Muthusamy Kamaraj

Hydraulic turbines often suffer material damage from combined cavitation and silt erosion (CSE), particularly in silt-laden rivers. This leads to frequent maintenance and significant revenue loss, even when using industry-standard High-Velocity Oxy-Fuel (HVOF) sprayed WC-CoCr coatings. To address these limitations, this study presents a systematic evaluation of four cermet coating systems to identify a more durable alternative. Two material systems (WC-CoCr and CrC-NiCr) are deposited by two thermal spray processes (HVOF, and High-Velocity Air-Fuel, HVAF) and subjected to comprehensive laboratory CSE testing and in-service field validation on Francis turbine sealing rings at Nathpa Jhakri hydropower station. The HVAF-sprayed WC-CoCr coating demonstrated unequivocally superior performance, exhibiting the lowest cumulative mass loss, the longest time to substrate exposure (8 minutes), and the smallest crater dimensions in CSE wear tests. This performance is directly attributed to its superior as-sprayed properties, including the highest average hardness (1236±82 HV0.5) and fracture toughness (5.7±0.55 MPa √m), a dense (<1% porosity) microstructure, and the suppression of brittle decarburised phases. Field tests in a Francis turbine further confirm that HVAF WC-CoCr is the most effective coating, consistent with laboratory findings. Coatings failed by binder plastic deformation, crack growth and carbide fracture. This work validates the HVAF WCCoCr coating as a high-performance solution capable of extending the operational lifetime of hydroturbine components in severe CSE environments.

Hydraulic turbines often suffer material damage from combined cavitation and silt erosion (CSE), particularly in siltladen rivers. This leads to frequent maintenance and significant revenue loss, even when using industry-standard High-Velocity Oxy-Fuel (HVOF) sprayed WC-CoCr coatings. To address these limitations, this study presents a systematic evaluation of four cermet coating systems to identify a more durable alternative. Two material systems (WC-CoCr and CrC-NiCr) are deposited by two thermal spray processes (HVOF, and High-Velocity Air-Fuel, HVAF) and subjected to comprehensive laboratory CSE testing and in-service field validation on Francis turbine sealing rings at Nathpa Jhakri hydropower station. The HVAF-sprayed WC-CoCr coating demonstrated unequivocally superior performance, exhibiting the lowest cumulative mass loss, the longest time to substrate exposure (8 minutes), and the smallest crater dimensions in CSE wear tests. This performance is directly attributed to its superior as-sprayed properties, including the highest average hardness (1236±82 HV0.5) and fracture toughness (5.7±0.55 MPa√m), a dense (<1% porosity) microstructure, and the suppression of brittle decarburised phases. Field tests in a Francis turbine further confirm that HVAF WC-CoCr is the most effective coating, consistent with laboratory findings. Coatings failed by binder plastic deformation, crack growth and carbide fracture. This work validates the HVAF WC-CoCr coating as a high-performance solution capable of extending the operational lifetime of hydroturbine components in severe CSE environments.

This study explores the effect of dispersion of Fe-doped SnO₂ rods and SnO₂ rod-based additives in transformer oil for lubricant applications. A notable reduction in friction and wear is achieved at a low weight percentage ∼0.025 wt % of additives along with oleic acid and oleyl amine as dispersants. Coefficient of friction, wear scar diameter, roughness, and wear depth for base oil are reduced by ∼32%, ∼15%, ∼73%, and ∼78%, respectively, by the addition of SnO₂ rods. Surface functionalization with Fe ions further helps to significantly decrease these properties up to ∼40%, ∼43%, ∼77%, and 89%, respectively. A marginal reduction of ∼4%, ∼4%, ∼21%, and ∼10%, respectively, is observed when only dispersants are added. This is attributed to the complete filling of asperities and the polishing effect. The synergistic effect of Fe-doped SnO₂ rods and organic dispersants induces low shear strength tribo-sintered patchy film formation on the tribo-contacts, thereby contributing to considerable enhancement in the lubrication behavior. High dispersion stability of the lubricants is observed. The results of robust bootstrap tests for analyzing the tribological data agree with the experimental outcomes. Ordering of materials and concentrations has helped in the selection of optimal lubricants. This work will stimulate the use of novel Fe-SnO₂ based additives for efficient energy applications.