High-temperature thin film lithium niobium oxide transducers for bolts

In the present work, we studied structure, surface morphology, and ultrasonic response of thin film Lithium Niobium Oxide (LNO) transducers deposited on Inconel bolts, stainless steel and silicon substrates by radio frequency magnetron sputtering. The deposited transducer material was a mixture of LiNbO₃/LiNb₃O₈ phases, having a well-developed columnar structure. Further, the in-situ high-temperature ultrasonic response was studied in the temperature range of 18–800 °C in ambient air during short-term annealing. It was observed that long-term annealing (at 700 °C for 160 h and 800 °C for 40 h) deteriorated the ultrasonic response, owing to the irreversible change from the initial columnar structure to the porous granular structure. Dielectric and piezoelectric properties of the thin film LNO transducers were also studied. The thin film LNO ultrasonic transducers have potential applications in bolts and screws up to 700 °C.     

Tribological behaviors of FeCoNiCrAlx sliding against Si3N4 ceramics under high temperature condition

Tribological behaviors are system responses that not only depend on material properties but also hinge on external environmental factors. This work investigated the tribological behaviors of FeCoNiCrAl_x (x = 0.1, 0.5, 1) sliding against Si₃N₄ ceramics under high temperature conditions. According to experimental findings, the tribological properties of FeCoNiCrAl_x were enhanced as the Al element content increased, particularly FeCoNiCrAl₁ could resist the material softening under high-temperature conditions to enhance the wear resistance. Based on the friction coefficient changes, wear morphology, phase composition, and chemistry element, the high-temperature wear mechanisms of FeCoNiCrAl_x were discussed including adhesive, attrition, and oxidative wear. These new studies will lead to the further improvement of tribological data of high-entropy alloys.     

Effect of Linz-Donawitz slag addition on the hot stage slag mineralogy and fuming conditions: Output slag modification during the industrial Zn fuming operation

Up to 39.35 wt% of CaO-rich Linz-Donawitz (LD) slag was gradually added to copper slag during an industrial Zn fuming process to investigate the influence of CaO content on the Zn fuming efficiency and slag high-temperature mineralogy. Multiple slag samples were taken from a standard fuming process and an LD slag modified fuming process. Microstructure analysis revealed that the fuming bath was primarily composed of the liquid phase and a small number of spinel particles prior to LD slag addition. In contrast, an additional wustite phase was observed after the LD slag addition. According to the FactSage simulation, the bath temperature in the standard fuming process was between 1139 and 1180 °C and the oxygen level was around 1 × 10⁻¹³ - 5 × 10⁻¹⁴ atm. Upon the addition of LD slag, the temperature decreased to 1085–1140 °C, while the pO₂ increased to 1 × 10⁻¹² - 5 × 10⁻¹³ atm. An increase in LD slag content facilitated the decomposition of fayalite and spinel phases, the generation of metallic Fe under pO₂ of 1 × 10⁻¹³ atm, the formation of wustite under pO₂ of 1 × 10⁻¹² atm, and the precipitation of melilite. The optimal fuming conditions for Zn recovery and slag modification without Fe formation were pO₂ of 1 × 10⁻¹² atm, the temperature of 1168–1210 °C and an LD slag content of 28.6 wt%. Under these conditions, the CaO content in the liquid phase can reach approximately 20 wt% and ensure that the fumed slag is a suitable raw material for cementitious materials production.     

High-temperature compressive creep behavior and mechanism of Hf6Ta2O17 ceramic as a candidate for thermal barrier coatings

A novel Hf₆Ta₂O₁₇ ceramics is prepared by a solid-state reaction method. High-temperature creep behavior of Hf₆Ta₂O₁₇ and 8YSZ ceramics are investigated by compressive creep test combined with a digital image correlation (DIC) method. It is found that the creep mechanism of Hf₆Ta₂O₁₇ ceramics is controlled by grain boundary sliding associated with dislocation movement (stress exponent ∼2-3, and activation energy of 600–620 kJ/mol). Grain boundary sliding accommodated to the interface reaction is the main creep mechanism of 8YSZ ceramics (stress exponent ∼2, and activation energy of 425∼465 kJ/mol). Hf₆Ta₂O₁₇ ceramics have higher creep resistance than 8YSZ ceramics under the same conditions.     

Elevated temperature tensile and bending strength of ultra-high temperature ceramic matrix composites obtained by different processes

This paper presents a comparison of microstructures and mechanical properties of different ZrB₂-based CMCs, which were manufactured in the frame of the Horizon 2020 European C³HARME research project through different processes: slurry infiltration and sintering (SIS), polymer infiltration and pyrolysis (PIP) and radio frequency chemical vapour infiltration (RF-CVI). Tensile testing with a novel optimized shape of the specimens was performed and compared with the results of flexural tests to assess the structural properties. For the first time, tensile tests up to 1600 °C were carried out on UHTCMCs. Despite the different microstructural features, all the ZrB₂-based CMCs demonstrated excellent structural properties even at elevated temperature. The characterization shows how the different amount of porosity and fibre properties, such as its stiffness, strength and elongation, affected the mechanical behaviour of the C³HARME’s composites. Finally, the role of the high level of residual thermal stresses is discussed.     

High temperature physical and mechanical properties of large-scale Ti2AlC bulk synthesized by self-propagating high temperature combustion synthesis with pseudo hot isostatic pressing

The electrical, thermal, and mechanical properties as well as the effect of the temperature of large-scale Ti₂AlC bulk synthesized by self-propagating high temperature combustion synthesis with pseudo hot isostatic pressing were investigated in detail. With increasing temperature, the lattice defects contribute to the decreasing phonon thermal conductivity, and the electrical resistivity increases linearly from room temperature (RT) to 900 °C. The RT flexural strength, compressive strength, fracture toughness, work of fracture, and Vickers hardness were measured to be 606 ± 20 MPa, 1057 ± 84 MPa, 6.9 ± 0.2 MPa m^1/2, 158 ± 12 J/m², and 4.7 ± 0.2 GPa, respectively. With increasing temperature, the flexural and compressive strengths both keep almost unchanged in the zone of brittle failure, but decrease sharply as the plastic deformation occurs. The brittle-plastic transition temperature under flexure (900–950 °C) is higher than compression (700–800 °C). Interestingly, a non-catastrophic failure is observed in the SENB test, with the high work of fracture (158 ± 12 J/m²).     

电机用环氧灌封胶粘剂的研制

通过对环氧树脂、增韧剂以及固化剂的筛选,研制了一种可室温固化亦可中温固化的电机用透明双组分环氧灌封胶粘剂。     

Ultrafast high-temperature sintering of barium titanate ceramics with colossal dielectric constants

Application of Ultrafast High-temperature Sintering (UHS) technique to rapidly densify barium titanate ceramics has been explored for the first time. Bulk ceramic with ~94% density was obtained by UHS at ~1340 °C for 60 seconds. The densification process was accompanied with progressive sample discolouration from light to dark grey. Further analysis indicates that oxygen vacancy and its associated Ti-rich phase Ba₄Ti₁₂O₂₇ are present in the ceramics. Their roles in ultrafast densification and sample discoloration are discussed. Due to the presence of oxygen vacancies, the UHSed ceramics generally exhibit a colossal dielectric constant of ~ 15–30k at 1 kHz, with dielectric loss of ~0.07–0.10, while the ceramics without oxygen vacancy retain a dielectric constant of ~3000–6000 and dielectric loss of ~ 0.06 at 1 kHz which are comparable to that of the conventionally sintered ceramics. Furthermore, the challenges in applying UHS to sinter thick BT ceramics are discussed, aided by thermal simulations.     

Experimental study on high temperature performances of silica-based ceramic core for single crystal turbine blades

Silica-based ceramic cores are widely utilized for shaping the internal cooling canals of single crystal superalloy turbine blades. The thermal expansion behavior, creep resistance, and high temperature flexural strength are critical for the quality of turbine blades. In this study, the influence of zircon, particle size distribution, and sintering temperature on the high-temperature performance of silica-based ceramic cores were investigated. The results show that zircon is beneficial for narrowing the contraction temperature range and reducing the shrinkage, improving the creep resistance and high-temperature flexural strength significantly. Mixing coarse, medium and fine fused silica powders in a ratio of 5:3:2, not only reduced high temperature contraction, but effectively improved the creep resistance. Properly increasing the sintering temperature can slightly reduce the thermal deformation and improve the high-temperature flexural strength of the silica-based core, but excessively high sintering temperature negatively impacts the creep resistance and high-temperature flexural strength.