Study On The Mechanism Of Resistive Thermal Drive Of NiTi Shape Memory Alloys

Shape memory alloys(SMAs)drivers are mainly used in aerospace,automotive,medical,bionic machinery and many other fields.At present,SMA actuators are increasingly required in terms of drive form,drive structure,reliability,fatigue,mechanical properties,and application environment,and it is increasingly urgent to improve the accuracy,complexity,and performance of the drive.The intelligent drive with NiTi shape memory alloy as the drive structure mainly realizes the deformation function by using the resistance heating to realize the phase change energy difference.In addition,the resistance heat drive has the characteristics of simple,convenient and easy to control,therefore,it is very meaningful to study the mechanism of resistive thermal drive of NiTi SMAs.The mechanism of resistive thermal drive of SMA is mainly to study the relationship between phase transition temperature,resistance and deformation recovery angle.There are two main technologies that affect the phase transition temperature: heat treatment and laser processing.The heat treatment is to put the entire SMA into the heat treatment furnace,which has the characteristics of mature technology,convenience,and low cost.Compared with heat treatment,laser processing can achieve local modification of SMA,that is,from pseudoelasticity(PE)to shape memory effect(SME),this is because the laser processing reduces the Ni content of SMA The phase transition temperature is high,which has the advantages of rapid processing,precise control,and material saving.This article focuses on the effects of heat treatment and laser processing on the phase change of SMA,as well as the resistance characteristics and deformation recovery characteristics at different currents.The first part is to study the effect of different heat treatment conditions on SMA phase transition temperature and DC resistance.Differential scanning calorimeter(DSC)was used to test the phase transition temperature to obtain the relationship between different heat treatment process parameters and SMA phase transition temperature.In addition,resistance changes under different heat treatment conditions were measured by a dc resistance tester,and temperature changes at different currents were measured using a thermal imager.The second part is to study the phase transition temperature change of SMA under different laser processing parameters,that is,the phase transition mechanism from PE to SME.The details are as follows:(1)Study the laser processing parameters: laser current,pulse width,shielding gas flow rate,welding speed and frequency,etc.for SMA welding joints.(2)Study the effect of process parameters such as processing current and pulse width of laser on the phase transition of SMA and obtain the relationship between current,pulse width and phase transition temperature.(3)Test the recovery characteristics of SMA welded joints under different currents and temperatures to obtain the relationship between the load current,temperature and recovery angle.