Slurry erosion performance analysis and characterization of high-velocity oxy-fuel sprayed Ni and Co hardsurfacing alloy coatings

In this paper, the performance of hardsurfacing Cobalt alloy (Stellite 6) and Nickel alloy (Colmonoy 88) was tested in tribological slurry conditions by using a pot tester. Thermal spraying powders were deposited on AISI 316L substrates by using a high-velocity oxy-fuel (HVOF) technique. Wear experiments are carried out using a lab-scale pot tester at low velocities like 1.81, 2.71, 3.61, and 4.59 m/s. The high mass flux of ashes (ranging 30–60 wt%) is used to produce severe accelerated conditions. The effect of the size fraction of eroding particles was evaluated by preparing the multi-sized slurries of size fractions (ASTM: −200, −140 + 200, −100 + 140, and −60 + 100). Results show that the microhardness of AISI 316L was improved by the HVOF depositing of Cobalt alloy-6 and Nickel alloy-88. The average surface microhardness of Cobalt alloy-6 was found lower (439 ± 19 HV₁₀₀₀) than the Nickel alloy-88 coating (601 ± 11 HV₁₀₀₀). Erosion performance of coatings was found to be increased with an increase in the value of the velocity, time, mass flux, and weighted mean size of eroding particles. Results show that the Ni-alloy improved the wear resistance of AISI 316L by 2.03 ± 0.021 times in fly ash slurry conditions and 3.21 ± 0.035 times in bottom ash slurry conditions. However, the Co-alloy was beneficial in reducing the wear of AISI 316L by 1.48 ± 0.019 times in fly ash and 2.50 ± 0.032 times in bottom ash slurry conditions. Moreover, the maximum wear of AISI 316L steel was observed at an impingement angle of 30° whereas 60° and 45° for Ni-alloy and Co-alloy coatings respectively in fly ash conditions. Although, the AISI 316L and Ni-alloy coating show maximum wear at the same impingement conditions under the bottom ash slurry conditions. However, the Co-alloy coating showed maximum wear at 60° in bottom ash slurry conditions.