All Optical Pump Probe Setup for Austenitic and Casted Steel Study

Gasteau, Damien
Chigarev, Nikolay
Ducousso-Ganjehi, Lili
Tournat, Vincent
Gusev, Vitali
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Polycrystalline materials are the most natural form of metals and are commonly used in industry. In particular, steels such as austenitic steels and casted steels are widely used for their specific properties in fatigue and resistance to heat in particular for application such as water pipes for cooling system in nuclear technologies. Usually studied by an effective approach, the characterization of the composing grains remains an essential aspect of their global physical behavior.

A sub nanosecond pump probe laser setup is used to generate and detect acoustic waves in a sample in order to explicit the anisotropy and morphology by the study of variations of velocities of surfaces waves. A statistical approach of the variation of flight time due to the anisotropy is used to estimate the elastic constants of the composing grains of an austenitic steel sample thanks to an inversion procedure. The method considers a distribution as a unique signature of the sample and allow an evaluation of the three elastic constants with a good agreement with the literature.

The all optical setup is also used to scan the surface of a piece of casted steel and automatically measure the local velocities of surface acoustic waves which opens the way to cartography in velocity of the sample surface structure. The local variations of velocities inside the macro-grains is shown to be the proof of the presence of sub-structures of recurrent orientations