| ZHANG Sheng-bo,XIANG Song,CHENG Tao,SHI Wei.Influence of Surface Nanocrystallization of 20CrMnTi on Behavior of Localized Corrosion by Ultrasonic Surface Rolling Processing[J],48(8):136-143 |
| Influence of Surface Nanocrystallization of 20CrMnTi on Behavior of Localized Corrosion by Ultrasonic Surface Rolling Processing |
| Received:November 18, 2018 Revised:August 20, 2019 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2019.08.018 |
| KeyWord:20CrMnTi ultrasonic rolling micro-area corrosion microstructure deformation EBSD fatigue crack initiation |
| Author | Institution |
| ZHANG Sheng-bo |
a.School of Materials and Metallurgy, Guizhou University, Guiyang , China |
| XIANG Song |
a.School of Materials and Metallurgy, b.National and Local Joint Engineering Laboratory for High Performance Metal Structural Materials and Manufacturing Technology, Guizhou University, Guiyang , China |
| CHENG Tao |
a.School of Materials and Metallurgy, Guizhou University, Guiyang , China |
| SHI Wei |
a.School of Materials and Metallurgy, b.National and Local Joint Engineering Laboratory for High Performance Metal Structural Materials and Manufacturing Technology, Guizhou University, Guiyang , China |
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| Abstract: |
| The work aims to study the effects of deformation-induced nano-surface on the local corrosion initiation behavior of 20CrMnTi under different static pressure conditions. The surface layer of 20CrMnTi was strengthened by ultrasonic rolling technique (USRP) and characterized by laser confocal microscopy, EBSD and electrochemical methods. The effects of corrosion and local corrosion of deformation-induced nano-surface on stress localization and microcracks were evaluated. Under the condition of weak alkaline corrosion, after the 20CrMnTi surface layer was ultrasonically rolled, the pitting breakdown potential of the sample showed a significant negative shift. At the same time, with the increase of rolling pressure, the surface passivation of 20CrMnTi showed significant hysteresis, and the passivation current and the blunt current increased synchronously, accompanied by the reduction of the passivation interval. Moreover, with the high-precision three-dimensional reconstruction of the laser confocal microscope, it was observed that under the simulated weak corrosion environment, the 20CrMnTi ultrasonic rolling surface showed a corrugated local corrosion texture protruding along the rolling direction and with the rolling pressure increasing, the local corrosion damage at corrugated interface showed a certain deepening and broadening, which led to a high risk of crack initiation. Through EBSD characterization, it was found that under the action of ultra-high frequency impact, the surface layer of 20CrMnTi was transformed into a refinement surface layer with randomly distributed grain orientation, but due to the orientation difference of crystal grains on both sides of the corrugation, under the impact of the high-frequency multi-point of the rolling head, there were differences in the refinement mechanism of grains with different orientations, so the local corrosion micro-cells with obvious difference in crystal grain composition on both sides of the corrugation showed higher solubility selectivity. Under the ultrasonic rolling process, the surface grain of 20CrMnTi shows obvious difference in the degree of refinement in the local micro-area. Under electrochemical action, the difference in micro-area potential between the refinement grains leads to selective dissolution on the surface. Corrugated local corrosion pits are generated at the grain folding interface, and as the ultrasonic rolling pressure increases, the corrugated corrosion pits are significantly broadened and deepened, and the risk of fatigue crack initiation is high. |
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