Effect Of Hydrogen On Microstructures And Properties Of Titanium Matrix Composites

Titanium matrix composites?TMCs?are widely used in aerospace and other fields as a new structural material with high strength,high temperature resistance,creep resistance and lightweight.However,because of its low plasticity at room temperature and low deformation limit,most titanium matrix composites must be formed in hot state.Some shortcomings in hot working,such as high temperature of hot deformation and high flow stress,limit the application of composite materials,to some degree.As a temporary alloying element,hydrogen can improve the hot working properties of titanium alloys and their composites,which has attracted much attention in recent years.In this paper,Ti-6Al-4V/?TiB+TiC?composites were treated by melt hydrogenation,the effect of hydrogen on the microstructures and properties of Ti-6Al-4V/?TiB+TiC?composites were studied.The results showed that:?1?With the increase of hydrogen content,the distribution of reinforcement in Ti-6Al-4V/?TiC+TiB?composites is more uniform and along the initial?phase grain boundary,the grain boundary is more obvious,and the grain size of?phase tends to be refined.?2?Hydrogen does not change the phase composition of titanium matrix composites.No hydride phase was detected because of the low hydrogen content,which is not satisfied for the formation condition of hydride.?3?The effect of hydrogen on the mechanical properties of Ti-6Al-4V/?TiC+TiB?composites at room temperature is as follows:with the increases of hydrogen content,the hardness and compressive strength increase,but the ultimate deformation decreases,that is,the strength increases and the plasticity decreases.?4?The effect of hydrogen on the high temperature mechanical properties of Ti-6Al-4V/?TiC+TiB?composites is that hydrogen can reduce the flow stress of the composites during high temperature deformation.When the hydrogen was 0.035 wt.%,peak resistance of TMCs decreased 16.4%from 309.6MPa,which corresponds to peak resistance of unhydrogenated TMCs,to 258.8 MPa.?5?The thermal deformation behaviour of TMCs before and after hydrogenation at 750-900?and0.001-1 s^-1 was studied,and the deformation resistance raises with increased strain rate and decreased deformation temperature.The constitutive equations of of TMCs before and after hydrogenation are deduced.?6?The establishment and analysis of the processing map in hot compression of TMCs before and after hydrogenation were constructed at a strain of 0.5.The optimum thermal processing parameters of TMCs before and after hydrogenation:830-880?,0.001-0.05 s^-1 and 780-840?,0.005-0.06 s^-1.The microstructures corresponding to optimum parameters are relatively uniform and fine reticular structure with no instability such as cracks and voids.The instability domain processing parameters of TMCs before and after hydrogenation:750-840?,0.7-1 s^-1 and 750-825?,0.1-1 s^-1,that is,the domain of low temperature and high strain rate.And the microstructures corresponding to instability domain are inhomogeneous and cracks occur,therefore,thermal processing should be avoided in this working environment.Therefore,the instability domain of the Ti-6Al-4V/?TiB+TiC?composite after hydrogen addition is smaller than that of the composites without hydrogen addition,the hot working properties of TMCs can be improved by melt hydrogenation.