In order to improve the wear resistance of offshore drilling equipment, CoCrFeNiMn high-entropy alloy coatings were prepared by cold spraying (CS) and high-speed oxygen fuel spraying (HVOF), and the coatings were subjected to vacuum heat treatment at different temperatures (500 °C, 700 °C and 900 °C). The friction and wear experiments of the coatings before and after vacuum heat treatment were carried out in simulated seawater drilling fluid. The results show that CoCrFeNiMn high-entropy alloy coatings prepared by CS and HVOF have dense structure and bond well with the substrate. After vacuum heat treatment, the main peaks of all oriented FCC phases are broadened and the peak strength is obviously enhanced. The two types of coatings achieve maximum hardness after vacuum heat treatment at 500 °C; the Vickers microhardness of CS-500 °C and HVOF-500 °C are 487.6 and 352.4 HV_0.1, respectively. The wear rates of the two coatings at room temperature are very close. CS and HVOF coatings both have the lowest wear rate after vacuum heat treatment at 500 °C. The CS-500 °C coating has the lowest wear rate of 0.2152 mm³ m⁻¹ N⁻¹, about 4/5 (0.2651 mm³ m⁻¹ N⁻¹) of the HVOF-500 °C coating. The wear rates and wear amounts of the two coatings heat-treated at 700 °C and 900 °C decrease due to the decrease in microhardness. The wear mechanisms of the coatings before and after vacuum heat treatment are adhesive wear, abrasive wear, fatigue wear and oxidation wear.

Microwave dielectric (1 − x)CoTiTa₂O₈-xMgNb₂O₆ composite ceramics (x = 0.625–0.725) were fabricated through a two-step method and sintering techniques. The applied CoTiTa₂O₈ and MgNb₂O₆ powders were both synthesized by calcining stoichiometric mixtures of their respective metal oxides at 1000 °C for 3 h. The optimal sintering parameters were determined using visual high-temperature deformation analysis. The influence of the MgNb₂O₆ content on the phase composition, microstructure, and microwave dielectric properties of the obtained composite ceramics was comprehensively investigated. It was observed that an increase in the MgNb₂O₆ content resulted in a reduction in the dielectric constant (ε_r) and a significant enhancement in the quality factor (Q × f). The ceramics with a compositional value of x = 0.675, sintered at 1193 °C for 4.5 h, demonstrated a near-zero temperature coefficient of the resonant frequency (τ_f), exhibiting optimal microwave dielectric properties: ε_r = 28.4, Q × f = 33,055 GHz, and τ_f = −3.1 ppm/°C. These findings underscore the potential of the present CoTiTa₂O₈-MgNb₂O₆ composite ceramics for advanced microwave applications.

ZnNb₂O₆-based microwave dielectric ceramics have attracted considerable attention due to their high quality factor (Q × f) and low sintering temperature, but their application was limited by poor temperature stability with a large negative temperature coefficient of resonant frequency (τ_f). Herein, novel (1 − x)ZnNb₂O_6−xCa_0.5Sr_0.5TiO₃ (x = 0.05–0.125) composite ceramics were designed and fabricated. The used ZnNb₂O₆ and Ca_0.5Sr_0.5TiO₃ were synthesized through solid-phase reaction by using stoichiometric metal oxides or carbonates as the raw materials at 650 and 1100 °C, respectively. The composite ceramics were prepared by solid-state sintering, and the sintering parameters were optimized at 1175 °C for 4 h by visual high-temperature deformation analysis. A focus was paid on the temperature stability and compositional effects of Ca_0.5Sr_0.5TiO₃ of the obtained composited ceramics. As the Ca_0.5Sr_0.5TiO₃ content increases, the dielectric constant (ε_r) and Q × f gradually decrease, while τ_f shifts toward positive values. At x = 0.075, the composite ceramics sintered at 1175 °C for 4 h exhibit near-zero τ_f (−8.99 ppm/°C), coupled with ε_r = 23.23 and Q × f = 21,686 GHz. This study provides theoretical guide and material support for designing and fabricating various high-performance thermally stable microwave dielectric ceramics for 5G communication devices and future communication technologies.