Cavitation Erosion Behavior Of Polymer Elastic Coating And Research On Biomimetic Anti-cavitation Erosion Composites

The operation of hydraulic machinery is always accompanied by pressure fluctuations.When the local pressure falls below the fluid’s saturation vapor pressure,it leads to the formation of cavities within the fluid.The formation of these cavities not only consumes energy from the system,but also creates shock waves and microjets when these cavities collapse,damaging flow components.This results in cavitation erosion or corrosion,altering the hydraulic characteristics and accelerating the failure of these flow components.Therefore,controlling cavitation in flow components is a crucial approach to enhance the efficiency of hydraulic machinery.Applying coatings to the surfaces of these flow components is an important method for protecting against cavitation.In comparison to metallic and ceramic,polymer coatings are considered to have greater research and development prospects due to their simple construction,stable chemical properties and excellent mechanical properties.Polymer elastic coatings undergo deformation under cavitation,being capable of absorbing cavitation impact and affecting the development of cavities.Therefore,the relationship between the elastic modulus of polymer coatings and cavitation characteristics has been widely studied.However,due to the chemical composition of polymers determining their mechanical properties,including variations in elastic modulus,these studies have resulted in relationships between elastic modulus and cavitation behavior that are influenced by multiple factors.This paper first explores the relationship between the elasticity of polymer coatings and cavitation characteristics from a mechanical perspective,providing an accurate depiction of the direct relationship between a single factor of polymer elasticity and cavitation behavior.It then conducts experimental research on the indirect cavitation erosion phenomenon occurring between the polymer elastic coating and the metal substrate due to deformation caused by external cavitation alternating pressure,thereby establishing the mechanical design principles for anti-cavitation materials.Finally,based on the above research theory,it employs a biomimetic design approach to construct and study the behavior of biomimetic anti-cavitation materials.To investigate the influence of a single elastic factor of polymer coating on its cavitation erosion characteristics,this paper designed a surface layer with the same material(0.21 MPa silicone rubber with a thickness of 1 mm)and a bottom layer with different modulus(3 mm thickness,elastic moduli of 0.16,0.21,0.40,0.88,1.21 MPa silicone rubber,respectively)to test the cavitation erosion behavior,and used the above five modulus silicone rubber(SR)as a single-layer sample(4 mm thickness)for comparison.Cavitation tests revealed that the cavitation erosion behavior of singlelayer samples was not correlated with elastic modulus.This is because the effects of elastic cushioning and high toughness against damage dominate cavitation protection at different cavitation erosion stages.The double-layer samples eliminated interference from other properties,allowing for the determination of the relationship between the single factor of elastic modulus and cavitation characteristics.Cavitation tests on double-layer samples indicated a negative correlation between elastic modulus and cavitation behavior.This is because as modulus increases,the dispersing effect of surface deformation on impact loads weakens,making the coating more susceptible to cavitation erosion.Furthermore,through the analysis of cavitation characteristics of single and double-layer structural samples,it was determined that polymer anticavitation coatings need to possess both elasticity and toughness.This means they should be capable of absorbing cavitation impact through elasticity and resisting impact tearing through toughness.In this paper,it was found that although the elastic deformation of polymer coating was conducive to cavitation protection,the elastic deformation could also cause indirect cavitation erosion: when the coating was partially separated from the substrate(bubbling),the coating vibrated under the external alternating stress,and cavitation occurred between the interface of the coating and the metal substrate.In this paper,through the design of indirect cavitation test,the indirect cavitation characteristics under the change of test time,substrate material and coating modulus were studied.The test results showed that the volume loss of indirect cavitation erosion of the coating was6.6 times that of direct cavitation erosion of the surface,and 1.7 times that of the copper substrate.This is because the metal particles shed by the metal substrate after cavitation erosion will be accompanied by additional particle erosion of the coating.Indirect cavitation will destroy the interface between substrate and coating,and accelerate the failure of coating,and the damage degree is affected by the substrate material.However,when the polymer coating modulus was 7.32 MPa,the high modulus coating was difficult to vibrate under the external alternating stress,and the interface between the coating and the substrate was not easy to occur indirect cavitation.To prepare anti-cavitation erosion materials with both toughness and resilience,inspired by the impact resistance of the fresh coconut shell’s husk fiber-matrix structure,from a structural perspective,a biomimetic co-continuous structure of porous reinforcement material plus a matrix was proposed.This composite material combined the impact and tear resistance of the porous reinforcement material with the energyabsorbing elasticity of the matrix.From a mechanical perspective,taking inspiration from the fact that coconut shell fibers have much higher strength than the matrix,but both have similar elasticity,resulting in similar strains when subjected to impact,and making phase separation less likely,a biomimetic elastic synergy design was proposed.Two different materials were constructed: one using low-modulus silicone rubber as the matrix and foam polyurethane as the porous reinforcement phase for a co-continuous anti-cavitation erosion material with elastic synergy,and the other using high-modulus epoxy resin as the matrix,which was less prone to indirect erosion,and high-adhesiveperformance foam silicon carbide as the porous reinforcement phase for a biomimetic co-continuous composite material.A biomimetic co-continuous material(Foam PU/Si C/SR)was prepared using a vacuum infiltration process,with Foam Polyurethane(Foam PU)as the reinforcement phase and silicon carbide/silicone rubber(Si C/SR)as the matrix.The modulus of Foam PU and SR used were 1.1 MPa and 0.4 MPa,respectively,and their tensile strengths were 14.7 MPa and 2.1 MPa,respectively.Tensile testing revealed that the composite with a 4 wt% Si C content(Si C/SR)had a tensile strength of 3.96 MPa and an elastic modulus of 0.53 MPa.Scanning electron microscope images showed good bonding at the interface between the surface-treated Foam PU and Si C/SR.Mechanical property testing demonstrated that the Foam PU/Si C/SR prepared with a 20 PPI pore size Foam PU had a modulus 1.1 times that of Si C/SR,a tensile strength 1.68 times that of Si C/SR,and a tear strength of up to 45.5 KN/m.After 24 hours of erosion testing,the anticavitation erosion resistance of Foam PU/Si C/SR was 1.72 times that of SR.Considering that low-modulus coatings can experience indirect erosion under special conditions,this study employed silicon carbide whiskers(Si C whiskers,Si Cw)in an epoxy resin(EP)matrix through a vacuum infiltration process to fill foam silicon carbide(Foam Si C),resulting in Foam Si C/Si Cw/EP.Mechanical testing showed that the optimal mechanical properties were achieved with a Si Cw mass fraction of 1.7 wt%.The Shore D hardness,tensile strength,and elongation at break of this composite were80,36.8 MPa,and 38.2%,respectively.Foam Si C/EP and Foam Si C/Si Cw/EP had impact strengths 6.6 times and 8.5 times that of EP,and thermal conductivities 2.1 and2.8 times that of EP,respectively.After 120 minutes of erosion testing in deionized water,the volume loss of Foam Si C/Si Cw/EP was only 25.6% of that of EP.In 0.1mol/L hydrochloric acid,the erosion volume loss of Foam Ni/Si C/EP,a foam metal cocontinuous material,was 1/5 of that of Foam Si C/Si Cw/EP.This indicates that Foam Si C/Si Cw/EP biomimetic anti-cavitation erosion material possesses both excellent cavitation erosion resistance and corrosion resistance.This paper reveals a direct relationship between the elasticity of polymer coatings and their anti-cavitation erosion properties.It identifies a new form of indirect cavitation erosion failure in polymer elastic coatings and proposes biomimetic cocontinuous structures and an elastic synergy design approach.Two biomimetic cocontinuous anti-cavitation erosion materials are developed.This research enriches the theoretical and methodological aspects of polymer anti-cavitation erosion coatings,offering potential materials for cavitation protection in hydraulic machinery.