Effect of nano-sized sintering additives on microstructure and mechanical properties of Si3N4 ceramics

Effect of particle size of Y2O3-Al2O3 additives on microstructure and mechanical properties of Si3N4 ceramic balls for bearing applications

“…The finer the particle size of sintering additives, the more uniform their dispersion in Si 3 N 4 matrix is. On the contrary, when the particle size of sintering additives is coarser, the distribution of sintering additives tends to be more agglomerated [26,27]. The homogeneous distribution of liquid phase contributes to the wrapping and wetting of Si 3 N 4 particles, thus the particles rearrangement and solutionreprecipitation process are enhanced.…”

“…The aspect ratio of the sample NSA is larger than that of the sample MSA under the same sintering process parameters, suggesting that the coarsening of sintering additives particles resulted in a decrease in the aspect ratio of β-Si 3 N 4 grains. The liquid phase would be formed from the nanosized additives at a lower temperature, which enhanced the α/β phase transformation and the growth of β-Si [26,27]. In contrast, the nano-sized sintering additives with high specific surface area would be more widely and evenly dispersed at the interface of the Si 3 N 4 matrix, and it is easier to form a uniformly distributed liquid phase under the same conditions [28].…”

Effects of Al 2 O 3 –Y 2 O 3 /Yb 2 O 3 additives on microstructures and mechanical properties of silicon nitride ceramics prepared by hot‐pressing sintering

“…It has become a potential material in high‐temperature and structural applications, wave‐transparent material such as gas engine parts, cutting tools, heat exchangers, bearings, orthopedic biomaterials, and so on 6–11 . However, Si 3 N 4 is not only a strong covalent compound but also its self‐diffusion coefficient, volume diffusion, and grain boundary diffusion rate during densification are small, so it is difficult to be densified by conventional solid‐state sintering 12 . Therefore, the introduction of additives for liquid phase sintering, pressureless sintering, hot‐pressing (HP) sintering, gas pressure sintering, spark plasma sintering, and other new technologies to prepare dense Si 3 N 4 ceramics has become a hot research topic 13–16 …”

Study of the Comparative Effect of Sintering Methods and Sintering Additives on the Microstructure and Performance of Si3N4 Ceramic

“…The selection criteria while sintering for sintering aids, in general, are as follows: (1) capable of forming liquid phase to promote densification and crystal phase transition from α-Si 3 N 4 to β-Si 3 N 4 by solution reprecipitation; (2) full or partial crystallization of the liquid phase upon cooling to reduce the proportion of glassy phase at grain boundaries; (3) enough high-temperature strength of grain boundary phase [1]. At present, the usual additives are Y 2 O 3 –Al 2 O 3 , Y 2 O 3 –Nd 2 O 3 , and MgO–SiO 2 [2,3,4,5] for liquid phase formation and good densification. However, the crystallization of the second phase at grain boundaries is incomplete.…”