Ti3SiC2助烧改性Si3N4陶瓷高温抗蠕变与导电增强机制

Silicon nitride (Si3N4) ceramics are well known for high-temperature strength, good oxidation, resistance, thermal–chemical corrosion resistance, thermal shock resistance and low thermal expansion coefficient in the field of thermal structure materials. Previous considerable efforts have demonstrated that fully dense Si3N4 ceramics with superior strength could be achieved through liquid phase sintering by addition of rare-earth oxides (most notably involving Y2O3 and La2O3) and metallic oxide (Al2O3, MgO, etc.). However, due to the limited eutectic temperature of grain boundary phase and inferior electrical conductivity, the wide application of Si3N4 ceramics as thermal structure material is limited by creep damage and undesirable machinability. Driven by demands of synergetic promotion of creep-resistance and electrical conductivity, Ti3SiC2, one of typical non-oxide MAX cermets, is chosen as a novel efficient sintering aid to densify Si3N4 ceramics. Mechanisms of densification and strengthening/toughening would be revealed based on microstructure investigation. Besides, the interaction effect of temperature and stress on the interphase characteristics and electrical transport properties would also be intensively discussed. Further, principle of synergetic enhanced High-temperature creep resistance and electrical conductivity is expected to be established based on change rate of conductivity-modulus. All these findings point to important guideline to reveal mechanism for MAX densified ceramics with strong covalent bond, including but not limited to SiC、AlN、ZrB2, and pave the way for the development of enhanced creep-resistant and precision machinable Si3N4 ceramics and interconnection with metals.

氮化硅（Si3N4）热结构陶瓷材料的高温蠕变和机械加工性差严重限制其进一步应用推广。针对现有金属氧化物和稀土氧化物助烧改性的Si3N4陶瓷高温蠕变显著、断裂韧性和电导率低、精密机械加工性差等不足，提出以非氧化物MAX相金属陶瓷Ti3SiC2作为新型烧结助剂，研究Ti3SiC2助烧Si3N4复合陶瓷的致密化和强韧化机理，探讨揭示高温-应力交互作用对Ti3SiC2-Si3N4复合陶瓷界面微结构和电荷输运的影响规律和作用机制，通过引入电导-模量变化率定量表征高温蠕变损伤，研究Ti3SiC2-Si3N4复合陶瓷高温抗蠕变性能和导电性能协同提高的技术原理，研制具有良好高温抗蠕变性、可精密机械加工的Si3N4复合陶瓷材料。对发展高可靠性、可精密加工Si3N4陶瓷及其与金属构件的互连技术具有重要理论价值与实际意义，也将进一步为SiC、AlN、ZrB2等热结构陶瓷材料的高效制备与性能提升提供借鉴。

针对现有金属氧化物和稀土氧化物助烧改性的Si3N4陶瓷断裂韧性和电导率低、精密机械加工性差等不足，提出以非氧化物MAX相金属陶瓷Ti3SiC2作为新型烧结助剂，并成功获得了致密化的Si3N4复合陶瓷，相比于未添加助剂而言，添加5vol%的Ti3SiC2助剂能使陶瓷密度提高到3.11g/cm3，提高幅度达20.54%，最高致密度可达到99%以上。进一步通过微观组织结构分析表征以及热力学计算进一步探明了原位反应生成的C0.3N0.7Ti-SiC相对Si3N4陶瓷致密化烧结起着决定性作用。其次，当Ti3SiC2助烧相含量达到5%时，Ti3SiC2-Si3N4复合陶瓷三点弯曲强度最大达到795 MPa，是传统 (Y2O3-Al2O3)助剂体系烧结后的2倍，断裂韧性也得到了显著提升（最高达到6.97 MPa.m1/2）。进一步发现Ti3SiC2分解生成的TiC相在高温下固溶于Si3N4晶粒中，并以化学键结合而非物理堆积的方式形成细小的硬质相C0.3N0.7Ti，而起到增强的晶粒界面结合强度的作用，表现为弯曲强度的增强。第三，随着Ti3SiC2助剂含量的增加，原位生成的C0.3N0.7Ti-SiC金属陶瓷相形成导电通路网络，氮化硅陶瓷的电导率逐渐升高，当Ti3SiC2助剂含量增加到10vol%时，氮化硅陶瓷的电导率急剧增加到15.6 S/m，相比于未添加的提高了近4个数量级，同时极大提升了Si3N4陶瓷的可加工性能，仅添加 5 vol% Ti3SiC2 的Ti3SiC2/Si3N4复合陶瓷的材料去除率接近 1.6 mm3 min-1 ，可加工性能也达到较好的水平，这也将进一步为SiC、AlN、ZrB2等热结构陶瓷材料的高效制备与性能提升提供借鉴。第四，提出了以电磁功能型为导向的非氧化物MAX相微结构设计方法，并结合第一性原理计算方法，从微观上发现了过渡金属掺杂Ti3C2 MXene体系的d轨道对态密度贡献显著，以及晶格膨胀带来的光谱吸收性能均显著提升，吸收系数最高可提升100%，进一步拓展了非氧化物助烧剂Ti3SiC2衍生物在微波吸收和可见光吸收领域的的应用。