was systematically evaluated for oxygen reduction reaction (ORR) electrocatalysis, with completely opposite catalytic performance in alkaline media. Interestingly, ordered meso‐i‐Ga1Pt1 catalyst with chiral atomic arrangements disclosed unexpected high ORR activity and stability with 5.9 and 3.2 enhancement factors in mass activity compared to those of meso‐i‐Ga3Pt5 and commercial Pt/C.
Ordered mesoporous intermetallic Ga‐Pt nanoparticles, including Ga3Pt5 with an orthorhombic phase and Ga1Pt1 with a non‐symmorphic chiral cubic phase, were successfully synthesized by a concurrent template method in presence of different Ga sources. The resulting mesoporous intermetallic Ga‐Pt disclosed remarkably phase‐dependent catalytic performance in oxygen reduction electrocatalysis, with unexpected high activity of Ga1Pt1 compared to the Ga3Pt5 counterpart.
The corrosion behaviour of a recently developed Al-Li-Cu-Mg alloy thick plate was investigated using correlative immersion testing in 3.5% NaCl solution with analytical electron and ion microscopy. ...Intergranular corrosion was observed along grain boundaries and the particle-matrix interface of Al7Cu2(Fe, Mn) and Al20Cu2Mn3 phases from 7 min of immersion. The Li-containing Al7Cu2(Fe, Mn) phases are electrochemically more active and susceptible to de-alloying than the Al20Cu2Mn3 phases. Intergranular T1 (Al2CuLi) precipitates are attacked via selective dissolution of Li and Al. In contrast to previous observation, the dissolution rates of T1 precipitates and the adjacent alloy matrix are almost the same.
•Clusters of Al7Cu2(Fe, Mn) phase act as preferred sites for corrosion initiation.•The Li-containing Al7Cu2(Fe, Mn) phases are more active than Al20Cu2Mn3 phases.•Corrosion along the particle-matrix interface is facilitated by galvanic coupling.•Intermetallic particles are de-alloyed via selective dissolution of Li and Al.•T1 (Al2CuLi) phases are dissolved at a similar rate as the adjacent alloy matrix.
Although ionic liquid electrolytes (ILs) are environmentally unfriendly, they are the most common electrolyte used in aluminum-ion batteries (AIB). Aqueous electrolytes offer a more sustainable ...alternative, but problem with oxide passivating barrier on Al surface becomes more profound. Recently, a new sub-class of aqueous electrolytes, water-in-salt (WIS) of (AlCl3·6H2O), has been considered, but experimental validation of the behavior of the Al electrode over cycling is required. This work investigates aluminum/graphitic cells using WIS electrolytes with a mass ratio of salt to water of 4, 8, and 12 and finds that they show similar trends in cycling performance. The degradation observed over cycling has been attributed to the formation of a detrimental solid electrolyte interphase (SEI) layer on the Al surface. It was found that WIS 4 increased Al corrosion, resulting in a slightly higher capacity and longer cycling life. Metallurgical observation showed that the Al matrix has a tendency to initiate corrosion around Al3Fe intermetallic phases in both WIS and ILs. This implies that the presence of Al3Fe particles allows the electrolyte to break the oxide barrier and access the bulk Al. These results suggests that metallurgical treatments are important to enhance the electrochemical performance of AIB.
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•Al anode are examined in cell with WIS electrolyte from metallurgical aspects.•SEI layer formed on Al surface is detrimental for electrochemical performance.•Al3Fe phase is a preferential site for electrolytes to accesses the Al bulk.•Al treatment with metallurgical method is crucial to improve the cell performance.
In this work, we present the results of the thermodynamic assessment of two equiatomic refractory High Entropy Alloys (HEAs), namely TaMoCrTiAl and NbMoCrTiAl, in the temperature range between 700 ...and 1500 °C. Particular attention is paid on the constitution of the intermetallic phases stable in these alloy systems. Thermodynamic calculations were performed using a self-developed thermodynamic database based on the CALPHAD (Calculation of Phase Diagram) approach. The details of the thermodynamic modelling and particular characteristics of the relevant phases within the Ta-Nb-Cr-Ti-Al system are presented. To verify the new database, the phase formation and stability of both quinary alloys in near-equilibrium conditions were studied experimentally by utilizing scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) as well as X-ray powder diffraction (XRD). Both equiatomic alloys reveal a complex microstructure including several intermetallic phases at intermediate temperatures. The alloy NbMoCrTiAl consists of an ordered B2 phase, Al(Mo, Nb)3 and two polytypes (C14 and C15) of the Cr2Nb Laves phase. Precipitations of Cr2Ta Laves phase (C14, C15 and C36-type) in the B2 matrix were observed in the alloy TaMoCrTiAl. Based on the results of thermodynamic calculations, it was concluded that: (i) Nb stabilizes the AlMo3 A15 phase in the alloy NbMoCrTiAl, (ii) Al and Ti play a crucial role in the formation of the ordered B2 phase in both alloys and (iii) the concentrations of Cr and/or Ta/Nb should be dramatically reduced to decrease the Laves phase volume fraction.
•Development of a thermodynamic database based on the CALPHAD approach for the Ta-Nb-Mo-Cr-Ti-Al system.•The phase formation and stability of both quinary alloys in near-equilibrium conditions were studied experimentally Al and Ti play a crucial role in the formation of the ordered B2 phase in both alloys.•Nb stabilizes the AlMo3 A15 phase in the alloy NbMoCrTiAl.•The concentrations of Cr and/or Ta/Nb should be dramatically reduced to decrease the Laves phase volume fraction.
The Co-Ta-V and Co-Nb-V ternary systems are investigated in a search for L12-ordered γ′ precipitation, based on recent computational predictions of stable γ+γ′ microstructures. Four alloys with ...nominal (at. %) composition Co-6Ta-6V, Co-5.4Ta-6.6V-xNi (x = 0 and 10), and Co-6Nb-6V are arc-melted, homogenized at 1250 °C, and aged at 900 °C for 2, 16 and 64 h. Nanometric, cuboidal γ′ precipitates within a fcc-γ matrix are discovered in the Co-Ta-V system after aging for 2 h, and in the Co-Nb-V system after cooling from homogenization. The compositions of these two new γ′-phases, as measured via atom probe tomography, are Co3(Ta0.76V0.24) and Co3(Nb0.65V0.35), respectively. Upon aging at 900 °C, the γ′ precipitates coarsen, dissolve and transform to lamellar C36-Co3(Ta,V) and needle-shape D019-Co3(Nb,V), measured as Co3(Nb0.81V0.19) by APT, respectively. This shows that these ternary γ′ phases are metastable and points to the need for their stabilization via additional alloying elements.
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Although Mg−Al−RE (RE: rare earth) alloys have significant weight saving potential in automotive industries, their applications were interrupted due to their unsatisfactory mechanical performance. ...Intermetallic phases in structural magnesium (Mg) alloys are of practical significance for being able to optimize their microstructures for specific applications. Here we report a new alloy design concept that can develop an alloy for a given system with out-standing mechanical performance and low cost. Such designed alloy exhibits even more excellent strength-ductility balance and cost creep-performance than the commercial/experimental die casting Mg alloys and A380 aluminum alloy. The alloy design concept used in this work is based on strictly controlling intermetallic phase components according to modifying alloy's compositions. Such developed alloy has huge potential to be widely applied in automotive powertrain components acted as the alternative of Mg alloys and even aluminum alloys.
•A new intermetallic phase was found in a high-pressure die-cast Mg-Al-La system.•Combination of various simulations and experimental results was adopted.•Strengthening mechanisms of the new intermetallic phase were revealed.•Faults were identified based on atomic resolution HAADF-STEM observations.•The newly developed alloy exhibits significantly excellent mechanical properties.
The tendency of AA3003 towards localized corrosion is one of the most challenging issues for its broader use. Intermetallic phases (IMPs) in AA3003 play dual contradictory roles: strengthening effect ...and initiating pitting. Solving this contradiction contributes to improvement of corrosion resistance and fully utilizing the potential of materials. Herein, a superhydrophobic surface with IMPs in-situ pinning effect was fabricated via a chemical etching approach combined with stearic acid (STA) modification. Thus, IMPs can provide sound support for the superhydrophobic surface and meanwhile eliminate the adverse effect of promoting localized corrosion. Formation mechanism of etching structure was attributed to the synchronous chemical reaction of IMPs and matrix phases in the etchant. Further modification with STA changed mico/nano hierarchical surface from hydrophilicity to superhydrophobicity. The as-prepared surface exhibited a maximum static contact angle of ~169° and a sliding angle of ~1°, possessing excellent superhydrophobicity. Besides, the wettability, self-cleaning, chemical stability, mechanical durability, and corrosion resistance properties of the superhydrophobic surface were comprehensively investigated. The results showed that the corrosion inhibition efficiency exceeded 99% in 3.5 wt% NaCl solution. The pinning direction of IMPs in superhydrophobic surface influenced its properties. It is anticipated that the construction of superhydrophobic surfaces will broaden its promising applications.
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•A superhydrophobic surface with intermetallic phases (IMPs) in-situ pinnning effect was prepared.•IMPs can strengthen superhydrophobic structure and inhibit localized corrosion.•It exhibited remarkable water-repellent and self-cleaning properties.•Pinning direction of IMPs influences its chemical stability, mechanical durability, and corrosion resistance.
Microstructures and mechanical properties of a Mg−8Gd−3Yb−1.2Zn−0.5Zr (wt%) alloy have been investigated. The dominant intermetallic phases in the as-cast sample are Mg5RE (RE = Gd,Yb) phase, ...14H-type long-period stacking ordered (LPSO) phase, and Mg2Zn2RE (W) phase and ordered Mg12RE phase. Furthermore, the ordered Mg12RE phase generally coexists with the W phase following an orientation relationship as 01¯1w//2¯30Mg12RE, and (1¯11)w//(001)Mg12RE. After extrusion, the microstructure is consisted of un-recrystallized regions along with a small part of fine dynamically recrystallized (DRXed) regions. Simultaneously, the coarse Mg5RE, W and Mg12RE particles were disintegrated and mainly distribute at extrusion stringers while the fine LPSO plates mainly distribute in un-recrystallized regions. Moreover, amounts of nanoscale Mg5RE particles were dynamically precipitated in DXRed regions. Then, the as-extruded Mg−8Gd−3Yb−1.2Zn−0.5Zr alloy exhibits clearly higher strength than the classic rare-earth-containing magnesium alloys with comparative or even much higher rare earth content at both room temperature and high temperatures. The dominant strengthening mechanism was finally revealed as precipitation/dispersion strengthening.
•Microstructures and mechanical properties of a Mg−Gd−Yb−Zn−Zr alloy were studied.•Four dominant intermetallic phases namely Mg5RE, 14H LPSO, W, and Mg12RE, were found.•W always coexists with Mg12RE following 01¯1w//2¯30Mg12RE, and (1¯11)w//(001)Mg12RE.•Amounts of nanoscale Mg5RE particles dynamically precipitated in the DRXed regions.•This alloy exhibits obviously high strength with UTS of 425 MPa and YS of 413 MPa.
A new high pressure die-cast (HPDC) magnesium (Mg) alloy with high performance, namely Mg–4Al–4Gd–0.3Mn (AGd44), was developed by using the heavy rare earth element Gd. The microstructures under ...as-cast and peak-aged states were investigated in detail, especially by transmission electron microscopy (TEM). The studied alloy has finer cells although clearly less intermetallic phases than the conventional Mg–Al–RE based alloys. However, the structures of intermetallic phases in AGd44 alloys are fairly complicated. Most of the blocky phases are Al2Gd while minor of them are Al10Gd2Mn7 and Al8GdMn4, and the petaloid and the lamellae phases are Al2Gd and Mg17Al12, respectively. Peak-aging treatment can further enhance the yield strength of the studied alloy, which is mainly attributed to more coarse lamellae Mg17Al12 phase and fine lath-shaped Mg17Al12 precipitate appearing at cell boundaries and in α-Mg cells, respectively. Furthermore, the relatively smaller cells as well as the novel intermetallic phase component contribute to the more excellent strength-ductility balance of the studied alloy than the commercial/experimental HPDC Mg–Al-based alloys. The results provide new insight into developing HPDC Mg alloys with high mechanical properties.
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Ti-15Zr-xCu (3 ≤ x ≤ 7, wt.%) novel antibacterial and antibiofilm alloys with competitive mechanical properties, biological responses and corrosion resistance were designed and ...fabricated. Annealing heat treatment on Ti-15Zr-7Cu (TZC-7A), after holding for 2 h at slightly above their beta transus temperature (BTT) ensured their tensile strength (UTS), yield strength (YS) and hardness (HRV) were improved by 31.2%, 20% and 12.3% respectively compared to the control without Cu, Ti-15Zr (T-15ZA). Although the 3 wt.% Cu alloy displayed the highest elongation (26%), the TZC-7A alloy also possessed a good ductility. Presence of evenly dispersed Ti2Cu and Zr2Cu Cu-rich intermetallic phases formed as interwoven and alternating lamellae within the α + β matrix as a result of Cu addition, as revealed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These greatly contributed to their strengthening and bactericidal properties. Over 98% antibacterial effect against E. coli and S. aureus have been imparted, coupled with excellent biofilm inhibition. Potentiodynamic polarization curves showed that the TZC-7A alloy possessed higher corrosion resistance than commercially pure titanium, cp-Ti; contact angle test revealed enhanced hydrophilicity; while confocal laser scanning microscopy (CLSM) and cell counting kit (CCK-8) assays also displayed drastically lowered bacterial adhesion rate with comparatively no cytotoxicity. Cell attachment on all alloys was similar but the best spread was obtained on TZC-7A after 24 h. The developed alloy has good potential as an antibacterial implant material with combination of optimized properties.
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