摘要
本文采用热压烧结工艺制备了不同粒径的α-Al_2O_3基体、不同助烧剂SiO_2含量和纳米TiNp含量的Al_2O_3-TiN基复合陶瓷材料。利用XRD、SEM、TEM分析了复合材料的微观组织结构;采用维氏压痕法、三点弯曲法和单边缺口梁法评定了复合材料的力学性能;通过电学性能试验系统地研究了TiN含量和α-Al_2O_3粒径对复合陶瓷电阻率、耐高压性能的影响,并探讨了导电机理。
研究发现,以SiO_2为助烧剂的Al_2O_3-TiN基复合陶瓷材料的致密度都达到了98%以上,说明添助烧SiO_2能有效地促进材料的致密化,同时控制其加入量,可使材料具有优异的力学性能,例如维氏硬度最高达到22.3GPa,断裂韧性在4~5MPa·m~(1/2)之间,三点弯曲强度最高达到561MPa。
基体α-Al_2O_3采用7.5μm和20nm两种粒径,复合陶瓷的力学性能试验表明,微米基体复合陶瓷的维氏硬度在20GPa以上,最大达到25.5GPa;断裂韧性在4~6MPa·m~(1/2)之间,三点弯曲强度最高达到578MPa。纳米基体复合陶瓷的维氏硬度在10GPa以上,最大值为16.0GPa,断裂韧性在4~6MPa·m~(1/2)之间,三点弯曲强度最高达到566MPa。与Micro-Al_2O_3基复合陶瓷材料相比,Nano-Al_2O_3基复合陶瓷材料的硬度小,强度和断裂韧性相近,而两种复合陶瓷的力学性能都是由于纳米颗粒TiN的加入而增强。
Al_2O_3-TiN基复合陶瓷材料具有高强度和高断裂韧性的主要原因在于,高熔点和高硬度的TiNp均匀分散在基体中,可以对基体的位错运动产生钉扎作用,同时TiN与Al_2O_3基体膨胀系数存在差别而造成热膨胀失配导致残余应力增韧。断裂类型主要是沿晶断裂。
电学性能试验发现,Micro/Nano-Al_2O_3基复合陶瓷的电阻率随TiNp含量的增加而降低,在TiNp含量为10vol.%时,电阻率都满足设计的要求。与Nano-Al_2O_3基复合陶瓷的电学性能相比,Micro-Al_2O_3基复合陶瓷的电阻率要高,而且耐压可达7000V/cm,耐高压性能较强,电压稳定性较好。从TEM显微组织观察分析得知,Nano-Al_2O_3基复合陶瓷材料中,导电相TiN分布在基体Al_2O_3边界较多;其次由于微米体系的基体比纳米体系的基体大,从而造成Micro-Al_2O_3基复合陶瓷材料的导电网络更难形成。
In this thesis, Al_2O_3-TiN composites with different content of SiO_2 or TiN and different particle size of Al_2O_3 were prepared by hot-pressing (HP) technique. Microrostructure was studied by XRD, SEM and TEM; mechanical properties were measured through Vickers indentation, three-point bending and single-edge-notch beam (SENB) bending tests; effects of TiN content and particle size of Al_2O_3 on the electrical conductibility behavior of the ceramics was investigated and the conductibility mechanism was discussed.
Results show that Al_2O_3-TiN ceramics stabilized by SiO_2, whose relative density reach above 98%, nearly full density was obtained in the composites with of SiO_2 as sintering aids, which show excellent mechanical properties: Vickers hardness attains about 22.3GPa, fracture toughness is 4.42MPa·m~(1/2), while flexural strength reaches 560.7MPa.
Average particle sizes of startinglα-Al_2O_3 powers are 7.5μm and 20nm, respectively. The Micro-Al_2O_3-TiN ceramics manifest more excellent mechanical properties: Vickers hardness attains to 20GPa, and the highest is 25.5GPa, fracture toughness is between 4 and 6MPa·m~(1/2), while flexural strength reaches 578.2MPa. While the mechanical properties of nano-Al_2O_3-TiN ceraMicros: Vickers hardness attains to 10GPa, whose the highest is 16.0GPa, fracture toughness is between 4 and 6MPa·m~(1/2), while flexural strength reaches 565.8MPa. In general, with the increase of TiNp content and the particle size of Al_2O_3, the mechanical properties of the ceraMicros are improved.
High flexural strength and fracture toughness of Al_2O_3-TiNp composite ceramics has been achieved by introduction of evenly distributed TiN particles with excellent mechanical, which in matrix materialα-Al_2O_3, as well as the difference coefficient of thermal expansion will involve the mismatch flexibilizer. The mode of fracture is primarily intergranular cracking.
Electrical conductibility tests indicate that the electrical resistivity of Micro/nano-Al_2O_3-TiN ceraMicros both are descending with the increasing content of TiNp, according to the STAR barrel TOF standard, the Micro/nano-Al_2O_3-TiN ceramics will be added 10vol.% TiNp. Electrical conductibility tests also show higher electrical resistivity than that of nano-Al_2O_3-TiN ceramics, and the high- voltage properties, the maximizing voltage is 7000V/cm. Microstructure study under TEM shows that the distribution of TiNp in nano-Al_2O_3-TiN ceramics concentrated on grain boundary of matrix materialα-Al_2O_3. The smaller size of theα-Al_2O_3 matrix particles, the more difficult the conductibility network of Micro-Al_2O_3-TiN ceramics is formed.
引文
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