The Research Of Cavitation Erosion And Hardness Of Pure Titanium In The Water Cavitation Peening

In this paper, Water Cavitation Peening(WCP) of varied time was used on the surface of pure titanium. The surface morphology, microstructure and surface roughness of the test specimens were analyzed by optical microscope, scanning electron microscope and transmission electron microscope after the Water Cavitation Peening(WCP) treatment. The cavitation erosion and surface strengthening on the surface of pure titanium was investigated at the same time. The results show that the damage zone is divided into the direct cavitating water jet damage zone(the-direct-water-jet-zone) and the mixed cavitating water jet damage zone(the-mixed-water-jet-zone) according to the cavitation erosion damage degree and the characteristics of submerged water jet. In the the-direct-water-jet-zone which is severe damaged, some pits of plastic deformation, needle shaped cavitation erosion and twin of deformation appear on the surface of pure titanium within a very short time(5 min),under the pressure of 30 MPa. Along with the extension of shot peening time(20 ~ 30 min), cracks start to initiation and propagatio in the twin boundaries. A large number of metal flak off at 60 minutes. The damage rate of the-mixed-water-jet-zone significantly lower than the-direct-water-jet-zone. The major changes of the-mixed-water-jet-zone is the twin number is bigger after the WCP, however, there is no plastic deformation and needle shaped cavitation erosion. In the progress of WCP, large number of twin is produced and the-mixed-water-jet-zone ’ s twin layer is thicker and its twin number is denser than the-direct-water-jet-zone in the cross-sectional microstructure. In the early of the WCP, a large number of twin appear, after that, the secondary twin and twin delivery come. The twin number and size of a single twin will increase over time, the biggest size is 120μm. A single twin will not across the grain boundary. Analysis of the EBSD shows that the surface of the specimen have certain residual stress after the WCP under the pressure of 30 MPa, 20 min. The surface roughness of two different damage zones rapidly rising between 20 min to 30 min,however, the-direct-water-jet-zone’s roughness is bigger than the-mixed-water-jet-zone. It reaches to 2.92 μm under the pressure of 60 MPa at 60 min, which meet the requirements of machining. The WCP could improve the microhardness of the surface of titanium,the-direct-water-jet-zone got a bigger surface hardness but smaller depth of hardening layer than the-mixed-water-jet-zone. The hardening effect on the pure titanium surface is best measured in experiment work pressure of 30 MPa, shot peening time between 30 min to 60 min. The average hardness of the-direct-water-jet-zone reach to 350 HV and the-mixed-water-jet-zone reach to 269 HV under the pressure of 30 MPa,30min.