Corrosion–wear mechanisms of hard coated austenitic 316L stainless steels

Austenitic stainless steels like 316L are amongst the most commonly selected structural alloys for use in corrosion environments. Unfortunately, their resistance to surface degradation caused during sliding contacts with other materials, in such environments is poor. Here, a synergistic combination of mechanical (wear) and chemical (corrosion) processes, known as corrosion–wear processes, are responsible for causing surface material loss. Accordingly, efforts are being made to identify surface treatments that can enhance the corrosion–wear resistance of 316L and similar alloys. One plausible solution is to apply thin hard coatings (∼5–10 μm thick) using various plasma-based technologies. In practice, this is often fraught with difficulty because of the complex nature of the pervading corrosion–wear mechanisms. This paper presents our recent work that has identified three major corrosion–wear mechanisms that must be minimised if a successful surface engineering design is to be achieved for corrosion–wear protection. These are: Type I—the removal of the coating passive film during sliding contact; Type II—galvanic attack of the substrate resulting in blistering of the coating and; Type III—galvanic attack of the counterface material leading to abrasion of the coating during subsequent sliding contact.