Multi-degradation behavior of austenitic and super duplex stainless steel – The effect of 4-point static and cyclic bending applied to a simulated seawater tribocorrosion system

Tribocorrosion can be significantly influenced by applied static and cyclic tensile stresses. This effect has been proposed recently and is known as multi-degradation. Components exposed to tribocorrosion are usually structural elements, also supporting applied loads both as sustained and dynamic strain causing additional surface and subsurface stresses at the rubbing interface. It is therefore important to understand how the tribocorrosion performance of materials is affected by applied mechanical tensile loads. Initial modeling work of the synergies of multi-degradation has been proposed with no experimental proof. In the present work the multi-degradation mechanisms of austenitic stainless steel (UNS S31603) and 25% Cr super duplex stainless steel (UNS S32750) are studied using a lab scale multi-degradation (LSMD) test rig. Experiments were performed at both OCP and 0 mV versus Ag/AgCl applied potential conditions (in 3.4 wt% NaCl) during reciprocating ball-on-plate sliding contact (Ø 4.76 mm, alumina ball) and at simultaneous static and cyclic 4-point bending exposures. These tests show that applied mechanical straining and electrochemical potential conditions significantly influence the material loss rate according to the multi-degradation model. These complex degradation mechanisms are dependent on microstructural changes at the surface and at subsurface affecting the mechanical properties controlled by the cyclic stress–strain response and passive film integrity of the alloys.