Microstructure and cavitation-silt erosion behavior of two HVOF-sprayed hardfacing coatings for hydro-turbine applications

Abstract

The cavitation-silt erosion (CSE) has caused severe technical challenges and economic losses to the hydro-turbine operated in silt-laden river. In this manuscript, two hardfacing (i.e., WC-20(Cr3C2)-7Ni and Cr3C2-25(NiCr)) coatings were manufactured via a high-velocity oxygen fuel (HVOF) spraying method, and effects of flow velocities (FVs) and sand concentrations (SCs) on their CSE behaviors with the help of a rotating disk rig facility were investigated. Results indicated that the WC-20(Cr3C2)-7Ni coating exhibited lower porosity, higher KIC, H/E and H3/E2 as well as superior CSE resistance, and its CSE resistance was less affected by FV as well as SC compared with the Cr3C2-25(NiCr) coating. Both FV and SC had a positive effect on the CSE degradation of the two hardfacing coatings, while SC had a greater effect on their CSE resistances than FV. With increasing FV and SC, the WC-20(Cr3C2)-7Ni coating experienced the CSE damage of the few micro-cracks, scattered cavitation pinholes, fracturing of carbide particles, pronounced scour marks, isolation and peeling off of carbide particles, and crater formation, while the CSE process of the Cr3C2-25(NiCr) coating primarily included the micro-cracks and scattered cavitation pinholes, peeling off of chromium carbide particles, long and deep scour marks, and coating spalling and crater formation.

Keywords

• Hardfacing
• Coating
• HVOF
• Cavitation-silt erosion