Study on crack-healing behavior of silicon nitride

系统地研究了化学成分、气氛、愈合时间和温度对可愈合裂纹尺寸、愈合区疲劳强度和愈合区高温强度的影响。本研究开发了具有良好裂纹愈合能力的氮化硅陶瓷材料，主要研究结果如下：（1）以Y_2O_3和Al_2O_3为烧结体的氮化硅陶瓷材料。添加剂具有优异的裂纹修复能力。特别是，SiC对提高愈合能力非常有用。(2)在真空、氩气、氮气和空气中具有裂纹愈合能力，该材料仅在空气中就能愈合裂纹。(3)Si_3N_4/Y_2O_3/SiC复合材料的修复能力最好，在800 ~ 1400℃温度范围内，材料均能修复较大的裂纹，且强度完全恢复。(4)Si_3N_4/SiC/Y_2O_3/Al_2O_3和Si_3N_4/SiC/Y_2O_3两种材料完全愈合了裂纹，大部分试样在母材处断裂。(5)裂纹愈合区的高温强度对化学成分非常敏感。(6)Si_3N_4/SiC/Y_2O_3/Al_2O_3材料的裂纹愈合区在1000℃以下仍有足够的强度。(7)Si_3N_4/SiC/Y_2O_3复合材料的裂纹愈合区在1400℃以下仍具有良好的强度

Effect of Chemical Compositions, Atmosphers, Healing Time and Temperature on Healable Crack Size, Fatigue Strength of Healed Zone and High Temperature Strength of Healed Zone have been studied systematically. The silicon nitride which has excellent crack-healing ability was developed by this research.The main conclutions are followings :(1) The silicon nitride which used Y2O3 and Al2O3 as a sintering. additive have excellent crack healing ability. Especially, SiC is very useful to improve healing ability. (2) Crack healing ability in vacuum, argon, nitrogen and air, the materials can heal a crack in only air. (3) The silicon nitride of Si3N4/Y2O3/SiC has the best healing ability and the material could heal the quite large crack at from 800℃ to 1400℃, and strength recovered completely. (4) The materials (Si3N4/SiC/Y2O3/Al2O3 and Si3N4/SiC/Y2O3) healed the crack completely and most specimens fracture at base metal. (5) High temperature strength of crack healed zone is very sensitive to chemical compositions. (6) The crack healed zone of the materials (Si3N4/SiC/Y2O3/Al2O3) has enough strength up to 1000℃. (7) The crack healed zone of the materials (Si3N4/SiC/Y2O3) has excellent strength up to 1400℃