Study On Properties Of Graphene-titanium Composites With Multi-scale Configuration

As promising structural materials used for aerospace applications,titanium and titanium alloy own many advantages of low density,high specific strength,good corrosion resistance and so on.However,with the rapid development of aviation industry,the performance of components is increasingly demanding.While affected by conventional view,researchers always pursue the goal of uniform distribution of reinforcing phase and matrix about titanium matrix composites,and only produce limiting strengthening effect.In this paper,graphene nanoplates(GNPs)as reinforcement,widely used pure titanium and Ti-6Al-4V(TC4)as matrix,the distribution and morphology of GNPs and the deformation of matrix were controlled by powder metallurgy to establish multi-scale structure of the composites to improve performance.By optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM),Raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD),the morphology and properties of composite powder and materials were characterized.Besides,the hardness and compression performance of composites as mechanical property were tested.The effects of graphene and scale-structure on composites microstructure and mechanical behavior in different high-energy ball milling systems were investigated.The single-scale configuration GNPs/TC4 composites were prepared by different high-energy ball milling times(0,2,5,10,15 h).With the increasing time,the refinement of composite powder became more obvious,and TiC was formed in situ.After sintering,the grains of composites were refined step by step,and the TiC phase layer at grain boundary was gradually thickened,improving the strength and hardness.But the ductility decreased.After milling for 10 h,the strength(1929 MPa)and plasticity(17%)reached a good balance,and 15 h sample gained the highest strength.The dual-scale configuration GNPs/TC4 composites were constructed by different grain size ratios(9:1,8:2,7:3,6:4,5:5).The ball milling powder with the highest strength as fine grain powder was mixed with GNPs,and then the coarse grain powder of original TC4 as matrix was added.With the increase of fine grain content,the "core-shell" structure became more obvious.The "shell" layer of fine grain became thicker,while the strength and hardness increased with decreasing ductility.The optimum ratio of better strength and plasticity matching was 7:3,thus the yield strength was 1287 MPa and the elongation was 13%.The hierarchical configuration GNPs/Ti composites were prepared by three different ball milling processes with the introduction of different GNPs contents.When GNPs was added hierarchically,a variety of TiC existed on microstructure and GNPs kept a better structural integrity,which improved the strength.When Ti was added hierarchically,the heterogeneous structure was formed,redistributing the stress between grains,leading a better ductility.The compressive yield strength and hardness of 0.5 wt.%GNPs/Ti composite were 1256 MPa and 480 HV,which were 402%and 238%higher than that of pure titanium,respectively.Compared with the limiting strengthening of homogeneous composites of the control group,the difference of grain size in the heterogeneous composites caused dislocation pile-up,which made the composites own coordinated deformation ability and improve the mechanical properties of materials.