High-throughput characterization of mechanical properties of Ti-Ni-Cu shape memory thin films at elevated temperature

Hardness and Young's moduli values for Ti_xNi_90−xCu₁₀ (37 at.% < x < 67 at.%) thin films from a continuous composition spread type materials library, annealed at 500 °C for 1 h, were determined at room temperature (martensitic state) and 80 °C (austenitic state) using high-throughput nanoindentation experiments. These values are found to increase as the compositions deviate from Ti contents close to 50 at.%. The increases in hardness is correlated to the presence of Ti-rich and (Ni,Cu)-rich precipitates resulting in precipitate hardening and grain size refinement (Hall-Petch effect). The increase of the Young's moduli is rationalized by considering the significantly higher Young's moduli of the different precipitate phases and applying the rule of mixtures. The contributions of the precipitate phases and the matrix to the combined Young's modulus were estimated by evaluating the load-displacement curves in detail. The obtained results are in good agreement with the Young's moduli determined from thin film curvature measurements R. Zarnetta et al., Smart Mater. Struct. 19 (2010) 65032]. Thus, the experimental restrictions for nanoindentation experiments at elevated temperatures are concluded to not adversely affect the validity of the results.