Preparation And Functional Properties Of Selective Laser Melting Of Component Gradient TiNi Alloy

In order to meet the demand of TiNi shape memory alloys in different fields and broaden the application range,the development of TiNi shape memory alloys with wide phase transition temperature range has become one of the hotspots in recent years.In this paper,a component gradient TiNi alloy was prepared by selective laser melting method,and the composition gradient was constructed inside the alloy by changing the laser process parameters.Scanning electron microscopy and energy spectrum analysis were used to study the relationship between different laser process parameters and compositional gradients.The microstructure of TiNi alloy was studied by means of metalloscpoe,XRD and SEM.The relationship between different laser process parameters and annealing process and the phase transition temperature and phase transition temperature range of homogeneous TiNi alloy and component gradient TiNi alloy were analyzed by DSC.The mechanical properties,shape memory effect and superelasticity of TiNi memory alloy were studied by an electronic universal material testing machine.Dynamic mechanical analysis was used to study the effects of frequency,process parameters and annealing process on the damping properties of homogeneous TiNi alloys and component gradient TiNi alloys.The results show that during the process of selective laser melting to prepare TiNi alloy,the change of process parameters leads to the change of Ni content in TiNi alloy,and the composition gradient TiNi alloy is prepared.The compositional gradient TiNi alloy coexists with the parent phase and the martensite phase at room temperature,and the martensite phase decreases as the annealing temperature increases.The martensitic transformation temperature interval M_s-M_f of the component gradient TiNi alloy is 95?,and the temperature range A_f-A_s of the reverse phase transformation is 77?.The maximum value of the martensitic transformation temperature interval M_s-M_f of the homogeneous TiNi alloy is 66?,and the martensitic transformation temperature interval of the component gradient TiNi alloy with different energy density is about30? wider than that of the homogeneous TiNi alloy.The component gradient TiNi alloy prepared by different powers has a compressive fracture strength of 2205 MPa and an elongation of 36%.The compressive fracture strength of TiNi alloy with different energy density is 3068 MPa and the elongation is 39%.As the annealing temperature increases,the elongation,yield strength and fracture strength of the composition gradient TiNi alloy increase.When the pre-deformation of the composition gradient TiNi alloy is 8%,the room temperature recoverable strain is 7.8%,and the superelasticity of the composition gradient TiNi alloy is 7%.After annealing,the temperature range of the component gradient TiNi alloy with a damping value greater than 0.04 is about 90?.This is wider than this temperature interval of the TiNi alloy when not annealed.