Effect Of Annealing Temperature And Substrate Temperature On Structure And Phase Transformation Behavior Of TiNi Films

In this paper, the near atomic ratio TiNi alloy films were deposited by magnetron sputtering using TiNi shape memory alloy sheet material as target. Crystallized TiNi films were obtained through vacuum annealing or heating substrate. Then, the influence of annealing temperatures, substrate temperature and the content of Ti on the microstructure and phase transformation of the films were discussed systematically by TEM,SEM,XRD,DSC.,respectively.Through the analysis, the experimental results were as follows:The films,which growed as prismatic were amorphous when the TiNi films were prepared by magnetron sputtering process at room temperature. The content of Ti and the sputtering power can change the crystallization temperature of TiNi amorphous films. As the increasing of the content of Ti and the sputtering power, the crystallization temperature could be decreased. Precipitated phase was formed in the annealing process of the films riched Ni, the process of crystallization can be described as follows, amorphous→amorphous+B2+Ti₃Ni₄→B2+Ti₃Ni₄. B2 equiaxed grains were obtained after the amorphous films riched Ni annealed at 520℃, and the grain size was about 50nm. As the increasing of annealing temperature, the grains of Ti3Ni4 and B2 growed, and the grain size of B2 was about 500nm at 560℃. As the increasing of annealing temperature, the change process of Ti₃Ni₄ morphology can be described as follows, small grain→small elliptical flake→elliptical lens flake→big flake.The films riched Ni, with uniform grain size, obtained by heating substrate to 480℃was crystal, and the films growed in the mode of two-dimensional layer and three-dimensional island alternatively. As the increasing of thickness of the film, B2 phase changed from equiaxed grain to prismatic, and the farther the distance to substrate was the more obvious this growth model. Crystallization temperature of the films could be decreased through heating substrate, and the formation of precipitated phase could also be depressed effectively.A→R and R→M phase transformation of the films riched Ni occurred at the temperature dropping, but only M→B2 phase transformation occurred at the process of heating-up.The films contained three different phase, B2,Ti2Ni and Ti3Ni4 phase, after TiNi films riched Ti were annealed at 530℃. Only B2 phase existed in TiNi films riched Ni through heating substrate to 530℃. Phase transformation behavior of crystallized films obtained by these two process is consistent with TiNi films riched Ni. Phase transformation temperature of the films riched Ti increased obviously comparing with the films riched Ni because of appearance of second phase Ti₂Ni. Residual stress of austenitic TiNi film obtained at different sputter conditions is tensionstress. When the sputtering power,argon gas pressure were all the same, the higher annealing temperature was, the smaller residual stress is; As the increasing of the sputter time, thickness of the film increased and the residual stress decreased. The higher substrate temperature is, the larger residual stress is, and it is obviously larger than the vacuum annealing films.