Fabrication And Martensitic Transformation Behavior Of TiNiCu Shape Memory Alloy Ribbon With High Cycling Stability

TiNiCu shape memory alloys have been regarded as potential materials in in the micro-electromechanics field due to its narrow hysteresis,fast response speed,excellent fatigue resistance,damping performance and corrosion resistance.However,with the increase of cycling number,the martensitic transformation of these alloys degrades.In order to improve the cycling stability,the amorphous Ti₅₄Ni₃₄Cu₁₂ alloy ribbons were prepared by different melting-spinning processes in this paper.The influence of processing parameters on the macromorphology,microstructure and crystallization behavior of the prepared ribbons was analyzed.The melt-spinning process parameters were optimized.Different crystallization annealing processes were used to treat the amorphous ribbons.The effects of the melt-spinning processing and annealing processes on the microstructure,martensitic transformation behavior and its thermal cycling stability of theseribbons were studied.The process parameters for the preparation of Ti₅₄Ni₃₄Cu₁₂ alloy ribbons by melt-spinning are optimized as follows:jet pressure is 0.03MPa,furnace cavity pressure-0.035MPa,roll speed 3600r/min.The ribbon obtained by such a processing is characterized by smooth surface,less rag,void-free and high volume fraction of amorphous phase.The higher the rotating speed of the copper roll is,the higher the proportion of the amorphous phase and the higher the crystallization temperature are.The crystallization activation energy increases with the increase of the volume fraction of amorphous phaseAfter annealing,the amorphous part of as-fabricated ribbons changes into crystalline part.When annealed at 500?,the microstructure is confirmed to be the parent phase at room temperature;when annealed at 600?and 700?,the microstructure mainly consists of B19martensite at room temperature.With the increase of annealing time or annealing temperature,the grain size increases gradually.Ti₂Cu precipitates form at the grain boundary during the crystallization process.With the increase of annealing temperature or time,the amount of Ti₂Cu phase increases first and then decreases.The size and amount of Ti₂Ni phase form in the interior of grains increases with the increase of annealing temperature and time.Martensitic transformation of the annealed ribbons is characterized by B2?B19single-step transformation during heating and cooling,The phase transformation characteristic temperatures of ribbons increase with the increase of annealing temperature and time.The martensitic transformation of ribbons with the copper roll speed of 3600r/min and annealed at500?and 600?for 15min show an excellent thermal cycling stability.After 3000 thermal cycling,martensitic transformation start temperature decreases by 0.27?and 0.19?,respectively.