Slurry Erosion Performance of Ni-Al 2 O 3 Based Thermal-Sprayed Coatings: Effect of Angle of Impingement
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. S. Grewal, Anupam Agrawal, H. Singh, and B. A. Shollock (Submitted May 10, 2013; in revised form August 9, 2013) In this paper, slurry erosion performance of high velocity flame-sprayed Ni-Al2O3 based coatings was evaluated. The coatings were deposited on a hydroturbine steel (CA6NM) by varying the content of Al2O3 in Ni. Using jet-type test rig, erosion behavior of coatings and bare steel was evaluated at different impingement angles. Detailed investigation of the surface morphology of the eroded specimens was undertaken using SEM/EDS to identify potential erosion mechanism. A parameter named ‘‘erosion mechanism identifier’’ (n) was used to predict the mode of erosion. It was observed that the coating prepared using 40 wt.% of Al2O3 showed a highest resistance to erosion. This coating enhanced the erosion resistance of the steel by 2 to 4 times. Spalling in the form of splats and chunks of material (formed by interlinking of cracks) along with fracture of Al2O3 splats were identified as primary mechanisms responsible for the loss of coating material. The erosion mechanism of coatings and bare steel predicted by n was in good agreement with that observed experimentally. Among different 1=3 2 parameters, KIC H , a function of fracture toughness (KIC) and hardness (H) showed excellent correlation with erosion resistance of coatings at both the impingement angles.
Keywords
abrasion, alumina, cermets, erosion resistant coatings, flame spraying, slurry erosion
1. Introduction Hydropower machines suffer from various degradation problems such as slurry and cavitation erosion. The interaction of sand particles present in the river water with the solid surfaces results in the degradation of target surfaces (Ref 1, 2) through a phenomenon known as slurry erosion. Although, erosion is a phenomenon responsible for loss of material from the solid surfaces, however, continuous exposure to erosive environment could produce deleterious effects resulting in bulk failure of components (Ref 3). A prolonged exposure to erosion could prove to be detrimental for the working life of submerged components. Various solutions have been suggested in the literature for controlling the erosion; however, none of them have achieved overwhelming response. Among the common solutions available to tackle the erosion problem, use of coatings is the one that has been widely explored (Ref 4-10). The major advantage of coatings is their highly flexible nature. Several techniques are available using H.S. Grewal, Anupam Agrawal and H. Singh, School of Mechanical, Materials and Energy Engineering, Indian Institute of Technology Ropar, Rupnagar, India; and B.A. Shollock, Department of Materials, Imperial College London, London SW7 2BP, UK. Contact e-mails: [email protected] and hnr97@ yahoo.com.
Journal of Thermal Spray Technology
which almost all categories of materials can be coated with possibly any desired composition. Among them, thermal spray is one such coating technique that has shown huge potential in hydroturbine industry (Ref 11). T
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