High-throughput study of martensitic transformations in the complete Ti-Ni-Cu system

The shape memory properties of the complete Ti-Ni-Cu thin film system were investigated using combinatorial methods, i.e. fabrication and high-throughput characterization of thin film materials libraries. Thin film composition spreads were deposited using a wedge-type multilayer technique and annealed at 500 degrees C, 600 degrees C and 700 degrees C for 1 h for alloy formation. The complete composition regions showing reversible phase transformations were identified for each annealing temperature. These regions are well extended in comparison to prior knowledge. Furthermore, the composition-structure-property relations governing the phase transformation characteristics in the thin film samples were determined. For films annealed at 500 degrees C and 600 degrees C the transformation temperatures are highest for compositions close to Ti50Ni50-xCux and decrease as the thin film compositions deviate. Similarly, the thermal transformation hysteresis is found to be smallest for "stoichiometric" (Ti50Ni50-xCux) compositions. Precipitation of Ti-rich and (Ni,Cu)-rich phases is found to be responsible. With increasing annealing temperature the transformation temperatures increase and the thermal hysteresis values decrease for compositions showing B2 -> B19 phase transformation paths, due to coarsening of the precipitate phases. The alloying process of the multilayer thin films leads to the formation of the equilibrium phases. The formation of Guinier-Preston zones is suppressed. For thin films annealed at 700 degrees C the transforming composition region is comparatively smaller and the phase transformation properties are influenced by Ti2Ni precipitates. (C) 2012 Elsevier Ltd. All rights reserved.