Study On Multiple Memory Effect And Driving Characteristics Of NiTi Alloy

NiTi-based shape memory alloys(SMAs)have excellent shape-memory effect(SME),pseudo-elastic(PE)and high damping properties,therefore have tremendous potential for applications in the fields of mechanics,biomedicine and space technology.Among them,the shape memory effect of NiTi memory alloy is related to the reversible martensitic transformation.The one-way and two-way memory effects have been studied systematically and have been widely used.Based on the application of shape memory effect in actuator,this paper systematically studies the four-way shape memory effect of NiTi shape memory alloy ribbon;Secondly,the optimal treatment process and driving characteristics of the shape memory alloy spring alone as a driving element were deeply studied.The main research contents and results are as follows:In this paper,NiTi alloy ribbons were prepared by rapid solidification rejection method.After annealed and pre-deformed,the ribbon samples exhibited four-way memory effect during heating and cooling.We studied the microstructure of the ribbon by SEM and TEM,tested the mechanical properties of the ribbon by universal tensile testing machine,and studied the martensitic transformation behavior of the NiTi alloy ribbon before and after predeformation by DSC.It is found that the NiTi alloy ribbons prepared by the rapid solidification technology exhibit the features of inconsistent grain size and unsynchronized martensitic transformation on both sides,and the lower the rotational speed,the thicker the obtained ribbon samples.Based on the experimental results,we analyzed the four-way memory effect mechanism of NiTi alloy ribbons.The grain size on both sides of the ribbon is different,after the tensile pre-deformation treatment,the difference in phase transition temperature between the two sides of the ribbon sample is more obvious,so that during the heating or cooling process,an asynchronous phase transition occurs on both sides of the ribbon,which shows four-way shape memory effect.Through the study of NiTi shape memory alloy springs of different sizes anddifferent heat treatment processes,it is found that the spring wire diameter d is 1.5 mm and the spring inner diameter D is 4.5 mm and the highest recovery strain of SMA spring is obtained at 500 ? for 20 min.Since the SMA springs introduce dislocations in the reorientation of martensite during the deformation process and hinder the transformation of martensite to the parent phase,the one-way memory effect decreases with the increase in the number of cycles,making the recovery strain of the SMA springs decreased rapidly during the initial cycle.With a further increase in the number of cycles,dislocation density reached a certain degree of saturation,the SMA spring recovery strain remained almost constant.