Adaptive Damping in Shape Memory TiNi during Cavitation

Abstract

AbstractRecent studies by this author and others has demonstrated that cavitation-erosion of NiTi coatings or bulk NiTi is exceptional. Studies were undertaken to ascertain whether this property is a consequence of either the general intermetallic properties of NiTi or by an adaptive stress-dissipation mechanism of the cavitation-generated shock wave by A microstructural mechanism related to the shape memory effect.In cavitation, an oscillating pressure field causes the formation and implosion of air bubbles. As a surface easily nucleates bubbles, the subsequent implosion of the bubbles generates stresses approaching several MPa, which are large enough to ablate material, and are also high enough to generate stress-induced Martensite or Austenite, depending on whether the applied stress is tensile or compressive. The implication is that the stress wave may be partially accommodated by the stress-induced transformation, which can dissipate the energy as heat on retransformation to the materials unstressed phase.Calculations concerning the variation of the cavitation-induced stresses and temperature distribution with depth into the TiNi coupled with the associated problems of heat transfer will be presented. It will be shown that an adaptive mechanism is plausible.