Improved Resistance of Nanoparticle-Laden Polymer Coatings Subjected to Combined Silt and Cavitation

Abstract

Abstract Hydropower generation, particularly in the Himalayan region during monsoons, suffers because of the erosion of turbine components, which is due to the high concentration of silt present in water. These high-power machines also suffer from cavitation, especially at off-design conditions. However, erosion caused by the synergistic effects of silt and cavitation can cause more serious degradation, is more complex, and remains an unsolved problem in hydraulic machines. The present work addresses this concern through the systematic study of different polymeric coatings under a controlled silt and cavitation environment. This article discusses the design and development of an experimental facility, where a specimen can be subjected to combined submerged slurry jet along with acoustic cavitation produced by a focused ultrasonic transducer. Novel polymeric coatings made of polyurethane (PU) reinforced with hard nanoparticles (B4C and SiC) of varying concentrations (from 1 to 75 weight percentage [wt. %] being defined with respect to polymer weight) are used in this work. These coatings show erosion resistance superior to the base material (16Cr-5Ni martensitic stainless steel) commonly used to make hydroturbine blades. Results are divided into three divisions. At first, we present erosion kinetics and discuss possible erosion wear mechanisms based on pure silt erosion experiments. Afterwards, pure cavitation erosion and synergistic studies of silt and cavitation studies under different experimental conditions are presented. Base material showed the maximum mass loss rate of ∼22 mg/h, pure PU suffered ∼9 mg/h, while nanoparticle-reinforced PU (10 wt. % B4C or 2 wt. % SiC) has a loss of ∼1.5 mg/h. This shows the tremendous potential that this approach of using polymer laden with hard nanoparticles has in combating the synergetic effects of silt and erosion. The results are well-supported by detailed scanning electron microscope images and analyses to explain the reason behind the successful performance of the coatings.