Effects of two-step hot-pressing on microstructure, thermal conductivity and flexural strength of silicon carbide (SiC) ceramics were investigated. A novel combination of aluminium nitride (AlN), La₂O₃ and LaF₃ was employed as sinter additives in this study. SiC ceramics prepared through both one-step (OS samples) and two-step (TS samples) hot-pressing method exhibited high relative densities. Compared with OS samples, the TS samples yielded finer microstructures with both higher thermal conductivities and flexural strengths. Impedance spectroscopy analysis was employed to reinforce the investigation on thermal conductivity variations in different samples. According to the analysis results, TS samples exhibited higher fitting grain and grain boundary resistances, which stood for a lower concentration of vacancies, indicating that two-step hot-pressing is more beneficial to the elimination of defects and improvement of thermal conductivity in SiC ceramics. On the other hand, TS samples were strengthened by a combined effect of finer microstructure and formation of SiC-AlN solid solution, thereby obtained higher flexural strengths. Hence, the present study suggests that two-step hot-pressing is more favorable to the improvement of both thermal conductivity and flexural strength of SiC ceramics with AlN-La₂O₃-LaF₃ additive combinations.

研究了两步热压对碳化硅（SiC）陶瓷显微组织、导热系数和抗弯强度的影响。氮化铝 (AlN)、La ₂ O ₃和 LaF _{3的新型组合}在本研究中被用作烧结添加剂。通过一步（OS样品）和两步（TS样品）热压法制备的SiC陶瓷表现出较高的相对密度。与 OS 样品相比，TS 样品产生了更精细的微结构，同时具有更高的热导率和抗弯强度。阻抗谱分析被用来加强对不同样品热导率变化的研究。根据分析结果，TS样品表现出较高的拟合晶粒和晶界电阻，代表较低的浓度空位，表明两步热压更有利于SiC陶瓷缺陷的消除和导热性能的提高。另一方面，TS样品通过更精细的微观结构和SiC-AlN固溶体形成的综合作用得到强化，从而获得更高的抗弯强度。因此，本研究表明，两步热压更有利于提高具有AlN-La ₂ O ₃ -LaF ₃添加剂组合的SiC陶瓷的热导率和抗弯强度。