Abstract
To increase the performance of high pressure submerged cavitation jet that has been used for cavitation peening, the effect of stand-off distance and the nozzle geometry on the impact capacity is investigated and optimized. High speed photography of the cavitation bubble clouds taken to reveal the unsteady characteristics of the cavitating jet. The impact ability of the jet with different nozzles and standoff distance is tested using Al 1060 at first, and the optimized jet is used then for cavitation peening on 304 stainless steel. The surface profile as well as the grain structures before and after peening using different nozzles are observed from SEM images. It is found that, the divergent angle of the nozzle has a great effect on the impact capability of the submerged high-pressure jet, which is important for improving the peening efficiency. In the nozzles with divergent angle 40°, 60° and 80°, the 60° nozzle shows the best performance. After peening, grain cells under the metal surface are changed and a twin layer is formed. The current research reveals the transient characteristics of the submerged cavitation jet and main factors that affect its impact rate, which provides guide for the nozzle design and application for the high-pressure cavitation jet peening.
Highlights
Cavitation is the generation of vapour phase in liquid phase without chemical reaction, when the local pressure of the liquid is reduced below the saturated vapour pressure under a stable temperature
Comparison between the various peening methods including water jet peening, laser peening and shot peening shows that cavitation peening can create a residual stress close to that of the laser peening while keeping the surface smooth, which is positive to increase the fatigue strength of stainless steels [14]
For the cavitation cloud generated by the nozzle with 60° divergent angle, the cavitation cloud is obviously wider than that of other two nozzles
Summary
Cavitation is the generation of vapour phase in liquid phase without chemical reaction, when the local pressure of the liquid is reduced below the saturated vapour pressure under a stable temperature. Comparison between the various peening methods including water jet peening, laser peening and shot peening shows that cavitation peening can create a residual stress close to that of the laser peening while keeping the surface smooth, which is positive to increase the fatigue strength of stainless steels [14]. It follows that the unsteady flow characteristics of high-pressure cavitation jet has a great effect on the cavitation impact performance. Hitoshi Soyama et al [16] captured the evolution process of cavitation jet generated by three different nozzles using high-speed photography and used pressure test paper to measure the distribution of the impact pressure of the bubble collapse at the outlet of the nozzles.
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