Improving cavitation erosion resistance of austenitic stainless steel in liquid sodium by hardfacing – comparison of Ni and Co based deposits

• Paper discusses results of cavitation erosion experiments in liquid sodium.
• Improvement in cavitation erosion resistance by hardfacing is studied.
• Materials studied are SS 316L and coatings of Stellite6 and Colmonoy5.
• Results are explained using material stacking fault energy and fracture toughness.

Cavitation affects the performance of hydraulic machinery and also results in erosion damage. Although the damage produced in sodium is more intense than that in water, it is uneconomical to design hydraulics to totally avoid cavitation. The designer is left with the choices of improving hydraulic design and/or using materials/coatings with good resistance to cavitation. Susceptibility to cavitation is evaluated for two different hardfaced coatings, viz. Co-based Stellite6® alloy coatings and Ni-based Colmonoy5® coatings, and the results compared with that for 316L austenitic stainless steel. Study reveals that Stellite6 alloy coating is more resistant to cavitation than Colmonoy5 in liquid sodium. However, the cavitation resistance of Colmonoy5 coating is better than that of austenitic stainless steel 316L, the substrate material on which these alloys are deposited. Results are explained based on the differences in the stacking fault energy and fracture toughness of the materials.