Corrosion preserving high density plasma treatment of precipitation hardening stainless steel

Specialty alloys such as precipitation hardening stainless steels are routinely used in critical applications requiring high strength and corrosion resistance, e.g. in aeronautics, in ground transportation and the biomedical field. Nonetheless, their tribological properties remain poor, while the application of surface treatments results in loss of corrosion resistance. Therefore, typically a not fully satisfactory compromise must be adopted. In the present work, the improvement of tribological features, without loss of corrosion resistance, of the 1.4545 (15-5PH) steel has been explored with the use of high density plasmas. The work has focused on long cylindrical geometries, close to those of real applications. The microstructure and composition of the treated surfaces were studied and the corresponding corrosion resistance stablished. The characteristics of the high density plasmas as well as the sample disposition were key factors in the outcomes, which ranged from fully corroded to corrosion resistant surfaces. Results also showed in certain cases the high density plasmas causing surface cracks followed by local corrosion. Additionally tribological studies demonstrated improvement in wear resistance, and electrical contact resistance (ECR) was found to be a good indicator of the wear phenomena occurring along the tests. An equivalent electric circuit is proposed. Actually ECR could be a useful and simple way of monitoring the surface status and assist in assuring safe and dependable operational lives of the components. In conclusion, treatment conditions of cylindrical 1.4545 (15-5PH) have been defined, which provide with an improved tribological performance, preserving corrosion resistance, with ECR a useful performance monitoring parameter.