Martensitic Transformation Behavior And Functional Properties Of Precipitated Ti-Ni-Cu Alloy Films

Ti-Ni-Cu shape memory alloy,as a good potential candidate for MEMS,has advantages of narrow hysteresis,high response rate and excellent mechanical properties.In this study,investigates the effect of precipitation on the martensitic transformation behavior of Ti-Ni-Cu alloy films.After the crystallization of the amorphous Ti-Ni-Cu alloy film,different types,sizes and distributions of the second phase can be precipitated.The martensitic transformation and functional properties of precipitation phase alloy films have a significant effect.The phase composition,microstructure,martensitic transformation,mechanical properties and damping properties of Ti-Ni-Cu alloy films were investigated by XRD,TEM,DSC and DMA.The sputtered Ti_51.67Ni₃₈Cu_10.33 alloy film was amorphous,its crystallization temperature was about 460°C,and the crystallization activation energy was 342KJ/mol.It is shown that the annealing process did not effect the grain size of the Ti-Ni-Cu alloy film,and the size of grain was about 3?m.After annealing at different temperatures,there are different types of precipitates in Ti-Ni-Cu thin films:when the annealing time is constant,the annealing temperature increases,and the precipitated phase consists of plate-like 6 nm GP?the size of thin-plateles Ti₂Cu is 17 nm and a small amount of Ti₂Ni phase with a diameter of 6 nm?thin-plateles Ti₂Cu phase with a diameter of 42 nm and a large number of Ti₂Ni phases with a diameter of 13 nm;when the annealing temperature is constant,the precipitation phase changes to a GP region of 12 nm?thin-plateles Ti₂Cu phase with a diameter of 21 nm and a small amount of spherical Ti₂Ni of 10 nm phase?spherical Ti₂Ni phase with a diameter of 25 nm.The Ti_51.67Ni₃₈Cu_10.33 alloy film undergoes a one-step phase change.As the annealing temperature increases,the phase transition temperature gradually decreases.It was shown that the Ti_51.67Ni₃₈Cu_10.33 alloy film exhibits a good shape memory effect,and no unrecoverable strain occurs when the strain reaches 7%during constant stress drawing.At the same time,it exhibits good superelasticity.The strain recovery of Ti_51.67Ni₃₈Cu_10.33 alloy film reaches 8%when the test temperature was 65°C after the annealing condition was 600°C-1 h.It was shown that the maximum internal friction value increases with the increase of annealing temperature in the damping test from-50°C to 150°C,and the maximum could reach 0.18.The elastocaloric effect of the material are similar to the damping performance.As the annealing temperature increases,the entropy change and the adiabatic temperature difference increase.The maximum theoretical calculation of the adiabatic temperature difference can reach 14.95°C,and the maximum entropy becomes 65.95 JKg^-1K^-1...