Corrosion and Protection of Sintered Metal Parts

Abstract

An analysis of the mechanism of corrosion and protection of sintered powder metal parts reveals that the role of surface pores is an unusual and incompletely understood characteristic. Electrochemical principles can be enunciated and interpreted in the context of pores, which may or may not be interconnected throughout the structure, and models can be proposed on the basis of well-known metallographic features. In these models the main bulk surface may be assumed to be covered with an oxide film and acts as cathode with respect to the pores themselves which are relatively anodic and therefore corrosion sites. Any protective mechanism must therefore be primarily concerned with the elimination of pores by sealing, several processes being available for this stage. Subsequent coating may then be directed towards galvanic protection rather than the micro-throwing power problems of filling the pores.