Study on crack-healing behavior of silicon nitride

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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℃