Slurry Erosion Conditions Research Articles

Slurry erosion behaviour of HVOF sprayed WC–10Co–4Cr and Al2O3+13TiO2 coatings on a turbine steel

Hydroturbine components generally suffer from severe wear due to slurry erosion caused by solid particles entrained in the flowing water. High-velocity oxy-fuel (HVOF) spray process is known for depositing protective coatings on the materials. In this work, WC–10Co–4Cr and Al2O3+13TiO2 coatings were deposited on CF8M turbine steel by HVOF spray process and studied with regard to their performance under slurry erosion conditions. High speed erosion test rig was used for slurry erosion tests and effect of three parameters namely average particle size, speed (rpm) and slurry concentration on slurry erosion of these materials was investigated. The bare steel and Al2O3+13TiO2 coating followed ductile and brittle mechanisms respectively under slurry erosion, whereas the WC–10Co–4Cr coating exhibited mixed behaviour (mainly ductile). WC–10Co–4Cr coating was found to be useful to increase the slurry erosion resistance of steel remarkably.

Examining corrosion effects and corrosion/erosion interactions on metallic materials in aqueous slurries

In this paper aspects of the corrosion behaviour of two materials (Co-base Stellite X-40 and austenitic cast iron BS 3468 S2W) under aggressive slurry erosion conditions are considered. Electrochemical techniques are used to assess the rate of corrosion in impingement conditions. The material degradation has been separated into components of mechanical erosion, electrochemical corrosion and interactive effects. It has been shown that the erosion significantly enhances the corrosion rate of both materials and has the effect of moving Stellite X-40 from a passive to an active corrosion regime. However, in terms of the magnitude of the material loss component the effect of corrosion on erosion (often referred to as synergy) is a much more prominent feature for both materials.

Erosion of alumina ceramics by air- and water-suspended garnet particles

The erosion behaviour of three kinds of commercial alumina ceramics with different microstructures and mechanical properties has been investigated under airborne and slurry erosion conditions. The effect of the angle of impact of the erodent stream on the erosion rate of these materials was determined. A large difference in erosion rates corresponding to shallow angle and normal impact was observed. Such a difference is accounted for by variations in the erosion mechanism. Marked differences were observed in the erosive wear behaviour of the three alumina ceramics. It is concluded that the primary factor controlling the erosion behaviour of alumina ceramics is the microstructure. The effects of varying erodent particle velocity and flux on the erosion rate were also studied. It was found that the erosion rate of alumina ceramics increased with increasing erodent particle velocity and decreasing flux. Finally, a comparison between airborne and slurry erosion of these materials was made. The results indicate that when extrapolated to similar erosion conditions, the slurry erosion rate would be expected to be significantly higher than the airborne erosion rate. Such a difference is attributed to the effects of water on the erosive wear of alumina ceramics.

Comparison of slurry and dry erosion behaviour of some HVOF thermal sprayed coatings

The performance of 10 high velocity oxy-fuel (HVOF) sprayed coatings has been evaluated under both dry particle and slurry erosion conditions at 90° and 20° impingement angles. The coatings were six WC cermets with Co- or Ni-based matrices, a Cr 3C 2–NiCr composite and three metallic alloys. Slurry jet erosion experiments were carried out using a 9 wt.% alumina/water slurry with 35 and 200 μm angular alumina particles, at an impingement velocity of 15 m/s and flow rate of 18 l/min in a re-circulating loop apparatus. Dry erosion was effected in a once-through mode with 50 μm diameter alumina particles at a velocity of 84 m/s and feed rate of 2 g/min. Dry erosion rates three orders of magnitude greater than slurry erosion rates were due mainly to the differences in actual particle-target impact velocities. Coating composition, microstructural integrity and hardness were the major determinants of relative erosion resistance in all tests, with matrix corrosion resistance influencing the surface damage resistance of cermets in longer duration aqueous slurry tests.