Transformation and deformation behavior in sputter-deposited Ti-Ni-Cu thin films

Ti-Ni-Cu thin films were prepared by RF magnetron sputtering. Their compositions were determined by EPMA to be ranging in Cu-content from 0 to 18.0at%. All the thin films were solution-treated at 973R for 3.6ks followed by quenching into water. Transformation and deformation characteristics and lattice constants in the thin films have been investigated systematically by means of differential scanning calorimetry(DSC), constant load thermal cycling tests and X-ray diffractometry, respectively. The martensite transformation. temperatures of all the thin films were around 323K; they decreased only slightly with increasing Cu-content in the range within 9.5at%, while they slightly increased in the range beyond 9.5at%. The temperature hysteresis associated with the transformation showed a strong dependence on Cu-content, i.e., it decreased from 27R to 10K with increasing Cu-content from 0at% to 9.5at%. In the 9.5at%Cu specimen, a two-stage transformation appeared and it was determined as B2 <----> Orthorhombic <----> Monoclinic by the X-ray diffractometry. Perfect shape memory effects were observed corresponding to these transformations. By the addition of Cu, the maximum recovery strain decreased from 3.9% to 1.1% and the critical stress for slip greatly increased from 55MPa to 350MPa with increasing Cu-content.