Abrasive and erosive wear characteristics of plasma nitriding and HVOF coatings: their application in hydro turbines

This paper describes the abrasion and silt erosion characteristics of plasma nitriding and HVOF coatings along with commonly used steels in hydro turbines. For silt erosion characterisation, hydrofoils scaled down to 1/10 of the actual hydro turbine blade were selected. Angles of incidence, velocity and Reynolds numbers were maintained similar to those that commonly occur in hydro turbines, simulating low as well as high-energy impingement wear. The abrasive wear characterisation was carried out as per ASTM G-65. HVOF coated steel performed much better than plasma nitrided 12Cr and 13Cr–4Ni steels. Plasma nitrided 12Cr steel performed better than plasma nitrided 13Cr–4Ni steel. This is due to its higher microhardness and its ability to absorb more nitrogen under identical plasma nitriding experimental conditions. Based on this experimental study, HVOF and plasma nitrided 12Cr steel are being field-tried on a hydro turbine component, which is severely affected due to abrasion and silt erosion.