In a continuously or intermittently moving component like a compressor blade in an aeroengine, corrosion may occur both at static as well as in the running state. By this, I mean that corrosion may occur singly as well as with an additional influence of fatigue loading. My specific question is, whether there is any research work, anybody has ideas, on the distinguishing traits between those two cases, as far as the corroded surface morphology before any type of crack initiation is concerned?
Dear Mrityunjoy
Surface corrosion phenomenon could occur in most metals/alloys in specific environments. In contrast, corrosion fatigue could only occur to metals/alloys that are susceptible to corrosion under cyclic deformation. This implied that, the manifestation of the corrosion fatigue should be a combine interaction between the surface corrosion and fatigue crack initiation and subsequently, fatigue crack propagation.
So, to answer your question;
It is neither easy to distinguish between corroded surface morphologies prior fatigue crack initiation for pure corrosion nor corrosion fatigue conditions.
Thanks a lot Dr. Habib for your thoughtful reply. Basically, I was looking for some ideas (if exists) on the change in surface and/or subsurface morphology as a result of corrosion under cyclic loading (i.e. corrosion fatigue) prior to initiation of crack.
Yes, one can tell a metal/an alloys is susceptible to corrosion fatigue prior the crack initiation, i.e., in the incubation period of the crack initiation, if the metal/alloys under cyclic loading in corrosive environment has manifested morphologies for instance such as cracking of second phase particles leading to disbonding of second phase particles from the microstructure of the metal/alloys, instrusion/extrusion of surface structures, present of stress raisers ,i.e., notches, manufacturing defects, and so on.
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