TABLE OF CONTENTS Surface coating should be chosen with regard to the application it has to serve, along with a consideration for the basic metal it has to cover. Some coatings are used as a protection against abrasion, corrosion, oxidation, and for a host of other reasons. Surface coating creates a barrier between the basic metal itself and the environment, sometimes detrimental to its stability. There are coatings to alter the frictional properties and to enhance the an aesthetic appeal of the part. Various coatings may be used for various applications but are most often chosen to protect the basic metal, the basic product, from outer influences.
Even two metallic parts within an assembly are capable of attacking each other by forming a galvanic cell, the same way a basic material may react adversely to its coating if chosen improperly. Evaluation of the possibility of a galvanic couple formation must therefore be considered when choosing the type and amount of protection a coating should offer. This involves a survey of whether the coating is in its nature cathodic or anodic toward the metal underneath it.
For example, a steel may be protected from other influences by nickel or zinc coating, even though nickel is cathodic to iron and zinc is anodic. Nickel protects the steel by successfully blocking the influence of the outer corrosive environment on the material, for the purpose of which, such coating must be free of pores. Zinc provides protection by corroding more readily than steel, and...
