Berlin 2015 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 17: Postersession I

MM 17.21: Poster

Monday, March 16, 2015, 18:00–20:00, Poster E

In-situ TEM of phase transitions in TiNi based shape memory alloys — •Timo Wuttke and Cynthia Ann Volkert — Institute of Materials Physics, University of Göttingen, Friedrich-Hund-Platz 1, Germany

Shape memory alloys (SMA) are known for their ability to recover plastic deformation upon heating and thus may be used for applications such as actuation in a wide range of industry, science and medical related fields.

The key mechanism responsible for this behavior is a reversible diffusionless solid-state phase transition between a highly twinned martensitic state and an untwinned austenitic phase of higher crystal symmetry.

We studied the martensitic phase transition of TiNi and TiNiCu alloys utilizing in-situ TEM techniques. Both commercially available wires and samples prepared with vacuum arc melting were used. All samples were annealed at 600°C for 1,5h and water quenched to ensure that the phase transition takes place between RT and 100°C thus making it easily accessible in the TEM.

The movement of the austenite-martensite reaction front can be directly observed and manipulated by applying temperature gradients to the TEM lamella. This allows us to study the phase transformation with high spatial resolution. Atomic level information obtained at the moving phase boundary using HRTEM will be discussed.