Grain Boundary and High-Temperature Strength of Sintered SiC
Grain Boundary and High-Temperature Strength of Sintered SiC
复制标题
烧结SiC的晶界和高温强度
DOI：
10.2109/jcersj1950.95.1102_638
复制
发表时间：
1987
影响因子：
1.1
通讯作者：
H. Yoshinaga
中科院分区：
文献类型：
--
作者：
Y. Ikuhara;H. Kurishita;H. Yoshinaga
为了研究晶界结构对SiC高温强度的影响，采用无压烧结法制备了3种SiC材料；A材料含B+C助烧剂，B材料含B+C+AlN， C材料不含任何助烧剂。在室温至2070K的温度下，用三点弯曲法测量了它们的强度。用HR-TEM观察了晶界结构。得到了以下结果：(1) A材料的强度随温度升高而升高，温度可达2070K。在研究的所有温度下，断裂模式均为穿晶断裂。在观察到的晶界处，总能发现厚度为2-5nm的非晶相。该相被认为是B和C的化合物或扩展的晶界。(2)材料B的强度在1770K时升高，但在1770K以上强度迅速下降。在该温度下，断裂模式也由穿晶向晶间转变。在晶界处还存在2 ~ 5nm厚的非晶相。边界相被认为是B-C-AlN体系中的化合物。在1770K以上，该相被认为在应力作用下发生粘性流动，导致边界滑动，从而导致强度下降。(3)材料C的强度几乎与温度无关。在晶界处再次存在3 ~ 5nm厚的非晶相，但该晶界相被认为是延伸晶界。(4)在材料C中观测到的二面角往往远大于60°的临界角。这一观测结果违背了Prochazka热力学极限γgb/γsv<√3。大的二面角可能是由于晶界相的存在，降低了晶界能。(5)材料A和B的致密化被认为是通过晶界相的扩散进行的。
In order to in vestigate the effect of grain boundary structure on the high-temperature strength of SiC, three kinds of SiC materials were prepared by pressureless sintering; material A with sintering aids of B+C, material B with B+C+AlN, and material C without any sintering aid. Their strength was measured by three-point bending at temperatures from room temperature to 2070K. The grain boundary structure was observed by HR-TEM. The following results were obtained.(1) The strength of material A increases with increasing temperature up to 2070K. The fracture mode is transgranular at all temperatures studied. At the grain boundaries observed, a non-crystalline phase of 2-5nm in thickness is always found. This phase is thought to be either a compound of B and C or an extended grain boundary.(2) The strength of material B increases up to 1770K, but above that temperature it decreases rapidly. The fracture mode also changes at that temperature from transgranular to intergranular. There exists also a 2-5nm thick non-crystalline phase at grain boundaries. The boundary phase is thought to be a compound in the system B-C-AlN. Above 1770K this phase is considered to flow viscously under stress to bring about boundary sliding which causes the strength to decrease.(3) The strength of material C is almost independent of temperature. There exists again a 3-5nm thick non-crystalline phase at grain boundaries, but the boundary phase is thought to be an extended grain boundary.(4) The dihedral angles observed in material C are frequently much larger than the critical angle of 60°. This observation is against the Prochazka's thermodynamic limitation, γgb/γsv<√3. The large dihedral angles may come from the existence of a grain boundary phase, which lowers the boundary energy.(5) Densification of materials A and B is thought to proceed by the diffusion through the grain boundary phases.