It is still highly desired to develop efficient, resource-abundant and inexpensive electrocatalysts to improve the sluggish kinetics of oxygen evolution reaction (OER) in electrochemical water splitting systems. In this work, the large-area ultrathin (2.52 nm thick) Ce-doped La ₂ O ₃ nanofilms were developed via a facile and reliable ionic layer epitaxy method with different Ce content. The ultrathin Ce-doped La ₂ O ₃ nanofilm with optimum composition of La _1.22 Ce _0.78 O ₃ exhibited an excellent OER performance with a very low overpotential of 221 mV at 10 mA cm ⁻² and a small Tafel slope of 33.7 mV dec ⁻¹ . A remarkable high mass activity of 6263.2 A g ⁻¹ was also obtained from ultrathin La _1.22 Ce _0.78 O ₃ nanofilm at the overpotential of 221 mV. Such a high mass activity was three orders of magnitude higher than state-of-the-art commercial IrO ₂ powders (3.8 A g ⁻¹ ) and more than 30 times higher than La ₂ O ₃ nanofilm (196.7 A g ⁻¹ ) without Ce doping at the same overpotential. This high mass activity was even significantly higher than other recently reported typical OER catalysts. The substantial OER performance gain by the Ce doping was attributed to the improved conductivity and electrochemical active surface areas of nanofilms as a result of favorable tuning on the charge transfer and electronic structures. This work provides a promising approach to develop high-performance two-dimensional (2D) electrocatalysts by effective heteroatom doping strategy.

Al–Cu3–Si–Mg wheel hubs were prepared by molten metals die forging (MMDF). The as-cast microstructure morphology of the alloy formed under pressure was observed by optical microscope and scanning electron microscope. The granular phases θ (Al₂Cu) were distributed in the α–Al grains, and the cross phases β (Mg₂Si) grew near the grain boundary in the α–Al grains. Polygonal compounds φ (Al_xTi₉La₂Ce₆Cu) and irregular eutectic structures mainly formed by (α + Al₂Cu) eutectic formed under non-equilibrium solidification were found at the grain boundaries. Q (Al₅Cu₂Mg₈Si₆) phases were found at the intersection of grain boundaries. With the increase of pressure, the proportion of irregular eutectic structures (α + Al₂Cu) decreased from 7.3% to 5.2%. Combined with microstructure analysis and thermodynamic software analysis, the non-equilibrium solidification path was determined as follows: L → L + φ → L + α + φ → L + (α + e) + α + φ → (α + e) + Q + α + φ → (α + e) + Q + [α + θ] + φ → (α + e) + Q + [α + θ + β] + φ

In this study, the heat treatment process of a high-chromium cast iron (HCCI) alloy prepared via 128 MPa squeeze casting at different subcritical quenching temperatures was investigated. The results showed that subcritical heat treatment can change the martensite content, the carbide type and size of the squeeze casting HCCI microstructure. Furthermore, it was revealed that the subcritical quenching heat treatment can improve the hardness of the liquid-forged HCCIs. When the quenching temperature increased from 500 °C to 530 °C, the hardness of the alloy increased significantly, reaching a maximum value of 57 HRC. Thereafter, if the temperature continued to rise to 630 °C, the hardness decreased rapidly. For impact toughness, when the quenching temperature was 500 °C, the toughness of alloy increased by 0.9 J/cm² than that of the no heat treatment group. If the quenching temperature continued to increase, the toughness was reduced. Taking hardness and toughness into account, the microstructure evolution diagram of the optimal process-500 °C subcritical quenching process was established, various characterisation techniques were used to gain insights into the optimal heat treatment process. Compared with high temperature heat treatment, subcritical heat treatment can improve the performance of the HCCI alloy and reduce costs.

Al-Cu3-Si-Mg alloy prepared by molten metal die forging (MMDF) under a pressure of 118 MPa was solution-treated at different temperatures and times, and the evolution behavior of the non-equilibrium eutectic in the microstructure was observed using an optical microscope and scanning electron microscope. The results show that the initial solidification structure of Al-Cu3-Si-Mg before solution treatment consists of irregular eutectic (α+Al₂Cu), strip compound Q (Al₅Cu₂Mg₈Si₆), polygonal phase φ(Al_xTi₉La₂Ce₆Cu), spherical particle θ(Al₂Cu) and cross-shaped β(Mg₂Si) near the grain boundary. After solution treatments, the irregular eutectic at grain boundaries is dissolved. In the solution temperature range of 480 °C~510 °C, the irregular eutectic fraction decreased with the increase in solution temperature, and the grain size of other compounds such as Q (Al₅Cu₂Mg₈Si₆) and the spherical particle phase θ(Al₂Cu) also showed a decreasing trend. However, all phases do not change significantly with the increase in solution temperature when the solution temperature is between 510 °C and 540 °C. It was determined experimentally that the holding time of 30 min at each temperature is the solution limit. Based on the experimental results, a dissolution model of intergranular irregular eutectic was established as ${\displaystyle \frac{dE}{dt}}=-{\displaystyle \frac{4P\sqrt{\pi tD}+2rk}{kPD}}$.

In this paper, the supersaturated solid solution of Al-Cu3-Si-Mg alloy prepared by molten metal die forging (MMDF) was used as the research object. The formation and evolution of precipitates during aging treatment were investigated through experiments at different temperatures and times, and the precipitation mechanisms and sequences of various precipitates were analyzed. The main precipitated phases formed in the supersaturated solid solution of the Al-Cu3-Si-Mg alloy after aging treatment are θ(Al₂Cu), θ′(Al_3.6Cu₂), γ′(Al_0.63Mg_0.37), and η′(Cu, Si). Based on XRD and TEM analysis under different aging treatment conditions, the precipitation sequence is determined as follows: SSS → GP₀ → GP₀ + γ′ → GP₀ + (γ′ + γ) + θ″ + η′ → (γ′ + γ) + (θ″ + θ′) + (η′ + η) → (γ′ + γ) + (θ + θ′) + (η′ + η) → (γ′ + γ) + (θ + θ′) + η → γ + θ + η. After aging treatment at 165–185 °C for 4 h, chain-like θ(Al₂Cu) precipitates are discontinuously distributed at the α-Al grain boundaries, and disc-shaped θ′(Al_3.6Cu₂) and θ″(Al₂Cu) phases mainly precipitate within the grains. When the temperature exceeds 185 °C, the chain-like θ(Al₂Cu) precipitates at the grain boundaries gradually become continuous, and the fraction increase from 1.5% to 15.2%. The amount of the θ(Al₂Cu) phase in the grains increases from 2 to 6, and the size of θ′(Al_3.6Cu₂) decreases obviously. After aging treatment at 185 °C for 5–6 h, the chain-like θ(Al₂Cu) precipitates become more continuous, and the fraction continues to increase from 32.1% to 52.6%. The effect of chain-like precipitates at grain boundaries on the mechanical properties of the matrix is opposite to the strengthening contribution of dispersed intragranular precipitates. When the aging condition exceeds 185 °C × 5 h, the excessive formation of chain-like grain boundary precipitates causes both the strength and hardness of the alloy to show a decreasing trend.