Evolution of phase transformation behavior and mechanical properties with crystallization in NiTi thin films

The phase transformation and nanoindentation response as a function of crystallinity of NiTi thin films were assessed. A phase change was detectable in samples with 1% crystallization. Measured mechanical properties indicate that the films soften with crystallization. Films partway through crystallization presented a bimodal response: crystalline regions had moduli similar to fully crystallized films; and amorphous regions had larger moduli (larger than as-deposited amorphous films) attributable to structural relaxation. A modified Voigt model describes the evolution of the modulus in crystallizing films.