Experimental Investigations on Slurry Erosion Behaviour of HVOF and HVOLF Sprayed Coatings on Hydraulic Turbine Steel

Abstract

Slurry erosion behaviour of high velocity oxy fuel (HVOF) and high velocity oxy liquid fuel (HVOLF) sprayed coatings on hydraulic turbine material (i.e. CA6NM steel) was investigated at different levels of various parameters. The 50 % (WC–Co–Cr) and 50 % (Ni–Cr–B–Si) coating powder was deposited on CA6NM steel samples by HVOF and HVOLF thermal spraying techniques. Erosion tests were conducted on self-made erosion test rig with various factors as explained in the "experimentation" section. Coated and uncoated samples of CA6NM steel were investigated by following a design of experiments based on the L9 Taguchi technique, which was used to obtain the data of erosion test in a controlled way. Four parameters used in L9 experiment were velocity, impact angle, slurry concentration and average particle size. The study revealed that the velocity, impact angle and slurry concentration were most significant among various parameters, influencing the wear rate of the coatings. The average particle size did not show any significant effect on both the coatings. In comparison, coated samples showed approximately two times better results in erosion resistance than uncoated samples. Scanning electron microscopy of eroded surface showed different mechanisms of erosion on different samples under various conditions.