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In the present paper we use nanoindentation to investigate two shape memory alloys, austenitic Ti 50 Ni 48 Fe 2  and martensitic Ti 50 Ni 40 Cu 10  which both show two step martensitic transformations on cooling from the high temperature regime. No such two step features were observed during nanoindentation. Load controlled nanoindentation experiments were performed using a Berkovich indenter using maximum loads ranging from 0.5 to 85 mN resulting in maximum indentation depths between 30 and 1350 nm. For small maximum indentation loads below 5 mN, longer indentation times result in larger indentation depths (austenitic Ti 50 Ni 48 Fe 2 ). At loads of about 1 mN the indentation curves show an abrupt change in slope which we suggest to be related to an interaction of the deformation and failure of a thin oxide layer and the formation of stress induced martensite (austenitic Ti 50 Ni 48 Fe 2 ) or the de-twinning of martensite (martensitic Ti 50 Ni 40 Cu 10 ). Nanohardnesses and shape recovery ratios strongly increase with decreasing indentation depths below 400 nm. For larger indentation depths, constant values are observed (austenitic Ti 50 Ni 48 Fe 2 : nanohardness 2.45 GPa/recovery ratio 0.25, martensitic Ti 50 Ni 40 Cu 10 : nanohardness 1.6 GPa/recovery ratio 0.4).

Nanoindentation of Ti 50 Ni 48 Fe 2 and Ti 50 Ni 40 Cu 10 shape memory alloys