HVOF coating and surface treatment for enhancing droplet erosion resistance of steam turbine blades

This paper describes the water droplet erosion characteristics of high velocity oxygen fuel sprayed (HVOF) coated and laser hardened 12Cr steels along with steels and titanium alloys used in steam turbine blades at two different energy fluxes. For droplet erosion study, round samples as per ASTM G73-98 were used. At low energy flux, the HVOF coated 12Cr steel performed much better than 12Cr and 13Cr–4Ni steels. This is due to integrity of hard carbide particles in cobalt chrome matrix and its ability to absorb shocks due to high hardness of the carbide particles. During incubation as well as in the long run, laser hardened 12Cr steel performed exceptionally well followed by 17Cr–4Ni ‘PH’ and heat-treated 12Cr steel. From the experimental study, it appears that ultimate and modified resilience of materials play significant role to combat droplet erosion. Droplet erosion test results of all these materials and HVOF coating along with their properties and scanning electron micrographs are reported and discussed in this paper.