Study On Microstructure And Mechanical Properties Of Ti-based Laminated Composites

In recent years,it has been proved that the intrinsic extraordinary mechanical properties of nanowires(sheets)cannot be achieved in the matrix deforming by dislocation slip,while it can be achieved in the matrix deforming by atomic lattice shear.It can be speculated that a laminated composite material composed of a nanoscale lattice shear element(sheets)and high-strength nanosheet may be expected to have excellent mechanical properties.Therefore,this dissertation attempts to use the accumulative roll-bonding method to form metallic Ti and Nb(Ta)sheets into nanoscale composites.Using atomic diffusion between them,the TiNb or TiTa phase with martensitic transformation(atomic lattice shear deformation)is formed.Thereby Ti/TiNb(phase transition)/Nb and Ti/ TiTa(phase transition)/ Ta composites are obtained.In this paper,Ti/TiNb/Nb and Ti/TiTa/Ta laminated composites sheets and wires are prepared by accumulative roll-bonding method.The atomic diffusion behaviors of Ti and Nb(Ta)in the stack rolling(annealing)process and the microstructure evolution of composites are studied.By using differential scanning calorimetry,tensile testing machine and in-situ tensile synchrotron XRD,the phase composition,martensitic transition behavior,mechanical properties and the phase transformation and deformation behavior of components during loading of the composites are analyzed.The main research contents and results are as follows:Nano-scale Ti/TiNb/Nb and Ti/TiTa/Ta laminated composites can be obtained by the cumulative roll-bonding process.It is found that atomic diffusion occurs between Ti and Nb(Ta)during the rolling process.TiNb or TiTa component with martensitic transformation is formed between the nanoscale Ti and Nb(Ta)plates.Both of them undergo martensitic transformation and reverse phase transformation during the heating and cooling process,and stress-induced martensitic transformation occurs during the loading process.It is found that the yield strength of Ti/TiNb/Nb laminated composites increases first and then decreases with the decrease of the diameter of the wires,and the amount of martensite transformation decreases.With the increase of heat treatment temperature,the yield strength gradually decreases and the amount of martensite transformation decreases.The plasticity at 600°C for 10 minutes is the best.The lattice strain on different crystal faces of the composite material is different,and the maximum lattice strain reaches 1.2%.It is found that the yield strength of Ti/TiTa/Ta laminated composites increases with the decrease of the diameter of the wires.With the increase of heat treatment temperature,the yield strength decreases and the plasticity increases.After the secondary rolling,the plasticity of the Ti/TiTa/Ta composite plates and wires are poorer than that after primary rolling.