| In recent years,with the increasing demand for high thrust weight ratio of aero engine,it is urgent to develop a new-type high temperature structural material with lightweight,high toughness,and high temperature resistance.The novel metal-intermetallic composite lamiante Ti/Al3 Ti has excellent performances,combining with low density,high specific strength,and excellent high temperature oxidation resistance of Al3 Ti and strong absorption of impact energy of Ti layers.It becomes one of the most potential high temperature structural materials in the aerospace field.Therefore,research in the domain of itsdesign,fabrication,forming and service performanceevaluation has been a hot topic.At present,the researchers devote their attentions mainly on the preparation,basic mechanical properties and damage evolution of the Ti/Al3 Ti composite lamiantes.Whereas,the mechanism of the phase transition during the preparation process is far less investigated.Especially,the research about the effect of the pre-deformation on the formation of new phase has not been carried out.Hence,Ti/Al composite lamiantes and Ti/Al3 Ticomposite lamiantes were prepared by hot-press bounding to investigate the mechanism of the phase transition and the effect of pre-deformationin in this study to provide statistical guidance for the manufacture process.Firstly,the titanium foils and aluminum foilswere alternately stacked at different temperature and kept at different time to investigate the mechanism of the phase formation and to set up thereactionkineticequation.It was found thatnointermetallic compound formed below 550℃,and the bonding interfaces were straight without any defects.When the temperature was higher than 550℃,Al3 Ti was the only reaction product during the diffusion process of Ti and Al atoms,which wasdetermined by the thermodynamic and diffusion kinetics.Besides,the diffusion reaction kinetic equation indicated that the thickness of Al3 Ti layer increases exponentially with temperature and increaseds with time.Secondly,the effect of pre-deformation on the formation of the new phase was investigated by performing hot pressing tests on Ti/Al composite lamiantes followed by 0%-10% tensile pre-deformation.The results indicated that the type of the phase formed at the interface was not changed with the pre-deformation,and Al3 Ti was the only reaction product.Moreover,the growth of Al3 Ti was accelerated with the increased amount of pre-deformation.However,the distribution of the new phase layer was not uniform when the pre deformation reached 10% owing to the delamination at the interface.This phenomenon was not eliminating in the subsequent hot pressing bonding.Therefore,the pre-deformation of Ti/Al composite lamiantes should be controlled within 8%.Finally,the hot pressing parameters of the fabrication for Ti/Al3 Ticomposite lamiantes were studied.And the tensile tests at elevated temperature were conducted to investigate the effect of the new phase forming at the Ti/Al3 Ti interface on the coordinate deformation of Ti/Al3 Ti composite lamiantes.It was found that the Al layers were consumed completely by controlling appropriate hot pressing time,and the defect of center hole in the Al3 Ti layer,caused by the Kirkendall effect in the diffusion process,could be improved by the increase of hot pressing pressure.Additionally,Al Ti3,Al Ti and Al2 Ti layers were formed at the Ti/Al3 Ti interface when the Al layer was completely consumed.More importantly,the thin layer of a new phase had no effect on the high temperature properties of Ti/Al3 Ti composite lamiantes.However,when the thickness of the new phase was more than 6 μm,the new phase layer would significantly accelerate the crack growth,resulting in the decrease of the toughness of Ti/Al3 Ti composite lamiantes. |
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