Temperature and surface potential correlations with serrated flow of low carbon steel

摘要

The Portevin-Le-Chatelier (PLC) effect manifests itself as serrated plastic flow in strain controlled tensile tests of dilute alloys. The effect causes most of the material qualities to suffer, including the ductility. Monitoring the effect is important since the induced loss of ductility can cause premature failures on structural materials under load. Surface potential fluctuations of AISI 1020 low carbon steel during its serrated flow was investigated by a combined set-up of an electrochemical cell and a slow strain tensile test. The steel was exposed to an aqueous electrolyte under a strain rate of 1.6 x 10 -6/s, and the surface potential was monitored in situ during the creation, magnification, and annihilation phases of the serrated flow achieved by changing test temperatures stepwise between 50 and 85 °C. The serration amplitude showed strong correlations both with test temperatures and the surface potential. A rather large potential shift around 110 mV through active direction during the burst of serrations hinted that the slip bands, in addition to temperature and strain, could also be responsible for the charge release due to the dislocation domains carried in them. The study verifies a potential use of the set-up for monitoring the PLC events in aqueous environments where load cells, extensometers etc. are not utilizable.