SURFACE LAYER NANO-MECHANICAL RESPONSESTO INTERACTION BETWEEN CAVITATIONAND ELECTROCHEMICAL CORROSION

Abstract

Cavitation corrosion resistances of metals have a very much closed relationship with the mechanical properties of their surface layer.It is very important to investigate effects of surface layer mechanical properties on cavitation corrosion to understand synergistic mechanism.Nano-indentation technology is a sensitively power tool for measuring surface layer mechanical properties in nanometer scale.In this work,it was used to study the effects of anodic polarization on the surface layer nano mechanical properties(nano-hardness,H_(nano) and nano-elastic modulus,E_(nano)) of austenitic stainless steel under cavitation.The synergistic mechanism of cavitation corrosion caused by anodic polarization was also investigated by weight loss in conjunction with SEM.The surface layer comprehensive nano-mechanical parameter was defined as(H/E)_(nano).It was found that the profiles of H_(nano),E_(nano) and(H/E) _(nano) with displacement into surface(L) are very different at different anodic polarized potentials.H_(nano) and(H/E)_(nano) decrease and E_(nano) increases with the increment of logarithm of anodic current density.When the samples under cavitation were polarized at passive region,cavitation corrosion of austenitic stainless steel is mainly controlled by erosion.However,it is mainly dominated by corrosion-induced erosion and erosion-induced corrosion,respectively,if anodic polarized potentials were controlled at the beginning of passive to super-passive and super-passive regions.The surface layer nano-hardness is a key factor dominating cavitation corrosion resistances of metals.During the interaction of cavitation with electrochemical corrosion,mass loss of corrosion-induced erosion,which is called non-Faraday weight loss,increases as a result of electrochemical corrosion.The corresponding corroded morphologies with microgrooves,micro-holes and micro-pits were observed.