Cavitation Erosion of Polyurea Composite Coatings

Abstract

Polyurea (PU) was synthesized by reacting oligomeric poly (tetramethylene oxide) (PTMO) diamines (Versalink, Air Products) with aromatic 4,4’- Methylenediphenyldiisocyanate (Isonate 143L Modified MDI, Dow Chemicals). Two Versalink prepolymers were used: VP-1000, VP-650, where 1000, and 650 refer to the molecular weight of the PTMO repeating units. PU-105 and PU-605 were synthesized by mixing VP-1000 and VP-650 with Isonate 143L. It has been observed that the temperature within the polyurea coating under cavitation erosion could increase to a considerable amount, resulting in degradation of its mechanical properties and an accelerated onset of failure. To improve the relevant thermo-mechanical properties of polyurea, milled carbon fibers of 3% and 10% volume ratios were added to the PU- 605 matrix. In the present work, accelerated cavitation erosion tests based on ASTMG32 standard were performed to study the effect of substrate, coating thickness, and formulation on cavitation resistance. The substrates of interest were aluminum and carbon fiber reinforced polymer (CFRP) plates. The experimental investigations were done on two coating thicknesses, 0.5 mm and 1 mm. Surface roughness measurements were performed after regular exposure time intervals using the stylus profilometer. Results showed that the cavitation erosion of polyurea coated substrates are different depending on the chemistry of the coating and properties of the substrate. PU-105 was more susceptible to cavitation erosion. Average depth of erosion for the composite formulation with 10% volume ratio of milled carbon fibers, was among the highest after 3 hours of erosion test.