Effects on trends in negative pressure of surface pre-treatments for the sealing plugs of a water-metal Berthelot tube system

Trends in negative pressure over a few thousand cavitation events have been investigated for a Berthelot system comprising water/stainless steel/tube/sealing Ni plug in order to study the effects and extents of surface pre-treatments for the sealing metal, polishing, etching, and electroplating. The polishing and etching pre-treatments separated two kinds of cavitation nuclei on the metal surface; gases trapped within pores (crevices) (i) in the metal surface, and (ii) extending deep into the metal bulk. The latter, although much tougher, influenced negative pressure for a thousand cavitation events at most. The rise in negative pressure after a total of 1800 temperature cycles levelled off at around -115 bar (-11.5 MPa) irrespective of the surface finishes of the plugs. Electroplated plugs gave poor increasing trends owing to the co-deposited hydrogen. Impurity gases in the metal did limit the rise in negative pressure. These results, together with those reported before, have validated the authors extended gas-trapping crevice model, negative pressure is eventually limited by a supply of gas from sources in the metal bulk to surface crevices.