Comparaison entre cavitation ultrasonore et hydrodynamique : point de vue du matériau

International audienceThis study investigated the difference of mechanical response of the martensitic stainless steel X3CrNiMo13-4/S41500/CA6NM QT780 between hydrodynamic and acoustic cavitation erosion. Results show that acoustic cavitation erosion generates small pits at high temporal frequency on the material while hydrodynamic cavitation erosion produces larger pits at a lower frequency. Acoustic cavitation erosion tests have been performed using a 20 kHz ultrasonic horn located at 500 µm in front of a specimen. This experimental setup, known-as indirect method, is inspired by the ASTM G32 standard. Hydrodynamic cavitation erosion tests were performed at a constant cavitation number equal to 0.870 corresponding to a flow velocity of 90 m.s-1 and upstream pressure of 40 bars. In addition, for a given exposure time the percentage of surface covered by the pits is smaller for acoustic cavitation than for hydrodynamic cavitation. Three successive steps have been identified during the damage process: persistent slip bands (PSB) first appear on the surface, cracks initiate and propagate at the PSB locations and non-metallic interfaces and finally parts of matter are torn off. A careful time examination of the same small area of the exposed sample surface by scanning electron microscopy (SEM) reveals that acoustic cavitation is faster to initiate damage than hydrodynamic cavitation