In order to evaluate the increase in the flexural strength of a 3D braided C/SiC composite comprised with a thin pyrolytic carbon (PyC) interlayer (TI C/SiC) under a load of 60 MPa with an amplitude of ±20 MPa at an oxygen partial pressure of 8000 Pa, the effect of temperature, oxidation and stress value on the length change in the sample, fracture behavior, residual flexural strength and fracture morphology were studied up to 1500 °C. It was found that the gauge length change behaviors of the material are related to (i) the positive damage of the thin interlayer and (ii) to the negative damage of the C phase. The most serious damage of TI C/SiC under 60 ± 20 MPa occurs in an oxygen partial pressure of 17,000 Pa at 1300 °C. When the oxygen partial pressure and/or the temperature are reduced, the positive C phase damage is relieved. In the case that the oxygen partial pressure, temperature and stress increase, the negative C phase damage is facilitated. The oxidation mechanism of the C phase is controlled by the inward diffusion of oxygen from the sample surface to the center; however, a higher stress is considered to change the oxygen diffusion mechanism by increasing the reaction of the C phase, with oxygen causing a widening of microcracks.

The pre-sintered preform (PSP) is an advanced technology for repairing the Ni-based superalloy blade in a turbine. In general, boron is added to the Ni-based superalloys in small quantities (1.0 wt.%) on the microstructure evolution and mechanical properties in Ni-based superalloys for the PSP application is rarely studied. The variety, composition and evolution of the precipitates during solution heat treatment in the alloy with high B content were determined by EBSD, EPMA and SEM. The results indicate that Cr, W and Mo-rich M₅B₃ type borides precipitate from the matrix and its area fraction reaches up to about 8%. The area fraction of boride decreases with the prolonging of solution time and the increase of temperature higher than 1120 °C. The borides nearly disappear after solution treatment at 1160 °C for 2 h. The redissolution of boride and eutectic results in the formation of B-rich area with low incipient melting (about 1189 °C). It can bond metallurgically with the blade under the melting point of the blade, which decreases the precipitation of harmful phases of the blade after PSP repairing. The microhardness within the grain in the PSP work-blank first decreases (lower than 1160 °C) and then increases (higher than 1185 °C) with the increase of solution heat treatment temperature due to the dissolving and precipitation of borides. The tensile strength of the combination of PSP work-blank and Mar-M247 matrix at room temperature after solution treatment is related to the area fraction of boride, incipient melting and the cohesion between PSP work-blank and Mar-M247 matrix.

The effects of Ru on Re segregation and low-cycle fatigue (LCF) behavior were investigated in two model single-crystal superalloys, Ni-8.5Al-4Re and Ni-8.5Al-4Re-2Ru (wt.%). Microstructural morphology, elemental distribution, fatigue deformation behavior, and dislocation structures were systematically compared, and density functional theory (DFT) calculations were performed to examine the associated atomic and electronic effects. The results show that Re segregates at the γ′/γ interface in both alloys, whereas the addition of 2 wt.% Ru reduces the extent of interfacial Re segregation. The Gibbsian interfacial excess of Re decreases from 18.19 ± 1.75 to 11.42 ± 0.01 atom nm⁻², while the maximum interfacial Re concentration ratio decreases from 1.36 ± 0.01 to 1.17 ± 0.02 after Ru addition. DFT calculations further show that Re increases the unstable stacking-fault energy of the γ′/γ interface by 10.34% relative to the unalloyed interface, whereas the corresponding increase is 5.05% in the Re–Ru co-doped system. Fatigue-deformed NiAlRe exhibits interfacial dislocation networks along the γ′/γ interfaces, whereas more extensive dislocation penetration into the γ′ precipitates is observed in NiAlReRu. At a strain amplitude of 0.6%, the Ru-containing alloy exhibits a lower cyclic stress response and more pronounced crack initiation and coalescence. These results show that Ru modifies the interfacial segregation behavior of Re and is associated with changes in the post-fatigue dislocation structures and high-temperature LCF response of the model superalloys.

Two types of coatings, NiCrAlY and NiCrAlY/YSZ, were fabricated on the surface of M247 alloy by the atmospheric plasma spraying (APS) technique. Under pure Na₂SO₄ and 25 wt.% NaCl-containing mixed salt deposits at 900 °C in air, the M247 alloy underwent rapid catastrophic corrosion. The non-protective corrosion products formed on the surface included NiO and (Ni,Co)Cr₂O₄ spinel. The hot corrosion of M247 under the pure Na₂SO₄ salt deposit followed a basic fluxing mechanism, whereas under the NaCl-containing mixed salt deposit, it was dominated by an active oxidation mechanism. During hot corrosion, the NiCrAlY coating developed a continuous, dense, and highly protective α-Al₂O₃ oxide scale on its surface, endowing it with superior hot corrosion resistance. The thermal barrier coating of NiCrAlY/YSZ exhibited the best hot corrosion resistance, attributed to the physical barrier and thermal barrier effects of the outer YSZ ceramic layer.