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

Received 27 October 2009; received in revised form 18 February 2010; accepted 24 February 2010. published online 02 March 2010.

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.

Keywords: Amorphous materials, Thin films, Crystallization, Nanoindentation, Mechanical properties

a Department of Mechanical Engineering, Yale University, New Haven, CT 06520, USA

b Dept. Fisica Materia Condensada, Universidad del Pais Vasco, Apdo 644-48080 Bilbao, Spain

c Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Corresponding author. Address: Department of Mechanical Engineering, Yale University, New Haven, CT 06520, USA.

PII: S1359-6462(10)00121-1

doi:10.1016/j.scriptamat.2010.02.037

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