Effects Of Ta₂O₅ On The Preparation And Mechanical Properties Of Ti/Al₂O₃ Composites

Fracture toughness of alumina ceramic has been significantly improved by fabricating the Ti/Al₂O₃ composite with Ti,which broadens the application range of alumina ceramic.However,the intermetallic compound of Ti and Al generated by the strong interfacial reactions between Ti and Al₂O₃ at high temperature will reduce the mechanical properties of Ti/Al₂O₃ composite.At the same time,we find that Ti is hard to be well sintered.In this thesis,Ta₂O₅ is chosen as the sintering additive to prepare Ti/Al₂O₃ composites via hot pressing sintering and pressureless sintering.The effects of different volume fraction of Ta₂O₅ on phase composition,microstructure and mechanical properties of Ti/Al₂O₃ composites have been researched.Ti/Al₂O₃ composites with different volume percentages of Ta₂O₅ added?0-10.0 vol.%?were prepared via hot pressing sintering at 1300?,1350?,1400? and 1450? under 30 MPa for 1.5 h,respectively.The sample prepared at 1400? with 7.0 vol.% Ta₂O₅ addition showed the best comprehensive properties,whose relative density,Vickers harness,flexural strength and fracture toughness were 99.01%,14.92 GPa,414.45 MPa and 6.72MPa·m1/2.Ti/Al₂O₃ composites with different vol.ume percentages of Ta₂O₅ added?0-10.0 vol.%?were prepared via pressureless sintering at 1450?,1500? and 1550? for 1.5 h,respectively.The sample prepared at 1550 ? with 5.0 vol.% Ta₂O₅ addition showed the best comprehensive properties,whose relative density,Vickers harness,flexural strength and fracture toughness were 94.02%,11.84 GPa,314.92 MPa and 4.51MPa·m1/2.XRD results show that Ta₂O₅ inhibits the production of the intermetallic compound of Ti and Al,such as TiAl and Ti3 Al,by forming solid solution with Ti.This solid solution melts and fills the void of Al₂O₃ phase to increase the density of Ti/Al₂O₃ composites at high temperature.SEM results show that grain size of alumina has grown obviously in the samples with Ta₂O₅ addition.It is because that more Ti O2 will be generated with the consistently adding of Ta₂O₅,which can promote the crystallization of Al₂O₃.TEM analysis on the interface of Al₂O₃ and Ti shows that bonding strength Al₂O₃ and Ti has been improved by forming the semi-coherent interface.And because of this improvement,when fracture occurs,ladder-like or layeredcleavage fracture can be observed in the composite.These phenomena prolong the crack propagation path and consume the rack propagation energy.By these means mechanical properties of Ti/Al₂O₃ composites have been improved.