Rare-earth phosphates (REPO₄) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiC_f/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO-MgO-Al₂O₃-SiO₂ (CMAS). Nevertheless, relatively high thermal conductivity of REPO₄ becomes the bottleneck for their practical application. In this work, novel xenotime‑type high entropy (Dy_1/7Ho_1/7 Er_1/7Tm_1/7Yb_1/7Lu_1/7Y_1/7)PO₄ (HE (7RE_1/7)PO₄) has been designed and synthesized for the first time to solve this issue. HE (7RE_1/7)PO₄ with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 °C and good chemical compatibility with SiO₂ up to 1400 °C. In addition, the thermal expansion coefficient (TEC) of HE (7RE_1/7)PO₄ (5.96 × 10^-6/°C at room temperature to 900 °C) is close to that of SiC-CMCs. What’s more, the thermal conductivity of HE (7RE_1/7)PO₄ (from 4.38 W·m^-1 K^-1 at 100 °C to 2.25 W·m^-1 K^-1 at 1300 °C) is significantly decreased compared to those of single-component REPO₄ with the minimum value ranging from 9.90 to 4.76 W·m^-1·K^-1. These results suggest that HE (7RE_1/7)PO₄ has the potential to be applied as T/EBC material for SiC-CMCs in the future.

Inconel 718 Ni-based polycrystalline superalloys exhibit excellent mechanical properties, while the type and nature of the grain boundaries are important for their corrosive properties. The effect of grain boundaries on initial oxidation is decisive for degradation, and the conventional method has difficulty revealing nanoscale grain boundaries with different angles. Atomic-scale initial oxidation on different boundaries in Inconel 718 alloys was systematically investigated by in situ environmental transmission electron microscopy (ETEM) with high spatial and temporal resolution. This study reveals the mechanism of intergranular oxidation in polycrystalline alloys and provides a new idea for improving the oxidation resistance of polycrystalline materials.

The service performance of single crystal blades depends on the crystal orientation. A grain selection method assisted by directional columnar grains is studied to control the crystal orientation of Ni-based single crystal superalloys. The samples were produced by the Bridgman technique at withdrawal rates of 100 μm/s. During directional solidification, the directional columnar grains are partially melted, and a number of stray grains are formed in the transition zone just above the melt-back interface. The grain selected by this method was one that grew epitaxially along the un-melted directional columnar grains. Finally, the mechanism of selection grain and application prospect of this grain selection method assisted by directional columnar grains is discussed.

By combined numerical simulations and unidirectional solidification experiments, the temperature field evolution of seeding for nickel-based single-crystal superalloys was studied. At the steady state, the position of the mushy zone in the seed moves down as the melt is poured into the mold. The holding time required for the temperature field of the seed segment to reach the steady state is less for seeds with casting than for those without casting. The holding time required to completely eliminate randomly oriented broken dendrites in the melt-back zone is much longer than that required for the temperature field to achieve a steady state. A short incubation stage is required before the temperature field evolution process; then, the migration rate of the isotherm gradually increases until it is the vicinity of the withdrawal rate. Finally, the effect of temperature field evolution on the formation of stray grains in seed segments is discussed.

Metal carbides (MCs) serve as essential strengthening phases in nickel-based superalloys, so the decomposition of MCs during high-temperature creep is regarded as detrimental to the mechanical properties and service life of these alloys. However, detailed investigations of the MC decomposition process at the microscale remain limited. In this study, the microstructure of MCs (where M is a mixture of Ti and Ta) in a nickel-based superalloy was characterized using aberration-corrected scanning transmission electron microscopy. The MCs exhibit a spherical core–shell structure, with Ta enrichment in the shell and Ti segregation in the core. Moreover, a high density of Cr-rich stacking faults, accompanied by Cr-rich M₂₃C₆ precipitates at their terminations, was identified in the Ti-rich cores, suggesting that these defects may be closely associated with the decomposition of MCs. This study may further expand the fundamental understanding of the interactions between defects and carbide properties.