Cavitation erosion behavior and anti-cavitation erosion mechanism of NiTi alloys impacted by water jet

Abstract

The cavitation erosion behavior and anti-cavitation erosion mechanism of NiTi alloys was explored by water jet equipment conforming to ASTMG134 international standard. The cumulative mass loss rate of NiTi alloys changed slowly by water jet impact within 180 min, then increased sharply and decreased obviously after 240 min. When the impact time lengths were prolonged from 30 min to 60 min, the macroscopic deformation did not significantly increase on the surface of the sample. It was mainly due to the superelasticity of NiTi alloys, resulting in a prolonged cavitation incubation period of NiTi alloys impacted by water jet. When the impact time length was 180 min, work hardening occurred along with the plastic deformation, and cavitation pits appeared on the surface of the sample. When the impact time lengths were extended from 240 min to 300 min, there was no obvious increase in cavitation pits and the material spalling. This is mainly due to the formation of new grains by the recombination of dislocations on the surface and the piling up of dislocations on the grain boundaries at a distance from the impact surface of NiTi alloys. The formation of new grains has consumed high-density dislocation and distortion energy, which can reduce the cavitation erosion damage on NiTi alloys caused by water jet impact. With the increase of water jet impact time, the surface of NiTi alloys undergoes a process of plastic deformation→ work hardening→ increase in dislocation density→ grain refinement→ proliferation of refined grains. Additionally, the residual stress of NiTi alloys with different impact time lengths remained high and they could inhibit the initiation and propagation of cavitation cracks.